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Modeling the effects of climatic and land use changes on phytoplankton and water quality of the largest Turkish freshwater lake: Lake Beyşehir
Abstract
Climate change and intense land use practices are the main threats to ecosystem structure and services of Mediterranean lakes. Therefore, it is essential to predict the future changes and develop mitigation measures to combat such pressures. In this study, Lake Beyşehir, the largest freshwater lake in the Mediterranean basin, was selected to study the impacts of climate change and various land use scenarios on the ecosystem dynamics of Mediterranean freshwater ecosystems and the services that they provide. For this purpose, we linked catchment model outputs to the two different processed-based lake models: PCLake and GLM-AED, and tested the scenarios of five General Circulation Models, two Representation Concentration Pathways and three different land use scenarios, which enable us to consider the various sources of uncertainty. Climate change and land use scenarios generally predicted strong future decreases in hydraulic and nutrient loads from the catchment to the lake. These changes in loads translated into alterations in water level as well as minor changes in chlorophyll a (Chl-a) concentrations. We also observed an increased abundance of cyanobacteria in both lake models. Total phosphorus, temperature and hydraulic loading were found to be the most important variables determining cyanobacteria biomass. As the future scenarios revealed only minor changes in Chl-a due to the significant decrease in nutrient loads, our results highlight that reduced nutrient loading in a warming world may play a crucial role in offsetting the effects of temperature on phytoplankton growth. However, our results also showed increased abundance of cyanobacteria in the future may threaten ecosystem integrity and may limit drinking water ecosystem services. In addition, extended periods of decreased hydraulic loads from the catchment and increased evaporation may lead to water level reductions and may diminish the ecosystem services of the lake as a water supply for irrigation and drinking water.
... Biophysical models facilitate the understanding of ecohydrological processes in hydrographic basins and the assessment and forecasting of multiple pressures [1]. Well-calibrated, validated models have numerous applications in water management, such as quantifying the effects of land use and climate change [4][5][6], assessing flood risk [7], and designing and evaluating forest restoration programs [8][9][10][11], in addition to generating and transferring historical data for unmonitored basins, which is critical for hydrological studies [12]. Such applications can help formulate and evaluate environmental conservation policies that support sound decision making in water resource management and land-use planning [13]. ...
... Hamel et al. [28] also found greater sensitivity for β, with BF varying by nearly 50% in some sub-basins. For α = 1/12 and α = 1/6, the decreasing BF was similar to Hamel et al. [28], but for alpha = 1/3, there was a BF increase (Figure 3), associated with the determination of AET i,m , which is conditioned by PET or water availability, according to Equation (4). The parameters α and β are associated with the fraction of the annual recharge of pixels upstream (upslope) available for evapotranspiration of a pixel downstream (downslope) [16]. ...
... InVEST's WES models enable spatial understanding since they are distributed at pixel scale, and the WES value in each pixel varies depending on its location, considering such key factors as land use, vegetation, relief, and soil types, which remain a major challenge for ecohydrological models [68,69]. Such characteristics make these models important tools for environmental planning, enabling an analysis of the effects of diverse future scenarios, such as climate and land-use changes, the primary drivers of WES degradation [4,5]. While WES model performance differs for each model and temporal and spatial scale, in general, the study results indicate the models' capacity to represent long-term average values, and, in the case of the SWY model, to simulate annual average values, enabling a representation of the variability of extreme annual values (see 1983 in Figure 4). ...
The biophysical modeling of water ecosystem services is crucial to understanding their availability, vulnerabilities, and fluxes. Among the most popular models, the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) models stand out. While many studies have used them, few have assessed their performance. This study evaluates the performance of InVEST’s Seasonal Water Yield, Nutrient Delivery Ratio, and Sediment Delivery Ratio models in a subtropical basin in southeastern Brazil on temporal and spatial scales, using 39 years of streamflow data, 29 for total phosphorus and total nitrogen, and 19 for total suspended solids. Statistical indicators R2, PBIAS, and NSE, were also calculated. The performance of the models varied according to the type of simulated WES and analysis scales used, with the Seasonal Water Yield model demonstrating the best performance and effectively representing the spatial and temporal variability of the average annual streamflow. All models performed well in simulating long-term mean values when compared to observed data. While one should bear in mind the study’s limitations, the results indicate that the models perform well in terms of relative magnitude, although their application in studies involving water-resource management and decision making is limited.
... Globally, cyanobacteria and other phytoplankton blooms have intensified since the 1980s (Ho et al., 2019) and are expected to worsen with global warming (Paerl et al., 2011;Zia et al., 2016;Bucak et al., 2018;Couture et al., 2018;Bartosiewicz et al., 2019;Gal et al., 2020;Messina et al., 2020;Weber et al., 2020). These blooms are hazardous to recreational water users (Chorus and Bartram, 1999;Brooks et al., 2016;Chapra et al., 2017;Funari et al., 2017) contaminate drinking water supplies (Ndong et al., 2014), reduce oxygen available to aquatic species (e.g., Paerl and Huisman, 2008), impact the physical and mental health of humans (Lévesque et al., 2014;Torbick et al., 2014), have regional economic consequences, including reduced tourism income and property values (Liu et al., 2017b;Voigt et al., 2015) and emit greenhouse gases (Downing et al., 2021). ...
... Moreover, the rising intensity, duration, and spatial extent of blooms has coincided not only with elevated nutrient inputs but also observed climatic changes, including warmer water and more extreme climatic events (e.g., Paerl and Huisman, 2008;Michalak et al., 2013;Bartosiewicz et al., 2019). Moreover, numerous studies employing both process-based Integrated Assessment Models (Couture et al., 2014;Zia et al., 2016;Chapra et al., 2017;Bucak et al., 2018) and statistical approaches (e.g., Rigosi et al., 2015;Couture et al., 2018) have projected these blooms to worsen with global warming. ...
... Modeling the effects of climate must include the hydrological and water quality impacts of a water body's contributing area, thereby requiring interdisciplinary modeling chains that link the atmosphere, lithosphere, hydrosphere, and biosphere. Such model chain studies tend to (i) use meteorological forcings directly from global and regional climate model outputs (Couture et al., 2014;Zia et al., 2016;Chapra et al., 2017;Bucak et al., 2018), (ii) perturb observed meteorological time series using change factors informed by climate models (e.g., Rolighed et al., 2016), or (iii) simulate time series with weather generators (Schlabing et al., 2014). To examine the effects of changes in the central tendency and variability of precipitation and temperature on blooms, we forced a previously developed Integrated Assessment Model (see Zia et al., 2016) with observed meteorological time series perturbed using change factors informed by CMIP5 global climate models (see Taylor et al., 2012). ...
Many recent studies have attributed the observed variability of cyanobacteria blooms to meteorological drivers and have projected blooms with worsening societal and ecological impacts under future climate scenarios. Nonetheless, few studies have jointly examined their sensitivity to projected changes in both precipitation and temperature variability. Using an Integrated Assessment Model (IAM) of Lake Champlain's eutrophic Missisquoi Bay, we demonstrate a factorial design approach for evaluating the sensitivity of concentrations of chlorophyll a (chl-a), a cyanobacteria surrogate, to global climate model-informed changes in the central tendency and variability of daily precipitation and air temperature.
An Analysis of Variance (ANOVA) and multivariate contour plots highlight synergistic effects of these climatic changes on exceedances of the World Health Organization's moderate 50 μg/L concentration threshold for recreational contact. Although increased precipitation produces greater riverine total phosphorus loads, warmer and drier scenarios produce the most severe blooms due to the greater mobilization and cyanobacteria uptake of legacy phosphorus under these conditions. Increases in daily precipitation variability aggravate blooms most under warmer and wetter scenarios. Greater temperature variability raises exceedances under current air temperatures but reduces them under more severe warming when water temperatures exceed optimal values for cyanobacteria growth more often. Our experiments, controlled for wind-induced changes to lake water quality, signal the importance of larger summer runoff events for curtailing bloom growth through reductions of water temperature, sunlight penetration and stratification. Finally, the importance of sequences of wet and dry periods in generating cyanobacteria blooms motivates future research on bloom responses to changes in interannual climate persistence.
... We note that numerous LWS projects that have omitted economic models would likely benefit from their inclusion, particularly those projects that consider land management scenarios with potentially large socio-economic impacts. Examples include several LWS models of lakes and rivers and their catchments (Guse et al. 2015;Zia et al. 2016;Bucak et al. 2018;Motew et al. 2019). In each of these cases, scenarios involving extensive changes in agricultural and/or urban land use were simulated. ...
... While excluding proprietary models reduces the choice of component models and model combinations, several recent LWS modelling projects have used combinations of opensource models exclusively (e.g. Shabani et al. 2017;Bucak et al. 2018). ...
Elevated contaminant levels and hydrological alterations resulting from land use are degrading aquatic ecosystems on a global scale. A range of land management actions may be used to reduce or prevent this degradation. To select among alternative management actions, decision makers require predictions of their effectiveness, their economic impacts, estimated uncertainty in the predictions, and estimated time lags between management actions and environmental responses. There are multiple methods for generating these predictions, but the most rigorous and transparent methods involve quantitative modelling. The challenge for modellers is twofold. First, they must employ models that represent complex land-water systems, including the causal chains linking land use to contaminant loss and water use, catchment processes that alter contaminant loads and flow regimes, and ecological responses in aquatic environments. Second, they must ensure that these models meet the needs of endusers in terms of reliability, usefulness, feasibility and transparency. Integrated modelling using coupled models to represent the land-water system can meet both challenges and has advantages over alternative approaches. The need for integrated land-water system modelling is growing as the extent and intensity of human land use increases, and regulatory agencies seek more effective land management actions to counter the adverse effects. Here we present recommendations for modelling teams, to help them improve current practices and meet the growing need for land-water system models. The recommendations address several aspects of integrated modelling: (1) assembling modelling teams; (2) problem framing and conceptual modelling; (3) developing spatial frameworks; (4) integrating economic and biophysical models; (5) selecting and coupling models.
... Numerous pressures can impact ecosystem status, such as the construction of dams for energy and irrigation and of other river works, the introduction of exotic species, and water pollution [82]. Several studies have cited climate change and land use as the principal drivers that can affect the WES [83][84][85][86]. ...
... The environmental effects of the latter have altered matter and energy flow, which, in turn, impacts the health of ecosystems and their capacity to provide goods and services for human well-being and economic development [6]. While WES are affected by a series of factors that involve interaction among physical, biological, and anthropic factors, climate and land use changes are the primary present and anticipated threats to their integrity, and understanding how they affect ecosystems is essential to formulating sustainable water policies [84,85]. The ecosystem services-based approach systematically examines the complexity of river basins, linking ecosystem status, services, and pressures and enabling the assessment of additive, synergistic, and antagonistic effects of anthropic activities on ecosystem services and their economic value [7,85]. ...
Ecosystem services are goods and services provided by ecosystems for human well-being. This study canvasses the literature to identify knowledge areas and understand concepts relevant to addressing water ecosystem services. The potentialities and challenges of this approach applied to the planning and management of water resources were also discussed. The study addressed relevant topics such as ecosystem services, eco-hydrological processes, climate change, land use, ecosystem-based adaptation, biophysical modeling, economic valuation, and integrated water resources management. The ecosystem services-based approach has practical applications in water resource management; however, this study has identified knowledge gaps that should be addressed to ensure its effectiveness. Further research is in order to: 1) understand the synergic effects of multiple water resource drivers, 2) identify the ecohydrological processes of natural ecosystems and how restoration can enhance water ecosystem services and mitigate climate change, 3) expand knowledge of and validation in the use of biophysical models, 4) intensify the integration of biophysical assessment and economic valuation, and 5) include all dimensions of ecosystem service values to increase user and stakeholder participation in water resource management.
... Additionally, Beyşehir Lake, which is surrounded by two national parks, is a site of ecological importance that has been designated a national site by the Turkish Ministry of Culture since 1991 (Nas et al., 2009). Thus, several studies have been conducted to evaluate the water quality and quantity in Beyşehir Lake (Nas et al., 2009;Aktumsek and Gezgin, 2011;Özparlak, Arslan and Arslan, 2012;Bucak et al., 2018;Sanli et al., 2021;Sanli et al., 2022). Predicting water levels is also crucial to ecological sustainability and resilience planning. ...
Beyşehir Lake is the largest freshwater lake in the Mediterranean region of Turkey that is used for drinking
and irrigation purposes. The aim of this paper is to examine the potential for data-driven methods to predict long-term
lake levels. The surface water level variability was forecast using conventional machine learning models, including
autoregressive moving average (ARMA), autoregressive integrated moving average (ARIMA), and seasonal
autoregressive integrated moving average (SARIMA). Based on the monthly water levels of Beyşehir Lake from
1992 to 2016, future water levels were predicted up to 24 months in advance. Water level predictions were obtained
using conventional time series stochastic models, including autoregressive moving average, autoregressive integrated
moving average, and seasonal autoregressive integrated moving average. Using historical records from the same period,
prediction models for precipitation and evaporation were also developed. In order to assess the model’s accuracy,
statistical performance metrics were applied. The results indicated that the seasonal autoregressive integrated moving
average model outperformed all other models for lake level, precipitation, and evaporation prediction. The obtained
results suggested the importance of incorporating the seasonality component for climate predictions in the region. The
findings of this study demonstrated that simple stochastic models are effective in predicting the temporal evolution of
hydrometeorological variables and fluctuations in lake water levels
... Therefore, understanding water quality is required as it provides the bases for a healthy living. However, water quality is potentially extremely vulnerable to rainfall fluctuation (or climate change) (Bucak et al., 2018;Woodward et al., 2016). This is particularly desirable owing to the exacerbation of the interactions already happening in the local environmental systems, as well as the development of new interactions concerning human systems and their subsequent impact on availability and quality of water sources. ...
The global dry-lands constitute a unique ecological system which is primarily
characterized by low rainfall, high rate of evaporation and scanty vegetation cover.
These in conjunction with environmental and land-use changes, exert heavy
pressure on water resources. The objective of this review is to assess the influence
of natural geogenic and anthropogenic activities on the hydrochemical
composition of streams and aquifers in drier parts of Africa. Water quality studies
were scrutinized, in order to identify the natural geogenic and anthropogenic
origin of ions in water. Results indicated that the hydrochemical composition of
streams and aquifers is controlled by natural geogenic processesas well as
anthropogenic activities. Also, the current environmental change has further
worsened the water quality situation through declines in annual rainfall with its
resultant consequences on the over-abstraction of groundwater aquifers, which
has led to saltwater intrusion in coastal aquifers. Thus, it is difficult to separate
natural geogenic and anthropogenic controls on water quality. This is because ions
that are derived naturally from rock minerals are increasingly being added into
the environment through human activities. Hence, the rationality for establishing
the origin of ions in streams and aquifers proved to be very difficult. Consequently,
water quality results must be interpreted within the framework of the existing
environmental conditions, land use types and regularly essential standard
application for reporting water quality in the literature.
... Generally, inland rivers in China are often polluted, experiencing phytoplankton blooms and reduced water clarity associated with eutrophication due to excessive nutrient inputs (Vadde et al., 2018). Water pollution influences the ecosystem's phytoplankton structure and functioning (Bucak et al., 2018). Hence, studying phytoplankton community composition and factors influencing their abundance and diversity in water systems is vital. ...
For the first time, this study explored spatio-temporal variation in water quality and phytoplankton community structure in Changwang, Meishe, and Wuyuan Rivers in tropical Hainan Island, China. Phytoplankton samples and water were collected between March and December 2019 and analyzed using standard methods. Two-way ANOVA revealed significant spatial and seasonal variation in physico-chemical parameters (p < 0.05). Wuyuan had high TP (0.06 ± 0.04 mg L⁻¹), TN (1.14 ± 0.71 mg L⁻¹), NH4⁺-N (0.07 ± 0.09 mg L⁻¹), Secchi depth (2.28 ± 3.79 m), salinity (3.60±5.50 ppt), and EC (332.50 ± 219.10 µS cm⁻¹). At the same time, Meishe had high TP (0.07 ± 0.03 mg L⁻¹), TN (1.04 ± 0.74 mg L⁻¹), NH4⁺-N (0.07 ± 0.10 mg L⁻¹), EC (327.61 ± 63.22 µS cm⁻¹), and turbidity (40.25 ± 21.16 NTU). In terms of seasons, spring recorded high average TP, TN, NH4⁺-N, COD, and DO, while summer had a high temperature, Chl-a, salinity, and EC. Generally, the physico-chemical parameters met the China water quality standard limits (GB 3838–2002). Overall, 197 phytoplankton species belonging to Cyanophyta, Chlorophyta, Cryptophyta, Bacillariophyta, Pyrrophyta, Euglenophyta, Xanthophyta, and Chrysophyta were identified, with Cyanophyta being dominant. Phytoplankton density showed spatial changes varying from 18 × 10⁶ cell L⁻¹ to 84 × 10⁶ cell L⁻¹. The phytoplankton diversity ranged from 1.86 to 2.41, indicating a mesotrophic state. One-way ANOSIM showed no significant spatial dissimilarity in phytoplankton composition (R = 0.042, p = 0.771) but indicated a significant seasonal difference (R = 0.265, p = 0.001). Therefore, SIMPER analysis revealed that Lyngbya attenuata, Merismopedia tenuissima, Cyclotella sp., Merismopedia glauca, Merismopedia elegans, and Phormidium tenue contributed to the seasonal differences. Furthermore, CCA demonstrated that TP, TN, NH4⁺-N, COD, Chl-a, and Secchi depth greatly influenced the phytoplankton community. This study shows the spatio-temporal variation in water quality and phytoplankton communities, useful for managing riverine quality.
... The influx of nitrogenous or phosphorus compounds from nonpoint source inputs is also a major factor driving changes in freshwater biodiversity [3][4][5]. The increase in the influx of nitrogenous or phosphorus compounds from the external environment due to land use change (e.g., agriculture, urbanization, etc.) near freshwater ecosystems [6] or precipitation sludge [7] could affect freshwater biodiversity by causing harmful algal blooms and hypoxic conditions [8][9][10]. ...
Rapid and cost-effective eDNA-based approaches are valuable for understanding biological communities and monitoring the biodiversity of inaccessible areas, such as large rivers and lakes. To determine temporal dynamics and precipitation effects on micro-eukaryotic assemblages, we monitored upstream (SJ) and downstream (MG) sites of the Nakdonggang River, monthly or bimonthly, from March 2019 to April 2021 using an eDNA metabarcoding technique. We observed 775 unique operational taxonomic units during the entire sampling period using the V4 region of the 18S rRNA gene as a marker. In the cluster analysis and non-metric multidimensional scaling analysis based on the relative abundance ratio of the micro-eukaryotic assemblages at the SJ and MG sites, respectively, both regions were classified by four seasons, with dominant taxa for each season being different. Whereas Chlorophyta was relatively abundant in the MG site during summer, diatoms were most abundant at the SJ site during winter. Further, metazoan taxa were relatively abundant at the MG site. Total detection of metazoa, protozoa, and microalgae taxa significantly increased with heavy rainfall. In addition, the indicator taxa representative for heavy rainfall and tolerance ranges of the amount of precipitation were predicted at both sites. As the frequency of drought and heavy rain is expected to increase owing to climate change, efforts to standardize the relation between precipitation and eDNA analysis are required.
... Nevertheless, significant rising trends of trophic state were highlighted by both the Mann-Kendall trend analysis and the GAMs in a few occasions, such as the cases of lakes Beysehir and Ergidir in Turkey. TSI clearly increased in those two lakes between 2002 and 2012 which possibly indicates symptoms of increased eutrophication, albeit at relatively moderate levels, since the lakes are characterized as mesotrophic to eutrophic (Bucak et al., 2018;Kaçikoç and Beyhan, 2014). In both cases, the increase of lake productivity is likely linked with significant water level declines that occurred during 2000s (Keskin et al., 2015;Yılmaz et al., 2021) and are known to enhance eutrophication, particularly in shallow lakes (Coppens et al., 2020;Zohary and Ostrovsky, 2011). ...
Water turbidity is one of the more important water quality parameters that is strictly linked with the productivity of the lake and is commonly used as an indicator of the trophic state. However, limited field data availability across wide geographic gradients may hinder the conduction of large scale longitudinal studies. In this study, time series of lake turbidity and trophic state index (TSI) between 2002 and 2012 were obtained from the Copernicus Lake Water products to create a large longitudinal dataset of lake variables for 22 European lakes. The dataset was combined with estimates of nutrient concentrations and surface water temperature obtained from the Hydrological Predictions for the Environment (HYPE) and ERA5-Land data repositories, that were used as environmental predictors. Hence, the validity of the lake water quality parameters was tested by a) exploring their spatial and temporal variability and b) identifying associations with the environmental predictors. For this purpose, seasonal Mann-Kendall tests were applied to find significant inter-annual trends of turbidity and TSI for each lake, and generalized additive models (GAMs) were employed to identify the main parameters that shape their temporal dynamics. Although we did not find significant inter-annual changes, our findings highlighted the strong influence of seasonality and surface water temperature in defining the temporal variability patterns in most of the lakes. In addition, the importance of nutrients varied among lakes as several lakes exhibited narrow nutrient gradients reflecting relatively stable nutrient conditions during the examined period. Other lake intrinsic factors, such as local climate and biotic interactions, are important drivers of shaping turbidity and nutrient dynamics. This study highlighted the usefulness of combining lake data from large repositories in conducting large scale spatial studies as a valuable asset for future lake research and management purposes.
... Most studies argued that the upward trends in air temperatures and downward trends in precipitation will continue to exist particularly at the central parts of Turkey until the end of the century (Christensen et al. 2013;Erol and Randhir 2012;Önol and Unal 2014). In recent years, a few studies were carried out in Turkey to investigate the future climate change impacts on water resources (Bucak et al. 2018;Coppens et al. 2020, Cuceloglu andOzturk 2019;Ertürk et al. 2014;Fujihara et al. 2008;Gorguner et al. 2019). The majority of them aimed to determine climate change impacts on streamflow. ...
Climate change can have severe impacts on the water availability in semi-arid regions. In this study, we assessed the impact of climatic changes on water availability in the Altınapa Reservoir Watershed, located in the Konya province, south-central Turkey. Altınapa Reservoir supplies drinking water to Konya, a city of about 2 million population. We investigated possible changes in streamflow and reservoir storage over 2021–2098 under two representative concentration pathway scenarios (RCP4.5 and RCP8.5) developed based on GFDL-ESM2M, HadGEM2-ES, and MPI-ESM-MR global circulation models. We used a physically based model (SWAT-Soil and Water Assessment Tool) for understanding the hydrologic response of the basin to climatic changes. Results show that upward trends in air temperatures in the range of 0.01–0.04 °C/year and 0.005–0.06 °C/year are expected from 2021 to 2098 under the RCP4.5 and RCP8.5 scenarios, respectively. According to the HadGEM2-ES model, precipitation and streamflow would show a downward trend at a rate of 0.96 mm/year and 0.007 m³/s/year under the RCP4.5 scenario and at a rate of 1.62 mm/year and 0.01 m³/s/year under the RCP8.5 scenario, respectively. GFDL-ESM2M and MPI-ESM-MR models project upward trends in precipitation and streamflow under the RCP4.5 scenario (in the range of 0.64–1.28 mm/year and 0.0003–0.006 m³/s/year, respectively), and downward trends under the RCP8.5 scenario (in the range of 0.47–0.76 mm/year and 0.0015–0.003 m³/s/year, respectively). Reservoir storage is projected to increase slightly according to GFDL-ESM2M model and decrease according to the HadGEM2-ES, and MPI-ESM-MR models under both scenarios. Precipitation, streamflow, and reservoir storage predictions of GFDL-ESM2M and MPI-ESM-MR models are considerably lower than those observed in the basin in recent decades, showing that water resources will decrease in the future. The changes in water withdrawal patterns could cause further reductions in water availability. Good resilience to climate change can be achieved by a flexible water management system and by reducing water consumption and water losses in the watershed and from the reservoirs.
... Their reproduction is particularly rapid in spring, summer, and autumn, and the growth in patches can change the quality and color of a water body by forming a bloom (Cui 2012). Since the 1980s, phytoplankton blooms such as cyanobacteria have been increasing globally (Ho et al. 2019) and worsening with global warming (Zia et al. 2016;Bucak et al. 2017; Bartosiewicz et al. 2019;Paerl et al. 2011;Gal et al. 2020). The increasing number of toxic cyanobacterial bloom incidents around the world has caused widespread concerns . ...
Cyanobacterial bloom is by far one of the most common water quality hazards. As cyanobacteria are rich in nitrogen, phosphorus, and other organic matter, the potential for beneficial use of cyanobacteria is promising. Aerobic composting is currently a hot topic of research in cyanobacteria treatment, which can effectively achieve reduction, recycling, and removal of the harmful impact of cyanobacteria. In this review, the characteristics of cyanobacteria in aerobic composting processes, the effects of physical, chemical, and biological factors on the composting process, and the degradation of microcystic toxins were systematically discussed and summarized. This review epitomizes the large quantities of research data collected by many scholars around the world to address the characteristics of “one low and five highs” in the aerobic cyanobacterial composting process. The composting techniques developed are effective and easy to adopt in the real world, such as adjusting the substrate C/N ratio and moisture content and use of chemical and biological additives to achieve reduction, recycling, and detoxication of the cyanobacterial wastes. The aim of this comprehensive review is to provide theoretical guidance and reference for further development and application of aerobic cyanobacteria composting technology.
... To date, a vast number of freshwater studies have related cyanobacterial blooms to water quality parameters, such as nutrient concentrations, light, temperatures, pH, and turbidity (Bucak et al., 2018;Descy et al., 2016;Shi et al., 2017;Soares et al., 2009). Among them, ☆ This paper has been recommended for acceptance by Philip N. Smith. ...
Cyanobacterial blooms are important environmental problems in aquatic ecosystems. Researchers have found that cyanobacterial blooms cannot be completely prevented by controlling and/or eliminating pollutants (nutrients). Thus, more in-depth basic research on the mechanism of cyanobacterial blooms is urgently needed. Cyanobacteria, being primordial microorganisms, provide habitats and have various forms of interactions (reciprocity and competition) with microorganisms, thus having a significant impact on themselves. However, little is known about how environmental conditions and microbial communities in both water and sediment jointly affect cyanobacterial blooms or about the co-occurrence patterns and interactions of microbial communities. We investigated changes in environmental factors and microbial communities in water and sediment during different cyanobacterial blooms and revealed their interacting effects on cyanobacteria. Cyanobacteria had greater competitive and growth advantages than other microorganisms and had antagonistic and aggressive effects on them when resources (such as nutrients) were abundant. Furthermore, microbial networks from cyanobacterial degradation periods may be more complex and stable than those from bloom periods, with more positive links among the microbial networks, suggesting that microbial community structures strengthen interconnections with each other to degrade cyanobacteria. In addition, we found that sediment-enriched cyanobacteria play a key role in cyanobacterial blooms, and sediment microorganisms promote the nutrient release, further promoting cyanobacterial blooms in the water bodies. The study contributes to further our understanding of the mechanisms for cyanobacterial blooms and microbial community structural composition, co-occurrence patterns, and responses to cyanobacteria. These results can contribute to future management strategies for controlling cyanobacterial blooms in freshwater ecosystems.
... These studies did not only deal with the ES approach from an analytical perspective (e.g., mapping, modeling, valuation) but also provided several guidelines for real practices in land-use planning, watershed management, participatory governance, social engagement, and sectoral policymaking (e.g. Pamukcu et al., 2014Pamukcu et al., , 2016Serengil et al., 2016;DKM, 2018;Kuru and Tezer, 2020;Berkun, 2010;Delibas and Tezer, 2017;Erol and Randhir, 2013;Bucak et al., 2018;Tezer et al., 2020Tezer et al., , 2014Tezer et al., , 2015Baylan and Karadeniz, 2018). ...
The concept of “Ecosystem Services (ES)” has gained global importance since the 1990s. Today its link to sustainable development and human welfare is well documented. However, the level of know-how and the scale and effectiveness of practices differ significantly around the globe. The Ecosystem Services Partnership (ESP) National Network of Turkey aims to fill gaps in ES research and foster collaboration among experts in the public and academic sectors and non-governmental organizations. Therefore, a comprehensive review of ES studies was carried out with rigorous literature research. The review of 247 publications showed that ES research has advanced in the last two decades principally as a result of academia's impetus but increasing efforts in the science-policy interface have also supported its integration into diverse policy sectors. Among all ES, regulating ES were studied more intensely due to the growing effects of climate change on leading economic sectors such as agriculture, forestry, and water management. Monetary valuation and trade-off knowledge have remained low, based on the difficulties in data availability and assessment methods. Although protected areas are critical to biodiversity conservation, the ES concept has not been integrated into protected area management. Therefore, the ES knowledge in Turkey needs to be scaled up to cover the national level, with higher stakeholder engagement and more focused implementation driven by political will.
... Lake models have been used to support restoration actions from eutrophication (Brett et al., 2016;Cui et al., 2016;Allan 2018;Ladwig et al., 2018) and for maintaining fisheries (Kumar et al., 2016;Ofir et al., 2017;Natugonza et al., 2019). Lake models can provide information on the potential impacts of climate change and how to best mitigate those impacts (Koenigstein et al., 2016;Rolighed et al., 2016;Ladwig et al., 2018;Bucak et al., 2018;Gal et al., 2020;Heneghan et al., 2021) and for assessing management actions to maintain the lake ecosystem services (Gal et al., 2009;Ofir et al., 2017;Lewis et al., 2020). Lake ecosystem models can also be used for near real-time prediction to assist in immediate management decisions such as lake bathing suspension, halt drinking water consumption and actions to mitigate pollution events (Janssen et al., 2015;Robson et al., 2017). ...
... Human activities in the catchment areas, characteristics of the drainage basin, and the recipient ecosystem's size are the primary factors controlling the trophic status of lakes and reservoirs (Walker et al., 2007). Changes in land use and land cover have been linked to changes in water quality of inland waters as a result of sediment and nutrient input, which strongly influence the structure of biological communities and overall ecosystem functioning (Catherine et al., 2013;Kibena et al., 2014;Bucak et al., 2018;Leech et al., 2018;Namugize et al., 2018). Small and shallow waterbodies in tropical and subtropical regions are also associated with seasonal changes in wind speed and rainfall, which influence plankton assemblages through water mixing and nutrient loading (Geraldes and Boavida, 2004;Zhu et al., 2014). ...
Factors influencing the spatio-temporal dynamics of plankton communities in small tropical lakes are not well-understood. This study assessed plankton communities in response to spatial (six sampling sites) and seasonal (wet vs. dry seasons) changes in environmental variables in Lake Kanyaboli, a small satellite lake on the northern shores of Lake Victoria, Kenya. Water quality variables, including pH, conductivity (EC), dissolved oxygen (DO), temperature, Secchi depth (SD), nitrates (NO3-), nitrites (NO2-), ammonium (NH4+), soluble reactive phosphorus (SRP), total nitrogen (TN), total phosphorus (TP), and chlorophyll-a (Chl-a), were monitored monthly at six sites spread throughout the lake for 1 year. Phytoplankton and zooplankton samples were collected and analyzed for taxon composition and abundance. Two-way ANOVA showed no significant interaction between site and season for all variables. Likewise, there were no significant spatial differences for all variables except Chl- a. A t-test showed significant seasonal differences in SD, DO, NH4+, NO3-, NO2-, and TN. Thirty phytoplankton genera were identified belonging to Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Euglenoidae, Trebouxiophyceae, and Zygnematophyceae, with Chlorophyceae being the most dominant (42.30%). Zooplankton comprised of 15 genera, belonging to Copepoda (55.4%), Rotifera (27.9%), and Cladocera (16.7%). Two-way ANOVA for plankton abundance showed no significant interaction between site and season, but there were significant differences in community composition between the wet and dry seasons. Canonical correspondence analysis identified water clarity (Secchi depth) and concentrations of dissolved fractions of nitrogen and phosphorus as the major water quality variables driving variation in the composition of plankton communities in the lake. This study showed that seasonality was a major driver of changes in plankton community composition between dry and wet seasons through changes in the concentrations of nutrients (NH4+, NO3-, NO2-, TN, and TP). Lake Kanyaboli's phytoplankton community indicated a non-equilibrial state, perhaps due to short residence times of water, especially during the wet season, and dense macrophytes fringing the lake that increase nutrient uptake and limit the dominance of select phytoplankton species. This study shows the importance of long-term studies covering dry and wet seasons to understand the dynamics of plankton communities and their drivers in small tropical waterbodies to inform management and conservation.
... Anthropogenic factors can also affect such natural patterns (Feng et al., 2018;Han et al., 2020;Khazaei et al., 2019). Knowledge of coupled hydrodynamic processes and water quality numerical modeling could enhance the understanding of effects on lake water quality that can result from environmental water allocation (Bucak et al., 2018;Peng et al., 2021). However, applications of such complex environment models require a large amount of input data, such as lake topography, water quantity, and quality of lake inflow and outflow, which is not available for every lake system. ...
Lakes in arid/semiarid regions face problems of insufficient inflow and degradation of water quality, which threaten the health of the lake ecosystem. Baiyangdian Lake (BYDL), the largest lake in the North China Plain, is confronted with such challenges. The objective of this study was to improve understanding of how changes in water level influence water quality in the BYDL at different temporal scales, especially related to implementations of intermittent environmental water allocation activities in the past two decades, by using data on monthly lake water level, climate factors of precipitation and temperature, and lake water quality. The Mann-Kendal method and continuous wavelet analysis revealed that the lake water level shows a significant decreasing trend after 1967, and the period of 16-year was identified as the principal period for 1950–2018. Based on cross-wavelet transform and wavelet coherence analysis, the periodic agreement and coherence between water level and climatic factors decreased after 1997, when environmental water allocations started, indicating that the influences of climatic factors, i.e., precipitation and temperature, becomes weak. By utilizing the cross-wavelet transform and wavelet coherence analysis methods, the relationships between lake water level and water quality parameters of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus were investigated. We found that the change in source and amount of environmental water allocation is one possible reason for the temporal evolution in joint variability between lake water level and water quality. Meanwhile, a dilution effect of freshwater allocated to BYDL was detected in the time-frequency domain. However, the result also indicates that the driving mechanism of water quality is complex due to the combined impacts of water allocation, nonpoint source pollution in the rainy season, and nutrient release from lake sediment. Our findings improve the general understanding of changes in water levels in lakes located in arid and semiarid regions under climate change and intensive human activities, and also provide valuable knowledge for decision making in aquatic ecosystem restoration of BYDL and other similar lakes.
... Lake Beyşehir, similar to Lake Tuz, is a protected area in Turkey and a home to 545 plant species, 163 bird species, and 16 fish species. Many water birds migrate to Lake Beyşehir to hunt and breed (Bucak et al. 2018). The KCB has over 300 sinkholes, which hold 33.3% of the country's groundwater . ...
This study aims to investigate the trend of water-level changes in lakes (Lake Tuz and Lake Beyşehir) and sinkholes (Timraş and Kızören) in the Konya Closed Basin located in Turkey. Water-level changes in these lakes and sinkholes were investigated along with changes in meteorological parameters (precipitation, temperature, and evaporation) and groundwater trends that indicate the climate in the region. Several statistical tests can be used to determine the significance of hydrological trends over time. These tests are divided into two categories: parametric and nonparametric. In this study, the nonparametric Innovate Sen trend test, the Modified Mann–Kendall trend test, and the parametric Linear trend test were used. According to the trend analysis, the water levels of Kızören and Timraş sinkholes decreased over time, while the water levels of lakes Tuz and Beyşehir increased. These results are supported by the trends in the meteorological data and groundwater level data of the stations determined with the Thiessen polygons and sub-basin boundaries.
... Therefore, understanding water quality is required as it provides the bases for a healthy living. However, water quality is potentially extremely vulnerable to rainfall fluctuation (or climate change) (Bucak et al., 2018;Woodward et al., 2016). This is particularly desirable owing to the exacerbation of the interactions already happening in the local environmental systems, as well as the development of new interactions concerning human systems and their subsequent impact on availability and quality of water sources. ...
The global dry-lands constitute a unique ecological system which is primarily characterized by low rainfall, high rate of evaporation and scanty vegetation cover. These in conjunction with environmental and land-use changes, exert heavy pressure on water resources. The objective of this review is to assess the influence of natural geogenic and anthropogenic activities on the hydrochemical composition of streams and aquifers in drier parts of Africa. Water quality studies were scrutinized, in order to identify the natural geogenic and anthropogenic origin of ions in water. Results indicated that the hydrochemical composition of streams and aquifers is controlled by natural geogenic processesas well as anthropogenic activities. Also, the current environmental change has further worsened the water quality situation through declines in annual rainfall with its resultant consequences on the over-abstraction of groundwater aquifers, which has led to saltwater intrusion in coastal aquifers. Thus, it is difficult to separate natural geogenic and anthropogenic controls on water quality. This is because ions that are derived naturally from rock minerals are increasingly being added into the environment through human activities. Hence, the rationality for establishing the origin of ions in streams and aquifers proved to be very difficult. Consequently, water quality results must be interpreted within the framework of the existing environmental conditions, land use types and regularly essential standard application for reporting water quality in the literature.
... Delft3D was applied to simulate the effects of climate and nutrient changes in the IJsselmeer. Beyşehir (TUR) SWAT Beyşehir DYRESM-CAEDYM, PROTECH, PCLake [31][32][33] IJsselmeer (NLD) None IJsselmeer DELFT-3D, HABITAT [19] Once calibrated and tested (Section 3.2), the models were run for a baseline period of 1981-2010 and then for a scenario period of 2031-2060. The difference in the mean flow and concentrations simulated for the scenario and baseline periods were used to derive percentage changes. ...
Recent studies have demonstrated that projected climate change will likely enhance nitrogen (N) and phosphorus (P) loss from farms and farmland, with the potential to worsen freshwater eutrophication. Here, we investigate the relative importance of the climate and land use drivers of nutrient loss in nine study catchments in Europe and a neighboring country (Turkey), ranging in area from 50 to 12,000 km2. The aim was to quantify whether planned large-scale, land use change aimed at N and P loss reduction would be effective given projected climate change. To this end, catchment-scale biophysical models were applied within a common framework to quantify the integrated effects of projected changes in climate, land use (including wastewater inputs), N deposition, and water use on river and lake water quantity and quality for the mid-21st century. The proposed land use changes were derived from catchment stakeholder workshops, and the assessment quantified changes in mean annual N and P concentrations and loads. At most of the sites, the projected effects of climate change alone on nutrient concentrations and loads were small, whilst land use changes had a larger effect and were of sufficient magnitude that, overall, a move to more environmentally focused farming achieved a reduction in N and P concentrations and loads despite projected climate change. However, at Beyşehir lake in Turkey, increased temperatures and lower precipitation reduced water flows considerably, making climate change, rather than more intensive nutrient usage, the greatest threat to the freshwater ecosystem. Individual site responses did however vary and were dependent on the balance of diffuse and point source inputs. Simulated lake chlorophyll-a changes were not generally proportional to changes in nutrient loading. Further work is required to accurately simulate the flow and water quality extremes and determine how reductions in freshwater N and P translate into an aquatic ecosystem response.
... Countries across the Mediterranean basin are susceptible to climate change, as water availability is expected to decrease in the future with a simultaneous expansion of aridity [1][2][3]. The climate change influences the alternation of seasons by increasing the disparity between wet and dry ones [4][5][6], while it changes the spatiotemporal distribution of precipitation, thus strongly affecting ecosystems and human activities [2,4,7]. This phenomenon is expected to be strong in countries such as Greece, which is characterized by large landscape variability additionally affecting the local climatic characteristics [6,8]. ...
Precipitation is one of the most variable climatic parameters, as it is determined by many physical processes. The spatiotemporal characteristics of precipitation have been significantly affected by climate change during the past decades. Analysis of precipitation trends is challenging, especially in regions such as Greece, which is characterized by complex topography and includes several ungauged areas. With this study, we aim to shed new light on the climatic characteristics and inter-annual trends of precipitation over Greece. For this purpose, we used ERA5 monthly precipitation data from 1950 to 2020 to estimate annual Theil–Sen trends and Mann–Kendall significance over Greece and surrounding areas. Additionally, in order to analyze and model the nonlinear relationships of monthly precipitation time series, we used generalized additive models (GAMs). The results indicated significant declining inter-annual trends of areal precipitation over the study area. Declining trends were more pronounced in winter over western and eastern Greece, but trends in spring, summer and autumn were mostly not significant. GAMs showcased that the trends were generally characterized by nonlinearity and precipitation over the study area presented high inter-decadal variability. Combining the results, we concluded that precipitation did not linearly change during the past 7 decades, but it first increased from the 1950s to the late 1960s, consequently decreased until the early 1990s and, afterwards, presented an increase until 2020 with a smaller rate than the 1950–1960s.
... Por modificar os ciclos de água, energia e matéria, dados de uso e ocupação do solo são importantes para o desenvolvimento de estudos ambientais. Pesquisas sobre clima, modelagem hidrossedimentológica, ecossistêmica, ecologia, biodiversidade, poluição hídrica, planejamento e gestão ambiental são exemplos de estudos que demandam dados de cobertura do solo (Ellison et al., 2017;Bucak et al., 2018;Ferreira et al., 2019;Fendrich et al., 2020;Anjinho et al., 2021). A qualidade dos resultados dessas pesquisas é fortemente dependente da acurácia dos dados de uso e ocupação do solo. ...
Dados de uso e ocupação do solo são importantes em estudos de modelagem e planejamento ambiental. No Brasil, dados dessa natureza são fornecidos pelo Projeto de Mapeamento Anual da Cobertura e Uso do Solo do Brasil (MapBiomas), iniciativa nacional criada em 2015 com o propósito de monitorar e mapear a dinâmica de uso e ocupação do solo de todo território brasileiro. Considerando que os resultados de muitos estudos ambientais dependem da qualidade dos dados de cobertura do solo, essa pesquisa teve como objetivo avaliar a acurácia dos dados do MapBiomas, por meio de análise comparativa com mapeamento de referência, utilizando o índice estatístico Kappa para comparar e analisar os dados. Os resultados mostram que os dados do MapBiomas representaram de forma adequada o padrão espacial de uso do solo da área de estudo. A grande maioria dos erros observados nos dados do MaBiomas são aceitáveis e ocorrem, possivelmente, por causa da similaridade da resposta espectral entre as classes de uso do solo discordantes, o que gera maior dificuldade para os algoritmos de aprendizagem de máquina distingui-las corretamente. Conclui-se que os dados do MapBiomas são de boa qualidade e podem ser utilizados como dados de entrada de outros estudos ambientais.
... These lakes may be formed along large rivers when sediments from the main channel are deposited as dykes at the mouth of tributaries, forming a lateral lake, and are permanent in the landscape. Changes are reflected by lake water levels and by the provision of significant habitat for a diverse group of organisms (Hirata 2015;Tan Chao and Kuang 2017;Bucak et al. 2018;Tortajada 2020;Abbasi et al. 2020). ...
Water sustainability and universal access to water resources are essential requirements for the existence of
all living beings, even in remote regions where human actions are not yet being felt with intensity. Its
safeguard integrates global targets of the recognized 2030 Agenda for Sustainable Development, namely
concerning sustainable development goals (SDGs) 6, 10, 14 and 15. The call for a global commitment in
this sense is understood as one of the most challenging goals to which all sectors of society are called to
intervene. This work intends to analyse the perception of lotic and lentic ecosystems of Amazon Basin,
expressed by a local community. The methodology is based in interviews applied to eight inhabitants of the
Municipality of Mucajaí—Roraima, Brazil, as well as on official tourism information on the territory and
its contribution to the UN 2030 Agenda. The description of the results highlights that water resources in
places like the Amazon basin, recognized as the largest in the world, comprises rivers, lakes and waterfalls
that not only guarantee the aesthetics quality of the landscape but also contribute to the biodiversity and the
balance of ecosystems. Also, lotic and lentic ecosystems can be boosted in promoting the well-being and
leisure of local communities. It can be concluded that the lotic ecosystems are essential and relevant in
safeguarding the water heritage in Mucajaí, Brazil, being necessary the establishment of partnerships with
the government sectors, stakeholders and local communities, the latter understood as the main protagonists
of the change in favour of a more sustainable future in remote regions.
... Despite the absence of biogeochemical calibration and the likely uncertainties added to the modelling framework, the phytoplankton parameters and processes also consider the uptake of C, N and P to simulate the biomass of the groups. Previous studies performed calibration of DO, nitrogen and phosphorus parameters before the simulation of phytoplankton organisms to improve the simulation results (Bucak et al., 2018;Fenocchi et al., 2019) and that can be an alternative to improve the current modeling approach. ...
A process-based model was used to simulate a hindcast based on the worst historical water quality condition of a tropical urban reservoir. Paranoá Lake is located in Brasília-DF, Brazil, and went through intense eutrophication in the 70s and 90s, with an important cyanobacterial bloom event in 1978. The parameters of phytoplankton were calibrated, focusing on the group of Chlorophyta (green algae) and Cyanobacteria (blue-green algae) at four depths (1, 10, 15 and 20m). The results indicated that the model was able to reproduce the Cyanobacteria biomass in comparison with the observations (RMSE=22-29.10-3 mgC L-1). On the other hand, the simulated Chlorophyta biomass showed good agreement with the observed data only in the bottom layer (RMSE=29. 10-3 mgC L-1 at 20m). In the hindcast simulation, the model was able to predict a significant increase in cyanobacterial biomass facing a water quality deterioration. In the meantime, the simulated Chlorophyta biomass decreased, which may indicate the phytoplankton group succession in response to the environmental conditions.
... According to the distribution of DO (Fig. 3), the oxygen content in most area of the four lakes is apparently lower than the MAC (≤90%) except for the northern narrow region of Yamdrok-tso. The increased input of organic and nutrient matters notably consumes the oxygen component in high-altitude water bodies, leading to DO reduction (Sánchez-España et al., 2017;Bucak et al., 2018;Roșca et al., 2020). ...
Water resources in good quality guarantee the primary condition for the maintenance and development of the natural ecosystem and human society. Water quality status and health risk of the lake water bodies in the national nature reserve, the Yamdrok-tso basin, in the southern Tibetan Plateau are assessed by 25 water parameters including 12 heavy metal(loid)s. Results reveal that the lake water bodies possess relatively high pH (9.68), high concentrations of F (1.66 mg/L), Cu (13.92 μg/L), As (41.60 μg/L), Pb (26.69 μg/L), and U (19.53 μg/L), and a low value of dissolved oxygen (19.30%). The pollution indices (heavy metal pollution index of 0.88–22.88, heavy metal evaluation index of 0.18–3.75, and the degree of contamination of −8.82 to −5.25) demonstrate that the lake water bodies are in a low pollution level with respect to heavy metal(loid)s. The evaluation of water quality based on the fuzzy comprehensive assessment method suggests that 75.56% of the water samples meet the regulation of the China National Standard for water resources in national nature reserves. Health risk assessment shows that potential hazards exist on this region when the residents under long-term exposure to the lake water through oral and dermal pathways, of which children and adults are mostly exposed to As and F for non-carcinogenic and As for carcinogenic risks, especially for children. Results of this study contribute to targeted water resources management in the national nature reserves.
... Furthermore, future land use changes are expected to enhance the impact of climate change on inland waters, mostly because of an increase in the demand for domestic and agricultural use of water [13]. Thus, changes in the climatic conditions are very likely to affect lake productivity and water quality with possible implications for biotic communities [9,20]. ...
Climate change is known to affect world’s lakes in many ways. Lake warming is perhaps the most prominent impact of climate change but there is evidence that changes of precipitation and wind speed over the surface of the lakes may also have a significant effect on key limnological processes. With this study we explored the interannual trends of surface temperature, precipitation, and wind speed over 18 lakes of Greece using ERA5-Land data spanning over a period of almost four decades. We used generalized additive models (GAMs) to conduct time-series analysis in order to identify significant trends of change. Our results showed that surface temperature has significantly increased in all lakes with an average rate of change for annual temperature of 0.43 °C decade−1. With regard to precipitation, we identified significant trends for most lakes and particularly we found that precipitation decreased during the first two decades (1981–2000), but since 2000 it increased notably. Finally, wind speed did not show any significant change over the examined period with the exception for one lake. In summary, our work highlights the major climatic changes that have occurred in several freshwater bodies of Greece. Thus, it improves our understanding on how climate change may have impacted the ecology of these important ecosystems and may aid us to identify systems that are more vulnerable to future changes.
Climate change is altering thermal stratification in lakes worldwide. Reduction in winter mixing lead to prolonged oxygen depletion, lasting for years to centuries, potentially becoming permanent. Although there is convincing evidence of lake deoxygenation globally, its duration, timing, and impacts over decadal to centennial timescales remain uncertain. Here, we introduce a novel model-data assimilation approach using 150 years of limnological and paleolimnological data to evaluate the anthropogenic impact and future of deep dissolved oxygen in Lake Geneva. We find that climate change has influenced winter mixing, with divergent effects on bottom oxygen concentrations before and after eutrophication. Over centennial timescales, eutrophication, not climate warming, triggered unprecedented bottom-water hypoxia. However, by 2100, climate change will be the main driver of hypoxia in Lake Geneva and similar lakes, even with reduced phosphorus concentrations. With climate change locking in the effects of phosphorus loading on hypoxia, the significance of reducing loading remains intact.
The world has faced climate change that affects hydrology and thermal systems in the aquatic environment resulting in temperature changes, which directly affect the aquatic ecosystem. Elevated water temperature influences the physico-chemical properties of chemicals in freshwater ecosystems leading to disturbing living organisms. Owing to the industrial revolution, the mass production of zinc oxide (ZnO) has been led to contaminated environments, and therefore, the toxicological effects of ZnO become more concerning under climate change scenarios. A comprehensive understanding of its toxicity influenced by main factors driven by climate change is indispensable. This review summarized the detrimental effects of ZnO with a single ZnO exposure and combined it with key climate change-associated factors in many aspects (i.e., oxidative stress, energy reserves, behavior and life history traits). Moreover, this review tried to point out ZnO kinetic behavior and corresponding mechanisms which pose a problem of observed detrimental effects correlated with the alteration of elevated temperature.
A number of studies evidenced the impact of human activities on aquatic environments worldwide. The availability of nutrients in lakes is strongly influenced by watershed land use patterns depending on the share of forestry, agriculture and urbanization level. Nearly all the previous studies, which examined the relationships between the phytoplankton community and the land use pattern on the watershed of lakes or reservoirs were performed on a taxonomic basis. In this study, 78 lakes were sampled to analyse how the different land use types affect their phytoplankton functional group compositions. Our results concluded that land use is a complex driver, and it cannot provide an unequivocally straightforward forecast, which could result in the selection of a specific functional group or taxa. Thus, land use alone is a weak predictor, but the shared effects may structure the phytoplankton assemblage composition.
Göllerin ötrofikasyonu, günümüzde ekolojik endişe yaratan olgulardan biridir. Göller özellikle gelişmekte olan ülkelerde artan antropojenik faaliyetler nedeniyle su kalitesinde bozulma ve ekolojik dengesizlik sorunuyla karşı karşıyadır. Bu bağlamda, son birkaç on yıldır limnologlar ve çevre bilimcileri, sucul ekosistemlerin bu sorununa yönelik çalışmalarında, sayısal modellemeyi bir araç olarak kullanmaktadır. Ekolojik modeller, ekosistem proses-etkileşimlerini, geleceğe yönelik yönetim senaryolarını simule etmek ve ötrofikasyona karşı sistemin tepkisini değerlendirmek için kullanılmaktadır. Ekolojik modellerin kullanımı ile göllerde ötrofikasyonun tahmini ve kontrolü eskiye göre daha kolay hale gelmiştir. Ancak göllere özgü sorunlar nedeniyle modeller giderek daha ayrıntılı bir formata bürünmeye devam etmektedir. Bu derleme çalışmasında; a) Ötrofikasyon odaklı modelleme çalışmalarında kullanılan model tipleri özetlenmiş b) Farklı ötrofikasyon unsurlarını ve olaylarını esas alan çeşitli model kullanımlarına, güncel bazı yabancı ve yerli çalışmalarla dikkat çekilmiştir.
Excessive nutrient loads reduce ecosystem resilience, resulting in fundamental changes in ecosystem structure and function when exceeding a certain threshold. However, quantitative analysis of the processes by which nutrient loading affects ecosystem resilience requires further exploration. Food web stability is at the heart of ecosystem resilience. In this study, we simulated the dynamics of the food web under different phosphorus loads for Lake Baiyangdian using the PCLake model and calculated the food web stability. Our results showed that there was a good correspondence between the food web stability and ecosystem state response to phosphorus loads. This relationship confirmed that food web stability could be regarded as a signal for the state transition in a real lake ecosystem. Moreover, our estimates suggested that food web stability was influenced only by several functional groups and their interaction strength. Diatoms and zooplankton were the key functional groups that affected food web stability. Phosphorus loads alter the distribution of functional group biomass, which in turn affects energy delivery and, ultimately, the stability of the food web. Corresponding to functional groups, the interactions among zooplankton, diatoms and detritus had the greatest impact, and the interaction strength of the three was positively correlated with food web stability. Overall, our study explained that food-web stability was critical to characterize ecosystem resilience response to external disturbances and can be turned into a scientific tool for lake ecosystem management.
Process-based ecological models have been used to study freshwater ecosystems and water quality on a broad scale. However, it is also of pivotal importance to incorporate watershed dynamics and nutrient releases in the downstream freshwaters. Integrated modeling approaches have been used to understand the combined effect of climate warming and land use and land cover (LULC) changes in lake ecosystems. Moreover, most basin-scale water quality models require many datasets and parameters to perform reliable simulations which contributes to reduce studies in poorly monitored basins, most of them located in the Global South. In this study, we developed a coupled hydrological-biogeochemical-ecological modeling framework forced by two regionalized climate models and three LULC change scenarios to forecast trophic state changes in a subtropical multipurpose reservoir for the decade 2050-2060. The projections indicated an average air temperature increase between 2°C and 3°C and a downward trend of the average rainfall and longwave radiation for the 2050s in comparison to the last decade. We found a pattern of 28% increase in total phosphorus (TP) and total chlorophyll-a (TChla) concentrations in the reservoir compared with the historical baseline. The climate warming projections along the 2059 projected LULC and basin's increased economic development scenarios have predicted trophic state index (TSI) shifts between mesotrophic and eutrophic conditions (53.3<TSI<57.7). On the other hand, one of the climate projections along the reduced deforestation scenario indicated a trend towards oligotrophication between 2054 and 2056, however higher phosphorus availability (60µg.l−1<TP<100µg.l−1) and phytoplankton biomass (50µg.l−1<TChla<97µg.l−1) would be expected for the entire decade compared to recent years. The proposed coupled modeling framework demonstrated the potential of open-source tools in water quality management studies, especially for poorly monitored basins, based on climate change trends and human pressure.
The Soil and Water Assessment Tool (SWAT) is a well-established eco-hydrological model that has been extensively applied to watersheds across the globe. This work reviews over two decades (2002–2022) of SWAT studies conducted on Mediterranean watersheds. A total of 260 articles have been identified since the earliest documented use of the model in a Mediterranean catchment back in 2002; of which 62% were carried out in Greece, Italy, or Spain. SWAT applications increased significantly in recent years since 86% of the reviewed papers were published in the past decade. A major objective for most of the reviewed works was to check the applicability of SWAT to specific watersheds. A great number of publications included procedures of calibration and validation and reported performance results. SWAT applications in the Mediterranean region mainly cover water resources quantity and quality assessment and hydrologic and environmental impacts evaluation of land use and climate changes. Nevertheless, a tendency towards a multi-purpose use of SWAT is revealed. The numerous examples of SWAT combined with other tools and techniques outline the model's flexibility. Several studies performed constructive comparisons between Mediterranean watersheds' responses or compared SWAT to other models or methods. The effects of inputs on SWAT outputs and innovative model modifications and improvements were also the focus of some of the surveyed articles. However, a significant number of studies reported difficulties regarding data availability, as these are either scarce, have poor resolution or are not freely available. Therefore, it is highly recommended to identify and develop accurate model inputs and testing data to optimize the SWAT performance.
Beyşehir Lake, located in one of the important karstic discharge basins of the Anatolian Plate, is Turkey's largest freshwater lake with a surface area of 703 km2, and is a very important wetland in terms of bio-ecological, socio-economic and cultural aspects. Although the first records on Beyşehir Lake fishery date back to the 1910’s, the first scientific findings on fisheries began in the 1950’s. Although it is very difficult to reach reliable data about the fishery of Lake Beyşehir, the main processes that have been effective on fishing from the 1950s to the present are: i) used fishing gear and methods, ii) changes in the trophic structure of the lake, iii) foreign fauna elements entering the lake, iv) the lake water level changes, v) fishermen's socio-economic and awareness level, vi) fisheries management strategies. The catch yield in the lake, which was 3 kg/ha in the 1950s, was determined as 9.54 kg/ha in 2020. While there have been significant changes in the fauna in the intervening time, it has been determined that there has been a significant increase in the number of fishermen with the increasing amount of catch. Today, 21 fish species live in the lake, which is at mesotrophic-eutrophic level today, 75.68% of the 885,739 kg catch caught in the lake, according to the average of 2019-2020, is Prussian carp (Carassius gibelio), 21.34% is pike perch (Sander lucioperca) and 2.98% is carp (Cyprinus carpio). According to the data of 2020, it has been determined that 385 hunters actively hunting in the lake have gained 8250 kg/year hunting and 8250 TL/year income level. As another result of this study, it was concluded that the biggest factor on the fishing ecosystem of Lake Beyşehir is untimely and excessive fishing.
Persistent eutrophication frequently causes toxic algal blooms, which is a serious threat to drinking water safety, food security, and public health. Nutrient thresholds, the maximum nutrient load that an aquatic ecosystem can absorb while meeting management objective, are key to avoiding and reducing blooms. The determination of thresholds relies on nutrient load-response curves. The spatial heterogeneity of large shallow lakes in terms of lake characteristics results in different curves shape among areas of the lake, which leads to spatial differences in thresholds. However, the spatial heterogeneity of thresholds is typically neglected; there are few methods to analyse the relationship between river loads and lake-specific area thresholds. Here, we proposed the Area Threshold Analysis Framework to analyse the spatial patterns of nutrient loads and thresholds in lakes. We first quantified the flow and load of the rivers entering the lake. The lake was then zoned and modelled to analyse area thresholds. Finally, an intuitive link between the nutrient loads of specific rivers and the thresholds of specific areas of the lake was established. The results showed a nonlinear without hysteresis response in all areas of Chaohu Lake; the nutrient loads and thresholds were highly variable in space, showing a trend of increasing and then decreasing from west to east. Flow density and wind might be important in influencing the spatial distribution of thresholds. The different effects of the wind and flow density on total phosphorus (TP) and chlorophyll a (Chl-a) lead to large differences in the thresholds with TP and Chl-a as management objectives, respectively. The large gap between nutrient loads and thresholds made it important for management to consider appropriate management goals to deal with unrealistic nutrient reductions. Achieving year-round Chl-a ≤ 30µg/l in Chaohu Lake was easier than TP ≤ 0.05mg/l, since for the latter, the Shiwuli, Paihe, and Nanfei river loads needed reductions of > 80%. In addition, for Area 1 and 2, it was more practical to first start meeting TP ≤ 0.05 mg/l for 2 or 3 seasons of the year than for 4 seasons. Overall, we developed a new framework for spatial threshold analysis and established an intuitive link between nutrient loads and thresholds in large shallow lakes. These results are valuable for understanding the threshold properties of spatially heterogeneous ecosystems in general and provide a reference for watershed nutrient management and ecological restoration of lakes.
The present study assesses the risk of eutrophication of a large semiarid reservoir under SSP2-4.5 and SSP5-8.5 scenarios for three future periods and different conditions of influent total phosphorus (TP) concentration and reservoir withdrawal. An integrated approach coupling climate, hydrological and water quality models was proposed for forecasting the climate change impacts on the trophic condition of the reservoir. The projected TP concentrations were organized as probability-based cumulative distribution functions to quantify the risk of eutrophication. The results indicated changes of eutrophication status in the three future periods, with the end of the 21st century experiencing the highest impacts on water quality. On the other hand, major reductions both in the inlet TP concentration and the reservoir withdrawal are necessary to significantly improve the trophic status and minimize the risk of eutrophication. The results also showed that the dry period is more susceptible to eutrophication than the rainy period, suggesting that tropical semiarid reservoirs are more vulnerable to eutrophication under climate change than reservoirs in other regions of the world. The proposed approach and model results are important to better understand the impact of climate change on reservoir water quality and improve water resources management in tropical semiarid regions.
Models are widely used tools in aquatic science to understand the mechanism of phytoplankton growth and anticipate the occurrence of harmful algal blooms (HABs). However, model parameterization remains challenging and issues that may introduce prediction uncertainty exist. Many models use the Monod equation to predict cyanobacteria growth rate based on ambient nutrient concentrations. The half‐saturation concentrations in the Monod equation varies greatly among different studies and depends on environmental conditions. In this study we estimated the growth rate due to nutrient limitations for two cyanobacteria species (Microcystis aeruginosa and Dolichospermum flos‐aquae) using a modified Monod model which allows the half‐saturation concentration to vary according to initial nitrogen (N) conditions. The model is calibrated against observations from laboratory experiment where cyanobacteria growth and ambient nutrient concentrations were measured simultaneously, which is rarely done in the literature. Our results show this modified model produce better predictions on growth rate and biomass, indicating many commonly used mechanistic models may need improvement regarding phytoplankton growth representation. Furthermore, our study quantifies the flexibility in cyanobacteria growth parameter across a wide range of environmental N in eutrophic lakes thus provides important information for large‐scale modelling applications. This article is protected by copyright. All rights reserved.
An extensive artificial water diversion project aimed at alleviating the shortage of ecological water in lakes can change the original hydrological and physicochemical states and further affect the structure and distribution of phytoplankton communities. Therefore, it is important to fully evaluate the ecological restoration effect of the water diversion project on the water-receiving area before implementing water replenishment. For this purpose, we developed an integrated model framework based on the Environmental Fluid Dynamics Code (EFDC) and Random Forest (RF). We adopted a probability distribution method to address the uncertainty during model coupling. This framework was implemented to simulate and predict the evolution of phytoplankton diversity in Baiyangdian Lake (BL) in China. To solve the problem that the phytoplankton biodiversity in BL decreased especially in summer due to human activity, the Yellow River into BL, the south-to-north water diversion project, and joint replenishment of upstream reservoirs have been implemented in recent years. Our framework was used to analyze the biodiversity restoration effects of multi-source water replenishment through different routings. The results show that spatiotemporal coverage should be considered to reduce uncertainty during model coupling. Water replenishment has a positive impact on the biodiversity of BL; however, there are effective areas for phytoplankton diversity restoration, which are related to water quality and quantity, water replenishment routing and internal hydrological connectivity. The Xiaobai River has the most significant water ecological restoration potential among the routings, compared with that of the Baigou and Fu Rivers. Appropriate water replenishment in spring will play a vital role in alleviating the decrease in phytoplankton biodiversity in summer owing to flood control.
Wetlands, especially marshes, support many services such as carbon catchment control or water purification led by primary producers such as phytoplankton and microphytobenthos (PB). The impact of the sedimentary compartment, as source and sink of essential nutrients for the water column, is often neglected in the study of their dynamics and water purification capacity of the systems. This work compared monthly (between February 2020 and April 2021) the benthic and pelagic primary producers’ dynamics in two anthropised freshwater marshes (Marans and Genouillé), with the simultaneous follow-up of physico-chemical parameters of the water column and nutrient fluxes at the sediment-water (SWI) interface. It was suggested a strong contribution of phytoplankton (pumping) and the benthic compartment (denitrification) to the water purification of these two nitrates (NO3-)-rich marshes. Total phytoplankton production fluctuated between ~5 (winter) and 1500 mg C m-3 d-1 (fall) at Marans and between 40 (winter) and ~750 mg C m-3 d-1 (spring) at Genouillé. At Marans, soluble reactive phosphorus (SRP) benthic effluxes (-2.101 to -6.102 µmol m-2 d-1 in fall and summer respectively) coincided with phytoplankton bloom periods. These effluxes were inhibited by NO3- penetration in the sediment (0 to 5.104 µmol m-2 d-1), by inhibiting iron respiration. At Genouillé, inhibition of SRP effluxes depended on denitrification rate and on P stocks in the sediment, where slight SRP effluxes (-101 µmol m-2 d-1) could have co-occurred with slight NO3- influxes (5.102 µmol m-2 d-1) in spring. The presence of PB (between 10-60 and 40-120 mg gsed-1 at Marans and Genouillé respectively), suggested a strong contribution of the benthic compartment to the total primary production (benthic and pelagic through resuspension processes) in these environments. This work encourages to consider the benthos and the pelagos as a unicum to provide better sustainable management of such systems and limit eutrophication risks in coastal areas.
Mediterranean Basin is expected to be one of the regions most severely impacted by global climate change. However, the complex interactions of driving forces of climate in the region create a challenge for climate projections for the future. Findings from climate change studies support the inter-model and inter-regional variability of projections on climate change impacts. On the other hand, the studies on the evaluation of the simulation skills of high-resolution climate models for the region particularly for Turkey are still numbered. Hence, this study brings a 14-member ensemble together for the analysis of the performance efficiencies of 12 CORDEX RCMs and two high-resolution climate models, NHRCM and MRI-AGCM, of the Japanese Meteorological Research Institute (MRI). The skill of climate models to reproduce the spatial variability of baseline precipitation climatology is assessed through a benchmark with reference data from 59 ground-based meteorological stations across the study area. Additionally, potential changes in precipitation climatology in the short (2020−2030), medium (2031–2050), and long-term (2051–2100) future are studied with a 14-member ensemble analysis. Projections of 14 models show significant disagreement, especially in the short-term, but most models project a general decrease in the precipitation in the study area in medium- and long-term under both RCP4.5 and RCP8.5 scenarios. For RCP8.5 scenario, performance based weighted average of five climate models project a decrease in precipitation across the whole study area both for medium- and long-term future.
Reliable water quality prediction can improve environmental flow monitoring and the sustainability of the stream ecosystem. In this study, we compared two machine learning methods to predict water quality parameters, such as total nitrogen (TN), total phosphorus (TP), and turbidity (TUR), for 97 watersheds located in the Southeast Atlantic region of the USA. The modeling framework incorporates multiple climate and watershed variables (characteristics) that often control the water quality indicators in different landscapes. Three techniques, such as stepwise regression (SR), Least Absolute Shrinkage and Selection Operator (LASSO), and genetic algorithm (GA), are implemented to identify appropriate predictors out of 28 climate and catchment-related variables. The selected predictors were then used to develop the Random Forest (RF) and Boosted regression tree (BRT) models for water quality predictions in selected watersheds. The results highlighted that while both algorithms provided reasonable results (based on statistical metrics), the RF algorithm was easier to train and robust to model overfitting. Partial dependence plots highlighted the complex and nonlinear relationships between the individual predictors and the water quality indicators. The thresholds obtained from partial dependence plots showed that the median values of total nitrogen (TN) and total phosphorus (TP) in streams increase significantly when the percentage of urban and agricultural lands is above 40% and 43% of the watershed area, respectively. Furthermore, when soil hydraulic conductivity increases, the reduction in runoff results in decreased Turbidity levels in streams. Therefore, identifying the key watershed characteristics and their critical thresholds can help watershed managers create appropriate regulations for managing and sustaining healthy stream ecosystems. Besides, the forecasting models can improve water quality predictions in ungauged watersheds.
As a critical component of the global environment, aquatic ecosystems support a wide range of organisms, including bacteria, fungi, algae, invertebrates, plants, and fish [...]
A coupled hydrodynamic-biogeochemical model was applied to simulate scenarios of classic restoration practices to address eutrophication in a cascade system comprised of six reservoirs along the Tietê River (Brazil) from 2008 to 2016. Each restoration scenario was propagated along the cascade system by using a sequential modelling approach. The simulated scenarios revealed which on-land and in-lake restoration techniques are capable of promoting water quality improvements that are propagated to all downstream reservoirs along the cascade system. The present findings may provide a useful management strategy to develop better restoration practices at a basin catchment scale for other lakes and reservoirs along cascade systems worldwide, especially in highly anthropogenic impacted areas, taking advantage of the propagation of water quality improvements in a downstream direction due to a domino effect triggered by the feedback from one water body to the next in a chain.
Groundwater–surface water (GW–SW) interactions represent an important, but less visible, linkage in lake ecosystems. Periphyton is most abundant at the GW–SW interface and can rapidly assimilate nutrients from the water column. Despite the importance of periphyton in regulating whole‐lake metabolism, they are less well studied or monitored in comparison with planktonic taxa and pelagic systems. This is in stark contrast to studies of flowing waters and wetlands, where variability in GW–SW connectivity and periphyton productivity is more often incorporated into study designs. To bridge the gap between groundwater's influence on lake benthic communities, this synthesis aims to prime researchers with information necessary to incorporate groundwater and periphyton sampling into lake studies and equip investigators with tools that will facilitate cross‐disciplinary collaboration. Specifically, we (1) propose how to overcome barriers associated with studying littoral ecological‐hydrological dynamics; (2) summarize field, laboratory, and modeling techniques for assessing spatiotemporal periphyton patterns and benthic hydrological fluxes; and (3) identify paths for hydrological techniques to be incorporated into ecological studies, deepening our understanding of whole‐lake ecosystem function. We argue that coupling hydrological and periphyton measurements can yield dualistic insights into lake ecosystem functioning: how benthic periphyton modulate constituents within groundwater, and conversely, the extent to which constituents in groundwater modulate the productivity of periphyton assemblages. We assert that priming ecologists and hydrologists alike with a shared understanding of how each discipline studies the nearshore zone presents a tangible path forward for both integrating these disciplines and further contextualizing lake processes within the limnological landscape.
In this study, a coupled three-dimensional hydrodynamic-ecological model was developed to comprehensively understand the interaction between the hydrodynamics and ecological status of a lake. The coupled model was utilized to explore the hydrodynamics, water quality, and ecological status in an ecologically rich subalpine lake (i.e., Tsuei-Feng Lake (TFL), located in north-central Taiwan). The measured data of water depth, water temperature, water quality, and planktonic biomass were gathered to validate the coupled model. The simulated results with a three-dimensional hydrodynamic and water quality-ecological model reasonably reproduced the variations in observed water depth, water temperature, water quality, and phytoplankton and zooplankton biomass. Sensitivity analysis was implemented to determine the most influential parameter affecting the planktonic biomass. The results of sensitivity analysis indicated that the predation rate on phytoplankton (PRP) significantly affects the phytoplankton biomass, while the basal metabolism rate of zooplankton (BMZ) importantly affects the zooplankton biomass. Furthermore, inflow discharge was the most important environmental factor dominating the phytoplankton and zooplankton biomass of TFL. This implies that the runoff in the catchment area caused by rainfall and the heavy rainfall induced by climate change may affect the planktonic biomass of the lake.
Adaptation to inevitable climate change makes it necessary to re-think land use management paradigms and strategies and to suggest modifications to existing practices to render them functional in future environmental conditions, in particular in a warming climate.
We do so, by combining (i) quantitative assessment and cartographic representation of important ecosystem services in Austria using appropriate indicators and by (ii) adapting an agent-based model (ABM) for climate change driven land use changes recently developed for two representative Austrian case study regions. Using results and data from a recent study of the Austrian program on rural development 2014-2020 conducted by Environment Agency Austria, we assess and map ecosystem services (ESSs) related to high nature value farmland, habitats and species, fragmentation of habitat types, soil protection, insect pollination, C sequestration in soil, soil fertility, agricultural production (plants), and drinking water.
The ABM, developed by the University of Natural Resources and Life Sciences, Vienna, relies on relevant agents, primarily land managers such as farms, that make land-use decisions dependent on framework conditions (e.g. agricultural prices and subsidies) as well as intrinsic preferences and societal norms that may change over time. We develop three scenarios considering changes in socio-economic development and climate and use the ABM for predicting land use change at very high resolution of land parcels and can therefore assess changes in the supply of ESSs. Engaging local stakeholders, we identify key challenges and relevant policies to derive land use management recommendations that increase system resilience and counteract the loss of ESSs.
Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate how these factors jointly determine macrophyte dominance and growth, we conducted a highly standardised pan-European experiment involving the installation of mesocosms in lakes. The experimental design consisted of mesotrophic and eutrophic nutrient conditions at 1 m (shallow) and 2 m (deep) depth along a latitudinal
temperature gradient with average water temperatures ranging from 14.9 to 23.9 °C (Sweden to Greece) and a natural drop in water levels in the warmest countries (Greece and Turkey). We determined Percent Plant Volume Inhabited (PVI) of submerged macrophytes on a monthly basis for five months and dry weight at the end of the experiment. Over the temperature gradient, PVI was highest in the shallow mesotrophic mesocosms followed by intermediate levels in the shallow eutrophic and deep mesotrophic mesocosms, and lowest levels in the deep eutrophic mesocosms.
We identified three pathways along which water temperature likely affected PVI, exhibiting: (1) a direct positive effect if light was not limiting, (2) an indirect positive effect due to an evaporation driven water level reduction, causing a non-linear increase in mean available light, (3) an indirect negative effect through algal growth and, thus, high light attenuation under eutrophic conditions. We conclude that high temperatures combined with a temperature-mediated water level decrease can counterbalance the negative effects of eutrophic conditions on macrophytes by enhancing the light availability. While a water level reduction can promote macrophyte dominance, an extreme reduction will likely decrease macrophyte biomass and, consequently, their capacity to function as a
carbon store and food source.
Eutrophication continues to be the most important problem preventing a favorable environmental state and detrimentally impacting the ecosystem services of lakes. The current study describes the results of analyses of 20 year monitoring data from two interconnected Anatolian lakes, Lakes Mogan and Eymir, receiving sewage effluents and undergoing restoration. The first step of restoration in both lakes was sewage effluent diversion. Additionally, in hypertrophic Lake Eymir, biomanipulation was conducted, involving removal of benthi-planktivorous fish and prohibition of pike fishing. The monitoring period included high (H) and low (L) water levels (WL) enabling elucidation of the effects of hydrological changes on lake restoration. In shallower Lake Mogan, macrophyte abundance increased after the sewage effluent diversion in periods with low water levels even at turbid water. In comparatively deeper Lake Eymir, the first biomanipulation led to a clear water state with abundant macrophyte coverage. However, shortly after biomanipulation, the water clarity declined, coinciding with low water level (LWL) periods during which nutrient concentrations increased. A second biomanipulation was conducted, mostly during high water level (HWL) period, resulting in a major decrease in nutrient concentrations and clearer water, but without an expansion of macrophytes. We conclude that repetitive fish removal may induce recovery but its success may be confounded by high availability of nutrients and adverse hydrological conditions.
The location and persistence of surface water (inland and coastal) is both affected by climate and human activity and affects climate, biological diversity and human wellbeing. Global data sets documenting surface water location and seasonality have been produced from inventories and national descriptions, statistical extrapolation of regional data and satellite imagery, but measuring long-term changes at high resolution remains a challenge. Here, using three million Landsat satellite images, we quantify changes in global surface water over the past 32 years at 30-metre resolution. We record the months and years when water was present, where occurrence changed and what form changes took in terms of seasonality and persistence. Between 1984 and 2015 permanent surface water has disappeared from an area of almost 90,000 square kilometres, roughly equivalent to that of Lake Superior, though new permanent bodies of surface water covering 184,000 square kilometres have formed elsewhere. All continental regions show a net increase in permanent water, except Oceania, which has a fractional (one per cent) net loss. Much of the increase is from reservoir filling, although climate change is also implicated. Loss is more geographically concentrated than gain. Over 70 per cent of global net permanent water loss occurred in the Middle East and Central Asia, linked to drought and human actions including river diversion or damming and unregulated withdrawal. Losses in Australia and the USA linked to long-term droughts are also evident. This globally consistent, validated data set shows that impacts of climate change and climate oscillations on surface water occurrence can be measured and that evidence can be gathered to show how surface water is altered by human activities. We anticipate that this freely available data will improve the modelling of surface forcing, provide evidence of state and change in wetland ecotones (the transition areas between biomes), and inform water-management decision-making.
Complex lake ecosystem models can assist lake managers in developing management plans counteracting the eutrophication symptoms that are expected to be a result of climate change. We applied the ecological model PCLake based on 22 years of data from shallow, eutrophic Lake Søbygaard, Denmark and simulated multiple combinations of increasing temperatures (0–6 • C), reduced external nutrient loads (0%–98%) with and without internal phosphorus loading. Simulations suggest nitrogen to be the main limiting nutrient for primary production, reflecting ample phosphorus release from the sediment. The nutrient loading reduction scenarios predicted increased diatom dominance, accompanied by an increase in the zooplankton:phytoplankton biomass ratio. Simulations generally showed phytoplankton to benefit from a warmer climate and the fraction of cyanobacteria to increase. In the 6 • C warming scenario, a nutrient load reduction of as much as 60% would be required to achieve summer chlorophyll-a levels similar to those of the baseline scenario with present-day temperatures.
This study presents FABM-PCLake, a complete redesign of the PCLake aquatic ecosystem model, which we implemented into the Framework for Aquatic Biogeochemical Models (FABM). In contrast to the original model, which was designed for temperate, fully mixed freshwater lakes, the new FABM-PCLake represents an integrated aquatic ecosystem model that enables simulations of hydrodynamics and biogeochemical processes for zero dimensional, one-dimensional as well as three-dimensional heterogeneous environments. FABM-PCLake describes interactions between multiple trophic levels, including piscivorous, zooplanktivorous and benthivorous fish, zooplankton, zoobenthos, three groups of phytoplankton and rooted macrophytes. The model also accounts for oxygen dynamics and nutrient cycling for nitrogen, phosphorus and silicon, both within the pelagic and benthic domains. FABM-PCLake includes a two-way communication between the biogeochemical processes and the physics, where some biogeochemical state variables (e.g., phytoplankton) influence light attenuation and thereby the spatial and temporal distributions of light and heat. At the same time, the physical environment, including water currents, light and temperature influence a wide range of biogeochemical processes. The model enables studies on ecosystem dynamics in physically heterogeneous environments (e.g., stratifying water bodies, and water bodies with horizontal gradient in physical and biogeochemical properties), and through FABM also enables data assimilation and multi-model ensemble simulations. Examples of relevant model applications include climate change impact studies and environmental impact assessment scenarios for lakes and reservoirs worldwide.
Artificial mixing has been used as a measure to prevent the growth of cyanobacteria in eutrophic lakes and reservoirs for many years. In this paper, we give an overview of studies that report on the results of this remedy. Generally, artificial mixing causes an increase in the oxygen content of the water, an increase in the temperature in the deep layers but a decrease in the upper layers, while the standing crop of phytoplankton (i.e. the chlorophyll content per m2) often increases partly due to an increase in nutrients entrained from the hypolimnion or resuspended from the sediments. A change in composition from cyanobacterial dominance to green algae and diatoms can be observed if the imposed mixing is strong enough to keep the cyanobacteria entrained in the turbulent flow, the mixing is deep enough to limit light availability and the mixing devices are well distributed horizontally over the lake. Both models and experimental studies show that if phytoplankton is entrained in the turbulent flow and redistributed vertically over the entire depth, green algae and diatoms win the competition over (colonial) cyanobacteria due to a higher growth rate and reduced sedimentation losses. The advantage of buoyant cyanobacteria to float up to the illuminated upper layers is eradicated in a well-mixed system.
Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5–10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary.
The impacts of climate and land use changes on streamflow and sediment export were evaluated for a humid (São Lourenço) and a dry (Guadalupe) Mediterranean catchment, using the SWAT model. SWAT was able to produce viable streamflow and sediment export simulations for both catchments, which provided a baseline for investigating climate and land use changes under the A1B and B1 emission scenarios for 2071-2100. Compared to the baseline scenario (1971-2000), climate change scenarios showed a decrease in annual rainfall for both catchments (humid: -12%; dry: -8%), together with strong increases in rainfall during winter. Land use changes were derived from a socio-economic storyline in which traditional agriculture is replaced by more profitable land uses (i.e. corn and commercial forestry at the humid site; sunflower at the dry site). Climate change projections showed a decrease in streamflow for both catchments, whereas sediment export decreased only for the São Lourenço catchment. Land use changes resulted in an increase in streamflow, but the erosive response differed between catchments. The combination of climate and land use change scenarios led to a reduction in streamflow for both catchments, suggesting a domain of the climatic response. As for sediments, contrasting results were observed for the humid (A1B: -29%; B1: -22%) and dry catchment (A1B: +222%; B1: +5%), which is mainly due to differences in the present-day and forecasted vegetation types. The results highlight the importance of climate-induced land-use change impacts, which could be similar to or more severe than the direct impacts of climate change alone.
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Both climate and land use changes can influence water quality and quantity in different ways. Thus, for predicting future water quality and quantity trends, simulations should ideally account for both projected climate and land use changes. In this paper, land use projections and climate change scenarios were integrated with hydrological model to estimate the relative impact of climate and land use projections on a suite of water quality and quantity endpoints for a Canadian watershed. Climatic time series representing SRES change scenario A2 were generated by downscaling the outputs of the Canadian Regional Climate Model (version 4.1.1) using a combination of quantile–quantile transformation and nearest neighbor search. The SWAT (Soil and Water Assessment Tool) model was used to simulate streamflow, nitrogen and phosphorus loading under different climate and land use scenarios. Results showed that a) climate change will drive up maximum monthly streamflow, nitrate loads, and organic phosphorus loads, while decreasing organic nitrogen and nitrite loads; and b) land use changes were found to drive the same water quality/quantity variables in the same direction as climate change, except for organic nitrogen loads, for which the effects of the two stressors had a reverse impact on loading.
Both abiotic and biotic explanations have been proposed to explain recent recurrent nuisance/harmful algal blooms in the western basin and central basin of Lake Erie. We used two long-term (> 10 years) datasets to test (1) whether Lake Erie total phytoplankton biomass and cyanobacterial biomass changed over time and (2) whether phytoplankton abundance was influenced by soluble reactive phosphorus or nitrate loading from agriculturally-dominated tributaries (Maumee and Sandusky rivers). We found that whereas total phytoplankton biomass decreased in Lake Erie's western basin from 1970 to 1987, it increased starting in the mid-1990s. Total phytoplankton and cyanobacterial seasonal (May–October) arithmetic mean wet-weight biomasses each significantly increased with increased water-year total soluble reactive phosphorus load from the Maumee River and the sum of soluble reactive phosphorus load from the Maumee and Sandusky rivers, but not for the Sandusky River alone during 1996–2006. During this same time period, neither total phytoplankton nor cyanobacterial biomass was correlated with nitrate load. Consequently, recently increased tributary soluble reactive phosphorus loads from the Maumee River likely contributed greatly to increased western basin and (central basin) cyanobacterial biomass and more frequent occurrence of harmful algal blooms. Managers thus must incorporate the form of and source location from which nutrients are delivered to lakes into their management plans, rather than solely considering total (both in terms of form and amount) nutrient load to the whole lake. Further, future studies need to address the relative contributions of not only external loads, but also sources of internal loading.
1930 Climate change may have profound eff ects on phosphorus (P) transport in streams and on lake eutrophication. Phosphorus loading from land to streams is expected to increase in northern temperate coastal regions due to higher winter rainfall and to a decline in warm temperate and arid climates. Model results suggest a 3.3 to 16.5% increase within the next 100 yr in the P loading of Danish streams depending on soil type and region. In lakes, higher eutrophication can be expected, reinforced by temperature-mediated higher P release from the sediment. Furthermore, a shift in fi sh community structure toward small and abundant plankti-benthivorous fi sh enhances predator control of zooplankton, resulting in higher phytoplankton biomass. Data from Danish lakes indicate increased chlorophyll a and phytoplankton biomass, higher dominance of dinophytes and cyanobacteria (most notably of nitrogen fi xing forms), but lower abundance of diatoms and chrysophytes, reduced size of copepods and cladocerans, and a tendency to reduced zooplankton biomass and zooplankton:phytoplankton biomass ratio when lakes warm. Higher P concentrations are also seen in warm arid lakes despite reduced external loading due to increased evapotranspiration and reduced infl ow. Th erefore, the critical loading for good ecological state in lakes has to be lowered in a future warmer climate. Th is calls for adaptation measures, which in the northern temperate zone should include improved P cycling in agriculture, reduced loading from point sources, and (re)-establishment of wetlands and riparian buff er zones. In the arid Southern Europe, restrictions on human use of water are also needed, not least on irrigation. O n average, global surface temperatures have increased by about 0.74°C over the past 100 yr (Trenberth et al., 2007), with the majority of the increase (0.55°C) occurring over the past 30 yr. We may expect marked changes to occur in the global climate during this century (IPCC, 2007). Increasingly reliable regional climate projections are available for many regions of the world, but fewer projections are available for many developing countries than for the developed world (Christensen et al., 2007). Th e warming generally increases the spatial variability of precipitation with reduced rainfall in the subtropics and increases at higher latitudes and in parts of the tropics. Th e changes in temperature and rainfall lead to changes in agricul-tural land use and management, including changes in soil cultivation and in the rates and timing of fertilization (Howden et al., 2007). Th ese changes have cascading eff ects on the P cycling, directly and indirectly, that aff ect the aquatic environment. Th e direct eff ects are related to the increased temperatures, increased rainfall intensity, and changes in winter rainfall that are expected to enhance the P loading to freshwaters in the temperate zone (IPCC, 2007) and the Arctic (Arctic Climate Impact Assessment, 2002) and to reduce the loading, but not the concentrations, in streams and freshwater lakes in the Mediterranean region. However, a few quantitative studies are avail-able (Chang, 2004; Andersen et al., 2006). Th e indirect eff ects are related to changes in the choice of crops, crop rotations, use of catch crops, and agricultural practices, including tillage and fertilization. In northern temperate areas, new heat-demanding, warm-season crops (e.g., maize and sunfl ower) will replace many of the present grain cereals and oilseed crops (Olesen and Bindi, 2002). At the same time, changes occur in planting and harvesting times (Olesen, 2005) and in fertilization rates and strategies (Olesen et al., 2007). Crop rotation must be adapted to changes in crop choices, in crop maturing, and in the need to control weeds, pests, and diseases. Th is will aff ect the amount of P released to freshwaters and its seasonal pattern. More-Abbreviation: TP, total phosphorus.
General circulation models (GCMs) project an increasing frequency and
intensity of heavy rainfall events due to global climate change. This
rather holds true for regions that are even expected to experience an
overall decrease in average annual precipitation. Consequently, this may
be attended by an increasing frequency and magnitude of flood events.
However, time series of GCMs show a bias in simulating 20th century
precipitation and temperature fields and, therefore, cannot directly be
used to force hydrological models in order to assess the impact of the
projected climate change on certain components of the hydrological
cycle. For a posteriori correction, the so-called delta change approach
is widely-used which adds the 30-year monthly differences for
temperature or ratios for precipitation of the GCM data to each month of
a historic climate data set. As the variability of the climate variables
in the scenario period is not transferred, this approach is especially
questionable if discharge extremes are to be analyzed. In order to
preserve the variability given by the GCM, methods of statistical bias
correction are applied. This study aims to investigate the impact of two
methods of bias correction, the delta change approach and a statistical
bias correction, on the large scale modeling of flood discharges, using
the example of 25 macroscale catchments in Europe. The discharge
simulation is carried out with the global integrated model WaterGAP3
(Water - Global Assessment and Prognosis). Results show that the two
bias correction methods lead to distinctively different trends in future
flood flows.
The new scenario framework for climate change research envisions combining pathways of future radiative forcing and their associated climate changes with alternative pathways of socioeconomic development in order to carry out research on climate change impacts, adaptation, and mitigation. Here we propose a conceptual framework for how to define and develop a set of Shared Socioeconomic Pathways (SSPs) for use within the scenario framework. We define SSPs as reference pathways describing plausible alternative trends in the evolution of society and ecosystems over a century timescale, in the absence of climate change or climate policies. We introduce the concept of a space of challenges to adaptation and to mitigation that should be spanned by the SSPs, and discuss how particular trends in social, economic, and environmental development could be combined to produce such outcomes. A comparison to the narratives from the scenarios developed in the Special Report on Emissions Scenarios (SRES) illustrates how a starting point for developing SSPs can be defined. We suggest initial development of a set of basic SSPs that could then be extended to meet more specific purposes, and envision a process of application of basic and extended SSPs that would be iterative and potentially lead to modification of the original SSPs themselves.
Impact of climate change on ecohydrologic processes of Mediterranean watersheds are significant and require quick action toward improving adaptation and management of fragile system. Increase in water shortages and land use can alter the water balance and ecological health of the watershed systems. Intensification of land use, increase in water abstraction, and decline in water quality can be enhanced by changes in temperature and precipitation regimes. Ecohydrologic changes from climatic impacts alter runoff, evapotranspiration, surface storage, and soil moisture that directly affect biota and habitat of the region. This paper reviews expected impacts of climatic change on the ecohydrology of watershed systems of the Mediterranean and identifies adaptation strategies to increase the resilience of the systems. A spatial assessment of changes in temperature and precipitation estimates from a multimodel ensemble is used to identify potential climatic impacts on watershed systems. This is augmented with literature on ecohydrologic impacts in watershed systems of the region. Hydrologic implications are discussed through the lens of geographic distribution and upstream-downstream dynamics in watershed systems. Specific implications of climatic change studied are on runoff, evapotranspiration, soil moisture, lake levels, water quality, habitat, species distribution, biodiversity, and economic status of countries. It is observed that climatic change can have significant impacts on the ecohydrologic processes in the Mediterranean watersheds. Vulnerability varied depending on the geography, landscape characteristics, and human activities in a watershed. Increasing the resilience of watershed systems can be an effective strategy to adapt to climatic impacts. Several strategies are identified that can increase the resilience of the watersheds to climatic and land use change stress. Understanding the ecohydrologic processes is vital to development of effective long-term strategies to improve the resilience of watersheds. There is need for further research into ecohydrologic dynamics at multiple scales, improved resolution of climatic predictions to local scales, and implications of disruptions on regional economies.
A probabilistic framework is presented for combining information from an ensemble of four general circulation models (GCMs), two greenhouse gas emission scenarios, two statistical downscaling techniques, two hydrological model structures, and two sets of hydrological model parameters. GCMs were weighted according to an index of reliability for downscaled effective rainfall, a key determinant of low flows in the River Thames. Hydrological model structures were weighted by performance at reproducing annual low-flow series. Weights were also assigned to sets of water resource model (CATCHMOD) parameters using the Nash-Sutcliffe efficiency criterion. Emission scenarios and downscaling methods were unweighted. A Monte Carlo approach was then used to explore components of uncertainty affecting projections for the River Thames by the 2080s. The resulting cumulative distribution functions (CDFs) of low flows were most sensitive to uncertainty in the climate change scenarios and downscaling of different GCMs. Uncertainties due to the hydrological model parameters and emission scenario increase with time but were less important. Abrupt changes in low-flow CDFs were attributed to uncertainties in statistically downscaled summer rainfall. This was linked to different behavior of atmospheric moisture among the chosen GCMs.
The literature was reviewed to determine the direct temperature effects on photosynthetic capacity (Pmax), specific respiration rate (Rest), and growth rate of bloom‐forming cyanobacteria (Anabaena, Aphanizomenon, Microcystis, Oscillatoria) and to assess the importance of direct tern‐perature effects on cyanobacterial dominance in lakes. This analysis is supported by field studies of Microcystis aeruginosa in a hypertrophic lake. The literature and field data show that Pmax, Rest, and growth rate are temperature‐dependent with optima usually at 25 °C or greater. The four genera varied in their response to low temperatures with Microcystis being most severely limited belw about 15 °C. Oscillatoria tended to tolerate the widest range of temperatures. However, an examination of field data from representative lakes around the world indicated that direct temperature effects were secondary to indirect temperature effects (mixing) and nutrients in determining the dominance of bloom‐forming cyanobacteria in lakes, direct tern‐perature effects probably act synergistically with other factors in this process.
Cyanobacteria are the Earth's oldest known oxygen-evolving photosynthetic microorganisms, and they have had major impacts on shaping our current atmosphere and biosphere. Their long evolutionary history has enabled cyanobacteria to develop survival strategies and persist as important primary producers during numerous geochemical and climatic changes that have taken place on Earth during the past 3.5 billion years. Today, some cyanobacterial species form massive surface growths or 'blooms' that produce toxins, cause oxygen depletion and alter food webs, posing a major threat to drinking and irrigation water supplies, fishing and recreational use of surface waters worldwide. These harmful cyanobacteria can take advantage of anthropogenically induced nutrient over-enrichment (eutrophication), and hydrologic modifications (water withdrawal, reservoir construction). Here, we review recent studies revealing that regional and global climatic change may benefit various species of harmful cyanobacteria by increasing their growth rates, dominance, persistence, geographic distributions and activity. Future climatic change scenarios predict rising temperatures, enhanced vertical stratification of aquatic ecosystems, and alterations in seasonal and interannual weather patterns (including droughts, storms, floods); these changes all favour harmful cyanobacterial blooms in eutrophic waters. Therefore, current mitigation and water management strategies, which are largely based on nutrient input and hydrologic controls, must also accommodate the environmental effects of global warming.
Cyanobacteria are the Earth's oldest oxygenic photoautotrophs and have had major impacts on shaping its biosphere. Their long evolutionary history (∼3.5 by) has enabled them to adapt to geochemical and climatic changes, and more recently anthropogenic modifications of aquatic environments, including nutrient over-enrichment (eutrophication), water diversions, withdrawals, and salinization. Many cyanobacterial genera exhibit optimal growth rates and bloom potentials at relatively high water temperatures; hence global warming plays a key role in their expansion and persistence. Bloom-forming cyanobacterial taxa can be harmful from environmental, organismal, and human health perspectives by outcompeting beneficial phytoplankton, depleting oxygen upon bloom senescence, and producing a variety of toxic secondary metabolites (e.g., cyanotoxins). How environmental factors impact cyanotoxin production is the subject of ongoing research, but nutrient (N, P and trace metals) supply rates, light, temperature, oxidative stressors, interactions with other biota (bacteria, viruses and animal grazers), and most likely, the combined effects of these factors are all involved. Accordingly, strategies aimed at controlling and mitigating harmful blooms have focused on manipulating these dynamic factors. The applicability and feasibility of various controls and management approaches is discussed for natural waters and drinking water supplies. Strategies based on physical, chemical, and biological manipulations of specific factors show promise; however, a key underlying approach that should be considered in almost all instances is nutrient (both N and P) input reductions; which have been shown to effectively reduce cyanobacterial biomass, and therefore limit health risks and frequencies of hypoxic events.
The functioning of shallow lakes is supposedly very sensitive to water level fluctuations (WLF). Relationships between WLF and submerged macrophyte development were investigated in five Turkish shallow lakes located in a semi-arid to arid Mediterranean climate where the hydrological event of WLF is a common phenomenon. In all lakes, WLF emerged as a major factor determining submerged plant development. High submerged plant coverage was observed in four of the study lakes, Lake Beyşehir, Lake Uluabat, Lake Marmara and Lake Mogan when the water level was low throughout the year or during growing season, submerged plants expanded; however, in Lake Işıklı extensive submerged plant development was observed at high water levels during winter. In Lake Işıklı, an increase of 25 % in the surface area was recorded, which, in turn, might have resulted in an increased potential for expansion of submerged plants. Furthermore, in all the lakes excluding Lake Beyşehir, high sub-merged plant coverage coincided with a significant decrease in the amplitude of intra-annual water level fluctuations. The depth profile, expressed as the morphometry index (Zmean/Zmax), appeared to be critical for the development of extensive vegetation. Expansion of vegetation coincided with either an increased morphometry index or a flatter bottom profile. However, the impact of hydrology on lake morphometry differed between the lakes. In Lake Işıklı, the high water level generated a slightly flatter, albeit not significantly so, bottom; however, in the remaining lakes the same effect was observed at low water level. Differences in the morphometry index in response to WLF appeared to depend on the original bottom profile, which is either conical or ellipsoid. Therefore, the impact of hydrology on the bottom profile of a lake may profoundly affect the extent of the littoral zone. Biomass of carp (Cyprinus carpio) had a strong inverse correlation with vegetation development in Lake Marmara and Lake Uluabat, therefore, carp might also have been important in macrophyte development. It may be concluded that littoral plant communities in shallow lakes located in semi-arid to arid regions appear to be particularly susceptible to water level fluctuations.
The study area (Alegria watershed, Basque Country, Northern Spain) considered here is influenced by an important alluvial aquifer that plays a significant role in nitrate pollution from agricultural land use and management practices. Nitrates are transported primarily from the soil to the river through the alluvial aquifer. The agricultural activity covers 75% of the watershed and is located in a nitrate-vulnerable zone. The main objective of the study was to find land management options for water pollution abatement by using model systems. In a first step, the SWAT model was applied to simulate discharge and nitrate load in stream flow at the outlet of the catchment for the period between October 2009 and June 2011. The LOADEST program was used to estimate the daily nitrate load from measured nitrate concentration. We achieved satisfactory simulation results for discharge and nitrate loads at monthly and daily time steps. The results revealed clear variations in the seasons: higher nitrate loads were achieved for winter (20,000 kg mo(-1) NO3-N), and lower nitrate loads were simulated for the summer (<1000 kg mo(-1) NO3-N) period. In a second step, the calibrated model was used to evaluate the long-term effects of best management practices (BMPs) for a 50-yr period by maintaining actual agricultural practices, reducing fertilizer application by 20%, splitting applications (same total N but applied over the growing period), and reducing 20% of the applied fertilizer amount and splitting the fertilizer doses. The BMPs were evaluated on the basis of local experience and farmer interaction. Results showed that reducing fertilizer amounts by 20% could lead to a reduction of 50% of the number of days exceeding the nitrate concentration limit value (50 mg L-1) set by the European Water Framework Directive.
Dominance by cyanobacteria hampers human use of lakes and reservoirs worldwide. Previous studies indicate that excessive nutrient loading and warmer conditions promote dominance by cyanobacteria, but evidence from global scale field data has so far been scarce. Our analysis, based on a study of 143 lakes along a latitudinal transect ranging from subarctic Europe to southern South America, shows that although warmer climates do not result in higher overall phytoplankton biomass, the percentage of the total phytoplankton biovolume attributable to cyanobacteria increases steeply with temperature. Our results also reveal that the percent cyanobacteria is greater in lakes with high rates of light absorption. This points to a positive feedback because restriction of light availability is often a consequence of high phytoplankton biovolume, which in turn may be driven by nutrient loading. Our results indicate a synergistic effect of nutrients and climate. The implications are that in a future warmer climate, nutrient concentrations may have to be reduced substantially from present values in many lakes if cyanobacterial dominance is to be controlled.
Mediterranean catchments experience already high seasonal variability alternating between dry and wet periods, and are more vulnerable to future climate and land use changes. Quantification of catchment response under future changes is particularly crucial for better water resources management. This study assessed the combined effects of future climate and land use changes on water yield, total nitrogen (TN) and total phosphorus (TP) loads of the Mediterranean Onkaparinga catchment in South Australia by means of the eco-hydrological model SWAT. Six different global climate models (GCMs) under two representative concentration pathways (RCPs) and a hypothetical land use change were used for future simulations. The climate models suggested a high degree of uncertainty, varying seasonally, in both flow and nutrient loads; however, a decreasing trend was observed. Average monthly TN and TP load decreased up to − 55% and − 56% respectively and were found to be dependent on flow magnitude. The annual and seasonal water yield and nutrient loads may only slightly be affected by envisaged land uses, but significantly altered by intermediate and high emission scenarios, predominantly during the spring season. The combined scenarios indicated the possibility of declining flow in future but nutrient enrichment in summer months, originating mainly from the land use scenario, that may elevate the risk of algal blooms in downstream drinking water reservoir. Hence, careful planning of future water resources in a Mediterranean catchment requires the assessment of combined effects of multiple climate models and land use scenarios on both water quantity and quality.
