Article
To read the full-text of this research, you can request a copy directly from the authors.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Aquatic macrophyte loss is another rising global phenomenon (Zhang et al. 2017), especially submerged aquatic vegetation which is declining dramatically in many freshwater (e.g. Hilt et al. 2006;Zhang et al. 2017) as well as marine and brackish (e.g. ...
... Aquatic macrophyte loss is another rising global phenomenon (Zhang et al. 2017), especially submerged aquatic vegetation which is declining dramatically in many freshwater (e.g. Hilt et al. 2006;Zhang et al. 2017) as well as marine and brackish (e.g. Shafer and Bergstrom 2010;Orth et al. 2017) ecosystems. ...
... Vol:. (1234567890) In a global change scenario, SAV is deemed to further decrease while eutrophication, turbidity, and water temperature have been predicted to increase (Waycott et al. 2009;Zhang et al. 2017;Miguel-Chinchilla et al. 2019). Estimating the association between fish species and habitat features is important to infer future environmental changes. ...
Article
Full-text available
Many freshwater ecosystems worldwide are threatened by increasing water turbidity and extensive submerged aquatic vegetation (SAV) loss, with potential consequences on aquatic communities. Such changes in water quality and habitat features affect the relative abundance of species in the community and/or the composition of ecological guilds altering the trophic network. Here, we estimated the relationship between fish species and both SAV abundance and water quality in Lake St. Pierre (Québec, Canada), a shallow fluvial lake of the St. Lawrence River. To explain the association between the fish community and environmental variables, we performed multiple linear regressions on fish abundance, species richness, and Shannon diversity calculated at 133 stations, along a gradient of turbidity, temperature, and SAV abundance. In addition, we estimated the relationship between dominant fish species abundance and environmental variables by using canonical correspondence analysis (CCA). Species richness and abundance were positively related to SAV. Turbidity was negatively related to fish abundance, but had an unexpected positive effect on diversity (Shannon and species richness). By quantifying the association between fish species and habitat features, this study contributes to a better understanding of mechanisms structuring fish communities in changing environments.
... For macrophytes, an accelerating decrease rate can be observed globally since the beginning of the last century (J. Y. Kim & Nishihiro, 2020;Y. Zhang et al., 2017). However, the trend is not uniform for all lakes and regions (Y. Zhang et al., 2017). The major local threats to freshwater macrophytes are assumed to be human use of lakes (e.g. boating, aquaculture, construction along shorelines) and human use of the surrounding catchment (e.g. excessive fertilisation of agricultural land leading to e ...
... However, the trend is not uniform for all lakes and regions (Y. Zhang et al., 2017). The major local threats to freshwater macrophytes are assumed to be human use of lakes (e.g. ...
... The major global threat is climate change (Y. Zhang et al., 2017). In general, it is hard to separate climate effects from other threats in lake environments (e.g. as result of land-use change or other anthropogenic pressures), since all effects interact with each other and build a complex network of direct and indirect effects (Lind et al., 2022). ...
Thesis
Full-text available
Macrophytes are key components of freshwater ecosystems because they provide habitat, food, and improve the water quality. Macrophyte are vulnerable to environmental change as their physiological processes depend on changing environmental factors, which themselves vary within a geographical region and along lake depth. Their spatial distribution is not well understood and their importance is publicly little-known. In this thesis, I have investigated the spatiotemporal dynamics of freshwater macrophytes in Bavarian lakes to understand their diversity pattern along different scales and to predict and communicate potential consequences of global change on their richness. In the introduction (Chapter 1), I provide an overview of the current scientific knowledge of the species richness patterns of macrophytes in freshwater lakes, the influences of climate and land-use change on macrophyte growth, and different modelling approaches of macrophytes. The main part of the thesis starts with a study about submerged and emergent macrophyte species richness in natural and artificial lakes of Bavaria (Chapter 2). By analysing publicly available monitoring data, I have found a higher species richness of submerged macrophytes in natural lakes than in artificial lakes. Furthermore, I showed that the richness of submerged species is better explained by physio-chemical lake parameters than the richness of emergent species. In Chapter 3, I considered that submerged macrophytes grow along a depth gradient that provides a sharp environmental gradient on a short spatial scale. This study is the first comparative assessment of the depth diversity gradient (DDG) of macrophytes. I have found a hump-shaped pattern of different diversity components. Generalised additive mixed-effect models indicate that the shape of the DDG is influenced mainly by light quality, light quantity, layering depth, and lake area. I could not identify a general trend of the DDG within recent years, but single lakes show trends leading into different directions. In Chapter 4, I used a mechanistic eco-physiological model to explore changes in the distribution of macrophyte species richness under different scenarios of environmental conditions across lakes and with depths. I could replicate the hump-shaped pattern of potential species richness along depth. Rising temperature leads to increased species richness in all lake types, and depths. The effect of turbidity and nutrient change depends on depth and lake type. Traits that characterise “loser species” under increased turbidity and nutrients are a high light consumption and a high sensibility to disturbances. “Winner species” can be identified by a high biomass production. In Chapter 5, I discuss the image problem of macrophytes. Unawareness, ignorance, and the poor accessibility of macrophytes can lead to conflicts of use. I assumed that an increased engagement and education could counteract this. Because computer games can transfer knowledge interactively while creating an immersive experience, I present in the chapter an interactive single-player game for children. Finally, I discuss the findings of this thesis in the light of their implications for ecological theory, their implications for conservation, and future research ideas (Chapter 6). The findings help to understand the regional distribution and the drivers of macrophyte species richness. By applying eco-physiological models, multiple environmental shaping factors for species richness were tested and scenarios of climate and land-use change were explored.
... Macrophytes such as submerged plants are key components of shallow lake ecosystems and maintain the basic functions and biodiversity of lake ecosystems [3]. However, due to multiple anthropogenic pressures such as climate change, eutrophication and aquaculture, the abundance of submerged plants in lakes has decreased [4]. Potamogeton crispus L. is a submerged aquatic macrophyte native to Europe and Asia that occurs in many freshwater ecosystems throughout China [5]. ...
... The content of NH 4 + -N in the water column was determined by Nessler's reagent colorimetric method, and NO 3 − -N content was determined by ultraviolet spectrophotometry method [36]. The concentration of PO 4 3− -P in the water column was determined using the molybdenum blue method [38]. ...
... Warming significantly enhanced conductivity and TN concentrations in all seasons (p < 0.05, Table 1). In summer, pH, DO and NO 3 − -N were significantly higher in the T treatment, and PO 4 3− -P contents were more pronounced by variable warming compared to the control (p < 0.05). ...
Article
Full-text available
Increased decomposition rates in shallow lakes with global warming might increase the release of atmospheric greenhouse gases, thereby producing positive feedback for global warming. However, how climate warming affects litter decomposition is still unclear in lake ecosystems. Here, we tested the effects of constant and variable warming on the bacterial metabolic potential of typically submerged macrophyte (Potamogeton crispus L.) litters during decomposition in 18 mesocosms (2500 L each). The results showed that warming reduced main chemoheterotrophic metabolic potential but promoted methylotrophy metabolism, which means that further warming may alter methane-cycling microbial metabolism. The nitrate reduction function was inhibited under warming treatments, and nitrogen fixation capability significantly increased under variable warming in summer. The changes in dissolved oxygen (DO), pH, conductivity and ammonium nitrogen driven by warming are the main environmental factors affecting the bacteria’s metabolic potential. The effects of warming and environmental factors on fermentation, nitrate reduction and ammonification capabilities in stem and leaf litter were different, and the bacterial potential in the stem litter were more strongly responsive to environmental factors. These findings suggest that warming may considerably alter bacterial metabolic potential in macrophyte litter, contributing to long-term positive feedback between the C and N cycle and climate.
... Aquatic plants inhabiting lakes and river ecosystems are susceptible to environmental and human-caused disturbances. In the past 50 years, different environmental changes, including water pollution, eutrophication, altered hydrological regimes, and habitat destruction, have caused many aquatic plant species' global decline and extinction (Orsenigo, 2018;Zhang et al., 2017;). Many aquatic plant species, including medicinal plants, are threatened with extinction putting the biodiversity of wetland and freshwater ecosystems at high risk. ...
... In the last few decades, water pollution and human over-exploitation of water bodies have caused significant damage to wetlands and a significant decline in aquatic plant species (Orsenigo, 2018;Zhang et al., 2017). According to Guo et al. (2019), the occupied areas of Ottelia acuminata represent a very small proportion of predicted potentially suitable ranges due to various detrimental human activities. ...
Article
Full-text available
Modeling and mapping the distribution of suitable habitats of aquatic plants are critical for assessing the impact of factors like changing climate on species habitat range shifts, declines, and expansions. Nymphaea is an aquatic perennial herb considered valuable because of its ornamental, economic, medicinal, and ecological importance. In India, the geographical distribution of Nymphaea is diverse, and the suitable habitats of individual species are vulnerable to the changing climate and global warming effects. Despite its increased vulnerability, only a few limited conservation efforts in aquatic environments are being made to date. In several places, the distribution of Nymphaea has been impacted by both anthropogenic and climate-related disturbances. A comprehensive strategy will be needed to meet the socio-ecological challenge of Nymphaea conservation. In this study, we employed maximum entropy (MaxEnt) method to assess how climate change affects the distribution of Nymphaea suitable habitat. The occurrence records of Nymphaea were collected from primary surveys, Global Biodiversity Information Facility (GBIF), and published works. Bioclimatic variables obtained from the Coupled Model Intercomparison Project (CMIP6) were employed as predictor variables in distribution modeling. The projections were made using three SSPs (stringent mitigation scenarios) for the future period of 2050. Our results showed shifts in the suitability ranges of Nymphaea under different projection scenarios. The study provides information about the distribution of suitable habitats for Nymphaea in India, which may be helpful for ongoing efforts to conserve and manage the aquatic plants, particularly in areas that are losing suitable climate conditions.
... Most importantly, the eco-physiological processes controlling their growth and survival are strongly affected by environmental conditions, as they depend on light availability, nutrient availability, and temperature. However, the accelerating global biodiversity loss, especially of submerged macrophytes, is well documented (Körner, 2002;Phillips et al., 2016;Sand-Jensen et al., 2000;Zhang et al., 2017) despite evidence of increasing species richness in some lakes (Murphy et al., 2018). The main influencing factors on the change of species richness seem to be global climate and regional land-use changes (Hofstra et al., 2020;Zhang et al., 2017) resulting in changes of light availability (due to changes in water turbidity), nutrient availability, or water temperature. ...
... However, the accelerating global biodiversity loss, especially of submerged macrophytes, is well documented (Körner, 2002;Phillips et al., 2016;Sand-Jensen et al., 2000;Zhang et al., 2017) despite evidence of increasing species richness in some lakes (Murphy et al., 2018). The main influencing factors on the change of species richness seem to be global climate and regional land-use changes (Hofstra et al., 2020;Zhang et al., 2017) resulting in changes of light availability (due to changes in water turbidity), nutrient availability, or water temperature. The ways in which climate change influences water temperature, nutrients, and turbidity in lakes are highly complex including direct and indirect effects (Lind et al., 2022). ...
... 远高于 同期全球湖泊的(33.6%±59.8%)/a [77] . 41个典型湖泊水生植被 面积已消失了3370 km 2 , 其中鄱阳湖自1983年以来水生植被 ...
... 面积降低了834 km 2 , 面积下降超过200 km 2 的还有太湖 ( 3 8 0 k m 2 ) 、 滇 池 ( 2 5 7 k m 2 ) 、 洪 泽 湖 ( 3 7 5 k m 2 ) 、 洪 湖 (288 km 2 )、南四湖(279 km 2 )和龙感湖(250 km 2 )等 [77] . 另外, ...
... Eutrophication of freshwater ecosystems, driven primarily by over enrichment of nitrogen (N) and phosphorus (P) (Carpenter et al., 1998), is a serious threat to water quality, biodiversity and other key ecosystem functions (Smith et al., 2006;Cook et al., 2018;Liu et al., 2021). Nutrient enrichment promotes the appearance and persistence of harmful algal blooms (Heisler et al., 2008;Conley et al., 2009) and the decline of submerged macrophytes (SMs) (Zhang et al., 2017), altering the food web structure (Fujibayashi et al., 2018;Briland et al., 2020). Occurrences of eutrophication are expected to increase with climate and land-use changes Bergström and Karlsson, 2019;Le Moal et al., 2019), inducing regime switches from a macrophyte-dominated clear state to phytoplankton-dominated turbid state (Jeppesen et al., 2007a). ...
Article
Full-text available
Freshwater ecosystems are threatened by eutrophication, which causes persistent and harmful algal blooms. Filter-feeding bivalve mollusks and submerged macrophytes (SMs) alleviate the eutrophication effects by inhibiting phytoplankton biomass blooms. However, very little is known about whether and how the combined manipulation of filter-feeding bivalves and SMs control eutrophication and influence phytoplankton assemblages. Here, we performed a nutrient-enriched freshwater mesocosm experiment to assess the combined effects of the filter-feeding bivalve Cristaria plicata, a cockscomb pearl mussel, and the macrophyte Hydrilla verticillate on the biomass and composition of phytoplankton assemblages. We found that addition of C. plicata and H. verticillate decreased the water nutrient concentrations and suppressed overall phytoplankton biomass. Further, distinct differences in taxa between restoration and control treatments were observed and noticeably competitive exclusion of cyanobacteria in the restoration treatments occurred. An antagonistic interaction between filter-feeding bivalves and SMs was only detected for total cyanobacteria biomass demonstrating that a larger magnitude of SM restoration may override the effect of filter-feeding bivalves. Our results suggest that manipulation, through the addition of bivalves as grazers, associated with the restoration of SMs, is an efficient approach for reducing cyanobacterial blooms and alleviating eutrophication.
... The loss of aquatic vegetation has been accelerating in the last four decades (Zhang et al., 2017). Oligotrophic waterbodies such as lakes and ponds are among the most threatened habitats in Europe and they harbor many endangered plant and animal species. ...
Article
Full-text available
Information provided by population genetic studies is often necessary to effectively protect endangered species. In general, such data is scarce for aquatic plants and this holds also for Luronium natans, an aquatic macrophyte endemic to northwestern and western Europe. It is threatened across its whole distribution range due to human influences, in particular due to eutrophication and intensive fish farming. In spite of habitat protection populations continue to decline and re-introductions are one possibility to prevent the species’ extinction. Therefore, insights in genetic diversity and relatedness of source populations is warranted. Thus, we performed Amplified Fragment-Length Polymorphism (AFLP) on two large populations in Saxony, Germany (Großenhainer Pflege and Niederspree), complemented with numerous additional occurrences from Europe. In addition, we conducted experiments on plant growth to assess optimal conditions for ex-situ cultivation taking water temperature, water level and substrate into account. We revealed considerably high levels of genetic diversity within populations (Shannon Indices ranged from 0.367 to 0.416) implying that populations are not restricted to clonal growth only but reproduce also by open-pollinated flowers. Remarkably, the two geographically close Saxon populations were genetically distant to each other but subpopulations within a locality were completely intermingled. Concerning optimal cultivation conditions, longest roots were obtained at temperatures >14°C and saturated, but not submerging water levels. Thus, our findings advocate for a re-introduction scheme from nearby source populations and provide detailed information on successful ex-situ cultivation.
... Article 53°33'N, and from 73°33'E to 135°05'E. Based on the analysis of the historical literature data of the interannual changes of aquatic vegetation in 41 typical lake sites in China, the degradation rate of aquatic vegetation in lakes is significantly higher than the global average, mainly concentrated in the shallow lakes in the middle and lower reaches of the Yangtze River (Zhang et al., 2017). As one of the most biodiverse countries worldwide, China has more than 800 aquatic plants (Chen et al., 2012;Wang et al., 2021). ...
Article
Studies on large‐scale geographic patterns of aquatic plant diversity can promote the research on generality of macroecological patterns in different ecosystems. Here, we compiled a checklist of 889 aquatic angiosperms in China, including 738 helophytes (emergent and marshy plants) and 151 hydrophytes (submerged, free‐floating and floating‐leaved plants). We explore the geographic patterns and environmental correlates of aquatic plant diversity, based on six metrics including species richness (SR), weighted endemism (WE), phylogenetic diversity (PD), phylogenetic endemism (PE), the standardized effect size of phylogenetic diversity (PDses), and the standardized effect size of mean phylogenetic distance (MPDses). Our results showe that the diversity of aquatic plants in China is extremely uneven, with high diversity in southeastern China and low diversity in northwestern China, and the geographic patterns of taxonomic and phylogenetic diversity are generally consistent. The pattern of helophytes differs from that of hydrophytes. Notably, the wavy‐shaped pattern of aquatic plant diversity (especially SR and PD for hydrophytes) across latitude observed in this study is not consistent with those previously observed for aquatic plants in other continents. Climatic variables and water environmental variables are the main drivers of the aquatic plant diversity in China; however, the effects of individual variables differ between helophytes and hydrophytes. Water environmental variables have greater impact on PDses and MPDses of hydrophytes than those of helophytes. Overall, our work provides insight into understanding the large‐scale patterns of aquatic plant diversity, and is a critical addition to previous studies on the macroecological pattern of terrestrial organisms. This article is protected by copyright. All rights reserved.
... Algal Bloom usually leads to the decline or even disappearance of submerged macrophytes in lake (Bakker et al., 2010;Zhang et al., 2017). It was found that the concentrations of nutrients such as nitrogen and phosphorus in the water and the release of nutrients from the sediment could be effectively controlled by planting submerged macrophytes, and algal bloom did not occur frequently. ...
Article
The issue of eutrophication of water bodies has attracted worldwide attention. Ecological restoration is a promising method to prevent and control eutrophic water bodies. Submerged macrophytes are widely used in the restoration processes. It can not only provide abundant food and habitat for zooplankton, but also inhibit the growth of algae through allelopathy or nutrient competition. This article provides a comprehensive review on research status on the remediation of eutrophic water by submerged macrophytes, with emphasis on the main affecting factors for their growth, including nutrients, light, water depth, sediment, temperature, biochar, transparency, and water flow. The optimum growth conditions of submerged macrophytes are further analyzed to provide guide for further studies and rear applications on the remediation of eutrophic water by submerged macrophytes.
... In recent decades, the natural lake ecosystems have faced a series of environmental problems, such as eutrophication and harmful algal blooms (Sinha et al., 2017;Zhou et al., 2021). Eutrophication leads to the degradation of lake habitat types from macrophyte-dominated habitats (MDH) to algae-dominated habitats (ADH) (Zhang et al., 2017), which has profoundly affected the structure of food webs therein (Su et al., 2019;Wang et al., 2017). Little is known about how diversity patterns and community assembly mechanisms of bacterioplankton change during the progression of lake eutrophication (Tang et al., 2017; ☆ This paper has been recommended for acceptance by Sarah Harmon. ...
Article
Eutrophication leads to the degradation of lake habitat types from macrophyte-dominated habitats (MDH)to algae-dominated habitats (ADH), which is a common environmental problem faced by many lakes. However, the variations in diversities and community assembly processes of bacterioplankton in the process of lake eutrophication have not been thoroughly elucidated. Here, we contrasted bacterial diversity patterns and processes of community assembly among ADH, MDH, and other habitats (OH) of Lake Taihu, a large shallow eutrophic lake in China with strong wind-induced disturbances. We found that the bacterial diversity patterns and potential functions between ADH and MDH were significantly different. Moreover, the contributions of purely environmental variables to the bacterial diversity patterns of all habitat types were much higher than those of spatial variables. However, the relative importance of stochasticity in the bacterial community assembly of each habitat type was much higher than that of determinism. Intriguingly, 'undominated' stochastic processes shape the diversity patterns of bacterioplankton in ADH, MDH, and OH of Lake Taihu. These findings demonstrate that the degradation of lake habitats caused by eutrophication can profoundly change the diversity and potential function patterns of the bacterioplankton community in lake ecosystems. Although the distinct diversity patterns of the bacterioplankton among the different aquatic habitats in Lake Taihu can be affected by deterministic processes (local environmental variables), they were dominated by stochastic processes (drift). Our study confirms that strong, disordered, wind-induced disturbances in shallow lakes could lead to strong hydrologic mixing, thus increasing the randomness of bacterial community assembly in each habitat.
... Submersed macrophytes are key components in freshwater ecosystems and play an important role in maintaining the health of ecosystem structure and function, and they help to maintain clearwater conditions (Jeppesen et al., 1998;Ali et al., 2019;Su et al., 2019a). However, as a result of high nutrient loading and eutrophication, submersed macrophytes in lakes are declining, causing global degradation of aquatic ecosystems (Kosten et al., 2009;Moss et al., 2013;Zhang et al., 2017). Therefore, it is important to explore the role of nitrogen stress on submersed macrophytes for this decline to help guide aquatic ecosystem protection managers. ...
Article
Full-text available
Benthivorous fish disturbance and nitrogen loading are two important factors that influence the community structure of submersed macrophytes, but their interactive effect is not well elucidated. We conducted an outdoor mesocosm experiment to examine the individual and combined effects of these two factors on the growth of two submersed macrophytes of different growth forms, i.e., the rosette-forming Vallisneria natans and the canopy-forming Myriophyllum spicatum. The treatments involved two levels of fish (Carassius auratus) disturbance crossed with two levels (0 and 12 g NH 4 Cl per month) of ammonium (NH 4 +-N) loading. For M. spicatum, we found that maximum height (MH) was reduced by 30.7%, 26.4%, and 51.0% in fish addition alone (F) and nitrogen addition treatments (N, F + N), respectively, compared with the control (C) treatment. The density of M. spicatum declined by 20%, 62% and 68.8% in the F, N and F + N treatment. The above-ground biomass (AGB) of M. spicatum respectively reduced by 56.7%, 94%, and 96.5% in the F, N and F + N treatments, and the roots/shoots ratio (R/S) increased by 114%, and 176% in N and N + F treatments, respectively. Regarding V. natans, only the MH in the N treatment was reduced (71.9%), and the density exhibited a reduction of 59.1% and 64.5% in the N and F + N treatments, respectively. The AGB of V. natans was significantly lower in the N (90.3%) and N + F (78.4%) treatments compared with the C treatment, while increased by 60.3% in F treatment. The R/S of V. natans increased by 227%, and 74.4% in the N and F + N treatments compared with the C treatment. The interactive effect of fish disturbance and high N on MH and AGB of V. natans and density of M. spicatum were antagonistic. However, the interactive effect on density and BGB of V. natans and AGB of M. spicatum were negatively synergistic.
... Meanwhile, the lacustrine wetlands have great potential in stabilizing the atmospheric abundance of carbon dioxide and other greenhouse gases to mitigate the risks of global warming (Eid and Shaltout 2013;Xu et al. 2021). However, human activities and climate change have posed threats to the water quantity and quality of lakes, leading to an increase in the frequency of cyanobacterial blooms and a decrease in water resources and food supply capacity (Phillips, Willby, and Moss 2016;Shi et al. 2017;Zhang et al. 2017). As the lake water is exposed to eutrophication, the water color and odor change, and the lake ecosystem eventually loses its original functionality (Chen, Huang, and Tang 2020). ...
Article
Full-text available
Water color is a crucial optical indicator of water quality, polluted water bodies often show water color anomalies. To comprehensively understand the occurrence of water color anomalies in inland lakes, an integrated method was designed using the hue angle based on the Forel-Ule Index (FUI) model, and other remote sensing indices, including the Turbid Water Index (TWI), Floating Algae Index (FAI), and Cyanobacteria and Macrophytes Index (CMI). Based on all available Landsat-8 OLI images from 2013 to 2020, continuous monitoring was conducted in three different lakes in the middle of the Yangtze River, China. The results demonstrated that: (1) The proposed method can accurately identify algal blooms, high sediment loads, and eutrophication from the abnormal water color areas; (2) The calculated hue angles of sediment-dominated water were significantly higher than those of algal blooms and aquatic vegetation, providing a noticeable visual discoloration of water; (3) These water color anomalies exhibited significant correlations with the water quality and environmental conditions. This study serves as an example for accurate and spatially continuous assessment of water color anomaly and supports practical information to facilitate local water environment conservation.
... In nature, there may also be submerged macrophytes living in the open water. The presence of these plants is essential, and affects the chemical and physical water properties including its quality (Kimmel and Groeger, 1984;Zhang et al., 2017;Yan et al., 2019). Furthermore, the species that are rooted in the sediment can stabilise the sediment by inhibiting its resuspension (Madsen and Cedergreen, 2002;Vymazal, 2013). ...
Article
Full-text available
The topic of evaporation estimates is fundamental to land-surface hydrology. In this study, FAO-56 Penman–Monteith equation (FAO56–PM), multiple stepwise regression (MLR), and Kohonen self-organising map (K–SOM) techniques were used for the estimation of daily pan evaporation (Ep) in three treatments, where C was the standard class A pan with top water, S was a pan with sediment covered bottom, and SM was class A pan containing submerged macrophytes (Myriophyllum spicatum, Potamogeton perfoliatus, and Najas marina), at Keszthely, Hungary, in a six-season experiment, between 2015 and 2020. The modelling approach included six measured meteorological variables. Average Ep varied from 0.6 to 6.9 mm d−1 for C, 0.7 to 7.9 mm d−1 for S, and from 0.9 to 8.2 mm d−1 for SM during the growing seasons studied. Correlation analysis and K–SOM visual representation revealed that air temperature and global radiation had positive correlation, while relative humidity had a negative correlation with the Ep of C, S, and SM. The results showed that the MLR method provided close compliance (R2=0.58–0.62) with the observed pan evaporation values, but the K–SOM method (R2=0.97–0.98) yielded by far the closest match to observed evaporation estimates for all three pans. To our best knowledge, no similar work has been published previously using the three modelling methods for seeded pan evaporation estimation. The current study differs from previous evaporation estimates by using neural networks even with those pans containing sediments and submerged macrophytes. Their evaporation will be treated directly by K–SOM, in which the modelling is more than the simple Ep of a class A pan filled with clean tap water.
... However, it is difficult to absolutely solve the taste and odor problems only by planting submerged macrophytes in natural water bodies. Submerged macrophytes have been decreasing in the last decades globally due to multiple stressors, such as eutrophication, global climate change, radiation dimming, land reclamation, and aquaculture cultivation (Phillips et al., 2016;Zhang et al., 2017Zhang et al., , 2020c. Therefore, this study provides an insight into the importance of combining the restoration of submerged macrophytes and the mitigation of the taste and odor issues in shallow freshwater ecosystems. ...
Article
The off-flavor compound 2-methylisoborneol (2-MIB) is generally associated with the proliferation and metabolism of filamentous cyanobacteria in shallow freshwater ecosystems. Here field monitoring in East Taihu Lake from July to October 2021, along with cultural experiments, was conducted to determine the impact of submerged macrophytes on the growth and 2-MIB production of filamentous cyanobacteria. Pseudanabaena sp. was identified as the 2-MIB producer with the highest detection rate (100%) and correlation coefficient (R=0.68, p<0.001). The 2-MIB concentration and algal growth in the macrophyte-dominated zones were markedly decreased compared with those in the phytoplankton-dominated zone. Five submerged macrophytes classified into flat-leaf type (Vallisneria natans and Potamogeton crispus) and thin-leaf type (Hydrilla verticillata, Ceratophyllum demersum, and Myriophyllum spicatum) exhibited strong inhibition effects against Pseudanabaena sp.: Overall inhibition efficiencies (IEs) of 92.7% ± 6.8% and 92.7% ± 8.4% for cell growth and 2-MIB production were achieved, respectively. Moreover, the thin-leaf macrophytes exhibited significant higher IEs for cell growth (94.0% vs. 84.7%) and 2-MIB production (99.4% vs. 82.6%) than the flat-leaf macrophytes and can be selected as pioneer species in controlling odor problems. Nutrient uptake, increasing water clarity, shading effects, and allelopathic effects of the submerged macrophytes were found to be the dominant inhibition mechanisms.
... Eutrophication, global change, and other factors have caused the rapid degradation of aquatic vegetation in lakes worldwide and have transformed lakes from a clear water state dominated by aquatic plants to a turbid water state dominated by algae, resulting in degradation of the structure and function of lake ecosystems [1][2][3][4]. Emergent plants absorb nitrogen, phosphorus, and other nutrients, as well as adsorb pollutants and heavy metals in the water, which purifies the water [5][6][7][8][9]. Thus, emergent plants are widely used to restore lake ecosystems. ...
Article
Full-text available
With the degradation of the global lake ecosystem, aquatic plants are more and more widely used in lake ecological restoration. The effects of water depths on the growth and photosynthetic fluorescence characteristics of two emergent plants (Typha orientalis and Zizania caduciflora) were studied in eutrophic Lake Gehu by in-situ experiments. The results showed that water depth had no significant effect on germination of emergent plants. The water depth changed the morphological characteristics of emergent plants. Plant height, tiller number, leaf length, leaf width, the number of leaf, and the root-shoot ratio decreased with increasing water depth, whereas the number of dead leaves increased with increasing water depth. The biomass of emergent plants was highest when water depth was 40 cm. Water depth had a significant effect on the photosynthetic fluorescence of the emergent plant. Fv/Fm tended to decrease first and then increase with increasing water depth. When the water depth was 20 cm, the ETRmax of emergent plants was significantly higher than that of plants at the other water depths. These results show the suitable water depth range for T. orientalis and Z. caduciflora is 20–60 cm. A deeper water depth for a long time is not conducive to the growth of emergent plants.
... Over the past decades, degradation of water quality due to human activities has emerged as one of the most severe environmental problems in lakes (Hou et al., 2022). Despite the substantial reduction in external nutrient loading (Schindler et al., 2016), deteriorated lakes with considerable internal loading still suffer from eutrophication risks, which may trigger a shift from a clear macrophyte-dominated state to a turbid phytoplanktondominated state (Scheffer et al., 1993;Zhang et al., 2017). Submerged aquatic vegetation (SAV) is of great importance in maintaining a clearwater state in shallow water (Carpenter and Lodge, 1986), which promotes habitat diversity by providing organic matter, producing shade and shelter, buffering temperature, and creating aquatic habitats (Yamasaki et al., 2021). ...
Article
Shallow lakes are greatly influenced by submerged aquatic vegetation (SAV), which affects hydraulic and water quality during their entire life cycle. An integrated model was developed based on the Environmental Fluid Dynamics Code (EFDC), which considers the dynamic bottom roughness and sediment release flux related to SAV growth and decomposition. Model results of hydrodynamics, water quality, and sediment-P release in Baiyangdian Lake (BL) were analyzed with and without the SAV module. The results showed that SAV played a critical and alterable role in regulating the internal loading in lakes. During the period of exponential growth, SAV reduced the velocity and sediment-P release in Zaozhadian by 20 % and 12 %, respectively. During the period of senescence, SAV reduced the velocity by 19 % and increased sediment-P release by 49 %, which was mainly attributed to dissolved oxygen (DO) consumption during residue decomposition. To mitigate the adverse effects of SAV on internal loading, measures should be taken to control the growth of SAV and ensure timely salvage before decomposition.
... Harmful algal blooms and loss of aquatic vegetation are typical ecological disasters faced by numerous lakes worldwide (Ho et al., 2019;Zhang et al., 2017). The increased algal blooms and decrease of macrophytes result in the shift of a clear state dominated by macrophytes to a turbid state dominated by algae, which is considered a key process in the evolution of eutrophic shallow lakes (Scheffer and Van Nes, 2007). ...
Article
In shallow lakes, eutrophication leads to a shift of the macrophyte-dominated clear state towards an algae-dominated turbid state. Phosphorus (P) is a crucial element during this shift and is usually concentrated in the suspended particulate matter (SPM) in water. However, the dominant processes controlling internal P release in the algae- (ADA) and macrophyte-dominated (MDA) areas under the influence of P-concentrated SPM remains unclear. In this study, we conducted monthly field observations of P exchange across the sediment-water interface (SWI) with the deposition of SPM in the ADA and MDA of Lake Taihu. Results revealed that both algae- and macrophyte-originated SPM led to the depletion of oxygen across the SWI during summer and autumn. Redox-sensitive P (Fe-P) and organic P (Org-P) were the dominant mobile P fractions in both areas. High fluxes of P across the SWI were observed in both areas during the summer and autumn. However, the processes controlling P release were quite different. In MDA, P release was mostly controlled by a traditional Fe-P dissolution process influenced by the coupled cycling of iron, sulfur, and P. In the ADA, Org-P control was intensified with the deterioration of algal bloom status, accompanied with the dissolution of Fe-P. Evidence from the current study revealed that the dominant process controlling the internal P release might gradually shift from Fe-P to a coupled process of Fe-P and Org-P with the shift of the macrophyte- to an algae-dominated state in shallow eutrophic lakes. The differentiated processes in the MDA and ADA should be given more attention during future research and management of internal P loadings in eutrophic lakes.
... Recent studies demonstrate that freshwater ecosystems, even in high latitude and altitude areas, face multiple stressors produced by human activities and the global climate change (Smol et al., 2005;Anderson et al., 2013Anderson et al., , 2014Zhang et al., 2017;Jeff et al., 2019;Liang et al., 2021). Lakes in high latitude and altitude areas generally have a simple ecosystem structure and low biodiversity and are, therefore, extremely sensitive to anthropogenic perturbations and climate changes (Smol et al., 2005;Lin et al., 2017). ...
Article
Glacier retreat in high altitude areas triggered by anthropogenic warming exerts a profound impact on the ecology of glacier-fed lakes. In this paper, we report on the results of a multi-proxy analysis of a Lateglacial (13.3–11.3 cal kyr B·P.) core obtained from the glacier-fed Kanas Lake in the Altai Mountains, China, to understand the responses of aquatic ecosystems to meltwater influxes. Core intervals with high sand fractions and enriched silicon dioxide and zirconium (~11.5, 11.7, 11.8, 12.2 and 13.0 cal kyrs B·P.) reflect intense meltwater pulses from alpine glaciers. In the core, these pulses generally coincide with low abundance of littoral cladocerans, high abundance of planktonic Pediastrum, and high phosphorus concentrations. Our results suggest that intense meltwater influxes not only brought nutrients (nitrogen and phosphorus) into the lake and promoted phytoplankton growth, they also generated cold, turbid water masses and restricted the growth of benthic algae and invertebrates. Therefore, we infer that future anthropogenic warming may lead to significant changes in the structure and function of aquatic ecosystems in glacier-fed lakes worldwide.
... Submerged macrophytes are key components in shallow aquatic ecosystems, as they provide multiple key functions and services and maintain the clear-state of shallow ponds and lakes Janssen et al. 2021;Scheffer et al. 1993). However, due to anthropogenic activities, the abundance of macrophytes has declined globally (Phillips et al. 2016;Zhang et al. 2017). Global environmental change leading to increased stress by nutrient loading, warming and pollutants could be responsible for these declines . ...
Article
Full-text available
Submerged macrophytes are vital components in shallow aquatic ecosystems, but their abundances have declined globally. Shading by periphyton and phytoplankton/turbidity plays a major role in this decline, and the competing aquatic primary producers are subject to the complex influence of multiple stressors such as increasing temperatures, nutrient loading and herbicides. Their joint impact has rarely been tested and is difficult to predict due to potentially opposing effects on the different primary producers, their interactions and their grazers. Here, we used 48 mesocosms (2500 L) to simulate shallow lakes dominated by two typical submerged macrophytes, bottom-dwelling Vallisneria denseserrulata and canopy-forming Hydrilla verticillata, and associated food web components. We applied a combination of nutrient loading, continuous warming, heat waves and glyphosate-based herbicides to test how these stressors interactively impact the growth of submerged macrophytes, phytoplankton and periphyton as competing primary producers. Warming or heat waves alone did not affect phytoplankton and periphyton abundance, but negatively influenced the biomass of V. denseserrulata. Nutrient loading alone increased phytoplankton biomass and water turbidity and thus negatively affected submerged macrophyte biomass, particularly for V. denseserrulata, by shading. Glyphosate alone did not affect biomass of each primary producer under ambient temperatures. However, heat waves facilitated phytoplankton growth under combined nutrient loading and glyphosate treatments more than continuous warming. As a consequence, H. verticillata biomass was lowest under these conditions indicating the potential of multiple stressors for macrophyte decline. Our study demonstrated that multiple stressors interactively alter the biomass of primary producers and their interactions and can eventually lead to a loss of macrophyte communities and shift to phytoplankton dominance. These results show the risks in shallow lakes and ponds in agricultural landscapes and underline the need for multiple stressor studies as a base for their future management.
... Despite the benefits provided by the wetland ecosystems, they are often over-utilized for immediate gains. Like any other natural ecosystems unsustainable use of resources has exerted pressure on wetlands (Bhatta et al., 2016;Calderon-Aguilera et al., 2012;Paumgarten & Shackleton, 2011;Ramsar Convention Secretariat, 2006;Rebelo et al., 2017;Sieben et al., 2018;Xu et al., 2020;Zhang et al., 2017), thereby potentially diminishing their regenerative capacity, and destabilizing the longstanding ecological resilience (Buma, 2015;DiMichele et al., 2004;McCauley et al., 2012). Hence, assessing the level of anthropogenic pressure on such ecosystems is essential, which may help in framing appropriate regulatory and policy measures for the sustainable resource utilization and management of the various natural ecosystems (Yang et al., 2013). ...
Article
Full-text available
Assessment of anthropogenic pressure on natural ecosystems is crucial for the formulation of appropriate policy measures for their conservation, sustainable utilization, and management. However, methodological and analytical issues arising due to the use of multiple variables with different frames of reference and units of measurement during such assessment may impede decision-making. We demonstrate a simple yet effective frequency-based protocol to assess anthropogenic pressure on natural ecosystems using the case study of a seasonal wetland in northeast India. For this purpose, we collected household and village-level data on the extraction of natural resources from 26 riparian villages of the wetland following standard survey and sampling methods. Using this protocol, we identified the wetland resources vulnerable to over-extraction by the riparian communities and prioritized them for adopting appropriate management actions. The proposed protocol would be useful for the researchers, stakeholders, and policymakers to assess and compare anthropogenic pressure on any natural ecosystems.
... The biotic environment will affect the abiotic environment (Suding et al., 2004). In recent decades, many shallow lakes have shifted from clear to turbid water states due to the submerged macrophytes loss and the algal bloom caused by intensified anthropogenic activities (Han and Cui, 2016;Zhang et al., 2017). The restoration of submerged macrophytes is necessary to achieve a clear-water state (Sondergaard et al., 2010;Stefanidis and Papastergiadou, 2019). ...
Article
The re-establishment of submerged macrophytes facilitates the formation of a clear-water state in shallow eutrophic lakes. But most restorations of submerged macrophytes are often unstable and cannot maintain a stable clear-water state, probably because the species and functional diversity have not been fully taken into account. In this study, we try to explore submerged macrophyte communities and water quality changes under different submerged macrophyte combinations through mesocosm experiments. We hypothesized that communities with high species and functional diversity would be more conducive to improving water quality. The results showed that the mean community biomass of single-species and 8-species were higher than 5-species. And the stability and mean relative growth rate of the 8-species community were higher than the 5-species community. With the same configuration of three functional groups, the 8-species community was more stable and had better water quality than the 5-species community. The path analysis revealed that different functional groups of submerged macrophytes play different roles. The erect and canopy-producing submerged macrophytes were conducive to reducing total suspended solids (TSS) concentrations in the water column during community construction. In contrast, bottom-dwelling submerged macrophytes were conducive to reducing total nitrogen, total phosphorus, and TSS concentrations during the stage of disturbances. Our results also suggested that canopy-producing groups may have a competitive advantage for light over bottom-dwelling species. Based on the above results and biodiversity insurance hypothesis, we conclude that the community consisting of multi-functional species-rich groups is conducive to building stable submerged macrophyte communities and obtaining a stable clear-water state. Our findings will improve water quality management and pollution control for eutrophic shallow lakes.
... As an important part of the shallow lake ecosystem, aquatic macrophytes could play vital roles in structure and function of the ecosystem, by reducing sediment resuspension, improving water quality, altering biogeochemical processes, as well as providing habitats and/or refuges for various aquatic organisms (Jeppesen et al., 1998). However, in recent years the degradation of aquatic macrophytes in shallow lakes has become a serious ecological problem worldwide (Jeppesen et al., 1998;Zhang et al., 2017). The reduced light conditions caused by eutrophication and water level changes perhaps are the key factors for this degradation of aquatic macrophytes (Zhang et al., 2022). ...
Article
Light quality strongly affect a great many physiological processes in terrestrial plants. Whatever, few studies have investigated how the submerged macrophytes response to different light quality. The present research aimed to understand how light quality affect morphogenesis, photosynthesis, as well as crassulacean acid metabolism (CAM) operation during the growth of Ottelia alismoides, a freshwater facultative CAM macrophyte. The plants were grown under three light qualities of white (W), red (R) and blue (B) lights with same light intensity of 100 μmol m⁻² s⁻¹. Leaf development, leaf anatomic characteristics, photosynthetic traits, as well as CAM metabolism were determined on the newly produced leaves during light treatment. Monochromatic R stimulated leaf blade and petiole elongation, leaf area and dry weight, but reduced leaf thickness, negatively influenced chlorophyll content and Fv/Fm. On the contrary, B- grown plants were dwarf and with compact size as well as lower leaf dry weight. The content of photosynthetic product starch under B was significantly lower as compared with R, moreover, combined with the analysis of ultrastructural characteristics of epidermal and mesophyll chloroplasts, it showed that B inhibited starch to be translocated out of epidermal chloroplasts. Furthermore, both R- and B- grown plants exhibited obvious diurnal acidity fluctuation comparable to W- grown plants, and had high activity of enzymes including ribulose-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK) that required for CAM cycle, indicating that CAM was present in both R- and B- grown plants and monochromatic R and B did not affect CAM activity. In conclusion, monochromatic red and blue light differentially played their special roles in regulating leaf growth and morphogenesis, as well as photosynthetic metabolism in O. alismoides.
... Our present study indicates that the INTRODUCTION Due to their complex external morphology, submersed macrophytes create habitat heterogeneity in aquatic ecosystems, and therefore play an important role in the structure and function of shallow lakes (Jeppesen et al., 1998;Su et al., 2019). However, submersed macrophytes are experiencing a global decline in shallow lakes, resulting in eventually a shift from a macrophyte-dominated healthy ecosystem state to a phytoplankton-dominated state (Scheffer et al., 1993;Chao et al., 2022) and the deterioration of various functions of aquatic ecosystems (Sayer et al., 2010;Zhang et al., 2017). Therefore, to explore the responses of submersed macrophytes to the stressors is necessary for the macrophyte restoration in the management of lake ecosystems. ...
Article
Full-text available
Ammonium (NH 4-N) produces a paradoxical effect on submersed macrophytes because it is not only the preferred nitrogen source for the growth of plants but also threatens the growth of plants at high concentration. Whether short-term and small-scale physiological toxicity experiments at an individual level can reflect the effects of high ammonium on populations of submersed macrophytes in natural conditions is still unclear. In this study, an 18-month experiment was conducted in six 600 m 2 ponds subjected to different levels of ammonium loading. The effects of high ammonium on populations of canopy-forming Myriophyllum spicatum and rosette-forming Vallisneria natans were explored. The results showed that M. spicatum and V. natans populations can develop high cover and height at high ammonium concentration (7 mg/L) at short-term exposures, and V. natans may be tolerant to 18 mg/L ammonium concentration. However, the cover of M. spicatum and the height of both species were inhibited at 2.4 mg/L at long-term exposures. The height of M. spicatum was two to six times higher than that of V. natans across all treatments and control by the end of the experiment, and the cover of M. spicatum was 7-11 times higher than that of V. natans in most NH 4-N loading treatments, except the cover of M. spicatum in the highest NH 4-N loading treatment with 18 mg/L NH 4-N. The rosette-forming V. natans resists ammonium stress by slow growth (shoot elongation) to reduce consumption, while canopy-forming species resist ammonium stress by shoot elongation and canopy development to capture light. Although increasing ammonium concentration may induce severe stress on M. spicatum, the morphological characteristics of this species may, to some extent, release the plants from this stress. Our present study indicates that the Frontiers in Plant Science | www.frontiersin.org 1 July 2022 | Volume 13 | Article 939589 Yu et al. Effects of High Ammonium on Submersed Macrophytes negative effects of ammonium stress on the development of populations increased with exposure duration, and the submersed macrophyte community with stronger ability for light capture and dispersal may resist high ammonium stress. Nevertheless, in strongly ammonium-enriched systems, competition and succession cannot be neglected.
... Neste sentido, os lagos são "ecossistemas sentinelas" para as mudanças climáticas porque são sensíveis ao clima, respondendo rapidamente à estas mudanças e integrando informações sobre as mudanças ocorridas na bacia de drenagem (Adrian et al. 2009). Na medida que são ambientes deposicionais preferenciais a aportes de sedimentos, matéria orgânica (MO) e nutrientes desde vastas áreas da bacia de drenagem, são considerados "ecossistemas sentinelas" das alterações climáticas (Adrian et al. 2009, Hayes et al. 2017) e atividades antrópicas (Sharma et al. 2007, Zhang et al. 2017, Beaulieu et al. 2019. Estimativas indicam que existem mais de 100 milhões destes ecossistemas no planeta (Verpoorter et al. 2014), compondo 87% da superfície líquida continental (Gleick 1993). ...
Article
Ecossistemas aquáticos como lagos, baías e lagoas costeiras são bem distribuídos entre as zonas climáticas do planeta, constituindo destinos preferenciais aos aportes de biomassa e nutrientes provenientes da bacia de drenagem. Grandes quantidades de matéria orgânica (MO) terrestre e aquática, as quais podem ser remineralizadas a gases de efeito estufa ou preservadas, lhe conferem um importante papel à ciclagem global de carbono (C) e subsequentemente ao clima da biosfera. Além disso, estes ambientes deposicionais têm sido considerados “ecossistemas sentinelas”, pois mudanças globais frequentes na rede de drenagem (e.g., desmatamento, eutrofização e intervenções físicas) têm alterado substancialmente as taxas de acumulação de sedimentos e MO. No entanto, a distribuição latitudinal dos dados publicados das taxas de ciclagem de C nos ecossistemas aquáticos, considerando os diferentes usos e coberturas da terra, ainda carece de melhor entendimento. Nesse contexto, o objetivo do presente estudo é avaliar a distribuição global do esforço amostral sobre as taxas de acumulação de MO em lagos, lagoas costeiras e baías, relacionando-os com a distribuição entre as latitudes e ecorregiões com diferentes graus de uso e cobertura da terra. As ecorregiões tropicais e subtropicais, boreais, outras latitudes médias e polar/subpolar representaram 76% da área relativa global de lagos em regiões menos alteradas, e, no entanto, concebem apenas ~18% dos dados publicados. Por outro lado, a classe de florestas temperadas em áreas menos alteradas de latitudes médias foi a única a apresentar uma representação de dados adequada em relação à sua distribuição em escala global. Esses resultados indicam que ecossistemas aquáticos tanto tropicais ou subtropicais, os quais apresentam taxas de ciclagem de C mais intensas e com maior variabilidade devido às condições mais quentes, quanto os de altas latitudes frias (i.e., boreais, subpolares e polares), ainda são altamente negligenciados nas compilações globais das taxas de acumulação de MO. Como conclusão, o presente estudo revelou a necessidade de maior esforço amostral para avaliar o papel dos sedimentos de fundo dos ecossistemas aquáticos como sumidouros de C (sob a forma de biomassa) nas áreas menos alteradas pela ação humana, o qual subsidie a identificação de áreas prioritárias à conservação nas áreas mais florestadas de baixas e altas latitudes.
... Unfortunately, due to increased anthropogenic activities, the abundance and diversity of submerged macrophytes have declined in many shallow freshwater ecosystems worldwide (Sand-Jensen et al., 2000;Zhang et al., 2017). Loss of submerged macrophytes also means the loss of a natural feedback loop that facilitates a clearwater phase, and may result in the shift into an alternative stable state typically consisting of phytoplankton dominance and thus more turbid conditions. ...
Article
Full-text available
Submerged macrophytes play a key role in maintaining a clear‐water phase and promoting biodiversity in shallow aquatic ecosystems. Since their abundance has declined globally due to anthropogenic activities, it is important to include them in aquatic ecosystem restoration programs. Macrophytes establishment in early spring is crucial for the subsequent growth of other warm‐adapted macrophytes. However, factors affecting this early establishment of submerged macrophytes have not been fully explored yet. Here, we conducted an outdoor experiment from winter to early spring using the submerged macrophytes Potamogeton crispus and Vallisneria spinulosa to study the effects of shading, nutrient loading, snail herbivory (Radix swinhoei), and their interactions on the early growth and stoichiometric characteristics of macrophytes. The results show that the effects strongly depend on macrophyte species. Biomass and number of shoots of P. crispus decreased, and internode length increased during low light conditions, but were not affected by nutrient loading. P. crispus shoot biomass and number showed hump‐shaped responses to increased snail biomass under full light. In contrast, the biomass of the plant linearly decreased with snail biomass under low light. This indicates an interaction of light with snail herbivory. Since snails prefer grazing on periphyton over macrophytes, a low density of snails promoted growth of P. crispus by removing periphyton competition, while herbivory on the macrophyte increased during a high density of snails. The growth of V. spinulosa was not affected by any of the factors, probably because of growth limitation by low temperature. Our study demonstrates that the interaction of light with snail herbivory may affect establishment and growth of submerged macrophytes in early spring. Macrophyte restoration projects may thus benefit from lowering water levels to increase light availability and making smart use of cold‐adapted herbivores to reduce light competition with periphyton. Our study demonstrates that the interactions of light with snail herbivory, but not nutrient loading, may affect establishment and growth of submerged macrophytes in early spring. Our study thus has implications for recovery of submerged macrophytes in deteriorative water bodies.
... Previous studies have revealed significant SAV reductions in global lakes and generally agree that the intensification of human activities, such as land reclamation, eutrophication and aquaculture, as well as global climate change, lead to the global expansion of cyanobacterial blooms (Harding et al., 2016;Qin et al., 2020). Recently, Zhang et al. (2017) performed a quantitative assessment of global trends in SAV coverage in lakes and found that SAV reduction was significantly accelerated, with reduction rates of 13.5 ± 16.9 %/yr, 21.8 ± 28.9 %/yr, and 33.6 ± 59.8 %/yr for the three periods of 1980, 1980-2000 and after 2000, respec-tively, and they also concluded that intensified human activities are likely the driving factors behind the decreasing trend in SAV coverage. The great impact of intensified human activities on lake ecosystems has been proven to accelerate eutrophication and increase external nutrient inputs, therefore expanding algal blooms (Michalak et al., 2013;Huisman et al., 2018). ...
Article
Six decades field observation data series on submerged aquatic vegetation (SAV), water level and water quality from Lake Taihu were compiled to reveal the dynamics in coverage and species composition of SAV and their anthropogenic drivers. We found that both SAV species composition and coverage area declined significantly in Lake Taihu during the period, and the increasing nutrient levels and water level as well as decreasing water clarity were responsible for these change trends. Specifically, the decrease in species richness could be particularly well predicted by total nitrogen (TN) and the ratio of water clarity (i.e., Secchi disk depth (SDD)) to water level (WL), contributing 47.3 % and 32.3 %, respectively, while the coverage of macrophytes was most strongly related to the water level, accounting for 70.1 % of the variation. A classification tree analysis revealed a threshold of TN of 3.2 mg/L and SDD/WL of 0.14 that caused a shift to a eutrophic low-macrophyte dominated state. Our results highlight that SDD/WL must be improved for SAV recolonization, rather than merely reducing nutrient input and regulating water level. Our findings provide scientific information for lake managers to prevent plant degradation in macrophyte-dominant lakes and facilitate a shift to a macrophyte-dominant state in eutrophic lakes.
... Over the past decades, degradation of water quality due to human activities has emerged as one of the most severe environmental problems in lakes (Hou et al., 2022). Despite the substantial reduction in external nutrient loading (Schindler et al., 2016), deteriorated lakes with considerable internal loading still suffer from eutrophication risks, which may trigger a shift from a clear macrophyte-dominated state to a turbid phytoplanktondominated state (Scheffer et al., 1993;Zhang et al., 2017). Submerged aquatic vegetation (SAV) is of great importance in maintaining a clearwater state in shallow water (Carpenter and Lodge, 1986), which promotes habitat diversity by providing organic matter, producing shade and shelter, buffering temperature, and creating aquatic habitats (Yamasaki et al., 2021). ...
... Specifically, cyanobacterial blooms can produce a variety of toxins which cause a range of diseases when ingested by organisms [7]. Moreover, the microbial degradation of cyanobacterial blooms reduce oxygen levels in lakes, resulting in the deaths of fish and inhibiting the growth of aquatic vegetation [8,9]. Mounting evidence shows that cyanobacterial blooms are highly likely to expand further, owing to ongoing eutrophication, in the future [10]. ...
Article
Full-text available
Frequent outbreaks of cyanobacterial blooms have become one of the most challenging water ecosystem issues and a critical concern in environmental protection. To overcome the poor stability of traditional detection algorithms, this paper proposes a method for detecting cyanobacterial blooms based on a deep-learning algorithm. An improved vegetation-index method based on a multispectral image taken by an Unmanned Aerial Vehicle (UAV) was adopted to extract inconspicuous spectral features of cyanobacterial blooms. To enhance the recognition accuracy of cyanobacterial blooms in complex scenes with noise such as reflections and shadows, an improved transformer model based on a feature-enhancement module and pixel-correction fusion was employed. The algorithm proposed in this paper was implemented in several rivers in China, achieving a detection accuracy of cyanobacterial blooms of more than 85%. The estimate of the proportion of the algae bloom contamination area and the severity of pollution were basically accurate. This paper can lay a foundation for ecological and environmental departments for the effective prevention and control of cyanobacterial blooms.
... Photosynthetically active radiation (PAR, 400-700 nm) and ultraviolet radiation (UVR, 280-400 nm) are two important parts of solar radiation. PAR affects the surface heat flux, energy flow, and photosynthesis of phytoplankton and aquatic macrophytes (Ralph et al. 2007;Zhang et al. 2017). The enhanced PAR attenuation may decrease aquatic macrophytes' photosynthesis and carbon uptake. ...
Article
Full-text available
Cyanobacterial bloom accumulation and dissipation frequently occur in Lake Taihu, a typically shallow, eutrophic lake due to wind wave disturbance. However, knowledge of the driving mechanisms of cyanobacterial blooms on underwater light attenuation is still limited. In this study, we collected a high-frequency in situ monitoring of the wind field, underwater light environment, and surface water quality to elucidate how cyanobacterial bloom accumulation and dissipation affect the variations in underwater light attenuation in the littoral zone of Lake Taihu. Results showed that cyanobacterial blooms significantly increased the diffuse attenuation coefficient of ultraviolet-B (Kd(313)), ultraviolet-A (Kd(340)), and photosynthetically active radiation (Kd(PAR)); the scattering of total suspended matter (bbp(λ)); and the absorption of phytoplankton (aph(λ)) and chromophoric dissolved organic matter (CDOM, ag(λ)) (p < 0.01). The Kd(PAR) decreased quickly during the processes of bloom dissipation, but the decrease of Kd(313) and Kd(340) lagged 0.5 day. Our results suggested that cyanobacterial blooms could increase particle matters and elevated the production of autochthonous CDOM, resulting in underwater light attenuation increase. Ultraviolet radiation (UVR) and PAR attenuation both have significant responses to cyanobacterial blooms, but the response processes were distinct due to the different changes of particle and dissolved organic matters. Our study unravels the driving mechanisms of cyanobacterial blooms on underwater light attenuation, improving lake ecosystem management and protection.
... Mäkelä et al. (2004) similarly found that an average of 6% (range: 1-100%) of total lake area was covered by macrophytes in a sample of 50 lakes and that total fractional macrophyte coverage per lake steeply declined with lake area. Zhang et al. (2017b) compiled a synthesis database of aquatic macrophytes in 155 global lakes and observed an average coverage of 26% (range: 0.000-100%) with an accelerating decline since 1900. ...
Article
Full-text available
Areas of lakes that support emergent aquatic vegetation emit disproportionately more methane than open water but are under‐represented in upscaled estimates of lake greenhouse gas emissions. These shallow areas are typically less than ∼1.5 m deep and can be detected with synthetic aperture radar (SAR). To assess the importance of lake emergent vegetation (LEV) zones to landscape‐scale methane emissions, we combine airborne SAR mapping with field measurements of vegetated and open‐water methane flux. First, we use Uninhabited Aerial Vehicle SAR data from the NASA Arctic‐Boreal Vulnerability Experiment to map LEV in 4,572 lakes across four Arctic‐boreal study areas and find it comprises ∼16% of lake area, exceeding previous estimates, and exhibiting strong regional differences (averaging 59 [50–68]%, 22 [20–25]%, 1.0 [0.8–1.2]%, and 7.0 [5.0–12]% of lake areas in the Peace‐Athabasca Delta, Yukon Flats, and northern and southern Canadian Shield, respectively). Next, we account for these vegetated areas through a simple upscaling exercise using paired methane fluxes from regions of open water and LEV. After excluding vegetated areas that could be accounted for as wetlands, we find that inclusion of LEV increases overall lake emissions by 21 [18–25]% relative to estimates that do not differentiate lake zones. While LEV zones are proportionately greater in small lakes, this relationship is weak and varies regionally, underscoring the need for methane‐relevant remote sensing measurements of lake zones and a consistent criterion for distinguishing wetlands. Finally, Arctic‐boreal lake methane upscaling estimates can be improved with more measurements from all lake zones.
... Many shallow lakes in the middle and lower reaches of the Yangtze River Basin favor the growth of aquatic macrophytes, while they have been seriously exposed to severe environmental stressors in recent decades [18]. The increased input of nutrients, the change in fluvial systems and hydrology, the intensified human activities such as urbanization and industrial development, and the rapid rates of climate and environmental changes all have been the major drivers of the succession of aquatic macrophytes in the middle and lower reaches of the Yangtze River Basin [19][20][21]. ...
Article
Full-text available
Aquatic macrophytes are one of the important biotic components of shallow lake ecosystems. Understanding the long-term evolution of the macrophyte community is crucial for lake management. Huanggai Lake, a typical shallow lake in the middle reach of the Yangtze River, was selected as the research site for this study. Based on 210Pb/137Cs dating, aquatic plant macrofossils were used to reconstruct the succession of aquatic macrophytes in the past century. Our results show that the lake maintained a consistent natural state before 1940, with a relatively low abundance of aquatic plants dominated by species such as Najas minor. From 1940 to 1974, human activities gradually intensified in the lake leading to the emergence of eutrophic species such as Potamogeton maackianus, along with the increasing abundance of other emergent and floating aquatic macrophytes. Since 1974, more pollution-resistant, emergent species such as Potamogeton maackianus and Potamogeton crispus have become dominant. The abundance of aquatic macrophytes reached its maximum in the early 1990s. Combined with macrofossil succession and other multiple sedimentary proxy analyses, driving mechanisms for aquatic macrophytes are discussed. Both the nearby Liangzi Lake and Huanggai Lake share many common features of aquatic plant evolution. This study is the first of its kind to use plant macrofossils (with identifiable images) as a proxy for aquatic macrophyte succession in a shallow Yangtze lake. In absence of long-term monitoring records, this study highlights the increased application of plant macrofossils for reconstructing the vegetation dynamics and restoration of degraded lakes exposed to severe anthropogenic impacts over the past century.
... Macrophytes have experienced major dynamics in terms of large-scale decline in keystone species (Waycott et al. 2009;Araújo et al. 2016;Zhang et al. 2017) and blooms of opportunistic species (Hussner et al. 2017;Vadeboncoeur et al. 2021) due to various stressors. The associated effects on CH 4 emissions are largely unknown (Hilt et al. 2017), but are even more important to be quantified given their potential role for OMP. ...
Article
Full-text available
Methane (CH 4) from aquatic ecosystems contributes to about half of total global CH 4 emissions to the atmosphere. Until recently, aquatic biogenic CH 4 production was exclusively attributed to methanogenic archaea living under anoxic or suboxic conditions in sediments, bottom waters, and wetlands. However, evidence for oxic CH 4 production (OMP) in freshwater, brackish, and marine habitats is increasing. Possible sources were found to be driven by various planktonic organisms supporting different OMP mechanisms. Surprisingly, submerged macrophytes have been fully ignored in studies on OMP, yet they are key components of littoral zones of ponds, lakes, and coastal systems. High CH 4 concentrations in these zones have been attributed to organic sub-strate production promoting classic methanogenesis in the absence of oxygen. Here, we review existing studies and argue that, similar to terrestrial plants and phytoplankton, macroalgae and submerged macrophytes may directly or indirectly contribute to CH 4 formation in oxic waters. We propose several potential direct and indirect mechanisms: (1) direct production of CH 4 ; (2) production of CH 4 precursors and facilitation of their bacterial breakdown or chemical conversion; (3) facilitation of classic methanogenesis; and (4) facilitation of CH 4 ebullition. As submerged macrophytes occur in many freshwater and marine habitats, they are important in global carbon budgets and can strongly vary in their abundance due to seasonal and boom-bust dynamics. Knowledge on their contribution to OMP is therefore essential to gain a better understanding of spatial and temporal dynamics of CH 4 emissions and thus to substantially reduce current uncertainties when estimating global CH 4 emissions from aquatic ecosystems.
... DO levels may not recover in freshwater ecosystems, especially large lakes (area ≥50 km 2 ), where aquatic vegetation has been lost because of human activities, such as nutrient enrichment, overfishing, boat propellers, and lake engineering. 49,50 Hydraulic facilities, such as dams, reduce the flow and circulation of water. Reservoir rivers are characterized by slow flow and low oxygen levels. ...
Chapter
Occurrence of the wetlands is characterized where the land is covered by water or the water table level is close to the land surface. Wetlands are the only ecosystems for whose conservation an international convention called Ramsar Convention was set up in the year 1971. According to Ramsar Convention, a wetland is “areas of fen, marsh, swamp, peat either artificial or natural with water which is flowing or static including areas of marine water the depth of which should not exceed six meters.” As per Ramsar Convention in 2019, there are 2341 Ramsar sites listed across the world, among which Loktak Lake is one of the Ramsar sites nestled in the North-Eastern Himalayan ranges. Distinctive feature of this lake is the presence of herbaceous floating biomass (herbaceous wetlands) locally known as phumdis. In this case study land use land cover (LULC) of Loktak Lake catchment was mapped with special emphasis on wetlands and herbaceous wetlands. Based on the driving factors and past LULC for the year 2007, 2014 and 2017, the future LULC for the year 2030 was predicted by Land Change Modeller (LCM) in TerrSet using Landsat 5 and Landsat 8 multispectral satellite imageries. Artificial neural network (ANN) and Markov chain algorithms embedded in the LCM were deployed to predict the future LULC condition. ANN was trained with driving factors, namely slope and elevation, distance from built-up area and distance from roads. Results indicate that there was decrease of 28.65% and 6.08% in herbaceous wetlands and wetlands, respectively, in the year 2017 as compared to the year 2007. Similar trends were observed in the future projected LULC map of 2030 with a decrement of 6.48% and 41.56% in wetlands and herbaceous wetlands as compare to the baseline scenario of 2007. Based on the result of projected scenario, it is evident that there is a need to devise proper environment conservation policies.KeywordsArtificial neural network (ANN)Markov chain (MC)Land use land cover change (LULCC)Land change modeller (LCM)
Article
Full-text available
Wetlands are among the highly threatened ecosystems due to anthropogenic activities. The Ramaroshan Wetland Complex (RWC) of Achham District, Nepal is one of the high-altitude wetlands facing human induced degradation and loss. Herpetofauna are key bio-indicators of environmental health and habitat quality and are useful to assess habitat conditions of such threatened ecosystems. This study quantified the land use and land cover (LULC) change in the RWC and documented the diversity and distribution pattern of herpetofauna. The LULC in the area (13.94 Km2) was analyzed for 1989, 2000, 2010 and 2021 by supervised classification of remote sensing images. Surveys were conducted along 25 transects, each of 200 m in length and environmental variables were recorded for every observation of herpetofauna. The LULC analysis revealed an overall loss of 16% of the total water body between 1989 (0.25 Km2) and 2021 (0.21 Km2). Eleven species of herpetofauna (five amphibians and six reptiles) within five families and two orders (i.e., Anura and Squamata), were recorded with low diversity (H’ = 1.88312) and evenness (E = 0.3642) indices. The herpetofauna had a hump-shaped distribution along the elevation gradient with the highest richness and abundance at 2300 m asl. Amphibian abundance decreased with increasing distance to nearest water sources, whereas reptile abundance increased. Amphibians were more abundant in agricultural field and marsh land, whereas reptile abundance was higher around human settlements. Results indicate that the wetland area in the RWC is declining at an alarming rate and, in turn, might account for the low diversity and abundance of the herpetofauna.
Article
The restoration of submerged macrophytes is an important step in lake ecosystem restoration, during which artificially assisted measures have been widely used for macrophyte recolonization. Compared with natural restoration, the impact of artificially assisted methods on methane (CH4) production and oxidation of lake sediments remains unclear. Therefore, after the restoration of submerged macrophytes in some parts of West Lake (Hangzhou, China), sediment samples from West Lake were collected according to restoration methods and plant coverage. The CH4 production potential, oxidation potential, and microbial community structure in the sediment were discussed through whole-lake sample analysis and resampling verification from typical lake areas. From the analysis of the whole lake, the average daily CH4 production potential (ADP) of artificially restored lake areas (0.12 μg g-1 d-1) was significantly lower than that of the naturally restored lake areas (0.52 μg g-1 d-1). From the resampling analysis of typical lake areas, the ADP of naturally restored lake areas was 1.8 times that of artificially restored lake areas (P < 0.01). Although there was no significant difference in the CH4 oxidation potential between the two restoration methods, the presence of submerged macrophytes significantly increased the abundance of the dominant methanotroph Methylocaldum in the sediment, and the rate of increase in the abundance of the dominant methanotroph Methylosium was significantly higher in artificially assisted restoration than in natural restoration. This study revealed that the artificially assisted restoration of submerged macrophytes reduced the potential for CH4 production and increased the abundance of dominant methanotrophs in the lake sediment, which would be beneficial for the reduction of CH4 emissions during lake ecological restoration and environmental management.
Article
Full-text available
Dissolved oxygen (DO) is crucial for the health of aquatic ecosystems, and plays an essential role in regulating biogeochemical processes in inland lakes. Traditional measurements of DO using the probe or analysis in a laboratory are time-consuming and cannot obtain data with high frequency and broad coverage. Satellites can provide daily/hourly observations within a broad scale and have been used as an important technique for aquatic environments monitoring. However, satellite-derived DO in waters is challenging due to its non-optically active property. Here, we developed a two-step model for retrieving DO concentration in Lake Taihu from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua images. A machine learning model (eXtreme gradient boosting) was developed to estimate DO from field water temperature, water clarity, and chlorophyll-a (Chla) (root-mean-square error (RMSE) = 0.98 mg L ⁻¹ , mean absolute percentage error (MAPE) = 7.9%) and subsequently was validated on MODIS-derived water temperature, water clarity, and Chla matchups with a satisfactory accuracy (RMSE = 1.28 mg L ⁻¹ , MAPE = 9.9%). MODIS-derived DO in Lake Taihu from 2002 to 2021 demonstrated that DO ranged from 7.2 mg L ⁻¹ to 14.2 mg L ⁻¹ , with a mean value of 9.3 mg L ⁻¹ . DO in the northern region was higher than in the central and southern regions, and higher in winter than in summer. We revealed that DO in this decade (2010–2021) was considerably lower than that in the last decade (2002–2009). Meanwhile, annual mean of DO increased in 2002–2009 and decreased from 2010 to 2021. The spatial distribution of DO in Lake Taihu was related to Chla and water clarity, while seasonal and interannual variations in DO resulted from air temperature primarily. This research enhances the potential use of machine learning approaches in monitoring non-optically active constituents from satellite imagery and indicates the possibility of long-term and high-range variations in more water quality parameters in lakes.
Article
Full-text available
No previous study has examined the large-scale distributional drivers of the entire global pool of 3,499 macrophyte species, despite the obvious importance of this for understanding the macro-ecology of these plants. To assess the hypothesis that natural rather than human-related transfer vectors act as the primary long-distance drivers of global movement of aquatic macrophytes, we analysed current macrophyte species distributions in relation to a set of human-related and natural transfer vectors. Most macrophytes (2,492 species: 71.2% of the global total) are endemic to a single ecozone, and generally lack the various functional adaptations needed for successful long-distance propagule transport. Such traits are, however, common in the 1,007 (28.8%) species native in > 1 ecozone. In total, 779 species (22.3%) are introduced, naturalised or invasive (I species) in one or more ecozones outwith their native range. The proportion of I species varies between ecozones and is best predicted by annual temperature and longitude. A migratory bird transfer vector and climatic variables strongly predict global native macrophyte species occurrence. Some native species Handling editor: Andre Andrian Padial Supplementary Information The online version contains supplementary material available at https:// doi. of Miocene origin (or older) may have had their world distribution influenced by ancient vicariance events, while inter-ecozone hydrochory and Late Quaternary climate change are also relevant factors influencing a few species.
Article
Full-text available
Freshwater lakes across the world have undergone dramatic changes in biological components and water quality over the past several decades. Previous studies focused on potential drivers mainly on nutrient enrichment in the catchment. However, the relative importance of climate change and the top-down cascade effects of fish stocking on water quality is not fully understood. Here, by compiling 155 lakes data with four periods of field investigation in subtropical lakes in China, we found no significant changes in water total nitrogen and total phosphorus in the past two decades. However, the phytoplankton abundance increased significantly, and the water clarity declined by 44.1%. We further found that carp stocking and climate change are potentially more important than nutrients driving water quality change, which is also evidenced in two lakes (Lake Donghu and Qiandao) with long-term monitoring histories. Specifically, carp stocking can decrease the water clarity directly by stirring up sediment and indirectly by trophic cascade along the food web. For climatic factors, mean annual temperature (MAT) has a positive effect on phytoplankton abundance, while mean annual precipitation has a negative one, with climates overall having little effect on water clarity. In addition, nutrient enrichment and climate change also have strong interactions with carp stocking, which may enhance the top-down effects on water quality. Our findings highlight that either MAT or carp stocking may become an overwhelming driver of water clarity decline, which provides new insights into the conservation strategy for water quality management in the subtropical lakes in China.
Article
Full-text available
The contrast in habitat complexity between emergent (EMV) and submerged vegetation (SUV) zones in aquatic ecosystems results from the differences in the structure of plant above- and belowground parts, subject to seasonal changes. Comparative studies on the influence of habitat complexity created by vegetation on benthic macroinvertebrates in coastal areas are scarce. In order to fill this knowledge gap, we performed a study on a seasonal basis in the brackish Vistula Lagoon (southern Baltic Sea) in two zones: EMV, dominated by a dense belt of Phragmites australis (Cav.) Trin. ex Steud, and SUV, with scattered stands of Potamogeton perfoliatus L. We assumed the following: i. Species richness, diversity, and density of invertebrates are higher in the EMV zone due to greater and less seasonally variable structural complexity than in the SUV zone, ii. High belowground complexity in the EMV zone due to the presence of the rhizome/root matrix, much more robust and denser than in the SUV zone limits the vertical distribution of macroinvertebrates. Both hypotheses were supported. Overall, our results pointing to higher animal diversity and density in more complex aquatic habitats are consistent with other studies, inferred mostly from comparative surveys of bare bottom and that covered with submerged vegetation. The results of this study highlight potentially far-reaching implications for benthic invertebrate fauna and their role in the aquatic ecosystem in the context of increasingly rapid loss of aquatic vegetation due to multiple anthropogenic stressors.
Article
To maintain submerged macrophyte beds (SMBs), a sound understanding of the factors that influence their succession is required. The aim of this study was to determine what influenced the succession of SMBs in a tidal river system, namely the Pearl River Delta, China (PRD). Surveys were carried out from 2015 to 2020 and a range of environmental (16) and ecological parameters were measured that could support an examination of the distribution and variation in SMBs. The coverage area, species richness, and biomass were measured at the community level, while nine morphological traits of the dominant species, Vallisneria denseserrulata, were measured at the population level. The results showed that, in 2015, the SMB community was distributed in sporadic patches and the community was dominated by multiple species. In 2018, V. denseserrulata grew continuously from February to August in all sections but its growth through the overwintering period (December) followed two patterns: recession (Pattern 1) or continuous growth (Pattern 2). Principal component analysis highlighted that the clonal growth ability, sexual propagation allocation, and perennial growth were related to different patterns of V. denseserrulata growth in the overwintering period. Pattern 1 was characterized by a low clonal growth ability and no sexual propagation, while Pattern 2 was characterized by a strong clonal growth ability and sexual propagation over winter. In 2019, the community was dominated by a single species of V. denseserrulata and macrophytes had disappeared from most river sections. The results from redundancy analysis implied that the decline in the SMBs from 2015 to 2020 was probably related to increases in the (1) TP concentrations in the sediment, (2) occupation of SMB habitats, and (3) annual river runoff in pre-flooding periods.
Preprint
Full-text available
Aquatic plants are crucial for an aquatic ecosystem, and their species and distribution reflect aquatic ecosystem health. Remote sensing technology has been used to monitor plant distribution on a large scale. However, the fine identification of aquatic plants is a great challenge due to large temporal-spatial changes in optical properties of water bodies and small spectral differences among plant species. Here, the identification method of each aquatic plant was developed by constructing the decision tree file of the C4.5 algorithm based on the canopy spectra of 8 plants in the Changguangxi Wetland water area measured with hyperspectral remote sensing technology, and then the method was finally used to monitor the distribution of different plants in Changguangxi Wetland water area and two other water areas. The results show that the spectral characteristics of plants is enhanced by calculating the spectral index of aquatic plants, thereby improving the comparability among different species. The total recognition accuracy of the constructed decision tree file for 8 types of plants is 85.02%, among which the recognition accuracy of Nymphaea tetragona , Pontederia cordata , and Nymphoides peltatum is the highest, and the recognition accuracy of Eichhornia crassipes is the lowest. The specific species and distribution of aquatic plants are consistent with the water quality in the water area. The results can provide a reference for the accurate identification of aquatic plants in the same type of water area.
Article
Understanding long-term environmental changes and man-land interactions within wetlands is important for their ecological maintenance and restoration. However, there has been little focus on the spatial heterogeneity of environmental variations of wetlands, especially large agricultural wetlands, which hinders the development of targeted management programs for specific areas. We conducted a multi-proxy study of the sediments of a typical agricultural wetland, Lake Baiyangdian in North China, to assess the spatial heterogeneity of environmental changes over the past 70 years. The results reveal that the environmental changes in Lake Baiyangdian were spatially heterogeneous, mainly reflected by the response to hydrological variations before the 1970 s, and by changes in trophic level and land cover transitions since the 1990 s, which are strongly linked to changes in agricultural land use. Pollen and grain-size analyses revealed the large-scale spatial heterogeneity of changes in the sedimentary environment. Areas with greater openness, shallower water depths, and proximity to inflowing rivers were generally more sensitive to hydrological processes and provided regional records of environmental change. In contrast, populated areas far from inflows tended to capture more local changes related to anthropogenic impacts. Intensive agricultural activity has led to a continuous increase in nutrient enrichment and significant land cover transitions in Lake Baiyangdian, mainly the loss of natural wetland. Variations in Humulus pollen were a key indicator of these anthropogenic impacts. Hydrological processes and land use changes were together responsible for the spatial heterogeneity of the environmental variations in Lake Baiyangdian over the last 70 years, indicating the dominant role of human impacts on the spatio-temporal pattern of the evolution of this wetland ecosystem, and the complexity of its environmental management.
Article
Full-text available
Potamogeton illinoensis is a North American macrophyte, commonly the focus of management, but limited knowledge of its life history hampers conservation and restoration efforts. We conducted greenhouse and growth chamber experiments and field monitoring to understand intraspecific variation in P. illinoensis reproduction and germination traits, monitoring one restored and three natural populations in Central Florida, USA. We assessed reproductive phenology, seed banks in the fall and spring, and germination across different light, temperature, sediment, and ethylene treatments. Flowering and seeding occurred spring through fall, with the highest seed bank densities in fall and minimal seeds detected in late spring. Seeds germinated at the highest percentages in light from 20 to 25°C, and at higher percentages in highly organic field-collected soil. Seeds treated with ethephon, which emits ethylene (commonly produced by submerged organic sediments), germinated at nearly twice the percentage as those exposed to water alone. While these reproductive and germination patterns were true across populations, there was variation among populations in seed bank densities, the most favorable germination temperatures, and overall germination percentages, indicating population differences contribute to reproductive performance. These results suggest restoration via seeds will be limited in conditions with low light or in unconsolidated sediments where burial is likely.
Article
MODIS surface reflectance product (R_land) has been used to monitor waters due to its free availability and higher spatial resolution than MODIS ocean bands. However, its applicability in aquatic remote sensing has not been sufficiently assessed. Some fundamental questions such as the following need to be addressed: How does the R_land product perform in global inland and coastal waters? What water color parameters can be mapped using R_land? This study provided a comprehensive evaluation of the performance of MODIS R_land products against a field optical dataset containing 4143 reflectance spectra, 2320 chlorophyll-a (Chla) samples, and 1467 suspended particulate matter (SPM) samples across global nearshore coastal and inland waters. The results showed that R_land significantly overestimated remote sensing reflectance, particularly in the bands of 469 nm and 859 nm. The noticeable negative values and patchiness were found in the R_land imagery, and existing algorithms did not estimate satisfactory Chla and SPM from R_land across the global inland and coastal waters. Furthermore, we tested popular machine-learning approaches, such as random forest (RF), support vector machine, XGBoost, and deep neural networks, to examine the potential of the R_land product in estimating SPM and Chla. Machine learning models were found to outperform the state-of-the-art algorithms for SPM retrievals from R_land. Specifically, RF and XGBoost showed the best performance with mean absolute errors of ~25.0% and mean absolute percentage error of ~23% for a broad SPM range of 10–500 mg L⁻¹. Yet, machine learning models cannot retrieve reliable Chla from R_land with approximately 55% uncertainty due to the limited spectral information and uncertainty of R_land products. This implicated that R_land might be able to quantify the parameters that are closely related to SPM (e.g., water clarity and extinction coefficients) in most waters; however, it is challenging to quantify pigments like Chla in waters from R_land. We conclude that R_land might not be an optimal data source for monitoring inland and coastal waters, despite the ease of using this product and its higher spatial resolution than the MODIS ocean bands.
Article
Full-text available
Reports of the Intergovernmental Panel on Climate Change (IPCC) indicate that temperature rise is still the general trend of the global climate in the 21st century. Invasive species may benefit from the increase in temperature, as climate can be viewed as a resource, and the increase in the available resources favors the invasibility of invasive species. This study aimed to assess the overwintering growth of the cosmopolitan invasive plant water hyacinth (Eichhornia crassipes) at its northern boundary. Using E. crassipes as a model plant, a cross-year mesocosm experiment was conducted to determine 17 plant functional traits, including growth, morphological, root topological, photosynthetic, and stoichiometric traits, under climate warming (ambient, temperature rises of 1.5°C and 3.0°C), and water drawdown or water withdrawal (water depths of 1, 10, and 20 cm) treatments. The overwintering growth of E. crassipes was facilitated by climate warming and proper water drawdown, and climate warming played a leading role. A temperature rises of 3.0°C and a water depth of 10 cm were the most suitable conditions for the overwintering and rooting behavior of the plant. Controlling the temperature to within 1.5°C, an ambitious goal for China, still facilitated the overwintering of E. crassipes. With climate warming, the plant can overwinter successfully, which possibly assists it in producing and spreading new ramets in the vernal flood season. The new rooting behavior induced by ambient low temperature may be viewed as a unique growth adaptation strategy for a niche change, as it helps these plants invade empty niches left by dead free-floating plants on the water surface following winter freezes. With continued global warming, the distribution of the plant may expand northward, and eradication of the plant during the winter water drawdown period may be a more effective strategy.
Article
Organic phosphorus (OP) is one of the main forms of phosphorus in lake ecosystems. Mounting evidence has shown that sediment OP has become a major but underestimated issue in addressing lake eutrophication and algal bloom. However, a holistic view of sediment OP remains missing. This review aims to provide an overview of progress on the studies of OP in lake sediments, focusing on the contribution of OP to internal P loading, its potential role in algal bloom, and the migration and transformation. In addition, this work systematically summarized current methods for characterizing OP content, chemical fraction, composition, bioavailability, and assessment of OP release in sediment, with the pros and cons of each method being discussed. In the end, this work pointed out following efforts needed to deepen the understanding of sediment OP, namely: (1) In-depth literature review from a global perspective regarding the contribution of sediment OP to internal P loading with further summary about its pattern of distribution, accumulation and historical changes; (2) better mathematical models for describing drivers and the linkages between the biological pump of algal bloom and the replenishment of sediment OP; (3) fully accounting the composition and molecular size of OP for better understanding its transformation process and mechanism; ; (4) developing direct, high-sensitivity and combined techniques to improve the precision for identifying OP in sediments; (5) establishing the response of OP molecular properties and chemical reactivity to OP biodegradability and designing a comprehensive and accurate composite index to deepen the understanding for the bioavailability of OP; and (6) integrating fundamental processes of OP in current models to better describe the release and exchange of P in sediment-water interface (SWI). This work is expected to provide critical information about OP properties and deliver perspectives of novel characterization methods.
Chapter
The Indian subcontinent has a vast mix of freshwater, saline, and marine wetlands. Wetlands in the Southern Kerala district (SKD) have a great natural wetlands ecosystem, but it is not well detailed. The present study investigates the anthropogenic factors that shift the ecological status (ES) of wetlands in the SKD because few surveys have been carried out. Seventy-five chosen wetlands were surveyed by a range of methods at five different districts, namely Alappuzha, Ernakulam, Kottayam, Thrissur, and Palakkad districts. Results revealed that most were hydrologically isolated wetlands, and a few were semi-parched in the summer. Dominant forms of wetlands were five acres in size. The human disturbance scores (HDS) showed that the Alappuzha district wetlands was high impacted (HI), the Palakkad district wetlands was mid impacted (MI), and the rest of the district wetlands were in the least impacted (LI) category. Overall, the population around the wetland habitat indicated 500 individuals were common in all wetlands. The Pearson correlation results revealed a statistically significant, positive interaction between the wetland habitat population and the HDS scores noted in riverine wetlands (n = 48), (r = 0.058, p <= 0.687) and palustrine wetlands (n = 13), (r = 0.817, p > 0.000). Also, the correlation test was not significant in Lacustrine wetlands (n = 8), (r = −0.21, p < .954). However, anthropogenic activities caused the all the wetland degradation. The factor-wise degradation of wetlands differs among the districts. The results propose fundamental details on the anthropogenic factors that impact the ecological status of wetlands in SKD, which will aid the extent of regional strategies for wetlands management.
Article
Full-text available
Florida's large number of shallow lakes, warm climate and long growing season have contributed to the development of excessive growths of aquatic macrophytes that have seriously interfered with many water use activities. The introduction of exotic aquatic macrophyte species such as hydrilla (Hydrilla verticillata) have added significantly to aquatic plant problems in Florida lakes. The use of grass carp (Ctenopharyngodon idella) can be an effective and economical control for aquatic vegetation such as hydrilla. Early stocking rates (24 to 74 grass carp per hectare of lake area) resulted in grass carp consumption rates that vastly exceeded the growth rates of the aquatic plants and often resulted in the total loss of all submersed vegetation. This study looked at 38 Florida lakes that had been stocked with grass carp for 3 to 10 years with stocking rates ranging from < 1 to 59 grass carp per hectare of lake and 1 to 207 grass carp per hectare of vegetation to determine the long term effects of grass carp on aquatic macrophyte communities. The median PAC (percent area coverage) value of aquatic macrophytes for the study lakes after they were stocked with grass carp was 14% and the median PVI (percent volume infested) value of aquatic macrophytes was 2%. Only lakes stocked with less than 25 to 30 fish per hectare of vegetation tended to have higher than median PAC and PVI values. When grass carp are stocked at levels of > 25 to 30 fish per hectare of vegetation the complete control of aquatic vegetation can be achieved, with the exception of a few species of plants that grass carp have extreme difficulty consuming. If the management goal for a lake is to control some of the problem aquatic plants while maintaining a small population of predominately unpalatable aquatic plants, grass carp carl be stocked at approximately 25 to 30 fish per hectare of vegetation.
Article
Full-text available
Invasive aquatic plants can cause local losses of species diversity throughout the world and they can also contribute to water quality deterioration. Although widely studied elsewhere, little information exists about invasive aquatic plants and their impacts in China. This study summarizes the taxonomy, origin, vector of introduction, current distribution, and the ecological impacts of invasive aquatic plants in China. This study provides useful information for the management of freshwater habitats and suggests strategies for curtailing the increasing problem of invasive aquatic plants and their impacts. We integrated data based upon original research and a literature review to compile an inventory of invasive aquatic plants in China. In total, we found 152 invasive aquatic plant species belonging to 84 genera and 39 families, representing four major growth forms including emergent (57.24%), submerged (27.63%), rooted floating leaf (9.87%), and free floating (5.26%) categories of aquatic plants. The Poaceae (Gramineae) (23 species) was the most represented and species-rich family, followed by Alismataceae (14 species), Cyperaceae (13 species), Nymphaeaceae and Araceae (both with 10 species). The majority of the invasive aquatic plant species were introduced from South America, and there were also many from North America, Asia, Africa, and Oceania. Most of these species (96.05%) are obligate freshwater species, while a minority (3.95%) is limited to marine or intertidal habitats. The ornamental trade has been the most frequent historic pathway for the introduction of invasive aquatic plants.
Article
Full-text available
Submerged aquatic vegetation (SAV) plays important roles in shallow lakes. In addition to its refuge effect for zooplankton, one key role of SAV is to provide diverse ecological niches to these organisms. The reduction of habitat complexity due to loss of SAV might thus have huge effects on zooplankton communities. The objective of this study was to investigate the relationship between SAV abundance and composition and zooplankton functional diversity and community structure. We used as model system the littoral zone of Lake St. Pierre (Québec, Canada), a shallow fluvial lake experiencing dramatic changes in SAV cover. Our sampling protocol allowed us to analyse the relationship between SAV and zooplankton along a gradient of SAV abundance. We showed that SAV abundance explained 41% of the variation in the zooplankton community structure and 25% of the variation in zooplankton functional diversity. Our results also indicated that the presence of the benthic cyanobacterium Gloeotrichia sp. in SAV beds had a structuring effect within the dominant family of Chydoridae, being negatively correlated to the abundance of relatively large-bodied species. Our findings suggest that loss in SAV biomass and complexity can affect both community structure and functional diversity of zooplankton in shallow fluvial lakes.
Chapter
Full-text available
Aquatic macrophytes are aquatic photosynthetic organisms, large enough to see with the naked eye, that actively grow permanently or periodically submerged below, floating on, or growing up through the water surface. Aquatic macrophytes are represented in seven plant divisions: Cyanobacteria, Chlorophyta, Rhodophyta, Xanthophyta, Bryophyta, Pteridophyta and Spermatophyta. Species composition and distribution of aquatic macrophytes in the more primitive divisions are less well known than for the vascular macrophytes (Pteridophyta and Spermatophyta), which are represented by 33 orders and 88 families with about 2,614 species in c. 412 genera. These c. 2,614 aquatic species of Pteridophyta and Spermatophyta evolved from land plants and represent only a small fraction (∼1%) of the total number of vascular plants. Our analysis of the numbers and distribution of vascular macrophytes showed that whilst many species have broad ranges, species diversity is highest in the Neotropics, intermediate in the Oriental, Nearctic and Afrotropics, lower in the Palearctic and Australasia, lower again in the Pacific Oceanic Islands, and lowest in the Antarctic region. About 39% of the c. 412 genera containing aquatic vascular macrophytes are endemic to a single biogeographic region, with 61–64% of all aquatic vascular plant species found in the Afrotropics and Neotropics being endemic to those regions. Aquatic macrophytes play an important role in the structure and function of aquatic ecosystems and certain macrophyte species (e.g., rice) are cultivated for human consumption, yet several of the worst invasive weeds in the world are aquatic plants. Many of the threats to fresh waters (e.g., climate change, eutrophication) will result in reduced macrophyte diversity and will, in turn, threaten the faunal diversity of aquatic ecosystems and favour the establishment of exotic species, at the expense of native species.
Article
Full-text available
Fluid macro-instability reflects fluid axial energy and mass transfer behavior. To reveal the unsteady flow rule in a mixer-settler with rigid-flexible impeller, oil and water were used as working fluid, and the wavelet analysis and Matlab numerical calculation were adopted to analyze the power spectrum of pressure fluctuation signal in the mixing tank. The influences of rigid-flexible impeller on the frequency of macro-instability were studied, and CFD simulation was adopted to explore the flow field structure in the mixer-settler. Experiments showed that, while the agitation speed (N) of rigid-flexible impeller was lower than 250 r·min-1, the relationship between macro-instability frequency (fMI) and N was linear. When N was higher than 250 r·min-1, much air was sucked into the liquid and fMI disappeared, so the flow field became multi scale structure and resulted in serious emulsification, which was unfavorable for the operation of clarification. Compared with rigid impeller, the rigid-flexible one can enhance the macro-instability and improve the efficiency of fluid mixing and energy transfer. Computational simulation shows that, the rigid-flexible impeller could obviously increase the blade suction ability and axial movement of fluid, realizing efficient mixing and avoiding excessive stirring of the fluid, which is helpful to mixing and clarification.
Article
Full-text available
Delineation of aquatic plants and estimation of its surface extent are crucial to the efficient control of its proliferation, and this information can be derived accurately with fine resolution remote sensing products. However, small swath and low observation frequency associated with them may be prohibitive for application to large water bodies with rapid proliferation and dynamic floating aquatic plants. The information can be derived from products with large swath and high observation frequency, but with coarse resolution; and the quality of so derived information must be eventually assessed using finer resolution data. In this study, we evaluate two methods: Normalized Difference Vegetation Index (NDVI) slicing and maximum likelihood in terms of delineation; and two methods: Gutman and Ignatov’s NDVI-based fractional cover retrieval and linear spectral unmixing in terms of area estimation of aquatic plants from 300 m Medium Resolution Imaging Spectrometer (MERIS) data, using as reference results obtained with 30 m Landsat-7 ETM+. Our results show for delineation, that maximum likelihood with an average classification accuracy of 80% is better than NDVI slicing at 75%, both methods showing larger errors over sparse vegetation. In area estimation, we found that Gutman and Ignatov’s method and spectral unmixing produce almost the same root mean square (RMS) error of about 0.10, but the former shows larger errors of about 0.15 over sparse vegetation while the latter remains invariant. Where an endmember spectral library is available, we recommend the spectral unmixing approach to estimate extent of vegetation with coarse resolution data, as its performance is relatively invariant to the fragmentation of aquatic vegetation cover.
Article
Full-text available
Lake Taihu, the third largest lake in China, is subjected to severe eutrophication and cyanobacterial blooms as a result of development and urbanization. In order to restore the degraded lake ecosystem, it is important to identify which environmental factors control the submerged macrophytes which declined during eutrophication. To characterize community structure of submerged macrophytes and to assess the plant–environmental relationships in Lake Taihu, a monthly investigation was conducted from May to October in 2010. A total of six species were recorded, dominated by Potamogeton malaianus and Vallisneria natans. Multivariate analysis showed that water depth, depth of soft sediments and nutrient variables (orthophosphate of water, organic matter of sediment, total nitrogen and total phosphorus of sediment) were the major factors determining growth and community composition of submerged macrophytes in the lake. A strong predictive association of soft-sediment depth and plant biomass indicated preference of submerged macrophytes for firm bottoms along the eastern shore and approximately 0.2 m could be regarded as an optimum depth for the growth of plants. The biomass of plants responded proportionately to water depth, and approximately 1.8 m could be regarded as the optimum depth for the growth of submerged macrophyte in Lake Taihu. Our results indicated that improvement of habitat and the selection of appropriate submerged macrophytes species are very important for ecological restoration in large eutrophic lakes. This study could provide useful information for managers and policy makers to evaluate and modify restoration practices in large, shallow lakes.
Article
Full-text available
'Blue Carbon', which is carbon captured by marine living organisms, has recently been highlighted as a new option for climate change mitigation initiatives. In particular, coastal ecosystems have been recognized as significant carbon stocks because of their high burial rates and long-term sequestration of carbon. However, the direct contribution of Blue Carbon to the uptake of atmospheric CO2 through air-sea gas exchange remains unclear. We performed in situ measurements of carbon flows, including air-sea CO2 fluxes, dissolved inorganic carbon changes, net ecosystem production, and carbon burial rates in the boreal (Furen), temperate (Kurihama), and subtropical (Fukido) seagrass meadows of Japan from 2010 to 2013. In particular, the air-sea CO2 flux was measured using three methods: the bulk formula method, the floating chamber method, and the eddy covariance method. Our empirical results show that submerged autotrophic vegetation in shallow coastal waters can be functionally a sink for atmospheric CO2. This finding is contrary to the conventional perception that most near-shore ecosystems are sources of atmospheric CO2 . The key factor determining whether or not coastal ecosystems directly decrease the concentration of atmospheric CO2 may be net ecosystem production. This study thus identifies a new ecosystem function of coastal vegetated systems; they are direct sinks of atmospheric CO2 .
Article
Full-text available
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.
Article
Full-text available
Although many lake restoration projects have led to decreased nutrient loads and increased water transparency, the establishment or expansion of macrophytes does not immediately follow the improved abiotic conditions and it is often unclear whether vegetation with high macrophyte diversity will return. We provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations. We found that the potential for restoration in many lakes is large when clear water conditions are met, even though the macrophyte community composition of the early 1900s, the start of human-induced large-scale eutrophication in Northwestern Europe, could not be restored. However, emerging charophytes and species rich vegetation are often lost due to competition with eutrophic species. Disturbances such as herbivory can limit dominance by eutrophic species and improve macrophyte diversity. We conclude that it is imperative to study the role of propagule availability more closely as well as the biotic interactions including herbivory and plant competition. After abiotic conditions are met, these will further determine macrophyte diversity and define what exactly can be restored and what not.
Article
Full-text available
Eutrophication resulting from high nutrient loading has been the paramount environmental problem for lakes world-wide for the past four decades. Efforts are being made in many parts of the world to reduce external nutrient loading via improved wastewater treatment or diversion of nutrient-rich inflows. However, even after a reduction of the external phosphorus loading, the effects obtained may be unsatisfactory. This may reflect an insufficient reduction in the external nutrient loading to effectively limit phytoplankton growth. However, the lack of success may also be due to chemical or biological within-lake inertia preventing or delaying improvements. To overcome the resilience and thereby reinforce recovery, a number of physico-chemical and biological restoration methods have been developed. In this chapter, we describe recent developments of biological restoration methods related to eutrophication, their short-term and long-term effects, and discuss the possibility of using combined physico-chemical and biological methods to improve the long-term stability of restoration and to reduce restoration costs. As comprehensive reviews of the effect of fish manipulation in cold temperate lakes are numerous, for these waterbodies, we highlight recent results, including effects on biodiversity and metabolism, and present new approaches of biomanipulation. Our particular focus is, however, directed at biomanipulation in warm lakes and on combined treatments which are far less well described in the literature.
Article
Full-text available
Shallow coastal lagoons are environments where a dynamic equilibrium exists between water quality and seagrass cover. Dense seagrass canopies limit the resuspension of bed sediments thereby creating a clearer water column and a positive feedback for seagrass growth. Positive feedbacks are often associated with the existence of bistable dynamics in ecosystems. For example, a bare and a seagrass covered sediment bed could both be stable states of the system. This study describes a one-dimensional hydrodynamic model of vegetation-sediment-water flow interactions and uses it to investigate the strengths of positive feedbacks between seagrass cover, stabilization of bed sediments, turbidity of the water column, and the existence of a favorable light environment for seagrasses. The model is applied to Hog Island Bay, a shallow coastal lagoon on the eastern shore of Virginia. The effects of temperature, eutrophication, and bed grain size on bistability of seagrass ecosystems in the lagoon are explored. The results indicate that under typical conditions, seagrass is stable in water depths < 2.2 m (51% of the bay bottom deep enough for seagrass growth) and bistable conditions exist for depths of 2.2–3.6 m (23% of bay) where the preferred state depends on initial seagrass cover. The remaining 26% of the bay is too deep to sustain seagrass. Decreases in sediment size and increases in water temperature and degree of eutrophication shift the bistable range to shallower depths, with more of the bay bottom unable to sustain seagrass.
Article
Full-text available
The role of the native species richness and density in ecosystem invasibility is a matter of concern for both ecologists and managers. We tested the hypothesis that the invasiveness of Urochloa arrecta (non-native in the Neotropics) is negatively affected by the species richness and abundance of native aquatic macrophytes in freshwater ecosystems. We first created four levels of macrophyte richness in a greenhouse (richness experiment), and we then manipulated the densities of the same native species in a second experiment (density experiment). When the native macrophytes were adults, fragments of U. arrecta were added, and their growth was assessed. Our results from the richness experiment corroborated the hypothesis of a negative relationship between the native species richness and the growth of U. arrecta, as measured by sprout length and root biomass. However, the resistance to invasion was not attributed to the presence of a particular native species with a greater competitive ability. In the density experiment, U. arrecta growth decreased significantly with an increased density of all five of the native species. Density strongly affected the performance of the Poaceae in a negative manner, suggesting that patches that are densely colonized by native macrophytes and less subject to disturbances will be more resistant to invasion than those that are poorly colonized and more commonly subjected to disturbances. Our density experiment also showed that some species exhibit a higher competitive ability than others (sampling effect). Although native richness and abundance clearly limit the colonization and establishment of U. arrecta, these factors cannot completely prevent the invasion of aquatic ecosystems by this Poaceae species.
Article
Full-text available
One of the major impediments to the integration of lentic ecosystems into global environmental analyses has been fragmentary data on the extent and size distribution of lakes, ponds, and impoundments. We use new data sources, enhanced spatial resolution, and new analytical approaches to provide new estimates of the global abundance of surface-water bodies. A global model based on the Pareto distribution shows that the global extent of natural lakes is twice as large as previously known (304 million lakes; 4.2 million km 2 in area) and is dominated in area by millions of water bodies smaller than 1 km2. Similar analyses of impoundments based on inventories of large, engineered dams show that impounded waters cover approximately 0.26 million km2. However, construction of low-tech farm impoundments is estimated to be between 0.1 % and 6% of farm area worldwide, dependent upon precipitation, and represents >77,000 km 2 globally, at present. Overall, about 4.6 million km2 of the earth's continental "land" surface (>3%) is covered by water. These analyses underscore the importance of explicitly considering lakes, ponds, and impoundments, especially small ones, in global analyses of rates and processes. © 2006, by the American Society of Limnology and Oceanography, Inc.
Article
Full-text available
The aquatic vegetation of Číčov Lake in the Danube floodplain, which is listed in the Ramsar Convention, was investigated to address three main questions: (1) how have landscape composition and the structures of the lake and its buffer zone changed from the mid-20th century; (2) how have species richness and the abundance of the aquatic macrophyte assemblage in this lake ecosystem changed over the last 34 years; and (3) which landscape metrics can best explain these temporal changes for floating-leaved macrophytes? Two methodological approaches, remote sensing and botanical field surveys, were applied. Historical (1949, 1970, 1990) and contemporary (2006) aerial photographs were analysed to determine land cover. Landscape configuration and structure were analysed using eight landscape metrics selected in advance to measure spatio-temporal changes and the fragmentation of the lake ecosystem and its corresponding buffer zone. The species diversity, abundance and distribution of true aquatic macrophytes were surveyed eleven times in five survey stretches between 1973 and 2007. At the landscape level, a decrease in the area covered by floating-leaved macrophytes, as well as an increase in open water surface and fragmentation of the land cover classes in the lake ecosystem, were recorded from 1949 to 2006. Overall, 30 true aquatic macrophytes were found from 1973 to 2007. Species richness did not change considerably, but the abundance of aquatic species fluctuated over the years. Three groups of true aquatic vegetation, based on common structural characteristics, were found in 1973–1983, 1989–2002, and 2004–2007 over the last 34 years. The landscape metrics NP, PD, LPI, and SHDI, which all express patterns of landscape fragmentation mostly indicate temporal changes in floating-leaved macrophytes.
Article
Full-text available
Seagrasses, marine flowering plants, have a long evolutionary history but are now challenged with rapid environmental changes as a result of coastal human population pressures. Seagrasses provide key ecological services, including organic carbon production and export, nutrient cycling, sediment stabilization, enhanced biodiversity, and trophic transfers to adjacent habitats in tropical and temperate regions. They also serve as “coastal canaries,” global biological sentinels of increasing anthropogenic influences in coastal ecosystems, with large-scale losses reported worldwide. Multiple stressors, including sediment and nutrient runoff, physical disturbance, invasive species, disease, commercial fishing practices, aquaculture, overgrazing, algal blooms, and global warming, cause seagrass declines at scales of square meters to hundreds of square kilometers. Reported seagrass losses have led to increased awareness of the need for seagrass protection, monitoring, management, and restoration. However, seagrass science, which has rapidly grown, is disconnected from public awareness of seagrasses, which has lagged behind awareness of other coastal ecosystems. There is a critical need for a targeted global conservation effort that includes a reduction of watershed nutrient and sediment inputs to seagrass habitats and a targeted educational program informing regulators and the public of the value of seagrass meadows.
Article
Full-text available
1 Freshwater habitats in cultivated and densely populated lowland regions of Europe have experienced profound changes during the last 100 years. We take advantage of the long interest in aquatic plants in Denmark to compare the submerged flora in lakes and streams in 1896 and 1996. 2 Most of the lakes which contained a diverse submerged vegetation 100 years ago now have the high phytoplankton biomasses and summer transparencies below 2.0 m characteristic of eutrophication. The majority of 17 lakes included in both old and recent studies have lost all or most of their submerged species. Species richness for those lakes that were vegetated did not, however, differ significantly between old and recent studies. 3 Species richness declined markedly in the 13 streams included in both studies. Over all sites, there was also a significant decline of species richness per locality. Potamogeton species declined from 16 to 9, despite an 8-fold increase in the number of sites surveyed. 4 Similar compositions and rank-abundances of Potamogeton species in lakes and streams studied 100 years ago reflect suitable growth conditions and mutual exchange of propagules. Today, low habitat diversity and frequent disturbance in streams and low recruitment from lakes favours only robust, fast-growing species capable of regrowth following weed cutting and dredging. 5 A positive interspecific relationship observed in the contemporary stream vegetation between mean local abundance and number of occupied sites was probably promoted by redistribution of plants as a result of disturbance and efficient dispersal in the interconnected stream network. 6 The freshwater macrophyte flora in north-west Europe presently includes a high proportion of rare species which are threatened by extinction. Both species typical for oligotrophic conditions (e.g. P. filiformis and P. polygonifolius) and another group of large, slow-growing species (e.g. P. alpinus, P. lucens, P. praelongus and P. zosterifolius), were once common but are now infrequent, while other transient species have remained rare (e.g. P. acutifolius, P. colouratus, P. densus and P. rutilus). The presence of many species that barely survive in small and distant populations will make re-assembly of submerged aquatic communities difficult.
Chapter
Full-text available
Lake Taihu is characterized by its shallowness (mean depth = 1.9 m) and large surface area (2,338 km2). Runoff sources are mostly from the mountainous west and southwest, and outflows are located throughout East Taihu. This causes shorter retention times in the south. In contrast, urban pollutants discharge into northern Taihu and result in poor water quality. Non-point pollution from rural areas and sewage wastewater is the primary pollution source. Water current velocity ranges from 10–30 cm s−1, and surface currents normally follow wind direction. Bottom currents appear to be a compensation flow. Most wave heights are less than 40 cm, and underwater irradiance correlates to seston in the water column. Lacustrine sediment is distributed in littoral zones, mostly along the western shoreline, with almost no accumulation in the lake center. Intensive aquaculture in East Taihu caused eutrophication and hampered water supply in surrounding areas. In addition, development of marshiness in the eastern littoral zones and East Taihu has occurred. The function of flood discharging of East Taihu has been limited by flourishing macrophytes. The problems facing in Lake Taihu will be alleviated by improving the management of nutrient sources into the lake.
Article
Full-text available
A five-year study examined the responses of submerged aquatic vegetation (SAV), emergent vegetation, and largemouth bass (Micropterus salmoides) to variations in water level in a large lake in Florida, USA. SAV was assessed using a combined transect survey/spatial mapping approach, emergent vegetation was quantified with aerial photography and GIS, and bass were surveyed by electro-shocking. During the period leading up to this study (1995–1999), water levels were high in the lake, and the SAV was reduced in spatial extent and biomass, compared to its condition in the early 1990s. Spatial extent of emergent vegetation also was low, and largemouth bass surveys indicated low densities and failure to recruit young fish into the population. This was attributed to the lack of critical vegetative habitat. In spring 2000, the lake was lowered by discharging water from major outlets, and this was followed by a regional drought. Water levels dropped by 1m, and there was widespread development of Chara lawns in shoreline areas, with coincident increases in water clarity. There was some germination of vascular SAV, but Chara was the extreme dominant, such that structural complexity remained low. There was no substantive improvement in bass recruitment. During 2001, water levels declined further, and emergent plants germinated in exposed areas of the lake bottom. SAV was restricted to sites farther offshore, and continued to be dominated by Chara. There again was no bass response. In 2002, conditions changed when water levels increased to a moderate depth, flooding shoreline habitat to 0.5m. Vascular SAV increased in biomass and spatial extent, such that the community developed a high structural complexity. At the same time, emergent aquatic plants developed dense stands along the western shoreline. Largemouth bass had a strong recruitment of young fish for the first time in 5years. Recruitment continued to be successful in 2003, when spatial extent of SAV was somewhat reduced by higher water but total biomass and diversity remained high. These results demonstrate an important effect of inter-annual variation in water depth on the population dynamics of aquatic plants and fish in a subtropical lake.
Article
Full-text available
Aquatic macrophytes are aquatic photosynthetic organisms, large enough to see with the naked eye, that actively grow permanently or periodically submerged below, floating on, or growing up through the water surface. Aquatic macrophytes are represented in seven plant divisions: Cyanobacteria, Chlorophyta, Rhodophyta, Xanthophyta, Bryophyta, Pteridophyta and Spermatophyta. Species composition and distribution of aquatic macrophytes in the more primitive divisions are less well known than for the vascular macrophytes (Pteridophyta and Spermatophyta), which are represented by 33 orders and 88 families with about 2,614 species in c. 412 genera. These c. 2,614 aquatic species of Pteridophyta and Spermatophyta evolved from land plants and represent only a small fraction (∼1%) of the total number of vascular plants. Our analysis of the numbers and distribution of vascular macrophytes showed that whilst many species have broad ranges, species diversity is highest in the Neotropics, intermediate in the Oriental, Nearctic and Afrotropics, lower in the Palearctic and Australasia, lower again in the Pacific Oceanic Islands, and lowest in the Antarctic region. About 39% of the c. 412 genera containing aquatic vascular macrophytes are endemic to a single biogeographic region, with 61–64% of all aquatic vascular plant species found in the Afrotropics and Neotropics being endemic to those regions. Aquatic macrophytes play an important role in the structure and function of aquatic ecosystems and certain macrophyte species (e.g. rice) are cultivated for human consumption, yet several of the worst invasive weeds in the world are aquatic plants. Many of the threats to fresh waters (e.g., climate change, eutrophication) will result in reduced macrophyte diversity and will, in turn, threaten the faunal diversity of aquatic ecosystems and favour the establishment of exotic species, at the expense of native species.