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Additive effects prevail: The response of biota to multiple stressors in an intensively monitored watershed
Abstract
Freshwater ecosystems are impacted by a range of stressors arising from diverse human-caused land and water uses. Identifying the relative importance of single stressors and understanding how multiple stressors interact and jointly affect biology is crucial for River Basin Management.
This study addressed multiple human-induced stressors and their effects on the aquatic flora and fauna based on data from standard WFD monitoring schemes. For altogether 1095 sites within a mountainous catchment, we used 12 stressor variables covering three different stressor groups: riparian land use, physical habitat quality and nutrient enrichment. Twenty-one biological metrics calculated from taxa lists of three organism groups (fish, benthic invertebrates and aquatic macrophytes) served as response variables. Stressor and response variables were subjected to Boosted Regression Tree (BRT) analysis to identify stressor hierarchy and stressor interactions and subsequently to Generalised Linear Regression Modelling (GLM) to quantify the stressors standardised effect size.
Our results show that riverine habitat degradation was the dominant stressor group for the river fauna, notably the bed physical habitat structure. Overall, the explained variation in benthic invertebrate metrics was higher than it was in fish and macrophyte metrics. In particular, general integrative (aggregate) metrics such as % Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa performed better than ecological traits (e.g. % feeding types). Overall, additive stressor effects dominated, while significant and meaningful stressor interactions were generally rare and weak.
We concluded that given the type of stressor and ecological response variables addressed in this study, river basin managers do not need to bother much about complex stressor interactions, but can focus on the prevailing stressors according to the hierarchy identified.
... Additionally, effects of hydro-morphological degradation on riverine assemblages have been reported in numerous studies. Anthropogenic alteration of riverine bed and bank structure and of riparian conditions, for example, affect temperature regimes, substrate compositions and flow dynamics and reduce the habitat diversity (Gieswein et al., 2017;Waite et al., 2021;Haase et al., 2023). Despite this large body of evidence on the adverse effects of water quality deterioration and hydro-morphological degradation, knowledge gaps remain for certain stressors within both groups, including micropollutants and hydrological alterations (EEA, 2019;Meißner et al., 2019;Reid et al., 2019;Heß et al., 2023). ...
... This misbalance of targeted biological response metrics available for individual stressor groups may bias the identification of key stressors and subsequently the identification of appropriate management and restoration measures (Hering et al., 2010;Lemm et al., 2019). For the future development of metrics, we recommend the development and testing of novel metrics to better address emerging stressors such as micropollutants (Birk et al., 2012;Gieswein et al., 2017). Sensitivity-related metrics seem appropriate, but should include both faunal and floral assemblages due to the different modes of action of micropollutants (Busch et al., 2016). ...
... Sensitivity-related metrics seem appropriate, but should include both faunal and floral assemblages due to the different modes of action of micropollutants (Busch et al., 2016). Additionally, future development of metrics should target fish community composition and function as many metrics available for fishes only showed weak stressor responses (Birk et al., 2012;Dahm et al., 2013;Gieswein et al., 2017). ...
... In this study, land use at the watershed scale associated to nutrients and hydromorphologic stress affected all considered organism groups. Another approach using 1095 sites in a German mountainous catchment, studied the responses of fish, benthic invertebrates and aquatic macrophytes to riparian land use, physical habitat quality like riparian structure and nutrient enrichment, and physical habitat quality had the most effect on communities (Gieswein et al., 2017). The direct and indirect effects of land use, hydromorphological alterations and nutrients and organic matter on the stream ecological status were also quantified in French streams for 1200 sites (Villeneuve et al., 2018). ...
... Multiple studies emphasized that eutrophication, hydromorphological stressors and pollution can have major impacts on biology. For instance, invertebrates are known to be sensitive to nutrients (Gieswein et al., 2017) as well as inputs of sediments influenced by hydromorphology (Miler and Brauns, 2020). But depending on studied conditions and chosen parameters the order of impact of stressors on communities could vary. ...
... It can also be useful to identify the taxonomic composition of communities present in the studied sites, because certain groups can be dominant and representative of the presented ecological status. Testing the same methodology on different communities (fish, macrophytes, etc.) can highlight supplementary links because each community can be sensitive to various dominant stressors and respond differently from the other, thus, the scales of management action could be different (Dahm et al., 2013;Gieswein et al., 2017). ...
In situ bioassays are used to measure the harmful effects induced by mixtures of toxic chemicals in watercourses. In France, national-scale biomonitoring data are available including invertebrate surveys and in-field chemical toxicity measures with caged gammarids to assess environmental toxicity of mixtures of chemicals. The main objective of our study is to present a proof-of-concept approach identifying possible links between in-field chemical toxicity, stressors and the ecological status. We used two active biomonitoring databases comprising lethal toxicity (222 in situ measures of gammarid mortality) and sublethal toxicity (101 in situ measures of feeding inhibition). We measured the ecological status of each active biomonitoring site using the I2M2 metric (macroinvertebrate-based multimetric index), accounted for known stressors of nutrients and organic matter, hydromorphology and chemical toxicity. We observed a negative relationship between stressors (hydromorphology, nutrients and organic matter, and chemical toxicity) and the good ecological status. This relationship was aggravated in watercourses where toxicity indicators were degraded. We validated this hypothesis for instance with nutrients and organic matter like nitrates or hydromorphological conditions like percentage of vegetation on banks. Future international assesments concerning the role of in-field toxic pollution on the ecological status in a multi-stressor context are now possible via the current methodology.
... A stressor is a measurable variable that exceeds its normal variation range (e.g., high nutrient concentrations such as from sewage discharges (Matthaei et al., 2010) and which negatively affects stream ecosystems. The assessment of multiple stressors can be complex because effects may differ depending on the aquatic organism, ecological indicators, ecosystem type, spatial scale, ecoregion, and stressor type (Birk et al., 2020;Feld et al., 2016a;Gieswein et al., 2017;Lemm and Feld, 2017;Wiederkehr et al., 2020). Also, multiple individual stressors may be additive or interactive, resulting in synergistic or opposing outcomes that have a larger or smaller combined effect than the individual effects (Piggott et al., 2015). ...
... For instance, in urbanised catchments, the individual effect of nutrient enrichment on shredder invertebrates can be more severe in streams with reduced substrate size (Zúñiga-Sarango et al., 2020) compared to streams with large substrate size. However, stressor interactions can be rare or weak and additive stressor effects can dominate the "scene" suggesting independently-acting stressors (Gieswein et al., 2017). Therefore, under a scenario of urbanisation displaying different pressures on streams, managers require adequate information to face multiple stressor effects and their manifold interactions to pursue the most effective monitoring and conservation actions (Segurado et al., 2018;Waite et al., 2019). ...
... Our findings suggest that the effect of environmental stressors associated with the urbanisation gradient on stream ecological integrity in the tropical Andes is largely dominated by individual-stressor effects and rarely by their interactions. These results complement the findings of Gieswein et al. (2017) who addressed the effects of several human-induced stressors on a set of biological metrics calculated from data obtained from extensive monitoring showing that stressor interactions were rare and that individual-stressor (additive) effects prevailed. This indicates a dominance of individual-acting stressors than intricate interactions among stressors in stream ecosystems affected by the urban process. ...
However, knowledge about multiple-stressors effects on urbanised Andean streams is lacking. In southern Ecuador, we assessed how multiple stressors determine the structural (aquatic invertebrate metrics) and functional (organic matter breakdown and delta N of primary consumers) attributes of streams in a densely populated watershed without wastewater treatment and with contrasting land uses. We found that urbanised streams exhibited individual-stressor effects and that stressor interactions were rare. While structural and function attributes responded negatively to urbanisation, ecosystem functioning metrics were influenced most. Stream ecosystem functions were influenced by water-chemistry stressors, whereas aquatic invertebrate metrics were influenced by physical-habitat stressors. We suggest that managers of urbanised streams in the Andes immediately focus on the most important stressors by reducing inputs of inorganic N and P, re-establishing stream flow and substrate heterogeneity, and restoring riparian vegetation instead of attempting to elucidate intricate interactions among stressors. Our result also demonstrate that stream biomonitoring programs would benefit from a combination of structural and functional indicators to assess anthropogenic effects in a multiple-stressors scenario.
... The application of Eq. (1) is relatively new in water quality modeling. Examples are given by Gieswein et al. (2017;Boosted Regression trees, followed by Generalized Linear Regression), Herrero et al. (2018;Random Forest models), Gebler et al. (2018;Neural Networks), and Lemm et al. (2021;various Boosted Regression Tree implementations). ...
... Another approach, not applied here, has been followed by Feld et al. (2016), Gieswein et al. (2017) and Herrero et al. (2018) who propose to analyze multiple-stressor models as a two-stage procedure: ...
... These choices are quite different from those given in our Tables 1 and 2. The study of Lemm et al. (2021) is also directed to rivers only, where 7 stressors are chosen, all output of models or based on satellite data. Gieswein et al. (2017) analyze 21 biological metrics (their Table 2) where only three EQRs are involved. Next to that, their choices of 14 stressors are quite different to our set of 15 stressors. ...
What policy is needed to ensure that good-quality water is available for both people's needs and the environment? The EU Water Framework Directive (WFD), which came into force in 2000, established a framework for the assessment, management, protection and improvement of the status of water bodies across the European Union. However, recent reviews show that the ecological status of the majority of surface waters in the EU does not meet the requirement of good status. Thus, it is an important question what measures water management authorities should take to improve the ecological status of their water bodies. To find concrete answers, several institutes in the Netherlands cooperated to develop a software tool, the WFD Explorer, to assist water managers in selecting efficient measures. This article deals with the development of prediction tools that allow one to calculate the effect of restoration and mitigation measures on the biological quality, expressed in terms of Ecological Quality Ratios (EQRs).
To find the ideal modeling tool we give a review of 11 predictive models: 10 models from the field of Machine Learning and, additionally, the Multiple Regression model. We present our results in terms of a ‘prediction-interpretation competition’. All these models were tested in a multiple-stressor setting: the values of 15 stressors (or steering factors) are available to predict the EQR values of four biological quality elements (phytoplankton, other aquatic flora, benthic invertebrates and fish). Analyses are based on 29 data sets from various water clusters (streams, ditches, lakes, channels). All 11 models were ranked by their predictive performance and their level of model transparency. Our review shows a trade-off between these two aspects. Models that have the best EQR prediction performance show non-transparent model structures. These are Random Forest and Boosting. However, models with low prediction accuracies show transparent response relationships between EQRs on the one hand and individual steering factors on the other hand. These models are Multiple Regression, Regression Trees and Product Unit Neural Networks. To acknowledge both aspects of model quality – predictive power and transparency – we recommend that models from both groups are implemented in the WFD Explorer software.
... However, as soon as management measures need to be defined to improve the ecological status, many assessment metrics bear only little information about the causal stressor(s) behind a moderate or worse ecological status. The metrics do not allow to disentangle the individual stressors' effects, which is a prerequisite for developing targeted measures (Gieswein et al., 2017). Consequently, the diagnosis of the causes of stream degradation merely from biological monitoring data constitutes a major challenge for river managers. ...
... This is notable, since the number of biological metrics that are linked to only one stressor (N = 7) is much lower than the number of metrics that are linked to more than one cause (N = 36) in the three BBNs. Both, community composition metrics (e.g., share of EPT taxa) and species trait metrics (e.g., proportion of feeding types) apparently respond to various sources of degradation (e.g., Gieswein et al., 2017;Hering et al., 2006;Pilière et al., 2016;Poff et al., 2006). Here, the highest diagnostic values per stressor-metric relationship were equally spread across the different metrics types. ...
Ecological status assessment under the European Water Framework Directive (WFD) often integrates the impact of multiple stressors into a single index value. This hampers the identification of individual stressors being responsible for status deterioration. As a consequence, management measures are often disentangled from assessment results. To close this gap and to support river basin managers in the diagnosis of stressors, we linked numerous macroinvertebrate assessment metrics and one diatom index with potential causes of ecological deterioration through Bayesian belief networks (BBNs). The BBNs were informed by WFD monitoring data as well as regular consultation with experts and allow to estimate the probabilities of individual degradation causes based upon a selection of biological metrics. Macroinvertebrate metrics were shown to be stronger linked to hydromorphological conditions and land use than to water quality-related parameters (e.g., thermal and nutrient pollution). The modeled probabilities also allow to order the potential causes of degradation hierarchically. The comparison of assessment metrics showed that compositional and trait-based community metrics performed equally well in the diagnosis. The testing of the BBNs by experts resulted in an agreement between model output and expert opinion of 17–92% for individual stressors. Overall, the expert-based validation confirmed a good diagnostic potential of the BBNs; on average 80% of the diagnosed causes were in agreement with expert judgement. We conclude that diagnostic BBNs can assist the identification of causes of stream and river degradation and thereby inform the derivation of appropriate management decisions.
Supplementary Information
The online version contains supplementary material available at 10.1007/s10661-023-11741-5.
... However, the achieved reduction of complexity might have several downsides. First, the detectability of a relevant predictor variable in a statistical model is directly dependant on the gradient length within a dataset (Feld et al., 2016;Gieswein et al., 2017). So, given the spatial clustering and potential reduction of predictor variables gradients, the impact of an environmental variable might be underestimted or even not detected (Feld et al., 2016;Gieswein et al., 2017). ...
... First, the detectability of a relevant predictor variable in a statistical model is directly dependant on the gradient length within a dataset (Feld et al., 2016;Gieswein et al., 2017). So, given the spatial clustering and potential reduction of predictor variables gradients, the impact of an environmental variable might be underestimted or even not detected (Feld et al., 2016;Gieswein et al., 2017). Further, the developed relationships might be valid only for smaller predictor ranges, with limited upscaling possibilities (Yates et al., 2018). ...
Freshwater bioassessment programmes yield valuable information for assessing the diversity and distribution of freshwater organisms, and can be related to environmental variables through the use of multivariate methods. Regionalization and subsetting strategies are widely used in this regard, but the effects on the discerned relationships are largely unexplored. In this paper, we used a partial redundancy analysis (pRDA) to investigate the influence of different environmental variables on (i) fish community structure, (ii) the explanatory power of spatial and environmental variables, and (iii) ranking of the most relevant variables for the fish community structure in Poland. We performed the analysis at the national level and for different regionalization/subsetting strategies based on hydrography (coarse resolution: river basins, fine resolution: water regions), topography, biogeography, and fish‐based river typology. Depth, slope and sediment type were three most relevant predictors at the national level and for the majority of subsets. However, compared to the national level, a significant misalignment in predictors rankings was found for a large fraction of the identified subsets. Overall, river basin subsetting provided limited gain in information compared to the national level, while water region subsetting yielded higher variability in the predictive capacity of the pRDA models and increased the share of variance explained by spatial pattern which might obscure environmental effects. Thus, it is recommended to use biotic relevant subsetting methods based on elevation or fish indicators to better capture the variability of the dataset and provide simple and informative relationships between the fish community structure and the environmental variables.
... While effects of coliform bacterial loads on aquatic vertebrates are relatively unstudied, coliform bacterial loads may indicate contamination by wastewater effluent and thus the presence of other more harmful and harder to remove or trace anthropogenic pollutants (i.e., pharmaceuticals and endocrine disruptors; Kim et al., 2007;Snyder et al., 2007;Vajda et al., 2011). Variable importance measures are conditional on the suite of variables included in the analysis (Gieswein et al., 2017). As such, variables such as pesticides, heavy metals, and pharmaceuticals which are not removed during wastewater treatment may contribute to changes in fish populations (Meador, 2020;Patel et al., 2019), but were not analyzed in this study. ...
... Variables related to physical habitat and land use were also missing components of our analysis yet may be key contributors to changes in species richness. For example, physical attributes related to longitudinal (basin slope, flow variation, backwaters, etc.) and lateral (depth variation, shoreline development, etc.) habitat were greater predictors of fish abundance and biomass across streams (Gieswein et al., 2017;Meador, 2020). It's also well documented that increasing urban land use changes (i.e., impervious surface area) affect fish species richness and abundance (Wang et al., 2001), often to the detriment of native species (McKinney, 2006). ...
Throughout much of the globe, rivers are used to dispatch treated and untreated wastewater to the detriment of receiving ecosystems. Surprisingly, few studies directly relate water quality variables to fish community responses in receiving waterways on timescales that encompass the incremental and compounding improvements to wastewater infrastructure over time. Chicago (Illinois, USA) represents one such city, within which sits a series of waterways whose flows are primarily controlled by effluent discharges from three large wastewater treatment plants. Random forest regressions are used to construct models which predict changes in fish species richness within the Chicago Area Waterways over a period of 35 years from data on water quality and weather. The average number of species found at any one location across the Chicago Area Waterway system increased from ~5 to ~12 between 1985 and 2019. Decreases in concentrations of variables related to wastewater effluents (i.e., phenols, fecal coliforms, and nitrogenous compounds) were identified as highly informative, allowing increases in species richness to be predicted with a relatively high accuracy (R2 ≥ 0.49). Weather variables (particularly those related to snow and freezing temperatures) were only important predictors in a section of waterway which does not receive wastewater effluent, although consistent increases in rainfall were noted for Chicago and in chloride concentrations within the waterways. Increased rainfall events and harsher winter conditions (induces greater chloride runoff) threaten the progress made to lessen the effects of wastewater on the region. Improvements to how wastewater is treated, and subsequent reductions to harmful constituents of effluents, have improved the aquatic ecosystem and are likely responsible for the increased species richness over the 35-year timeframe studied.
... Macroinvertebrate-based metrics are supposed to reflect and integrate a range of stressors based on their sensitivity to human disturbances, notably organic pollution, eutrophication land-use pressure and hydromorphological degradation Kaboré et al., 2016;Gieswein et al., 2017). Because they are continuously exposed to direct pollution, macroinvertebrates are good indicators for assessing aquatic environmental conditions. ...
... The high values for water parameters (e.g., conductivity) and nutrient concentrations observed in impaired sites indicated land-use impacts, rivers/streams siltation, and organic pollution. Furthermore, as demonstrated by the authors, the combined effect of these activities acts to influence the diversity, composition and functional organization of macroinvertebrate assemblages at the sampled sites (Kaboré et al., 2016;Gieswein et al., 2017). Thus, the tested SRMI and component metrics integrate multiple stressors of the local environment and can be easily applied to assess and preserve the ecological condition of natural rivers/streams in Burkina Faso. ...
Conserving aquatic resources in the West African Sahel requires water management tools to assess the ecological status of surface water bodies threatened by mounting pressures from agricultural intensification and urbanization. Macroinvertebrate communities of Sahelian rivers were examined to test if a multi-metric index approach could be developed to assess the ecological quality of rivers. A total of 40 sample sites falling within a continuum ranging from “unimpaired reference sites” to “impaired sites” were assessed during this study. Macroinvertebrates were sampled with a hand net following a multi-habitat sampling approach. Key environmental parameters, both physico-chemical and hydro-morphologic, were recorded. More than 20 candidate metrics were evaluated in four categories: composition, functional feeding, diversity, and tolerance. We used detailed analysis procedures to exclude unsuitable metrics from the data set. After excluding redundant metrics, six-core metrics were selected to compose the Sahel River Multimetric Index (SRMI): Total-taxa, Shannon & Weiner index, EPT-taxa, ASPT-NEPBIOS and ASPT-SASS and Collector-filterers. The final index derived from these metrics was divided into five ecological quality classes (high, good, moderate, poor, and bad). The results showed that the SRMI responded to a set of environmental parameters associated with a gradient of human pressures affecting the ecological integrity of water bodies (R²≥|0.50|; p < 0.05; p < 0.001). This work produced a data base and analysis that confirms the usefulness of an unprecedented and promising tool for biological monitoring and decision-making in Sahelian regions' water management.
... This can include increases in fish species that are more tolerant and reductions in those fish species that are relatively sensitive to changes in water quality, flow, and habitat (Scott and Helfman 2001;McGrane et al. 2016;Tlili et al. 2016;Lange et al. 2018). Understanding how fish communities respond to water quality changes and habitat stressors is important when evaluating the anthropogenic use of water resource (Schinegger et al. 2016, Gieswein et al. 2017, especially in critical water source areas (Schinegger et al. 2018). The growing economy in South Africa has resulted in the increased use of freshwater ecosystems, likely on an unsustainable level, and potentially resulting in relatively undocumented shifts in fish community structures (Du Plessis 2019; Sabater et al. 2019;O'Brien et al. 2019). ...
... It is important to continue to monitor KZN rivers through monitoring programme, such as REMP, and increase research outputs to improve on understanding the status and stressors for ecological indicators and threatened species. The broadscale monitoring plan for KZN dwarfs those done internationally on similar scales (Gieswein et al. 2017;Langa et al. 2018;Schinegger et al. 2018), and increasing sampling sites across KZN is recommended, especially in strategic water source areas, to assist in their protection (LeMaitre et al. 2019). Identifying important habitat types to conserve and protect riverine environments is important when improving species composition and abundances. ...
The degradation of freshwater ecosystems can be attributed to stressors associated with the increased demand for water and other aquatic resources. Freshwater ecosystems face such challenges in supporting agriculture, industry, and high-density urban areas in KwaZulu-Natal (KZN) province, South Africa. In this study, the presence of fish species and their abundance was quantified at 40 sites in KZN on 16 major rivers systems. Surveys were done during a drought period between February 2015 and April 2016, as part of the River Health Programme, a national river monitoring assessment. The Fish Response Assessment Index (FRAI) was used to evaluate the condition of the sites, and redundancy analysis was used to evaluate the habitat, water quality and fish community relationships. The FRAI scores showed four sites to be in a ‘Seriously Modified’ condition. These areas were associated with intensive agricultural activities and urban environments. The presence of invasive fish species, abstraction and industrial use all had negative impacts on the ecological state of the rivers. When compounded by excessive water use, the drought resulted in poor fish community integrity, highlighting the vulnerability of fish communities in this region. The absence or low abundances of some indigenous fish alongside the high presence of invasive fish requires additional investigation. Results highlight the importance of mitigation measures against anthropogenic impacts should be enforced to ensure sustainable use of KZN water resources.
... These include amongst others meandering of the watercourse, variation in stream depth and width as well as riparian conditions ( Commision, 20 0 0 ). Additionally, bed habitat structure described the presence of potential holding substrate for invertebrates ( Gieswein et al., 2017 ). This parameter represents the combined fraction of coarse particulate organic matter, plants, debris and stones > 2 mm in the stream bed. ...
... Interactions between these three stressor combinations were all additive; none resulted in measurable antagonistic and synergistic ecological effects. Other investigations yielded comparable results for the minor relevance of interactions ( Birk et al., 2020 ;Gieswein et al., 2017 ) explaining them with community adaptation processes which reduce non-additive stressor interactions ( Romero et al., 2019 ). ...
Despite elaborate regulation of agricultural pesticides, their occurrence in non-target areas has been linked to adverse ecological effects on insects in several field investigations. Their quantitative role in contributing to the biodiversity crisis is, however, still not known. In a large-scale study across 101 sites of small lowland streams in Central Europe, Germany we revealed that 83% of agricultural streams did not meet the pesticide-related ecological targets. For the first time we identified that agricultural nonpoint- source pesticide pollution was the major driver in reducing vulnerable insect populations in aquatic in- vertebrate communities, exceeding the relevance of other anthropogenic stressors such as poor hydro- morphological structure and nutrients. We identified that the current authorisation of pesticides, which aims to prevent unacceptable adverse effects, underestimates the actual ecological risk as (i) measured pesticide concentrations exceeded current regulatory acceptable concentrations in 81% of the agricultural streams investigated, (ii) for several pesticides the inertia of the authorisation process impedes the incor- poration of new scientific knowledge and (iii) existing thresholds of invertebrate toxicity drivers are not protective by a factor of 5.3 to 40. To provide adequate environmental quality objectives, the authorisa- tion process needs to include monitoring-derived information on pesticide effects at the ecosystem level. Here, we derive such thresholds that ensure a protection of the invertebrate stream community. PDF: https://td2ec2in5euwest.teamdrive.net/crhkpvxr/public/YNQMekG4?k=2PtTO4DmQYeCfqWhAp--aj49dQ5lEgIrTj4E54d7-d0
... Its intensive anthropogenic use has ended up causing severe ecological adverse effects to the entire ecosystem, i.e eutrophication. This ecological phenomenon is responsible of the uncontrolled proliferation of aquatic plants of all kinds in water bodies 1,2 . Nitrogen and P are considered its limiting factors, but P is its controlling factor. ...
... For the determination of the pseudo-order of P adsorption kinetics on the marine sedimentary layer from Vridi canal, the characteristics of the plot of log (qe-q (t)) as a function of t (2) were used for Lagergren model 29 (pseudo-order 1) and the plot of as a function of t (3) for Blanchard model 30 (pseudoorder 2). ...
This work focused on the study of phosphorus adsorption on the marine sedimentary layer from Vridi canal. The this work has lead on the study of phosphorus adsorption kinetics on these sediments and, the second part on the study of phosphorus adsorption isotherms at 25°C on these entities. These studies were carried out under three experimental conditions partially simulating the seasonal physical and chemical characteristics of the waters from this estuary, namely: (E1) pH = 6, Salinity = 5%; (E2): pH = 7; Salinity = 3 in batch mode. The results have showed that the rate of phosphorus adsorption on these sediments increases from E1 to E3. The kinetics of this reaction are all pseudo the diffusion kinetics of this nutrient in these substrates, and those in all the experiments carried out. Langmuir isotherm describes well the experimental isotherms obtained in E2, with favorable adsorption at the different concentrations of the synthetic phosphorus solutions, as illustrated by Hall adimensional number less than 1. The experimental isotherms obtained in E3 are in agreement with Freundlich isotherm, with a favorable adsorption shown by the heterogeneity factor less than 1. A good description of the isotherm obtaine different types of sites on these sediments surface, with a considerable difference in adsorption energy depending on their position.
... Through the lens of a multiple-stressor framework, heat waves and water limitation may pose additive costs to animals (i.e. where the cost from both stressors is the sum of the costs of each stressor alone; Gieswein et al., 2017). Alternatively, these two stressors may present non-additive costs, where together they have higher or lower costs than expected through an additive-costs model (e.g. ...
... TWC similarly incurred non-additive costs (Fig. 1, Table S1B), but neither a heat wave nor water limitation invoked stress to flight muscle, gonad mass or immunocompetence (Figs 2B and 3, Tables S2B,C and S4B). Although our study only found support for the non-additive model, other multiple-stressor studies have found a range of support for both additive and non-additive costs of multiple stressors (Løkke et al., 2013;Piggott et al., 2015;Gieswein et al., 2017); therefore, there may not be a general 'rule' for the manner in which complex environmental stressors affect animals. ...
The frequency, duration, and co-occurrence of several environmental stressors, like heat waves and droughts, are increasing globally. Such multiple stressors may have compounding or interactive effects on animals, resulting in either additive or non-additive costs, but animals may mitigate these costs through various strategies of resource conservation or shifts in resource allocation. Through a factorial experiment, we investigated the independent and interactive effects of a simulated heat wave and water limitation on life-history, physiological, and behavioral traits. We used the variable field cricket, Gryllus lineaticeps, which exhibits a wing dimorphism that mediates two distinct life-history strategies during early adulthood. Long-winged individuals invest in flight musculature and are typically flight capable, whereas short-winged individuals lack flight musculature and capacity. A comprehensive and integrative approach with G. lineaticeps allowed us to examine if life-history strategy influenced the costs and cost-limiting strategies due to multiple stressors. Concurrent heat wave and water limitation resulted in largely non-additive and single-stressor costs to important traits (e.g., survival and water balance), extensive shifts in resource allocation priorities (e.g., reduced prioritization of body mass), and a limited capacity to conserve resources (e.g., heat wave reduced energy use only when water was available). Life-history strategy influenced the emergency life-history stage because wing morphology and stressor(s) interacted to influence body mass, boldness behavior, and immunocompetence. Our results demonstrate that water availability and life-history strategy should be incorporated into future studies integrating important conceptual frameworks of stress across a suite of traits—from survival and life history to behavior and physiology.
... For instance, an increase in the relative abundance of Oligochaeta and Diptera may indicate an accumulation of fine sediments and organic matter at a sampling site [47]. Conversely, a decrease in the proportion of, e.g., Ephemeroptera, Plecoptera, and/or Trichoptera taxa may signal habitat homogenization (i.e., a man-made simplification of habitat conditions resulting in the loss of microhabitats), changes in food resource composition, or organic pollution [41,[47][48][49]. ...
... Other ecologically based modules have been developed following the SI example with substantial effort placed on acquiring the autecological characterization of species used as bioindicator taxa-culminating in a database now detailing ecological preferences all major bioindicator species [17]. The significance of such data for biomonitoring is tremendous: ecological metrics such as the RETI, or proportions of certain feeding guilds or taxa associated with specific hydromorphological conditions are widely used and enable differentiation of stressors [39,46,49]. In combination with properly defined reference conditions these high-resolution modules and metrics can be used to detect impact of organic pollution, hydromorphological alteration, or changes in land use relating to allochthonous matter input (e.g., large woody debris) [41,48,51,52]. ...
The Water Framework Directive requires that the ecological status of surface waters be monitored and managed if necessary. A central function in ecological status assessment has the Biological Quality Elements—organisms inhabiting surface waters—by indicating human impact on their habitat. For benthic invertebrates, a wide array of national methods are used, but to date no comprehensive summary of metrics and methods is available. In this study, we summarize the benthic invertebrate community metrics used in national systems to assess the ecological status of rivers, (very) large rivers, and lakes. Currently, benthic invertebrate assemblages are used in 26 national assessment systems for rivers, 13 assessment systems for very large rivers, and 21 assessment systems for lakes in the EU. In the majority of systems, the same metrics and modules are used. In the Red Queen’s race of ecosystem management this may be a disadvantage as these same metrics and module likely depict the same stressors but there is growing evidence that aquatic ecosystems are subject to highly differentiated, complex multiple stressor impacts. Method development should be fostered to identify and rank impacts in multi-stressor environments. DNA-based biomonitoring 2.0 offers to detect stressors with greater accuracy—if new tools are calibrated.
... In Reach 1, indicator taxa included a collection of all functional feeding groups (scrapers, shredders, collectors, and predators), whereas in regulated reaches there were no indicator taxa. The main reason is that hydropeaking has an impact on downstream regulatory structures, and changes associated with it include changes in water quality, habitat changes, and food availability (Gieswein et al., 2017;Elgueta et al., 2021). In terms of temporal variation, macroinvertebrates that mature quickly survived the Millennium Drought longer, and samples collected shortly after the drought (2010-12 cycle) had higher values of taxa richness, abundance, and diversity. ...
... deforestación de la vegetación ribereña para establecer pastos y agricultura anual o permanente (Suga & Tanaka, 2013); enriquecimiento en nutrientes del agua; eliminación o degradación del bosque de ribera (Escalona-Domenech et al., 2022); rectificación y canalización de ríos (Tovilla, 2005); y alteraciones al régimen de caudales por la construcción de presas, diques y bordos (Gieswein et al., 2017;Grill et al., 2019). ...
Conocer el estado ecológico de las riberas es un elemento esencial en la gestión de una cuenca hidrográfica, dado que refleja la calidad del agua y del hábitat acuático. En este estudio se evaluó la condición ecológica de las riberas en ocho sitios de muestreo del río Huixtla a través del Índice de Calidad Ecológica de las Riberas (RQI, por sus siglas en inglés) y se determinaron parámetros físico-químicos del agua (temperatura, conductividad, pH y sólidos totales disueltos). Las condiciones variaron de muy buenas hasta malas. El sitio S1 fue el de mejor calidad, observándose una franja de vegetación ribereña continua de amplitud y longitud considerable. Los sitios con pobre y mala condición presentaron vegetación ribereña en parches, muros de contención y cauce rectificado, suelo compactado y extracción de arena del río. Se concluye que las riberas necesitan medidas de restauración para la recuperación de sus condiciones hidrogeomorfológicas. Palabras clave: calidad del agua, cuencas hidrográficas, ecosistema fluvial, uso del suelo, vegetación ribereña
... These in turn can result in lower dissolved oxygen concentrations and decreased flow velocity. Furthermore, low flow and higher temperatures combined can result in higher saprobity through stagnation and increased organic matter breakdown rates (Birk et al., 2020;Elbrecht et al., 2016;Gieswein et al., 2017). Species can respond to this array of stressors in different ways, that are not necessarily captured by the categorization of the species, or their traits, based on their changes in abundance over time (Feld et al., 2014). ...
... Although this low current velocity has a natural origin due to the low slope compared to other geographical regions, it was further reduced during base flows due to the drainage intensity and other management measures, aimed at decreasing water retention capacity (Verdonschot and Nijboer, 2002). At low current velocity, excess nutrients may quickly lead to eutrophication, excessive plant growth, and cyanobacteria blooms, which in turn can cause a decrease in food quality, toxicity, and even anoxia (Elbrecht et al., 2016;Gieswein et al., 2017;Wurtsbaugh et al., 2019). This suggests that additional reduction of nutrient loads and organic pollution is needed for further recovery. ...
Lowland stream ecosystems are under threat from climate change, industrialization, urbanization, and intensive agriculture. Since the 1980s, improvements in water quality have led to an increase in lowland stream biodiversity. Despite restoration efforts, however, further recovery is often hampered by the presence of region-specific (combinations of) stressors, and species-specific stressor responses. Identification of these stressors may not be achieved by the analysis of abundance data over large areas for entire communities or species assemblages. Therefore, our study introduces an alternative in-depth approach, selecting Ephemeroptera as a model organism group and analyzing 41 years of species abundance data across distinct geographical regions. Our findings revealed that 15 Ephemeroptera species had already disappeared before 1985, emphasizing the importance of evaluating an extended historical period when analyzing biodiversity trends. While biodiversity was generally characterized by an initial recovery that stagnated over time, the analysis of the past 41 years of Ephemeroptera abundance data revealed strong differences in species' abundance trends between periods, regions, and species. Certain species were likely to have benefitted from local restoration measures in specific geographical regions, while others may have declined due to the presence of region-specific stressors. Our approach underscores the importance of studying the development of region- and species-specific stream biodiversity trends over time to aid the selection of the appropriate restoration measures to recover lowland stream biodiversity.
... Dadurch sind sie häufig besser für Umweltdaten geeignet, in denen die Stressoren und biologischen Metrics in einem nicht-linearen Zusammenhang stehen und deren Daten bestimmte statistische Kriterien, wie Normalverteilung oder Varianzhomogenität, nicht erfüllen. Darüber hinaus gelten Random Forests als robust gegenüber Ausreißern und können auch dann angewendet werden, wenn ein relativ kleiner Datensatz auf eine relativ hohe Anzahl von Umweltvariablen analysiert werden soll (KNUDBY et al., 2010;VISSER et al., 2022;methodische Beschreibung in BREIMAN (2001) MARZIN et al., 2012;VILLENEUVE et al., 2015;HERRERO et al., 2018;MEIßNER et al., 2019;CASTRO-CATALÀ et al., 2020;VALERIO et al., 2021;MIGNIEN und STOLL, 2023 (Birk et al., 2012;Dahm et al., 2013;Gieswein et al., 2017). Es ist daher empfehlenswert, für die Fische weitere Stressor-spezifische Metrics abzuleiten und in fiBS zu ergänzen. ...
... This ultimately causes eutrophication with direct effects on diatoms and macrophytes (O´Hare et al., 2018) and indirect effects on macroinvertebrates and fish (Hering et al., 2006). Nutrient surplus favors species that feed on algae detritus and dead plants, while oxygen depletion leads to declines in sensitive taxa (Lange, 2014), owing to interspecific competition and secondary saprobic load (Gieswein et al., 2017). However, a moderate nutrient influx can have positive impacts on macroinvertebrate abundance and richness in nutrient-deficient rivers due to elevated overall productivity (Matthai et al, 2010;Piggot et al., 2012;Piggott et al., 2015). ...
Biodiversity and the health of freshwater ecosystems is strongly impaired by human activities,
compromising the stability of these ecosystems and the ecosystem services they provide. Global
and European efforts to halt the biodiversity decline and protect ecosystem health were not very
successful, especially for rivers, so that for less than ten percent of the German rivers good
ecological status was reached in 2021. Present-day agriculture has been identified as the main
driver for this deterioration, as evident from a multitude of studies. However, the agricultural
effects differ between the organism groups and depending on environmental conditions like soil
and climatic conditions. Moreover, and most importantly, agriculture is not uniform. The
specific agricultural types and practices differ between regions, which in turn leads to
differences in the intensity of agrochemical usage as suggested by many small-scale studies.
Consequently, the magnitude of agricultural effects on biodiversity and health of river
ecosystems most probably depends on agricultural types and practices and differs between
regions. For the effective mitigation of these negative effects, several knowledge gaps need to
be closed, which were addressed in six chapters, shortly described in the following.
First, the current knowledge on the effect of agriculture on river biota was summarized and
analysed in a meta-analysis (Schürings et al., 2022). According to this meta-analysis described
in the first chapter, agriculture has an overall medium to high negative effect on river biota, and
results indicate that the effects of agriculture differ between agricultural types, practices, the
organism groups, and biological metrics considered. Second, a pan-European dataset was used
to establish an agricultural typology, based on agricultural production and agriculture-related
freshwater pressure by nutrients, pesticides, water abstraction and hydromorphological
alterations (Schürings et al., 2023). This chapter identified how agricultural types differ in their
pressures exerted on freshwaters and shows that accounting for agricultural pressure intensity
nearly doubles the correlation with the ecological status. Third, the effects of different
agricultural types on the ecological status according to the EU Water Framework Directive
(WFD) were investigated, using high resolution German-wide land use data, distinguishing
between different crop types (Schürings et al., 2024a). The effects on the ecological status
clearly differed between crop types, which typically are associated with different agrochemical
application rates. Macroinvertebrates and macrophytes were most strongly affected by pesticide
application intensive crops and diatoms were most affected by nutrient intensive crops. Fourth,
the results presented in Markert et al. (2023) provided evidence that urban areas and different
5
agricultural crop types with typical agrochemical application rates are indeed related to the
micropollutant concentrations monitored in rivers, which often exceeded Environmental
Quality Standards. Fifth, crop type-specific differences in agrochemical application rates
reported in literature were used to generate an agricultural intensity index (Schürings et al.,
2024b). This index improved the correlative strength between present-day agriculture and the
ecological status with most pronounced relations for macroinvertebrates in small mountain
streams. Sixth, experiences from implementing environmental legislations like the WFD were
used to advice for a successful implementation of the EU Nature Restoration Law (Hering et
al., 2023). This final chapter highlights that joining restoration efforts with a shift to more
sustainable agriculture, whose importance is reasoned in the previous chapters, would offer
unprecedented opportunities for successful protection of ecosystem health.
In conclusion, this thesis provides overwhelming evidence for the negative effects of present-
day agriculture on river biota, portraying influencing factors and highlighting strong
relationships between agricultural effects on river biota and agrochemical application,
particularly of pesticides. Therefore, to mitigate these effects, a transition of present-day
agriculture to more sustainable practices, such as organic farming or agroecology is of vital
importance. Such a transition would be beneficial both for the future viability of agriculture
itself but also for the protection and restoration of healthy ecosystems, including the successful
implementation of the European environmental legislation such as the Nature Restoration Law.
... Although this low current velocity has a natural origin due to the low slope compared to other geographical regions, it was further reduced during base flows due to the drainage intensity and other management measures, aimed at decreasing water retention capacity (Verdonschot and Nijboer, 2002). At low current velocity, excess nutrients may quickly lead to eutrophication, excessive plant growth, and cyanobacteria blooms, which in turn can cause a decrease in food quality, toxicity, and even anoxia (Elbrecht et al., 2016;Gieswein et al., 2017;Wurtsbaugh et al., 2019). This suggests that additional reduction of nutrient loads and organic pollution is needed for further recovery. ...
... Most of these large-scale empirical studies only distinguished between rather broad land use categories and mainly used gross agricultural land use types, often only distinguishing between crop-and grassland (e.g. Gieswein et al., 2017;Davis et al., 2022). Differential effects of specific crop types on river biota have rarely been considered in large-scale empirical studies yet (Wasson et al., 2010), as high-resolution land use data distinguishing specific crop types became available only recently (e.g. ...
While the general effects of agricultural land use on riverine biota are well documented, the differential effects of specific crop types on different riverine organism groups, remain largely unexplored. Here we used recently published land use data distinguishing between specific crop types and a Germany-wide dataset of 7748 sites on the ecological status of macroinvertebrates, macrophytes and diatoms and applied generalized linear mixed models to unravel the associations between land use types, crop types, and the ecological status. For all organism groups, associations of specific crop types with biota were stronger than those of urban land use. For macroinvertebrates and macrophytes, strong negative associations were found for pesticide intensive permanent crops, while intensively fertilized crops (maize, intensive cereals) affected diatoms most. These differential associations highlight the importance of distinguishing between crop types and organism groups and the urgency to buffer rivers against agricultural stressors at the catchment scales and to expand sustainably managed agriculture.
... EPT orders are composed of pollution-sensitive insect species with relatively specific habitat requirements, and thereby can be informative integrative metrics of stream biotic condition (Gieswein et al., 2017). EPT taxa richness, calculated as the total number of unique EPT taxa at a site, is commonly used in biomonitoring programs and cited as one of the most useful macroinvertebrate metrics by US state agencies to assess streams and address state and federal environmental requirements (Carter & Resh, 2013). ...
Stream macroinvertebrate assemblages are shaped by natural and human‐related factors that operate through complex hierarchical pathways. Quantifying these relationships can provide additional insights into stream ecological assessment. We applied a structural equation modeling framework to evaluate hypothesized pathways by which watershed, riparian, and in‐stream factors affect benthic macroinvertebrate condition in the Western Mountains (WMT) and Xeric (XER) ecoregions in the United States. We developed a conceptual model grounded in theory, empirical evidence, and expert opinion to evaluate the following hypotheses: (1) macroinvertebrate assemblages are primarily driven by proximal, in‐stream factors (e.g., water quality and physical habitat); (2) anthropogenic land uses affect macroinvertebrates indirectly by altering in‐stream characteristics; and (3) riparian vegetation cover attenuates land use effects. We tested our model separately on three measures of benthic macroinvertebrate assemblage condition: ratio of observed‐to‐expected taxonomic richness (O/E); a multimetric index (MMI); and richness of Ephemeroptera, Plecoptera, and Trichoptera taxa (EPT). In the WMT, site‐level riparian cover, in‐stream physical habitat (relative bed stability), and water chemistry (total nitrogen) were the top three predictors of macroinvertebrate assemblages, each having over two times the magnitude of effect on macroinvertebrates compared with watershed‐level predictors. In the arid XER, annual precipitation and stream flow characteristics were top predictors of macroinvertebrate assemblages and had similar magnitudes of effect as in‐stream water chemistry. Path analyses revealed that land use activities in the watershed and at the stream site degraded macroinvertebrate assemblages indirectly by altering relative bed stability, water quality, and riparian cover/complexity. Increased riparian cover was associated with greater macroinvertebrate condition by reducing land use impacts on stream flow, streambed substrate, and water quality, but the pathways differed among ecoregions. In the WMT, site‐level riparian cover affected macroinvertebrate assemblages partly through indirect pathways associated with greater streambed stability and reduced total nitrogen concentrations. In contrast, in the XER, watershed‐level riparian cover affected macroinvertebrate assemblages through greater specific stream power. Identifying the relative effects of and pathways by which natural and anthropogenic factors affect macroinvertebrates can serve as a framework for prioritizing management and conservation efforts.
... In Reach 1, indicator taxa included a collection of all functional feeding groups (scrapers, shredders, collectors, and predators), whereas in regulated reaches there were no indicator taxa. The main reason is that hydropeaking has an impact on downstream regulatory structures, and changes associated with it include changes in water quality, habitat changes, and food availability (Gieswein et al., 2017;Elgueta et al., 2021). In terms of temporal variation, macroinvertebrates that mature quickly survived the Millennium Drought longer, and samples collected shortly after the drought (2010-12 cycle) had higher values of taxa richness, abundance, and diversity. ...
River systems have been stressed by the construction of dams and regulation structures which influence aquatic ecosystem integrity. Previous studies considered the general significance of regional streamflow regimes for aquatic communities, but they did not investigate the influence of specific components of flow regimes on aquatic ecosystems under the combined impact of regulation and extreme drought events, limiting our ability to design and implement precise environmental flow management strategies. This study aims to quantify the relationship between macroinvertebrate biotic indices and ecologically important streamflow characteristics derived from five natural flow regime components by investigating the spatiotemporal variation in the macroinvertebrate assemblage in regulated and unregulated reaches and identifying specific flow indices that have a direct impact on macroinvertebrates in the Goulburn basin in Victoria, Australia during the Millennium Drought period. The relationship between dominant flow metrics and macroinvertebrates indices was investigated using boosted regression trees (BRT). The results revealed a significant difference in hydrological variability between regulated and unregulated reaches. The regulated reaches demonstrated reduced hydrological variability during low flow periods, and rapid increase in discharge during high flow periods when compared to unregulated reach. Unregulated reach had 38% more taxa richness than regulated reach impacted by hydropeaking. Eight indicator taxa were identified in the unregulated reach, and they exhibited a higher Stream Invertebrate Grade Number Average Level (SIGNAL 2) score, indicating that they were highly sensitive species. The maximum flow in June was the most important flow parameter that influences the macroinvertebrate indices as per the BRT model. Better management of environmental flows will benefit from identifying which aspects of the natural flow regime impact stream ecosystems and predicting the consequences of altered flow regimes on aquatic ecosystems.
... Multiple stressor ecological responses can be classified broadly as synergies, antagonisms, reversals, and additive effects (Côté et al., 2016). Additive effects on biota result from individual stressors (that do not interact) and whose joint effect equals the sum of the individual effects (Gieswein et al., 2017). A synergy is conventionally defined as an interaction where the combined impact of two or more stressors on a biological/ecological response (e.g., diversity, productivity, abundance, survival, growth, reproduction) is larger than the sum of the impacts of the individual stressors. ...
Multiple stressors resulting from anthropogenic actions are increasingly recognized as a major threat to aquatic ecosystems. In general, ecosystems change as they respond to multiple threats that interact in complex ways, depending on the natural environment. This scenario poses complex tasks for researchers, managers, and policymakers, which require a well-defined framework to provide a clear roadmap that identify steps to apply in adaptive management decisions, monitoring designs and policy implementation.
Building upon core elements of previous work, we present a Multiple Stressors Assessment Framework (MSAF) for aquatic ecosystems that provides a roadmap on the achievement of an improved integration between monitoring designs, data acquisition, evaluation processes, and management actions. The MSAF involves seven steps: 1) problem formulation and the definition of the ecosystem type and the spatial-temporal scale, 2) data compilation on the ecosystems' environmental characteristics and the definition of the type, identity and intensity of environmental stressors, 3) data compilation/collection on the biological/ecological receptors (endpoints) to stressors and selection of response variable to monitor (based on structure-based indicators and functional metrics), 4) characterization of the stressor-response relationships and their interactions, 5) construction of specific ecological conceptual models and choice of adequate statistical approaches to test the conceptual models' viability, 6) generation of hypotheses on interactive effects on biological/ecological endpoints, validation of models, hypotheses testing and, if possible, comparison of results with controlled experiments in realistic settings, and 7) recommendations to adaptive monitoring and if necessary, improvement of the study design, and eventual inclusion of other hypotheses and statistical approaches in the context of adaptive management actions.
We review progress made in Europe, the USA and Canada in this field using case examples, highlight the approaches taken by the different jurisdictions that align with our framework and identify the linkages between multiple stressors assessments and decision-making for each region. We conclude that a disconnection remains between the investigation of the combined effects of multiple stressors and the implementation of management practices and policy translation. The way forward is through a collaborative effort to create standardized methodologies and appropriate programmes in this field. We hope the proposed framework can be used as a foundation to diagnose multiple stressor interactions and identify responses of ecological indicators to inform effective adaptive management of freshwater ecosystems globally
... Understanding the mechanisms that drive the spatial patterns and the abundance of these communities is fundamental to the conservation of biological diversity (Vergés et al., 2011;Adeoba et al., 2019;Namiq & Mahmood, 2019). Furthermore, knowledge on how these fish communities respond to water quality changes and habitat stressors is important when evaluating the anthropogenic use of water resource (Schinegger et al., 2016;Gieswein et al., 2017;Schinegger et al., 2018). This is especially important for the genus Enteromius, with many species that require diverse ecological conditions and habitats. ...
... In contrast to micropollutants, there is a huge body of literature on the effects of hydrological and morphological stressors on riverine biota [1,12,[20][21][22][23]. The European Environment Agency recently listed hydromorphological impacts, such as channelisation, disconnection of floodplains or flow regulation, among the top stressor groups affecting Europe's rivers [24]. ...
Background
A variety of anthropogenic stressors influences the ecological status of rivers wordwide. Important stressors include elevated concentrations of nutrients, salt ions, heavy metals and other pollutants, habitat degradation and flow alteration. Some stressors tend to remain underrepresented in multiple-stressor studies, which in particular is apparent for micropollutants (e.g. pesticides, pharmaceuticals) and alterations of the flow regime. This case study analysed and compared the effects of 19 different stressor variables on benthic macroinvertebrates in the two German rivers Erft and Niers (Federal State of North Rhine-Westphalia, Germany). The stressors variables were assigned to four stressor groups (physico-chemical stress, mixture toxicity of 42 micropollutants, hydrological alteration and morphological degradation) and were put into a hierarchical context according to their relative impact on the macroinvertebrate community using redundancy analysis and subsequent variance partitioning.
Results
The results suggest a strong and unique effect of physico-chemical stress, yet at the same time reveal also a strong joint effect of physico-chemical and hydrological stressor variables. Morphological degradation showed subordinate effects. Notably, only a minor share of the explained variance was attributed to the mixture toxicity of micropollutants in these specific catchments.
Conclusions
The stressor hierarchy indicates that management measures for improving the ecological status still need to address water quality issues in both rivers. The strong joint effect of physico-chemical stress and hydrological alteration might imply a common source of both stressor groups in these two catchment areas: lignite mining drainage, urban area and effluents of wastewater treatment plants. The findings point at the important role of alterations in the flow regime, which often remain unconsidered in hydro-morphological surveys.
... Multiple stressors may have an additive effect on a given reproductive trait (e.g., mating) where the stress due to two factors is simply the sum of either factor alone (Todgham and Stillman 2013). Here, ALAN and a heat wave may exert independent, additive effects similar to those found in other multiple-stressor studies (Holliday et al. 2009;Kuehne et al. 2012;Gieswein et al. 2017; but see Jackson et al., 2016;Padda et al. 2021). In particular, both short-term ALAN and heat waves may improve mating efficiency given the effects of visual cues and warmer temperatures on sensory systems (discussed in Nguyen and Stahlschmidt 2019). ...
Animals are increasingly exposed to both artificial light at night (ALAN; a.k.a., ecological light pollution) and heat waves. Traditionally, the effects of ALAN and heat waves have been investigated in isolation, and results indicate mixed support for their costs to important decisions made at specific stages of reproduction (i.e., before, during, and after mating). Therefore, we used a factorial design to manipulate temperature and light conditions during adulthood in female variable field crickets (Gryllus lineaticeps) to determine (1) whether ALAN has stage-specific effects on reproductive decisions and (2) if ALAN effects on reproduction interact with a simulated heat wave. We found that ALAN simulating bright urban lighting promoted mating success, and a simulated heat wave resulted in even greater benefits to reproduction, including increased reproductive investment (ovary mass prior to mating), the efficiency by which food was converted into reproductive tissue, and reproductive output (number of eggs laid). Heat wave and ALAN did not modulate the effect of one another because we found no evidence of interactive (e.g., synergistic or antagonistic) effects of temperature and light treatments on any reproductive trait. Our study is the first to examine the combined effects of ALAN and heat waves across reproductive stages, and we found that these two increasingly common environmental factors may generally benefit reproduction in an insect.
Significance statement
Animals are increasingly exposed to artificial light at night (a.k.a., ecological light pollution) and heat waves, but the combined effects of these two potential stressors are unknown. Therefore, we manipulated temperature and light conditions during adulthood in female variable field crickets (Gryllus lineaticeps) to examine effects across three important reproductive stages—before, during, and after mating. We found that ALAN simulating bright urban lighting promoted mating success, and a simulated heat wave resulted in even greater benefits to reproduction, including increased reproductive investment (ovary mass prior to mating) and reproductive output (number of eggs laid after mating). Our results indicate that these two increasingly common environmental factors may generally benefit reproduction in an insect.
... Frequency of synergistic vs. antagonistic effects across the tree of life. Discrepancies between studies, some claiming that multiple global-change drivers promote interactive effects (31,32,51) and others suggesting that such interactions are rare or infrequent (44,52,53), could arise from different analytical approaches followed to estimate such effects or from differences in experimental design in the original studies. In the present analysis, given that we followed the same standardized procedure to quantify the magnitude, sign, and direction of the multiple interacting drivers addressed and selected studies that followed the same experimental design (i.e., factorial approach), we can rule out that the differences encountered in the frequency of interactive effects among trophic groups results from methodological differences. ...
Jensen’s inequality predicts that the response of any given system to average constant conditions is different from its average response to varying ones. Environmental fluctuations in abiotic conditions are pervasive on Earth; yet until recently, most ecological research has addressed the effects of multiple environmental drivers by assuming constant conditions. One could thus expect to find significant deviations in the magnitude of their effects on ecosystems when environmental fluctuations are considered. Drawing on experimental studies published during the last 30 years reporting more than 950 response ratios ( n = 5,700), we present a comprehensive analysis of the role that environmental fluctuations play across the tree of life. In contrast to the predominance of interactive effects of global-change drivers reported in the literature, our results show that their cumulative effects were additive (58%), synergistic (26%), and antagonistic (16%) when environmental fluctuations were present. However, the dominant type of interaction varied by trophic level (autotrophs: interactive; heterotrophs: additive) and phylogenetic group (additive in Animalia; additive and positive antagonism in Chromista; negative antagonism and synergism in Plantae). In addition, we identify the need to tackle how complex communities respond to fluctuating environments, widening the phylogenetic and biogeographic ranges considered, and to consider other drivers beyond warming and acidification as well as longer timescales. Environmental fluctuations must be taken into account in experimental and modeling studies as well as conservation plans to better predict the nature, magnitude, and direction of the impacts of global change on organisms and ecosystems.
... With decreasing stream width, the importance of the riparian vegetation for a stream increases, providing essential habitats for the adult stages of aquatic insects, buffers from terrestrial runoff and sources of shade and organic matter input for aquatic organisms (Death and Collier, 2009;Harrison et al., 2000;Harrison and Harris, 2002). In small and mid-sized streams, impacts on the channel morphology as well as sedimentation and other types of stream bed modifications have been identified as major morphological stressors on physical habitat quality (Gieswein et al., 2017;Piggott et al., 2012;Townsend et al., 2008). ...
Hydromorphological stressors, i.e. hydrological and morphological alterations, affect freshwater biota in running and standing waters in a multitude of ways. These vary depending on size, morphology and other abiotic characteristics of rivers and lakes and also the respective organism groups of which macroinvertebrates, macrophytes and fish are discussed in this chapter. Hydromorphological stressors interact with other stressors, most importantly eutrophication and acidification. Interactions can be characterized as additive, synergistic or antagonistic. Invasive species can modify the effects of hydromorphological alterations. Hydromorphological restorations projects vary considerably in scale, location and effectiveness and more efforts are necessary to design and evaluate these.
... Example: Physical and chemical stressors added up in their effects on various biological community parameters in a mountainous river catchment (Gieswein et al., 2017). ...
The article serves to introduce the environmental issue of ever-increasing multiple stressors acting on streams and rivers globally. It presents the most relevant stressors and outlines the state of knowledge in multi-stressor research. Stressor interactions are well documented, but full understanding of the cause-effect relationships remains scarce. This poses high uncertainties to predicting and effectively managing multi-stressor effects. Both a refined analytical approach and integrative, adaptive environmental management offer solutions to this intricate problem.
... Several recent large-scale ecological assessments have focused on improved understanding of multiple instream stressors arising from landuse modifications (Dahm et al., 2013;Feld, 2013;Villeneuve et al., 2015;Ponsati et al., 2016;Gieswein et al., 2017;Waite and Van Metre, 2017). In both urban-and agriculture-influenced watersheds, streams commonly exhibit disturbance resulting from increased temperature, lowered dissolved oxygen, and excessive nutrients and fine sediments (Waite, 2014;Birk et al., 2020;Herlihy et al., 2020). ...
Biological assemblages in streams are affected by a wide variety of physical and chemical stressors associated with land-use development, yet the importance of combinations of different types of stressors is not well known. From 2013 to 2017, the U.S. Geological Survey completed multi-stressor/multi-assemblage stream ecological assessments in five regions of the United States (434 streams total). Diatom, invertebrate, and fish communities were enumerated, and five types of potential stressors were quantified: habitat disturbance, excess nutrients, high flows, basic water quality, and contaminants in water and sediment. Boosted regression tree (BRT) models for each biological assemblage and region generally included variables from all five stressor types and multiple stressors types in each model was the norm. Classification and regression tree (CART) models then were used to determine thresholds for each BRT model variable above which there appeared to be adverse effects (multi-metric index (MMI) models only). In every region and assemblage there was a significant inverse relation between the MMI and the number of stressors exerting potentially adverse effects. The number of elevated instream stressors often varied substantially for a given level of land-use development and the number of elevated stressors was a better predictor of biological condition than was development. Using the adverse effects-levels that were developed based on the BRT model results, 68% of the streams had two or more stressors with potentially adverse effects and 35% had four or more. Our results indicate that relatively small increases in the number of stressors of different types can have a large effect on a stream ecosystem.
... Additionally, the riparian zone provides streams with structures that enhance and diversify habitats, such as woody debris, root formation, and overall organic matter [91,94]. Therefore, anthropological actions that impair the morphology of streams, such as bank and channel modifications, result in the decline of invertebrate communities, presenting lower taxonomic variety and abundance [90,91,95]. Such actions include channel stabilisation through armouring, resectioning, culverts, fords, weirs, and sluices [90,91]. ...
Urbanisation alters the natural hydromorphology of streams, affecting aquatic communities and ecological quality. Increasing efforts have been put into the rehabilitation of urban streams due to their importance for urban sustainability. Despite these efforts, many projects fail to achieve the improvement of aquatic communities. This study aims to provide specific recommendations to enhance the biological rehabilitation of urban streams by reviewing: (i) the impacts of urbanisation and climate change on urban stream hydrology, (ii) the responses of invertebrate assemblages to alterations in the hydrology and morphology of streams, and (iii) the hydromorphological rehabilitation measures applied to streams and their effect on invertebrate communities. This review found that commonly employed measures of habitat heterogeneity enhancement (such as the addition of meanders, boulders, and artificial riffles) are not enough to improve invertebrate communities. On the other hand, the most effective measures are those leading to the re-establishment of natural hydrological patterns and good water quality. Ultimately, an integrated ecohydrological approach that considers the entire watershed and its interactions between ecosystems and anthropological activities is the key to managing and rehabilitating urban streams.
... Risk tolerances among stakeholders may vary and "safe", or acceptable conditions may not be objectively characterized. There can also be unknown long-term consequences of low levels of environmental change (Soulé, 1985;Biber, 2011;Addison et al., 2016;Suter, 2016), obscure or unknown exposure of organisms (Tetreault et al., 2020), and various interactions of both anthropogenic and natural environmental stressors (Gieswein et al., 2017;Arciszewski et al., 2018). ...
Although challenging to develop and operate, some degree of integrated monitoring is often necessary, especially at regional scales, to address the complex questions of environmental management and regulation. The concept of integration is well-understood, but its practice across programs and studies can be diverse suggesting a broader examination of the existing general approaches is needed. From the literature, we suggest integration of monitoring can occur across three study components: interpretation, analysis, and design. Design can be further subdivided into partial and full integration. Respectively combining information, data, and designs, we further define these types of integration and describe their general benefits and challenges, such as strength of inference. We further use the Oil Sands Monitoring program in northern Alberta as an example to clarify the practices common among integrated monitoring programs. The goal of the discussion paper is to familiarize readers with the diverse practices of integrated monitoring to further clarify the various configurations used to achieve the wider goals of a program.
... Such mechanistic complexity of stressor-response relationships might obscure the interactions among multiple stressors (Gieswein et al., 2017). In addition, whether the stressors' effects are additive or not is dependent on the stressor combinations as well as the responsible variables addressed (Jackson et al., 2016). ...
Understanding the relative importance of multiple stressors is valuable to prioritize conservation and restoration measures. Yet, the effects of multiple stressors on ecosystem functioning remain largely unknown in many fresh waters. Here, we provided a methodology combining ecosystem modeling with linear regression to disentangle the effects of multiple stressors on matter flow, an important ecosystem function. Treating a shallow lake as the model ecosystem, we simulated matter flow dynamics during 1950s–2010s with different combinations of stressors by Ecopath with Ecosim (EwE) modeling and determined the relative importance of each stressor by generalized linear mixed models. We found that matter flow of the lake food web was highly dynamic, attributing to effects of multiple anthropogenic stressors. Biological invasion played the strongest role in driving the matter flow dynamics, followed by eutrophication, while biomanipulation (i.e., phytoplankton control by planktivorous fish stocking) was of little importance. Eutrophication had a stronger role on primary producers, pelagic food chain, and top predators, while biological invasion on consumers in the middle of food chains. The former was more important in driving the quantity of matter flow, while the latter on trophic transfer efficiencies. Scenario forecasting showed that reducing nutrients contents could largely shape the matter flow pattern, while biomanipulation had little effect. Our findings provided new insights into understanding the mechanistic links between anthropogenic stressors and ecosystem functioning by combining ecosystem modeling with linear regression.
... Thirdly, paired-stressor interactions may not capture the full complexity of outcomes, yet, are most commonly applied ( Gessner and Tlili, 2016 ), constraining the scope for detection of higher-order interactions ( Feld et al., 2016 ). In addition, stressors can affect multiple ecosystem components, with the predominant types of interactions varying amongst levels of ecological organisation (individuals, populations, communities) and the specific response variables considered ( Côté et al., 2016 ;Jackson et al., 2016 ;Gieswein et al., 2017 ), including functional traits ( Schinegger et al., 2016 ). ...
Despite advances in conceptual understanding, single-stressor abatement approaches remain common in the management of fresh waters, even though they can produce unexpected ecological responses when multiple stressors interact. Here we identify limitations restricting the development of multiple-stressor management strategies and address these, bridging theory and practice, within a novel empirical framework. Those critical limitations include that (i) monitoring schemes fall short of accounting for theory on relationships between multiple-stressor interactions and ecological responses, (ii) current empirical modelling approaches neglect the prevalence and intensity of multiple-stressor interactions, and (iii) mechanisms of stressor interactions are often poorly understood. We offer practical recommendations for the use of empirical models and experiments to predict the effects of freshwater degradation in response to changes in multiple stressors, demonstrating this approach in a case study. Drawing on our framework, we offer practical recommendations to support the development of effective management strategies in three general multiple-stressor scenarios.
... Lange et al. (2016) have also shown that factors related to land use, such as farm intensity, have greater impact on stream algae than does water abstraction. Effectively, the biology between rivers may be different, but this is attributed most often to a range of variables such as water trophy, habitat quality and riparian land use (e.g., Gieswein et al., 2017) and not to river regulation itself, which exerts influence through other components of the flow regime rather than the amount of water (Poff et al., 1997). The decision to include all sampling sites together in the analysis, regardless of river regulation type, can, in fact, impair the particular analysis of macroalgae biodiversity indices, but the authors' final decision was to lose some detail at the biological group level but gain greater robustness at the ecosystem response level. ...
This work assesses the effects of river regulation on the diversity of different instream and riparian biological communities along a relieve gradient of disturbance in regulated rivers. Two case studies in Portugal were used, with different river regulation typology (downstream of run-of-river and reservoir dams), where regulated and free-flowing river stretches were surveyed for riparian vegetation, macrophytes, bryophytes, macroalgae, diatoms and macroinvertebrates. The assessment of the regulation effects on biological communities was approached by both biological and functional diversity analysis. Results of this investigation endorse river regulation as a major factor differentiating fluvial biological communities through an artificial environmental filtering that governs species assemblages by accentuating species traits related to river regulation tolerance. Communities' response to regulation gradient seem to be similar and insensitive to river regulation typology. Biological communities respond to this regulation gradient with different sensibilities and rates of response, with riparian vegetation and macroinvertebrates being the most responsive to river regulation and its gradient. Richness appears to be the best indicator for general fluvial ecological quality facing river regulation. Nevertheless, there are high correlations between the biological and functional diversity indices of different biological groups, which denotes biological connections indicative of a cascade of effects leading to an indirect influence of river regulation even on non-responsive facets of communities' biological and functional diversities. These results highlight the necessary holistic perspective of the fluvial system when assessing the effects of river regulation and the proposal of restoration measures.
It is important to discover what change led to the improvement in European macroinvertebrate biodiversity in the period from 1990−2000s and what prevents further desirable gains from taking place today. A 30-year data set from 1,457 macroinvertebrate monitoring sites spread across England, with 65,032 discrete observations was combined with 41 chemical, physical, habitat, and geographic variables. This data set was analyzed using generalized linear mixed-effect models and generalized additive mixed models. To include all combinations of the variables required to address each question, required over 20,000 model runs. It was found that no variables were more consistently and strongly associated with the overall family richness than Zn and Cu. Zn and Cu led both for the era of large gains in richness up to 2005 and also in the later period of 2006–2018 when few further gains were made.
Objective
Rapid changes in the world's oceans make assessment of fish population responses to multiple stressors, especially on scales relevant to management, increasingly important. I used an existing agent‐based, spatially explicit model of Atlantic Croaker Micropogonias undulatus in the northern Gulf of Mexico to examine how temperature, hypoxia, and ocean acidification, singly and in combinations, affect long‐term population dynamics.
Methods
I performed a factorial simulation experiment with each stressor at three levels and analyzed various treatment combinations to assess the additivity and multiplicity of interactions. The response variables were long‐term equilibrium (final year) values of spawning stock biomass (SSB), recruitment, weight at age, and two measures of stock productivity (recruits per SSB and maximum recruitment) derived from the spawner–recruit relationship fitted to model output. I used the single‐stressor effects from the experiment to predict how the response variables would change when all three stressors were changed. Single‐stressor effects were combined as the sum of the fractional changes (additive scale) and the product of ratios of changes (multiplicative scale) and compared to the responses in simulations with all stressors imposed.
Result
Analyzing the factorial design for two‐way and three‐way interactions showed that there were many interactions on the additive scale but very few on the multiplicative scale. Thus, the responses to multiple stressors were well predicted from single stressor effects when combined as multiplicative effects.
Conclusion
I discuss how the lack of strong interactions could be due to model assumptions, the structure of the model, or oversimplified representation of stressor effects. Alternatively, the model and analysis may be sufficiently realistic and weak interactions on the multiplicative scale may be common. This would reduce a complicated multi‐factor situation to a series of more tractable single‐factor effects. A critical next step is to determine how we can a priori identify situations of low interactions (i.e., predictable from single‐stressor effects) without having to already know the multi‐stressor response.
In the pilot study “Kleingewässermonitoring” a comprehensive database was compiled on the pesticide contamination of small water bodies in the German agricultural landscape. The here presented in-depth analyses of the data aimed to identify driving factors for pesticide inputs in small streams, to assess the effectiveness of risk mitigation measures under field conditions and to provide further information on pesticide toxicity of single substances and mixtures as well. It was shown that vegetated buffer stripes can effectively reduce pesticide inputs and that intermittent ditches increase pesticide inputs into small streams. The large number of simultaneously found pesticides in the water samples underlines the additional risk for aquatic organisms caused by pesticide mixtures, which is so far not considered in the PPP approval procedure. A further monitoring campaign in 2021 supplements the data from 2018/2019 and shows a slow phase-out of the now banned neonicotinoids and the relevance of pyrethroids, which are increasingly used as substitutes for the neonicotinoids. The first evaluation of data on PPP use in the catchment areas of the monitoring sites indicates the connection between the use of pesticides on agricultural fields and concentrations found in the streams. This finding highlights the importance use data for the identification of driving factors for pesticide exposure and the validation of exposure models or mitigation measures. Recommendations for an adapted monitoring concept are presented on the basis of the results.
Freshwaters are considered among the most endangered ecosystems globally due to multiple stressors, which coincide in time and space. These local stressors typically result from land-use intensification or hydroclimatic alterations, among others. Despite recent advances on multiple stressor effects, current knowledge is still limited to manipulative approaches minimizing biological and abiotic variability. Thus, the assessment of multiple stressor effects in real-world ecosystems is required. Using an extensive survey of 50 stream reaches across North Portugal, we evaluated taxonomic and functional macroinvertebrate responses to multiple stressors, including marked gradients of nutrient enrichment, flow reduction, riparian vegetation structure, thermal stress and dissolved oxygen depletion. We analyzed multiple stressor effects on two taxonomic (taxon richness, Shannon-diversity) and two trait-based diversity indices (functional richness, functional dispersion), as well as changes in trait composition. We found that multiple stressors had additive effects on all diversity metrics, with nutrient enrichment identified as the most important stressor in three out of four metrics, followed by dissolved oxygen depletion and thermal stress. Taxon richness, Shannon-diversity and functional richness responded similarly, whereas functional dispersion was driven by changes in flow velocity and thermal stress. Functional trait composition changed along a major stress gradient determined by nutrient enrichment and oxygen depletion, which was positively correlated with organisms possessing fast-living strategies, aerial respiration, adult phases, and gathering-collector feeding habits. Overall, our results reinforce the need to consider complementary facets of biodiversity to better identify assembly processes in response to multiple stressors. Our data suggest that stressor interactions may be less frequent in real-word streams than predicted by manipulative experiments, which can facilitate mitigation strategies. By combining an extensive field survey with an integrative consideration of multiple biodiversity facets, our study provides new insights that can help to better assess and manage rivers in a global change context.
Multiple stressors affect freshwater systems and cause a deficient ecological status according to the European Water Framework Directive (WFD). To select effective mitigation measures and improve the ecological status, knowledge on the stressor hierarchy and individual and joined effects is necessary. However, compared to common stressors like nutrient enrichment and morphological degradation, the relative importance of micropollutants such as pesticides and pharmaceuticals is largely unaddressed. We used WFD monitoring data from Saxony (Germany) to investigate the importance of 85 environmental variables (including 34 micropollutants) for 18 benthic invertebrate metrics at 108 sites. The environmental variables were assigned to five groups (natural factors, nutrient enrichment, metals, micropollutants and morphological degradation) and were ranked according to their relative importance as group and individually within and across groups using Principal Component Analyses (PCAs) and Boosted Regression Trees (BRTs). Overall, natural factors contributed the most to the total explained deviance of the models. This variable group represented not only typological differences between sampling sites but also a gradient of human impact by strongly anthropogenically influenced variables such as electric conductivity and dissolved oxygen. These large-scale effects can mask the individual importance of the other variable groups, which may act more specifically at a subset of sites. Accordingly, micropollutants were not represented by a few dominant variables but rather a diverse palette of different chemicals with similar contribution. As group, micropollutants contributed similarly as metals, nutrient enrichment and morphological degradation. However, the importance of micropollutants might be underestimated due to limitations of the current chemical monitoring practices.
Natural and anthropogenic factors form stream macroinvertebrate communities depending on their combination, intensity, and spatial pattern. The study aimed to identify macroinvertebrate indicators that respond to land cover, hydromorphology, and wastewater releases individually and to their multiple-pressure pattern.
Environmental and macroinvertebrate data from 36 sites were used in the study. Pressure parameters representing hierarchy of their complexity and spatial scale were included in analyses. Correlation analyses were used for evaluation of relationships among pressure characteristics and also pressure–macroinvertebrate relationships. The pressure-based and biological classification of sites was compared and indicator taxa were identified.
The arable land in the sub-corridor extending 2–10 km upstream of an investigated site was the main pressure factor influencing the structure of macroinvertebrate communities in the studied streams. The biological effects of small-scale land cover were followed by catchment-scale land cover and hydromorphology. Almost no association of macroinvertebrates with the risk of point source pollution were detected. Classifications based on pressures and community composition corresponded only by the separation of most degraded sites from others. Among the macroinvertebrate indicators characterizing the severe impairment threshold, chironomids and oligochaetes dominated. Different responses of macroinvertebrates to hydromorphological degradation were observed under conditions of high small- and large-scale agricultural pressures (decrease in macroinvertebrate evenness and increase in oligochaete taxa richness, respectively). Linking biological indicators to pressure components and their combinations improves the efficiency of conservation and restoration strategies applied in fluvial ecosystems.
Rigorous assessments of the ecological condition of water resources and the effect of human activities on those waters require quantitative physical, chemical, and biological data. The U.S. Environmental Protection Agency’s river and stream surveys quantify river and stream bed particle size and stability, instream habitat complexity and cover, riparian vegetation cover and structure, and anthropogenic disturbance activities. Physical habitat is strongly controlled by natural geoclimatic factors that co-vary with human activities. We expressed the anthropogenic alteration of physical habitat as O/E ratios of observed habitat metric values divided by values expected under least-disturbed reference conditions, where site-specific expected values vary given their geoclimatic and geomorphic context. We set criteria for good, fair, and poor condition based on the distribution of O/E values in regional least-disturbed reference sites. Poor conditions existed in 22–24% of the 1.2 million km of streams and rivers in the conterminous U.S. for riparian human disturbance, streambed sediment and riparian vegetation cover, versus 14% for instream habitat complexity. Based on the same four indicators, the percentage of stream length in poor condition within 9 separate U.S. ecoregions ranged from 4% to 42%. Associations of our physical habitat indices with anthropogenic pressures demonstrate the scope of anthropogenic habitat alteration; habitat condition was negatively related to the level of anthropogenic disturbance nationally and in nearly all ecoregions. Relative risk estimates showed that streams and rivers with poor sediment, riparian cover complexity, or instream habitat cover conditions were 1.4 to 2.6 times as likely to also have fish or macroinvertebrate assemblages in poor condition. Our physical habitat condition indicators help explain deviations in biological conditions from those observed among least-disturbed sites and inform management actions for rehabilitating impaired waters and mitigating further ecological degradation.
Die Pilotphase Kleingewässermonitoring konnte als drittes Teilvorhaben zur „Umsetzung des Nationalen Aktionsplan zur nachhaltigen Anwendung von Pflanzenschutzmitteln (PSM)“ erfolgreich als zweijähriges Monitoring umgesetzt werden. Es wurden für mehr als 100 Fließgewässerabschnitte in 13 Bundesländern umfassend der chemische und biologische Zustand kleiner Fließgewässer in der Agrarlandschaft zwischen April und Juli erfasst. Zusätzlich zu Schöpfproben analog zu dem behördlichen Monitoring nach Wasserrahmenrichtlinie (WRRL) wurden ereignisbasierte Wasserproben genommen, um kurzfristige Peakkonzentrationen infolge von Niederschlägen zu erfassen. Zudem wurden anthropogene Stressoren wie Gewässerstruktur, Nährstoffe und Sauerstoffdefizite hochaufgelöst aufgenommen. Die biologische Untersuchung umfasste die Beprobung der aquatischen Invertebraten- und Algengemeinschaft sowie eine Untersuchung der Ökosystemfunktion in den Kleingewässern.
Die Ergebnisse zeigen, dass die im Rahmen des Zulassungsverfahrens von PSM festgelegten RAK-Werte (Regulatorisch Akzeptablen Konzentrationen) an über 73 % der untersuchten Standorte für mindestens einen PSM-Wirkstoff überschritten wurden. Besonders die Ereignisproben infolge von Regenereignissen wiesen erhöhte Konzentrationen auf, die durch Schöpfproben nicht erfasst wurden. Diese Belastungen korrelieren auch mit der ökologischen Situation der Gewässer. So erfüllt der Großteil (über 80 %) der untersuchten Fließgewässerabschnitte anhand des SPEARpesticides-Index nicht die Qualitätskriterien für einen guten Zustand.
Die Pilotphase Kleingewässermonitoring zeigt, dass eine realistische Bewertung und regulatorische Nutzung eines Monitorings von PSM-Rückständen in kleinen Gewässern nur dann erfolgen kann, wenn auch erhöhte Einträge infolge von Niederschlagsereignissen berücksichtigt werden. Weiterhin treten auch unterhalb der bestehenden RAK-Werte ökologische Effekte im Gewässer auf, so dass sich die Frage nach der Protektivität der aus Labordaten abgeleiteten RAK-Werte stellt. Die Daten der ermittelten PSM-Belastung der kleinen Gewässer in der Agrarlandschaft werden dazu beitragen, Ursachen für die regelmäßige Überschreitung der bestehenden Grenzwerte zu ermitteln und Schwächen der bisherigen Risikobewertung aufzudecken. Ziel wird sein, auf dieser Basis Möglichkeiten zur Reduzierung der Einträge zu erarbeiten und regulatorische Konsequenzen zu ziehen. Siehe dazu auch Liess et al. (2021) und Weisner et al. (2021).
Glyphosate (GLY) is a broad-spectrum herbicide that is the most commonly applied pesticide in terrestrial ecosystems in the U.S. and, potentially, worldwide. However, the combined effects of warming associated with climate change and exposure to GLY and GLY-based formulations (GBFs) on terrestrial animals are poorly understood. Animals progress through several life stages (e.g., embryonic, larval, and juvenile stages) that may exhibit different sensitivities to stressors. Therefore, we factorially manipulated temperature and GLY/GBF exposure in the variable field cricket (Gryllus lineaticeps) during two life stages—nymphal development and adulthood—and examined key animal traits, such as developmental rate, body size, food consumption, reproductive investment, and lifespan. A thermal environment simulating future climate warming obligated several costs to fitness-related traits. For example, warming experienced during nymphal development reduced survival, adult body mass and size, and investment into flight capacity and reproduction. Warming experienced by adults reduced lifespan and growth rate. Alternatively, the effects of GBF exposure were more subtle, often context-dependent (e.g., effects were only detected in one sex or temperature regime), and were stronger during adult exposure relative to exposure during development. There was evidence of additive costs of warming and GBF exposure to rates of feeding and growth in adults. Yet, the negative effect of GBF exposure to adult lifespan did not occur in warming conditions, suggesting that ongoing climate change may obscure some of the costs of GBFs to non-target organisms. The effects of GLY alone (i.e., in the absence of proprietary surfactants found in commercial formulations) were non-existent. Animals will be increasingly exposed to warming and GBFs, and our results indicate that GBF exposure and warming can entail additive costs for an animal taxon (insects) that plays critical roles in terrestrial ecosystems.
The pilot study “Kleingewässermonitoring” was successfully implemented as a two-year monitoring program on residues of plant protection products (PPPs) in small streams. The chemical pollution and biological status of small streams in the agricultural landscape was investigated in-depth between April and July for more than 100 stream sections in 13 federal states in Germany. In addition to grab water samples according to the Water Framework Directive (WFD), event-based water samples were taken. The event-based water samples represent short-term pulse concentrations of pesticide residues following precipitation events. Also passive samplers (Chemcatcher and Sorb-Star) were exposed over three-week periods to obtain time-weighted average (background) concentrations of pesticides. Other anthropogenic stressors such as poor structural quality, nutrients, and oxygen depletion were also recorded in high resolution for the whole data set. The biological investigations included sampling of the aquatic invertebrate community and the algal community as well the ecosystem functions in the small streams.
The results of the “Kleingwässermonitoring” show that the RAK values (Regulatory Acceptable Concentrations) from the authorization process for PPPs were exceeded for at least one active substance at over 73 % of the sites investigated. In particular, event-based samples showed high concentrations, which would not have been detected by the regular grab sampling. The revealed pollution resulting from the use of PPPs, correlates with the ecological quality of the water bodies. Findings of the bio indicator SPEARpesticides show that the majority (over 80 %) of the small streams in the German agricultural landscape fails a good ecological status.
The “Kleingewässermonitoring” confirms that a realistic assessment of PPP contamination in small streams needs to include exposure peaks caused by precipitation events if results should be used for regulatory consequences. The pilot study revealed, that existing thresholds for PPP residues are regularly exceeded in small streams in Germany, even though PPP authorization is complex and often criticized as over-conservative by industry and farmers. Furthermore, ecological effects even if pollution is below these thresholds indicate, that regulatory thresholds derived from laboratory studies may not always be protective for field conditions. The data from this pilot study can be used to derive measures to reduce pollution of small streams by PPP use in the future.
Abstract This work addresses human stressors and their impacts on fish assemblages at pan-European scale by analysing single and multiple stressors and their interactions. Based on an extensive dataset with 3105 fish sampling sites, patterns of stressors, their combination and nature of interactions, i.e. synergistic, antagonistic and additive were investigated. Geographical distribution and patterns of seven human stressor variables, belonging to four stressor groups (hydrological-, morphological-, water quality- and connectivity stressors), were examined, considering both single and multiple stressor combinations. To quantify the stressors' ecological impact, a set of 22 fish metrics for various fish assemblage types (headwaters, medium gradient rivers, lowland rivers and Mediterranean streams) was analysed by comparing their observed and expected response to different stressors, both acting individually and in combination. Overall, investigated fish sampling sites are affected by 15 different stressor combinations, including 4 stressors acting individually and 11 combinations of two or more stressors; up to 4 stressor groups per fish sampling site occur. Stressor-response analysis shows divergent results among different stressor categories, even though a general trend of decreasing ecological integrity with increasing stressor quantity can be observed. Fish metrics based on density of species ‘intolerant to water quality degradation’ and ‘intolerant to oxygen depletion” responded best to single and multiple stressors and their interactions. Interactions of stressors were additive (40%), synergistic (30%) or antagonistic (30%), emphasizing the importance to consider interactions in multi-stressor analyses. While antagonistic effects are only observed in headwaters and medium-gradient rivers, synergistic effects increase from headwaters over medium gradient rivers and Mediterranean streams to large lowland rivers. The knowledge gained in this work provides a basis for advanced investigations in European river basins and helps prioritizing further restoration and management actions.
The aim of the study was to evaluate whether riparian trees limit growth of aquatic plants in lakes. In the studied lake, sections of the littoral zone were shaded to different degrees. The maximum extent of shading in the studied lake did not exceed 15 m. Regardless of the amount of light reaching the lake three groups of macrophytes developed. The data suggest that shading by riparian vegetation was not limiting to growth of all aquatic plants in the studied lake but did significantly limit development of macrophyte communities. The extent of shading was correlated with both the structure of macrophyte communities in addition to their range. In shady areas density, colonization depth, biomass and diversity index of emergent macrophytes were significantly lower. Submerged macrophytes in the lake were generally outside the scope of shadow impact. Only macrophytes occurring between 0.5 and 1 m depth were influenced by shade. Generally, submerged macrophyes were outside of the influence of shade. However, along the northern shore, lush growth of adjacent rushes may have effected submerged macrophytes and in these areas their measured values (biomass, density, abundance) were lower. In the southern part of the lake, rushes achieve lower density and extent of occurrence, but submerged macrophytes grew better, and both biomass and species richness were higher than along northern shores.
Interactions between multiple ecosystem stressors are expected to jeopardize biological processes, functions and biodiversity. The scientific community has declared stressor interactions—notably synergies—a key issue for conservation and management. Here, we review ecological literature over the past four decades to evaluate trends in the reporting of ecological interactions (synergies, antagonisms and additive effects) and highlight the implications and importance to conservation. Despite increasing popularity, and ever-finer terminologies, we find that synergies are (still) not the most prevalent type of interaction, and that conservation practitioners need to appreciate and manage for all interaction outcomes, including antagonistic and additive effects. However, it will not be possible to identify the effect of every interaction on every organism’s physiology and every ecosystem function because the number of stressors, and their potential interactions, are growing rapidly. Predicting the type of interactions may be possible in the near-future, using meta-analyses, conservation-oriented experiments and adaptive monitoring. Pending a general framework for predicting interactions, conservation management should enact interventions that are robust to uncertainty in interaction type and that continue to bolster biological resilience in a stressful world. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
Examines what insights into habitat suitability and the abundance of specimens, population dynamics and potential biological interactions along rivers can be gained by a coupled modelling approach, and investigates how megaform (plate tectonics = abrupt changes of slope), macroform (floodplain changes = streams bordered by grassland or trees), mesoform (channel processes = riffle-pool sequences) and microform processes (annual flow fluctuations = bankfull or low flow discharge) potentially affect local ecological responses along rivers. A third objective of this review is to demonstrate how a physically oriented modelling approach can improve the process of hypothesis generation, which is one of the most critical parts of any piece of ecological research. -from Authors
The potential for complex synergistic or antagonistic interactions between multiple stressors presents one of the largest uncertainties when predicting ecological change but, despite common use of the terms in the scientific literature, a consensus on their operational definition is still lacking. The identification of synergism or antagonism is generally straightforward when stressors operate in the same direction, but if individual stressor effects oppose each other, the definition of synergism is paradoxical because what is synergistic to one stressor's effect direction is antagonistic to the others. In their highly cited meta-analysis, Crain et al. (Ecology Letters, 11, 2008: 1304) assumed in situations with opposing individual effects that synergy only occurs when the cumulative effect is more negative than the additive sum of the opposing individual effects. We argue against this and propose a new systematic classification based on an additive effects model that combines the magnitude and response direction of the cumulative effect and the interaction effect. A new class of “mitigating synergism” is identified, where cumulative effects are reversed and enhanced. We applied our directional classification to the dataset compiled by Crain et al. (Ecology Letters, 11, 2008: 1304) to determine the prevalence of synergistic, antagonistic, and additive interactions. Compared to their original analysis, we report differences in the representation of interaction classes by interaction type and we document examples of mitigating synergism, highlighting the importance of incorporating individual stressor effect directions in the determination of synergisms and antagonisms. This is particularly pertinent given a general bias in ecology toward investigating and reporting adverse multiple stressor effects (double negative). We emphasize the need for reconsideration by the ecological community of the interpretation of synergism and antagonism in situations where individual stressor effects oppose each other or where cumulative effects are reversed and enhanced.
1. Introduction Aquatic biological standards, established in law, can be an effective mechanism to promote restoration and ensure the ecological sustainability of aquatic resources (Adler, 2003; Hering et al., 2010). Several countries around the world have established legislation or policies to promote the restoration and maintenance of aquatic ecosystems (CWA, 2006; ANZECC, 2000; EC, 2000). However, the effectiveness of such policy initiatives depends upon the technical clarity of ecological goal statements, and the political clarity of intent that is written into the law. The United States Clean Water Act, for example, states a long-term, national objective to ''restore and maintain the . . . biological integrity of the Nation's waters'' (section 1251). However, the Act does not define the ecological components, or attributes, that constitute biological integrity. Neither does the Act recommend scientific methods to measure the condition of aquatic biota. Rather, the U.S. Clean Water Act delegates the technical implementation of the
Running water ecosystems of Europe are affected by various human pressures. However, little is known about the prevalence, spatial patterns, interactions with natural environment and co-occurrence of pressures. This study represents the first high-resolution data analysis of human pressures at the European scale, where important pressure criteria for 9330 sampling sites in 14 European countries were analysed. We identified 15 criteria describing major anthropogenic degradation and combined these into a global pressure index by taking additive effects of multiple pressures into account. Rivers are affected by alterations of water quality (59%), hydrology (41%) and morphology (38%). Connectivity is disrupted at the catchment level in 85% and 35% at the river segment level. Approximately 31% of all sites are affected by one, 29% by two, 28% by three and 12% by four pressure groups; only 21% are unaffected. In total, 47% of the sites are multi-impacted. Approximately 90% of lowland rivers are impacted by a combination of all four pressure groups.
Efforts to limit plant growth in streams by reducing nutrients would benefit from an understanding of the relative influences of nutrients, streamflow, light, and other potentially important factors. We measured macrophytes, benthic algae, nutrients in water and sediment, discharge, and shading from 30 spring-fed or runoff-influenced streams in the upper Snake River basin, ID, USA. We hypothesized that in hydrologically stable, spring-fed streams with clear water, macrophyte and benthic algae biomass would be a function of bioavailable nutrients in water or sediments, whereas in hydrologically dynamic, runoff-influenced streams, macrophyte and benthic algae biomass would further be constrained by flow disturbance and light. These hypotheses were only partly supported. Nitrogen, both in sediment and water, was positively correlated with macrophyte biomass, as was loosely sorbed phosphorus (P) in sediment. However, P in water was not. Factors other than nutrient enrichment had the strongest influences on macrophyte species composition. Benthic algal biomass was positively correlated with loosely sorbed sediment P, lack of shade, antecedent water temperatures, and bicarbonate. These findings support the measurement of bioavailable P fractions in sediment and flow histories in streams, but caution against relying on macrophyte species composition or P in water in nutrient management strategies for macrophytes in streams.
Classification and regression trees are ideally suited for the analysis of complex ecological data. For such data, we require flexible and robust analytical methods, which can deal with nonlinear relationships, high-order interactions, and missing values. Despite such difficulties, the methods should be simple to understand and give easily interpretable results. Trees explain variation of a single response variable by repeatedly splitting the data into more homogeneous groups, using combinations of explanatory variables that may be categorical and/or numeric. Each group is characterized by a typical value of the response variable, the number of observations in the group, and the values of the explanatory variables that define it. The tree is represented graphically, and this aids exploration and understanding. Trees can be used for interactive exploration and for description and prediction of patterns and processes. Advantages of trees include: (1) the flexibility to handle a broad range of response types, including numeric, categorical, ratings, and survival data; (2) invariance to monotonic transformations of the explanatory variables; (3) ease and robustness of construction; (4) case of interpretation; and (5) the ability to handle missing values in both response and explanatory variables. Thus, trees complement or represent an alternative to many traditional statistical techniques, including multiple regression, analysis of variance, logistic regression, log-linear models, linear discriminant analysis, and survival models. We use classification and regression trees to analyze survey data from the Australian central Great Barrier Reef, comprising abundances of soft coral taxa (Cnidaria: Octocorallia) and physical and spatial environmental information. Regression tree analyses showed that dense aggregations, typically formed by three taxa, were restricted to distinct habitat types, each of which was defined by combinations of 3-4 environmental variables. The habitat definitions were consistent with known experimental findings on the nutrition of these taxa. When used separately, physical and spatial variables were similarly strong predictors of abundances and lost little in comparison with their joint use. The spatial variables are thus effective surrogates for the physical variables in this extensive reef complex, where information on the physical environment is often not available. Finally, we compare the use of regression trees and linear models for the analysis of these data and show how linear models fail to find patterns uncovered by the trees.
The use of the CEN (European Committee for Standardization) standard method for sampling fish in lakes using multi-mesh gillnets allowed the collection of fish assemblages of 445 European lakes in 12 countries. The lakes were additionally characterised by environmental drivers and eutrophication proxies. Following a site-specific approach including a validation procedure, a fish index including two abundance metrics (catch per unit effort expressed as fish number and biomass) and one functional metric of composition (abundance of omnivorous fish) was developed. Correlated with the proxy of eutrophication, this index discriminates between heavily and moderately impacted lakes. Additional analyses on a subset of data from Nordic lakes revealed a stronger correlation between the new fish index and the pressure data. Despite an uneven geographical distribution of the lakes and certain shortcomings in the environmental and pressure data, the fish index proved to be useful for ecological status assessment of lakes applying standardised protocols and thus supports the development of national lake fish assessment tools in line with the European Water Framework Directive.
The majority of studies comparing the response of biotic metrics to environmental stress in rivers are based on relatively small, homogeneous datasets resulting from research projects. Here, we used a large dataset from Austrian and German national river monitoring programmes (2,302 sites) to analyse the response of fish, diatom and macroinvertebrate metrics to four stressors acting at different scales (hydromorphology, physico-chemistry, riparian and catchment land use). Nutrient enrichment and catchment land use were the main discriminating stressors for all organism groups, over-ruling the effects of hydromorphological stress on the site scale. The response of fish metrics to stress was generally low, while macroinvertebrate metrics performed best. The Trophic Diatom Index (TDI) responded most strongly to all stressors in the mountain streams, while different metrics were responsive in the lowlands. Our results suggest that many rivers are still considerably affected by nutrient enrichment (eutrophication), which might directly point at implications of catchment land use. We conclude that monitoring datasets are well-suited to detect major broad-scale trends of degradation and their impact on riverine assemblages, while the more subtle effects of local-scale stressors require stream type-specific approaches.
Global stressors, including climate change, are a major threat to ecosystems, but they cannot be halted by local actions. Ecosystem management is thus attempting to compensate for the impacts of global stressors by reducing local stressors, such as overfishing. This approach assumes that stressors interact additively or synergistically, whereby the combined effect of two stressors is at least the sum of their isolated effects. It is not clear, however, how management should proceed for antagonistic interactions among stressors, where multiple stressors do not have an additive or greater impact. Research to date has focussed on identifying synergisms among stressors, but antagonisms may be just as common. We examined the effectiveness of management when faced with different types of interactions in two systems - seagrass and fish communities - where the global stressor was climate change but the local stressors were different. When there were synergisms, mitigating local stressors delivered greater gains, whereas when there were antagonisms, management of local stressors was ineffective or even degraded ecosystems. These results suggest that reducing a local stressor can compensate for climate change impacts if there is a synergistic interaction. Conversely, if there is an antagonistic interaction, management of local stressors will have the greatest benefits in areas of refuge from climate change. A balanced research agenda, investigating both antagonistic and synergistic interaction types, is needed to inform management priorities.
This study was designed to test for synergism (increased stress) or antagonism (decreased stress) among multiple environmental stressors using additive, multiplicative, and simple comparative effects models. Model predictions were compared to empirical results of laboratory experiments measuring interactions among thermal stress, toxin exposure, and low food on reproduction and survival of two species of cladoceran zooplankton. Stress was defined operationally as a reduction in reproduction or survival relative to optimal conditions over a 7-d period. These experiments are particularly applicable to episodic stresses such as those associated with short-term heat waves. Toxin or low food in combination with 30°C temperatures were generally more harmful than high temperature alone. However, most multiple stress effects were antagonistic, in that effects in combination were not as severe as predicted based on the sum or the product of their individual effects. In rare cases, interaction among stressors even diminished effects of the worst single stressor. Optimal conditions for reproduction and survival occurred at 25°C, high food and 0 mg liter-1 toxin (a surfactant, sodium dodecyl sulfate). Suppressive effects of stressors examined individually ranked: high temperature (30°C) > SDS (10 mg liter-1 ≥ low food (~100 μg C liter-1) > low temperature (20°C). Daphnia pulex isolated from a pond which experiences high summer temperatures throughout was more tolerant of 30°C conditions than Daphnia pulicaria isolated from a lake with a cold-water refuge. Differences were observed in individuals exposed as either adults or as 24-h neonates.
Changes to land use affect streams through nutrient enrichment, increased inputs of sediment and, where riparian vegetation has been removed, raised water temperature. We manipulated all three stressors in experimental streamside channels for 30 days and determined the individual and pair-wise combined effects on benthic invertebrate and algal communities and on leaf decay, a measure of ecosystem functioning. We added nutrients (phosphorus+nitrogen; high, intermediate, natural) and/or sediment (grain size 0.2 mm; high, intermediate, natural) to 18 channels supplied with water from a nearby stream. Temperature was increased by 1.4°C in half the channels, simulating the loss of upstream and adjacent riparian shade. Sediment affected 93% of all biological response variables (either as an individual effect or via an interaction with another stressor) generally in a negative manner, while nutrient enrichment affected 59% (mostly positive) and raised temperature 59% (mostly positive). More of the algal components of the community responded to stressors acting individually than did invertebrate components, whereas pair-wise stressor interactions were more common in the invertebrate community. Stressors interacted often and in a complex manner, with interactions between sediment and temperature most common. Thus, the negative impact of high sediment on taxon richness of both algae and invertebrates was stronger at raised temperature, further reducing biodiversity. In addition, the decay rate of leaf material (strength loss) accelerated with nutrient enrichment at ambient but not at raised temperature. A key implication of our findings for resource managers is that the removal of riparian shading from streams already subjected to high sediment inputs, or land-use changes that increase erosion or nutrient runoff in a landscape without riparian buffers, may have unexpected effects on stream health. We highlight the likely importance of intact or restored buffer strips, both in reducing sediment input and in maintaining cooler water temperatures.
Study of the impacts of biological invasions, a pervasive component of global change, has generated remarkable understanding of the mechanisms and consequences of the spread of introduced populations. The growing field of invasion science, poised at a crossroads where ecology, social sciences, resource management, and public perception meet, is increasingly exposed to critical scrutiny from several perspectives. Although the rate of biological invasions, elucidation of their consequences, and knowledge about mitigation are growing rapidly, the very need for invasion science is disputed. Here, we highlight recent progress in understanding invasion impacts and management, and discuss the challenges that the discipline faces in its science and interactions with society.
1. The fundamental importance of freshwater resources, the rapid extinction rate among freshwater species and the pronounced sensitivity of freshwater ecosystems to climate change together signal a pre-eminent need for renewed scientific focus and greater resources. Against this background, the Freshwater Biological Association in 2008 launched a new series of ‘summit’ Conferences in Aquatic Biology intended to develop and showcase the application of ecological science to major issues in freshwater management.
2. This collection of studies arose from the first summit entitled ‘Multiple Stressors in Freshwater Ecosystems’. Although freshwater science and management are replete with mutiple-stressor problems, few studies have been designed explicitly to untangle their effects.
3. The individual case studies that follow reveal the wide array of freshwaters affected by multiple stressors, the spatial and temporal scales involved, the species and ecosystem processes affected, the complex interactions between ecology and socioeconomics that engender such effects, the approaches advocated to address the problems and the challenges of restoring affected systems. The studies also illustrate the extent to which new challenges are emerging (e.g. through climate change), but also they develop a vision of how freshwaters might be managed sustainably to offset multiple stressors in future.
4. More generically, these case studies illustrate (i) how freshwaters might be at particular risk of multiple-stressor effects because of conflicts in water use, and because the hydrological cycle vectors stressor effects so effectively and so extensively; (ii) that dramatic, nonlinear, ‘ecological surprises’ sometimes emerge as multiple-stressor effects develop and (iii) that good ecology and good ecologists add considerable value to other freshwater disciplines in understanding multiple stressors and managing their effects.
Aquatische Makrophyten (Gefaspflanzen, Wassermoose und Characeen) stellen eine Organismengruppe mit wesentlicher Bedeutung fur okologisch orientierte Aussagen an Fliesgewasser dar. Es werden zusammenfassend methodische Ansatze vorgestellt, die sich fur verschiedene Fragestellungen in der Fliesgewasserforschung bereits bewahrt haben. Wesentliche Aspekte sind zum Beispiel die Artenverbreitungsmuster der Makrophyten, die Ermittlung von Arten als Zeigerpflanzen (Bioindikatoren) und die Klassifizierung der Gewasser nach floristisch-okologischen Gesichtspunkten.
Keywords:
relative Areallange;
floristisch-okologische Flusszone;
Gewasserbelastung;
Kartierung;
mittlerer Mengenindex;
relative Pflanzenmenge;
Zeigerorganismus
Spatially intensive sampling by electrofishing is proposed as a method for quantifying spatial variation in fish assemblages at multiple scales along extensive stream sections in headwater catchments. We used this method to sample fish species at 10-m 2 points spaced every 20 m throughout 5 km of a headwater stream in France. The spatially intensive sampling design provided information at a spatial resolution and extent that enabled exploration of spatial heterogeneity in fish assemblage structure and aquatic habitat at multiple scales with empirical variograms and wavelet analysis. These analyses were effective for detecting scales of periodicity, trends, and discontinuities in the distribution of species in relation to tributary junctions and obstacles to fish movement. This approach to sampling riverine fishes may be useful in fisheries research and management for evaluating stream fish responses to natural and altered habitats and for identifying sites for potential restoration.
In the analysis of data it is often assumed that observations y1, y2, …, yn are independently normally distributed with constant variance and with expectations specified by a model linear in a set of parameters θ. In this paper we make the less restrictive assumption that such a normal, homoscedastic, linear model is appropriate after some suitable transformation has been applied to the y's. Inferences about the transformation and about the parameters of the linear model are made by computing the likelihood function and the relevant posterior distribution. The contributions of normality, homoscedasticity and additivity to the transformation are separated. The relation of the present methods to earlier procedures for finding transformations is discussed. The methods are illustrated with examples.
The implementation of the Water Framework Directive (WFD) of the European Union requires future routine assessment of the ecological status of rivers using physical, chemical and biological quality components. Fish communities referring to their species compositions, abundances, and age structures have to be considered as biological indicators. However, so far not only suitable standard sampling approaches but also an assessment method fulfilling the requirements of the WFD are lacking for Germany. Thus, the necessity of fundamental research work covering all mentioned aspects is obvious.
Function estimation/approximation is viewed from the perspective of numerical optimization iti function space, rather than parameter space. A connection is made between stagewise additive expansions and steepest-descent minimization. A general gradient descent "boosting" paradigm is developed for additive expansions based on any fitting criterion. Specific algorithms are presented for least-squares, least absolute deviation, and Huber-M loss functions for regression, and multiclass logistic likelihood for classification. Special enhancements are derived for the particular case where the individual additive components are regression trees, and tools for interpreting such "TreeBoost" models are presented. Gradient boosting of regression trees produces competitives highly robust, interpretable procedures for both regression and classification, especially appropriate for mining less than clean data. Connections between this approach and the boosting methods of Freund and Shapire and Friedman, Hastie and Tibshirani are discussed.
The accelerating rate of global change has focused attention on the cumulative impacts of novel and extreme environmental changes (i.e., stressors), especially in marine ecosystems. As integrators of local catchment and regional processes, freshwater ecosystems are also ranked highly sensitive to the net effects of multiple stressors, yet there has not been a large-scale quantitative synthesis. We analysed data from 88 papers including 286 responses of freshwater ecosystems to paired stressors, and discovered that overall, their cumulative mean effect size was less than the sum of their single effects (i.e., an antagonistic interaction). Net effects of dual stressors on diversity and functional performance response metrics were additive and antagonistic, respectively. Across individual studies, a simple vote-counting method revealed that the net effects of stressor pairs were frequently more antagonistic (41%) than synergistic (28%), additive (16%) or reversed (15%). Here, we define a reversal as occurring when the net impact of two stressors is in the opposite direction (negative or positive) from that of the sum of their single effects. While warming paired with nutrification resulted in additive net effects, the overall mean net effect of warming combined with a second stressor was antagonistic. Most importantly, the mean net effects across all stressor pairs and response metrics were consistently antagonistic or additive, contrasting the greater prevalence of reported synergies in marine systems. Here, a possible explanation for more antagonistic responses by freshwater biota to stressors is that the inherent greater environmental variability of smaller aquatic ecosystems fosters greater potential for acclimation and co-adaptation to multiple stressors. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Global climate change is likely to modify the ecological consequences of currently acting stressors, but potentially important interactions between climate warming and land-use related stressors remain largely unknown. Agriculture affects streams and rivers worldwide, including via nutrient enrichment and increased fine sediment input. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (2 levels each) and water temperature (8 levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms to determine the individual and combined effects of the three stressors on macroinvertebrate community dynamics (community composition and body size structure of benthic, drift and insect emergence assemblages). All three stressors had pervasive individual effects, but in combination often produced additive or antagonistic outcomes. Changes in benthic community composition showed a complex interplay among habitat quality (with or without sediment), resource availability (with or without nutrient enrichment) and the behavioural/physiological tendency to drift or emerge as temperature rose. The presence of sediment and raised temperature both resulted in a community of smaller organisms. Deposited fine sediment strongly increased the propensity to drift. Stressor effects were most prominent in the benthic assemblage, frequently reflected by opposite patterns in individuals quitting the benthos (in terms of their propensity to drift or emerge). Of particular importance is that community measures of stream health routinely used around the world (taxon richness, EPT richness and diversity) all showed complex three-way interactions, with either a consistently stronger temperature response or a reversal of its direction when one or both agricultural stressors were also in operation. The negative effects of added fine sediment, which were often stronger at raised temperatures, suggest that streams already impacted by high sediment loads may be further degraded under a warming climate. However, the degree to which this will occur may also depend on in-stream nutrient conditions. This article is protected by copyright. All rights reserved.
1. Biological traits, which may give insights into the mechanisms driving the distribution of organ- isms along gradients of stressor intensities, have been proposed as a tool for disentangling the effects of multiple stressors acting simultaneously on scales ranging from climatic region to river basins, val- leys, reaches and microhabitats. However, the combined effects of farming intensity and flow reduc- tion on biological traits of stream invertebrates remain to be studied.
2. We assessed the benthic invertebrate community and physicochemistry at 43 stream sites along gradients of farming intensity (0–95% of the catchment in intensively managed grassland) and water abstraction (0–92% streamflow reduction). Using general linear models and an information-theoretic approach, we studied individual and combined effects of agricultural stressors on invertebrate traits and community composition.
3. Traits often followed predictable patterns along stressor gradients, and non-additive interactions between paired stressors were common. Farming intensity was more frequently related to life-his- tory, resistance and resilience traits, whereas water abstraction was correlated more often with gen- eral biological traits such as feeding habits, dietary preference and respiration. Further, traits and traditional measures of community structure, such as taxon relative abundances and community indices, offered a similar level of distinction along the gradients of stressor intensities.
4. Our findings indicate that invertebrate traits can differentiate the effects of multiple stressors and provide insights into potential mechanisms. At the landscape scale, farming intensity exerted stron- ger effects via invertebrate habitat quality and water abstraction via food availability. At the reach scale, both fine sediment and nutrients affected habitat quality, whereas nutrients showed more marked effects via food availability. Finally, we propose a suite of traits that may provide the strong- est differentiation of stressor intensities.
1. Although many studies have focussed on the effects of catchment land use on lotic systems, the importance of broad (catchment) and fine (segment/reach) scale effects on stream assemblages remain poorly understood.
2. Nine biological metrics for macrophytes (498 sites), benthic macroinvertebrates (491) and fish (478) of lowland and mountain streams in four ecoregions of France and Germany were related to catchment and riparian buffer land use using partial Redundancy Analysis and Boosted Regression Trees (BRTs).
3. Lotic fauna was better correlated (mean max., r = 0.450) than flora ( r = 0.277) to both scales of land use: the strongest correlations were noted for mountain streams. BRTs revealed strong non‐linear relationships between mountain assemblage metrics and land use. Correlations increased with increasing buffer lengths, suggesting the importance of near‐stream land use on biotic assemblages.
4. Several metrics changed markedly between 10–20% (mountain ecoregions) and 40–45% (lowland) of arable land use, irrespective of the buffer size. At mountain sites with >10% catchment arable land use, metric values differed between sites with <30% and sites with >30% forest in the near‐stream riparian area.
5. These findings support the role of riparian land use in catchment management; however, differences between mountain and lowland ecoregions support the need for ecoregion‐specific management.
Fifteen years ago, the first mapping guidelines for the recording and evaluation of river physical habitat quality in Germany, closely following the Länder Arbeitsgemeinschaft Wasser (LAWA) field survey, have been published. In light of this experience, a revised version has now been developed for North Rhine-Westphalia (West Germany). For the assessment, the streams are divided into segments serving as survey units. The survey is performed primarily in the field from the mouth to the source by an on-site recording of data. Defined reference conditions of the relevant morphological stream types serve as basis of the evaluation. Two evaluation procedures are carried out independently to validate the quality of the data. The proven basic concept operates as follows: the local scale habitat variables are grouped into 31 single parameters, which are then aggregated into six main parameters. These can further be aggregated into three zones: streambed, banks and adjacent land. The main modifications of the presented version are the following: (1) a larger differentiation of morphological stream types and (2) a higher level of detail concerning the mapping of relevant habitat characteristics. The last point allows additional evaluation options related to the morphological needs of the instream biota and a differentiated survey of anthropogenic degradation. Despite all modifications, the comparability with previous surveys has been largely maintained. By qualitative comparison of this method with other European mapping guidelines, different concepts of hydromorphological mapping are finally discussed.
We propose that the Concept provides a framework for integrating predictable and observable biological features of lotic systems. Implications of the concept in the areas of structure, function, and stability of riverine ecosystems are discussed. -from Authors
Concern is growing about the potential effects of interacting multiple stressors, especially as the global climate changes. We provide a comprehensive review of multiple stressor interactions in coral reef ecosystems, which are widely considered to be one of the most sensitive ecosystems to global change. First, we synthesized coral reef studies that examined interactions of two or more stressors, highlighting stressor interactions (where one stressor directly influences another) and potentially synergistic effects on response variables (where two stressors interact to produce an effect that is greater than purely additive). For stressor-stressor interactions, we found studies that examined at least 2 of the 13 stressors of interest. Applying network analysis to analyze relationships between stressors, we found that pathogens were exacerbated by more co-stressors than any other stressor, with ~78% of studies reporting an enhancing effect by another stressor. Sedimentation, storms, and water temperature directly affected the largest number of other stressors. Pathogens, nutrients, and crown-of-thorns starfish were the most-influenced stressors. We found 187 studies that examined the effects of two or more stressors on a third dependent variable. The interaction of irradiance and temperature on corals has been the subject of more research (62 studies, 33% of the total) than any other combination of stressors, with many studies reporting a synergistic effect on coral symbiont photosynthetic performance (n=19). Second, we performed a quantitative meta-analysis of existing literature on this most-studied interaction (irradiance and temperature). We found that the mean effect size of combined treatments was statistically indistinguishable from a purely additive interaction, although it should be noted that the sample size was relatively small (n=26). Overall, although in aggregate a large body of literature examines stressor effects on coral reefs and coral organisms, considerable gaps remain for numerous stressor interactions and effects, and insufficient quantitative evidence exists to suggest that the prevailing type of stressor interaction is synergistic. This article is protected by copyright. All rights reserved.
The factors underlying population and community dynamics are almost invariably multivariate, and ecosystems worldwide are affected by many anthropogenic stressors. Inorganic dissolved nutrients and deposited fine sediment are common stressors in agricultural streams and can be expected to influence benthic algae and cyanobacteria.
We determined population‐ and community‐level responses of phototrophic periphyton along twin‐stressor gradients of dissolved nutrients and deposited fine sediment after 20 days of exposure in stream mesocosms. Multiple linear regression and an information‐theoretic approach were used to select the best predictive models for each response variable, accounting for potential subsidy‐stress responses for each stressor (where at low stressor levels, an ecological variable responds positively up to an inflection point, beyond which the effect is negative) and for multiple‐stressor interactions. This approach enabled us to test the subsidy‐stress hypothesis for each stressor and to investigate whether the two stressors operated singly or in concert (additively or with an interaction) on periphyton attributes.
Focussing further on three ecological guilds of periphyton (low profile, high profile, motile), we also tested the specific hypotheses, that sediment augmentation would produce a proportional increase in motile and a decrease in high‐profile forms, and that nutrient augmentation would produce proportional increases in both motile and high‐profile forms.
Unimodal subsidy‐stress patterns along the sediment gradient were found only for densities of two common N itzschia species. By contrast, unimodal patterns along the nutrient gradient occurred frequently at both population and community levels, supporting the subsidy‐stress hypothesis for nutrient enrichment. Some single‐stressor responses were observed, but the twin stressors sediment and nutrients mainly acted in a simple, additive way, probably because their modes of action are different. As a notable exception from this rule, potentially harmful cyanobacteria ( P hormidium and O scillatoria species) responded synergistically to the stressors. Our hypothesis about the representation of ecological guilds across the sediment gradient was fully supported, whilst the hypothesis regarding nutrients received partial support.
Categorisation of periphyton taxa into physiognomic guilds revealed predictable response patterns to the stressors. The prevalence of motile taxa in stream communities may be suitable for detecting sedimentation impacts and early signs of nutrient enrichment. Finally, based on periphyton response shapes along the nutrient gradient, thresholds could be identified at which community variables changed abruptly.
Aquatic ecosystems are amongst the most heavily altered ecosystems and exhibit a disproportional loss of biodiversity. Numerous stressors, such as nutrient enrichment, contaminant pollution, sedimentation and alterations in stream hydrology and habitat structure, account for these losses. Understanding these forces is of utmost importance to prevent riverine ecosystems from further deterioration and to provide helpful insights for restoration practices. In the present study, we analyse the response of biological indicators to a large number of environmental factors. For this, benthic invertebrate assemblages from 83 sites in Germany were described based on 25 metrics from four different metric types. The condition of the sites was described using 27 environmental factors: 13 for water quality, 4 for land use in the catchment and 10 for local scale habitat structure. The relative importance of single environmental predictors or predictor combinations for benthic invertebrate assemblages was analysed with single and multiple linear regression models. The results for the latter models were statistically supported via a bootstrap approach. The models revealed the importance of water quality and catchment-scale land use in explaining benthic invertebrate assemblages; in particular, chloride, oxygen, total organic carbon and the amounts of artificial surfaces and arable land were the most important predictors. Models including solely structural variables such as plan form, bank structures and substrate diversity had lower goodness of fit values than those for other variables. Regarding the four different assemblage metric types, functional metrics had on average lower goodness of fit values than composition/abundance, richness/diversity and sensitivity/tolerance metrics. Among the richness/diversity metrics, however, the model results for the Shannon–Wiener and Simpson diversity indices and evenness were poor. Our results show that catchment-related factors and water quality were of overriding importance in shaping biodiversity patterns and causing species loss. In contrast, structural degradation at a local scale was not the most significant stressor. This finding might explain why structural restoration at a reach scale often yields a low benefit–cost ratio and may be considered to represent inappropriate investment prioritisation.
River restoration is a central issue of present-day River Basin Management. Unfortunately, many studies have shown limited ecological improvements, hypothesizing catchment influences and missing donor populations as main impeding factors. This study evaluates the ecological status after restoration at 46 river reaches in light of catchment influences upstream. Three groups of environmental parameters were investigated: (i) riparian land use and (ii) physical habitat quality in different lengths upstream of the restorations and (iii) land use in the whole catchment upstream. Ecological quality ratios of standardized fish, invertebrate and macrophyte samples were used as response variables. The results imply that sub-catchment variables influence the ecological status more than local habitat improvements. In particular, fish and invertebrate ecological status was positively linked to percent deciduous forest upstream of restored sites, while macrophytes revealed an opposite trend. Furthermore, we found a strong linkage of site-scale ecological status and physical habitat quality up to 5 km upstream of the restorations; the more natural were riparian land use and river habitat quality upstream, the higher was the chance of a good ecological quality in restored reaches. We conclude that site-scale restoration measures are likely to be unsuccessful, if the sub-catchment physical habitat upstream is degraded.
From headwaters to mouth, the physical variables within a river system present a continuous gradient of physical conditions. This gradient should elicit a series of responses within the constituent populations resulting in a continuum of biotic adjustments and consistent patterns of loading, transport, utilization, and storage of organic matter along the length of a river. Based on the energy equilibrium theory of fluvial geomorphologists, we hypothesize that the structural and functional characteristics of stream communities are adapted to conform to the most probable position or mean state of the physical system. We reason that producer and consumer communities characteristic of a given river reach become established in harmony with the dynamic physical conditions of the channel. In natural stream systems, biological communities can be characterized as forming a temporal continuum of synchronized species replacements. This continuous replacement functions to distribute the utilization of energy inputs over time. Thus, the biological system moves towards a balance between a tendency for efficient use of energy inputs through resource partitioning (food, substrate, etc.) and an opposing tendency for a uniform rate of energy processing throughout the year. We theorize that biological communities developed in natural streams assume processing strategies involving minimum energy loss. Downstream communities are fashioned to capitalize on upstream processing inefficiencies. Both the upstream inefficiency (leakage) and the downstream adjustments seem predictable. We propose that this River Continuum Concept provides a framework for integrating predictable and observable biological features of lotic systems. Implications of the concept in the areas of structure, function, and stability of riverine ecosystems are discussed.Key words: river continuum; stream ecosystems; ecosystem structure, function; resource partitioning; ecosystem stability; community succession; river zonation; stream geomorphology
1. Degradation of freshwater ecosystems is a major concern worldwide. Agriculture introduces multiple stressors to streams, presenting a challenge for freshwater managers who must understand the relative strengths of individual stressor effects and their combined multiple-stressor effects.
2. Using a replicated regression design, we manipulated levels of fine sediment and nutrients to create a broad eight-point gradient for each stressor across 128 stream mesocosms to determine the shapes of macroinvertebrate responses after 21 days of exposure.
3. Subsidy–stress response patterns occurred along both stressor gradients. Sediment addition provided an initial subsidy for some pollution-tolerant taxa and total macroinvertebrate density, but produced consistently negative effects for other taxa, total taxon richness and the density and richness of pollution-sensitive Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa. Nutrient enrichment provided an initial subsidy for densities of two common EPT taxa, total EPT density, macroinvertebrate and EPT taxon richness.
4. Few macroinvertebrate variables were affected by a single stressor (always fine sediment). The majority of responses were additive multiple-stressor patterns, although Chironomidae density and EPT taxon richness followed complex synergistic patterns.
5. Fine sediment was a much more pervasive stressor than augmented nutrient concentrations. Overall, macroinvertebrate traits responded to stressors as strongly as community variables or individual taxa.
6. Synthesis and applications. Managing both fine sediment and nutrient inputs from agriculture is crucial to achieve good stream condition but priority should be given to minimizing fine sediment, which should be maintained below a threshold of 5% cover and 0·5-mm depth. Managers also need to be wary of interactive multiple-stressor effects because ecological outcomes of an increase in stressor load may be worse than predicted based on the knowledge of single-stressor effects.
1. Many ecosystems are influenced simultaneously by multiple stressors, and the consequences of stressors are often unpredictable on the basis of knowledge of single effects. Agriculture affects streams world-wide via nutrient enrichment, elevated fine sediment and water abstraction for irrigation, but the combined impacts of these stressors are unknown.
2. We manipulated all three stressors simultaneously in an 18-day experiment and determined their individual and pair-wise combined effects on benthic invertebrates, algal biomass and leaf decay. We added nutrients (phosphorus plus nitrogen) and/or fine sediment (grain size 0·2 mm) to 18 experimental stream channels (dimensions 250 × 15 × 15 cm) supplied with water from a nearby stream. Three sediment and three nutrient treatments (high, intermediate, natural) were applied to each of six channels while flow was reduced by 80% in half the channels. Invertebrates (composition, abundance) and algae (chlorophyll a) were assayed using ceramic tile substrata and leaf decay was assayed using bundled leaves of a native shrub. Invertebrates colonizing leaf packs were also sampled.
3. Effects of sediment addition and flow reduction on biological response parameters were twice as common as nutrient enrichment effects. Nutrient enrichment increased total invertebrate abundance on tiles, algal biomass accrual and leaf decay rates, whereas both sediment addition (at the highest level) and flow reduction had mostly negative effects (e.g. reduced algal biomass, invertebrate abundance and/or taxonomic richness).
4. Stressors interacted often, and interactions between sediment and flow were particularly common. The negative impact of added sediment on aquatic biota was stronger at reduced flow, especially on tile substrata that were more exposed to the current than leaf-pack substrata.
5. Synthesis and applications. Our key findings imply that abstracting water from a stream already subjected to high fine sediment inputs may have far worse effects on the invertebrate fauna than abstraction from a similar stream with lower sediment levels. Aquatic resource managers should be aware of this important interaction between multiple stressors.
Compared to other ecosystem types, a wide variety of biomonitoring methods are available for rivers. Few studies have, however, compared the response of bioindicators (i.e. different river inhabiting taxonomic groups) to different types of environmental stress.
We regressed diversity, taxonomic distinctness and assemblage composition of fish, invertebrates, macrophytes and benthic diatoms to multivariate gradients in nutrient enrichment and habitat degradation using data from 66 lowland and 77 mountain streams.
In lowland streams, the composition of benthic diatom assemblages, measured by Detrended Correspondence Analysis, showed the strongest response to elevated nutrient concentrations ( R ² = 0·830), followed by macrophytes (0·711), fish (0·443) and invertebrates (0·391). Macrophyte richness was slightly better correlated with the habitat gradient (0·253) than diatom richness (0·235) and both were better predictors than either fish (0·147) or invertebrate (0·140) assemblage composition.
For mountain streams, invertebrate assemblage composition was the best predictor of changes in nutrient concentrations ( R ² = 0·749), followed by macrophyte (0·396) and benthic diatom (0·325) assemblages and fish diversity (0·099). Invertebrate assemblage composition was also slightly better correlated with the habitat gradient (0·391) compared to macrophyte richness (0·323) and both were better than either benthic diatom assemblage composition (0·206) or fish abundance (0·161).
Macrophyte and benthic diatom assemblages in lowland streams and fish and invertebrate assemblages in mountain streams were correlated with the other taxonomic groups, implying that these taxonomic groups may be used as surrogates for indicating wholesale change in diversity.
Synthesis and applications . Our findings show that response trajectories differ between taxonomic groups and stressor, and even with stream type. For this reason, streams and other ecosystem type's response signatures and first and second principle relations should be considered in the selection of robust, complementary and cost‐effective measures for biomonitoring. For instance, our findings of asymmetric response to stress show how different taxonomic groups can be used to strengthen inference of change.
The significance of light climate and water movement for the absence of submerged vegetation in the largest part of the River Vecht was investigated at three stations along the river during the summer of 1991.
The underwater light climate was found to be quite adverse for the development of waterplants due to turbidity and periphyton development. Attenuation coefficients of the water were found to be high: on average 2.6, 2.8 and 3.0 m ⁻¹ for the southern, central and northern stations, respectively. In spring most of the light attenuation (90–100%) was due to the water layer; in summer periphyton and water were equally important. The light climate limited the potential occurrence of submerged macrophytes to a zone shallower than 1m. The observed distribution of the waterplants along the river's length, however, could not be explained by the light climate alone. Presence of submerged vegetation is restricted to the southern section of the river where there is relatively little boat traffic.
Wave action caused by the (mainly recreational) boat traffic was observed to negatively affect plant growth in an in situ experiment with a breakwater. This points to physical damage by wave action caused by passing boats as the main factor determining waterplant distribution. An alternative explanation is the much higher density of houseboats in the northern section. When present, houseboats effectively shade out the zone shallower than 1 m, thus preventing the development of a submerged vegetation.
1. The articles in this Special Issue on pressure‐response relationships in stream ecology cover a range of pressures including acidification, excess loading of metals, nutrients and organic matter to stream ecosystems and changes in riparian and catchment land use. Impacts on the biota (macroinvertebrates), ranging from single species to community responses, are addressed over a multitude of spatial scales using large data sets.
2. The majority of articles are based on monitoring data compiled as part of the EU‐funded project REBECCA, but the Special Issue also includes articles from outside Europe (US and New Zealand) as well of studies using other data sources.
3. Results from the six articles gave new insights of relevance to water managers and documented that large‐scale monitoring can be an asset to freshwater science. The large data sets enable a range of analytical approaches that single out important patterns in highly variable data.: importance of humic substances in reducing the negative impact of low pH; impact of very low levels of BOD (<2 mg L ⁻¹ ); higher sensitivity of trait‐based metrics compared with identity‐based metrics and importance of catchment and riparian vegetation for the ecological quality of streams.
3. We advocate an increased use of monitoring and survey data in addressing questions relevant to scientist and end‐users, but issues relating to especially data quality should be considered. In future, the use of these data could increase knowledge exchange between the scientific community and managers with the ultimate aim of improving our freshwater resources.
A new assessment system for macrophytes and phytobenthos in German rivers meeting the requirements of the Water Framework Directive (WFD) of the European Community is described. Biocoenotic types based on biological, chemical and hydromorphological data from over 200 river sites covering the main ecoregions, hydromorphological stream types and degradation forms have been defined. For developing a classification system the quality element macrophytes and phytobenthos was divided into three components: macrophytes, benthic diatoms and remaining phytobenthos. For macrophytes seven types including one subtype, for benthic diatoms 14 types including three subtypes and for the remaining phytobenthos five river types were identified. The benthic vegetation at reference condition was described for most of the river types. Degradation is characterised as deviation in benthic vegetation species composition and abundance from the reference biocoenosis. For classification in five ecological status classes, several metrics were developed and used in combination with existing indices. For some of the described river types additional investigations are necessary before a classification system can be developed.