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All living cells are characterized by certain cell shapes and sizes. Many bacteria can change these properties depending on the growth conditions. The underlying mechanisms and the ecological relevance of changing cell shape and size remain unclear in most cases. One bacterium that undergoes extensive shape-shifting in response to changing growth conditions is the freshwater bacterium Caulobacter crescentus When incubated for an extended time in stationary phase, a subpopulation of C. crescentus forms viable filamentous cells with a helical shape. Here, we demonstrated that this stationary-phase-induced filamentation results from downregulation of most critical cell cycle regulators and a consequent block of DNA replication and cell division while cell growth and metabolism continue. Our data indicate that this response is triggered by a combination of three stresses caused by prolonged growth in complex medium, namely, the depletion of phosphate, alkaline pH, and an excess of ammonium. We found that these conditions are experienced in the summer months during algal blooms near the surface in freshwater lakes, a natural habitat of C. crescentus , suggesting that filamentous growth is a common response of C. crescentus to its environment. Finally, we demonstrate that when grown in a biofilm, the filamentous cells can reach beyond the surface of the biofilm and potentially access nutrients or release progeny. Altogether, our work highlights the ability of bacteria to alter their morphology and suggests how this behavior might enable adaptation to changing environments. IMPORTANCE Many bacteria drastically change their cell size and morphology in response to changing environmental conditions. Here, we demonstrate that the freshwater bacterium Caulobacter crescentus and related species transform into filamentous cells in response to conditions that commonly occur in their natural habitat as a result of algal blooms during the warm summer months. These filamentous cells may be better able to scavenge nutrients when they grow in biofilms and to escape from protist predation during planktonic growth. Our findings suggest that seasonal changes and variations in the microbial composition of the natural habitat can have profound impact on the cell biology of individual organisms. Furthermore, our work highlights that bacteria exist in morphological and physiological states in nature that can strongly differ from those commonly studied in the laboratory., (Copyright © 2019 Heinrich et al.)

Previous studies showed that continuous exposure to ammonia nitrogen (AN) contributed to regional losses of benthic invertebrate diversity in China. Yet, the overall ecological risk of AN to aquatic organisms in major riverine systems of China has not been appropriately studied. Our research then investigated temporal (seasonally/yearly) and spatial distributions of AN and un-ionized ammonia (NH 3 ) in major Chinese river basins using historic data generated between 2007 and 2014, and developed risk assessment criteria. Our results showed that the highest average AN concentrations occurred during winter (0.82-2.76 mg/L) and the lowest during summer (0.36-0.78 mg/L). NH 3 exhibited the opposite trend with the highest average concentrations mostly observed during spring (15.13-92.84 μg/L) and the lowest concentrations mainly during winter (10.53-45.43 μg/L). Both AN and NH 3 concentrations steadily increased and reached maximum levels in 2008 (AN: 1.22 mg/L and NH 3 : 50.65 μg/L), and then decreased. Temporal trends showed that the Yellow, Hai, and Huai river basins had the highest AN and NH 3 concentrations. Subsequently, conventional (hazard quotients) and probabilistic (joint probability curves) methods were applied to assess the hazards and risks posed by AN and NH 3 . The results showed that the probability of exceeding the acute toxicity threshold for 5% of species (exposed to AN or NH 3 ) was less than 13.3% and gradually decreased over time. To protect aquatic organisms, an acute criterion of 51.4 μg NH 3 /L and a chronic criterion of 1.14 mg AN/L at pH = 7.5, 20 °C were developed and are recommended for future risk assessment studies., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Zoanthids are conspicuous and abundant members of intertidal environments, where they are exposed to large environmental fluctuations and subject to increasing loads of anthropogenic nutrients. Here we assess the trophic ecology and stoichiometric consequences of nutrient loading for symbiotic zoanthids inhabiting different intertidal habitats. More specifically, we analysed the stable isotope signature (δ 13 C and δ 15 N), elemental composition (C, N and P) and stoichiometry (C:N, C:P, N:P) of Zoanthus sociatus differently exposed to nutrification. Results suggest that autotrophy is the main feeding mode of zoanthids and that the effect water nutrient content differently affects the elemental phenotype of zoanthids depending on tidal habitat. Additionally, habitat effects on Z. sociatus P-related stoichiometric traits highlight functional differences likely associated with variation in Symbiodinium density. These findings provide an innovative approach to assess how cnidarian-dinoflagellate symbioses response to ecosystem changes in environmentally dynamic reef flats, particularly nutrient loading., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Enhanced ecological floating beds were implemented to reduce nutrient quantity and improve the water quality of a eutrophic lake. The results showed that average removal efficiencies of CODCr, total nitrogen, NH3-N and total phosphorus for Canna indica L. set-up were 23.1%, 15.3%, 18.1% and 19.4% higher, respectively, than that of the setup with only substrate, and 14.2%, 12.8%, 7.9% and 11.9% higher than Iris pseudacorus L. ecological floating bed. The microbial community structure had obvious differences between devices and low similarity; bacteria were mainly attached on the fiber filling. The microbial population was abundant at the start and end of the experiment. Shannon index of samples selected ranged from 0.85 to 1.05. The sequencing results showed that fiber filling collected most uncultured bacteria species and the majority of bacteria on the plant roots were β-Proteobacteria and α-Proteobacteria. The co-dominant species attaching to the filling and plant was Nitrosomonadaceae., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study presents a methodological framework for the meso-level eco-efficiency assessment of agricultural water systems using a life-cycle system-based approach. The methodology was applied to the Sinistra Ofanto irrigation scheme, located in Southern Italy, where about 28,165 ha are under irrigation. The environmental performance of the system was evaluated through a set of selected mid-point environmental impact categories while the economic performance was measured using the total value added to the system's final products due to water use and the adopted management practices. Both economic performance and environmental performance were measured at different stages and for each stakeholder in the value chain. A distinction was made between foreground and background systems referring, respectively, to the processes that occurred inside the water system boundaries and those used for the production of supplementary resources. The analysis revealed that the major environmental burdens are: i) the freshwater resource depletion (i.e. excessive groundwater pumping), ii) climate change (i.e. direct emissions due to fertilizer use and diesel combustion), and iii) eutrophication (as a result of excessive application of N and P fertilizers). A considerable impact was observed on the background system where energy, fuel and agrochemicals were produced thereby confirming the prominent role of background processes in the comprehensive eco-efficiency assessment. The presented methodology aimed at the quantitative assessment of the eco-efficiency level rather than at the identification of the most affected environmental category. Hence, the results can be used to compare the performance of the system from one year to the next, among different stakeholders (water users) and/or to assess the impact of adopting innovative technologies and management practices. Moreover, the presented approach is useful for comparing the performance among different agricultural water systems and also in respect to other meso-level water systems in a cross-sectorial analysis., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Given the important role of lake ecosystems in social and economic development, and the current severe environmental degradation in China, a systematic diagnosis of the ecological security of lakes is essential for sustainable development. A Driving-force, Pressure, Status, Impact, and Risk (DPSIR) model, combined with data screening for lake ecological security assessment was developed to overcome the disadvantages of data selection in existing assessment methods. Correlation and principal component analysis were used to select independent and representative data. The DPSIR model was then applied to evaluate the ecological security of Dianchi Lake in China during 1988-2007 using an ecological security index. The results revealed a V-shaped trend. The application of the DPSIR model with data screening provided useful information regarding the status of the lake's ecosystem, while ensuring information efficiency and eliminating multicollinearity. The modeling approach described here is practical and operationally efficient, and provides an attractive alternative approach to assess the ecological security of lakes.

While the ecological impact of anthropogenically introduced exotic species is considered a major threat for biodiversity and ecosystems functioning, it is generally not accounted for in the environmental life cycle assessment (LCA) of products. In this article, we propose a framework that includes exotic species introduction in an LCA context. We derived characterization factors for exotic fish species introduction related to the transport of goods across the Rhine-Main-Danube canal. These characterization factors are expressed as the potentially disappeared fraction (PDF) of native freshwater fish species in the rivers Rhine and Danube integrated over space and time per amount of goods transported (PDF·m(3)·yr·kg(-1)). Furthermore, we quantified the relative importance of exotic fish species introduction compared to other anthropogenic stressors in the freshwater environment (i.e., eutrophication, ecotoxicity, greenhouse gases, and water consumption) for transport of goods through the Rhine-Main-Danube waterway. We found that the introduction of exotic fish species contributed to 70-85% of the total freshwater ecosystem impact, depending on the distance that goods were transported. Our analysis showed that it is relevant and feasible to include the introduction of exotic species in an LCA framework. The proposed framework can be further extended by including the impacts of other exotic species groups, types of water bodies and pathways for introduction.

Early warning signals have been proposed to forecast the possibility of a critical transition, such as the eutrophication of a lake, the collapse of a coral reef or the end of a glacial period. Because such transitions often unfold on temporal and spatial scales that can be difficult to approach by experimental manipulation, research has often relied on historical observations as a source of natural experiments. Here, we examine a critical difference between selecting systems for study based on the fact that we have observed a critical transition and those systems for which we wish to forecast the approach of a transition. This difference arises by conditionally selecting systems known to experience a transition of some sort and failing to account for the bias this introduces--a statistical error often known as the prosecutor's fallacy. By analysing simulated systems that have experienced transitions purely by chance, we reveal an elevated rate of false-positives in common warning signal statistics. We further demonstrate a model-based approach that is less subject to this bias than those more commonly used summary statistics. We note that experimental studies with replicates avoid this pitfall entirely.

Two approaches for setting ecological class boundaries, response curves and a simplified mathematical boundary-setting protocol, were tested for coastal, transitional and open waters in the Gulf of Riga, Baltic Sea. The simplified mathematical boundary-setting protocol defines acceptable ecological status based on expert judgment by a uniform relative deviation from reference conditions. In contrast, response curves derive class boundary definitions from observed changes in biological quality elements along environmental pressure gradients for class boundary definitions. Identification of relevant environmental pressures for the construction of response curves was based on a conceptual model of eutrophication in the Gulf of Riga. Response curves were successfully established for summer chlorophyll a and transparency, as well as for macrozoobenthos abundance in the Central Gulf, macrozoobenthos biotic coefficient in the Southern Gulf, and maximum depth of phytobenthos in the Northern Gulf. In the Gulf of Riga response curves almost always permitted a larger deviation from reference conditions than the 50% deviation applied for the simplified mathematical boundary-setting protocol. The case study clearly demonstrated that class boundary definitions should take into account the sensitivity of the target water body. Also, the class boundaries for different ecological quality elements were internally more consistent than those derived by the simplified mathematical boundary-setting protocol.

This research was carried out in Tha Chin Watershed in the central part of Thailand with attempts to apply multidisciplinary knowledge for understanding ecosystem structure and response to anthropogenic pollution and natural impacts leading to a proposal for an appropriate zonation management approach for sustainable utilization of the area. Water quality status of the Tha Chin River and Estuary had been determined by analyzing ecological, hydrological, and coastal oceanographic information from recent field surveys (during March 2006 to November 2007) together with secondary data on irrigation, land utilization, and socio-economic status.Results indicated that the Tha Chin River and Estuary was eutrophic all year round. Almost 100% of the brackish to marine areas reflected strongly hypertrophic water condition during both dry and high-loading periods. High NH(4)(+) and PO(4)(3-) loads from surrounding agricultural land use, agro-industry, and community continuously flew into the aquatic environment. Deteriorated ecosystem was clearly observed by dramatically low DO levels (ca 1 mg/l) in riverine to coastal areas and Noctiluca and Ceratium red tide outbreaks occurred around tidal front closed to the estuary. Accordingly, fishery resources were significantly decreased. Some riverine benthic habitats became dominated by deposit-feeding worms e.g. Lumbriculus, Branchiura, and Tubifex, while estuarine benthic habitats reflected succession of polychaetes and small bivalves. Results on analysis on integrated ecosystem responses indicated that changing functions were significantly influenced by particulates and nutrients dynamics in the system.Based on the overall results, the Tha Chin River and Estuary should be divided into 4 zones (I: Upper freshwater zone; II: Middle freshwater zone; III Lower freshwater zone; and IV: Lowest brackish to marine zone) for further management schemes on water remediation. In this study, the importance of habitat morphology and water flow regimes was recognized. Moreover, nearshore extensive shrimp culture ponds, irrigation canals, and surrounding mangrove habitats belonging to local households seemed to act as effective natural water treatment system that can yet provide food resources in turns. These remediation-production integrated functions should be deserved depth considerations for water quality development of the Tha Chin areas., (IWA Publishing 2008.)

Sampling was conducted at three site groups, group E (in East Taihu Bay), G (in Gonghu Bay) and M (in Meiliang Bay) in Lake Taihu. TN and TP concentrations among site groups was in the increasing order of E < G < M. TP level at G sites is at the critical threshold for loss of submersed macrophytes. Mean values of DO and Transparence showed different trend, i.e., E > G > M. The mean phytoplankton fresh-weight biomass at M sites was 5.81 mg/l, higher than that at E sites (4.96 mg/l) and G sites (5.18 mg/l). Mean zooplankton fresh-weight biomass was in the decreasing order of M (6.4 mg/l) > G (4.9 mg/l) > E (2.7 mg/l). However, Rotifera density was in the sequence of E > G > M. Both zooplankton biomass and phytoplankton biomass increased with the rise of TN and TP concentrations. Relationships between zooplankton biomass and phytoplankton biomass showed that zooplankton played a limited role in the control of algae in eutrophic lakes. Nutrient availability is much more important than zooplankton grazing pressure in controlling phytoplankton growth in lakes. For most sites in Lake Taihu, reduction of nutrient loading, as well as macrophyte conservation, zappears to be especially important in maintaining high water quality and regulating lake biological structure, but for M sites, it's urgent to control nutrient inputs rather than to restore macrophyte community.

We describe a novel method to study drastic change in ecosystems, based on generic functions used in the study of phase transitions and related physical phenomena. We illustrate its use by applying it to the problem of shallow lake eutrophication, and express our results in terms of an interplay between phosphorus content in the water column and fluxes of this substance between the lake and both its biological community and its surroundings. We contrast our solution to this problem with a previous one based on the concept of resilience, and on bifurcation analysis of a dynamical equation that also involves phosphorus concentration and fluxes. We then suggest a generalized dynamical scheme incorporating the generic functions above, that reduces to our original method in the stationary condition, and allows in addition dealing with cyclic and chaotic regimes, as illustrated through a particular example.

Lake Taihu is the third largest freshwater lake in China. It serves many social, economic, and ecological purposes in the drainage basin. Unfortunately, the water has been heavily polluted due to rapid industrialization and urbanization during the last two decades. Notwithstanding great efforts made so far to improve the water quality, the environmental situation is still far from being optimistic. The basin and the lake are facing a range of severe environmental challenges: rapid socio-economic development continues to place great pressures on the environment, current pollution control projects have many problems from the viewpoint of effectiveness and efficiency of their implementations, and the non-point sources of pollution such as agricultural fields, for which control is more difficult than for industrial point sources, have become the main contributors to serious eutrophication of the lake. Considering the characteristics of the environmental challenges and problems confronting the basin and the lake, we focus on integrated environmental management (IEM) as a promising and effective approach to overcome these predicaments. Current practices and problems of environmental management in the basin are examined, and potential future developments are discussed. Three aspects of the IEM are emphasized: institutional cooperation, public participation, and internalization of environmental externalities. We think these are the most critical for not only the basin but also for the whole of China to achieve a sustainable society.

More than half the world's human population lives within 100 km of the coast, and that number is expected to increase by 25% over the next two decades. Consequently, coastal ecosystems are at serious risk. Larger coastal populations and increasing development have led to increased loading of toxic substances, nutrients and pathogens with subsequent algal blooms, hypoxia, beach closures, and damage to coastal fisheries. Recent climate change has led to the rise in sea level with loss of coastal wetlands and saltwater intrusion into coastal aquifers. Coastal resources have traditionally been monitored on a stressor-by-stressor basis such as for nutrient loading or dissolved oxygen. To fully measure the complexities of coastal systems, we must develop a new set of ecologic indicators that span the realm of biological organization from genetic markers to entire ecosystems and are broadly applicable across geographic regions while integrating stressor types. We briefly review recent developments in ecologic indicators and emphasize the need for improvements in understanding of stress-response relationships, contributions of multiple stressors, assessments over different spatial and temporal scales, and reference conditions. We provide two examples of ecologic indicators that can improve our understanding of these inherent problems: a) the use of photopigments as indicators of the interactive effects of nutrients and hydrology, and b) biological community approaches that use multiple taxa to detect effects on ecosystem structure and function. These indicators are essential to measure the condition of coastal resources, to diagnose stressors, to communicate change to the public, and ultimately to protect human health and the quality of the coastal environment.

Great strides have recently been made in identifying and characterizing the staggering diversity of microorganisms conducting primary and secondary production, nutrient transformation and mineralization processes that underlie ecosystem and regional biogeochemical, trophodynamic and ecological change. We are now faced with the challenge of assigning and coupling function to structure in highly complex and interactive microbial communities mediating such change. Previous and ongoing ecophysiological work has shown that microbial processes controlled by environmental variables and limiting resources are highly specific in terms of what, when, where and why they are active, not to mention how they impact ecosystem dynamics. As such, it is imperative that we assess the activities and roles of key microbial 'players' along the appropriate environmental scales and gradients catalysing ecological change. Here, we discuss conceptual and technical challenges for some key microbially mediated environmental processes, problems and extremes that require synthesizing our growing knowledge of microbial community structure with emerging knowledge of function in aquatic ecosystems. We emphasize the importance of assessing ecological change over a range of relevant time scales that vary from minutes to millennia and spatial scales that range from microscale aggregates to ocean basins.

Eutrophication has many known consequences, but there are few data on the environmental and health costs. We developed a new framework of cost categories that assess both social and ecological damage costs and policy response costs. These findings indicate the severe effects of nutrient enrichment and eutrophication on many sectors of the economy. We estimate the damage costs of freshwater eutrophication in England and Wales to be $105-160 million yr(-1) (pound 75.0-114.3 m). The policy response costs are a measure of how much is being spent to address this damage, and these amount to $77 million yr(-1) pound 54.8 m). The damage costs are dominated by seven items each with costs of $15 million yr(-1) or more: reduced value of waterfront dwellings, drinking water treatment costs for nitrogen removal, reduced recreational and amenity value of water bodies, drinking water treatment costs for removal of algal toxins and decomposition products, reduced value of nonpolluted atmosphere, negative ecological effects on biota, and net economic losses from the tourist industry. In common with other environmental problems, it would represent net value (or cost reduction) if damage was prevented at source. A variety of effective economic, regulatory, and administrative policy instruments are available for internalizing these costs.

Ground water exchange affects the ecology of surface water by sustaining stream base flow and moderating water-level fluctuations of ground water-fed lakes. It also provides stable-temperature habitats and supplies nutrients and inorganic ions. Ground water input of nutrients can even determine the trophic status of lakes and the distribution of macrophytes. In streams the mixing of ground water and surface water in shallow channel and bankside sediments creates a unique environment called the hyporheic zone, an important component of the lotic ecosystem. Localized areas of high ground water discharge in streams provide thermal refugia for fish. Ground water also provides moisture to riparian vegetation, which in turn supplies organic matter to streams and enhances bank resistance to erosion. As hydrologists and ecologists interact to understand the impact of ground water on aquatic ecology, a new research field called "ecohydrology" is emerging.

The remediation method--namely, a hybrid system combined with DAF and CRM--is studied in this paper for the size reduction of aqua-ecological circulation and for the elution control in lakes. Results show that two effects on water quality purification, the sediment washout effect and the elution control effect, can be induced by this system, and the biota inhabiting the lake is therefore shifted into an oligotrophic aspect, from blue algae to green algae and/or diatoms.

This paper provides some introductory information on the history, development, and characteristics of various lake ecosystem models. The modeling of lake ecological processes began to gain importance in the early 1960s. There are a number of models available today, with varying levels of complexity to cope with the variety of environmental problems found in lake environments, e.g. eutrophication, acidification, oxygen depletion, wetland management, heavy metal and pesticide pollution, as well as hydrodynamic problems. In particular, this paper focuses on lake eutrophication and wetland models, as well as addressing strategies appropriate for the design and development of reliable lake ecological models.

This paper examines the nature of the risk to riverine ecosystems from artificially enhanced loads of phosphorus, considers the key sources of phosphorus enrichment and ways of controlling them, and provides a framework for developing control strategies. The aquatic plant community is the foundation for a healthy and diverse riverine ecosystem, providing food, shelter and breeding habitats for a wide range of animal species. Phosphorus enrichment in rivers can degrade the plant community by altering the competitive balance between different aquatic plant species, including both higher plants and algae. This has consequences for the whole ecosystem. To promote healthy riverine plant communities and the wide range of animal species dependent on them, phosphorus concentrations need to be reduced to as near to background levels as possible. The risk of adverse effects declines as phosphorus concentrations approach background levels, such that any incremental reduction should be seen as a positive step towards trophic restoration. Pragmatic management targets vary between 0.02 and 0.1 mg(-1) soluble reactive phosphorus, depending on river type, with an interim target of 0.2 mg(-1) for heavily enriched rivers. Continuous point sources of phosphorus, dominated by sewage treatment works, have a highly important influence on levels of bioavailable phosphorus in the water column through the growing season. It is important to tackle point sources comprehensively so that reductions in phosphorus concentrations are maximised during this critical time of year. Diffuse sources of phosphorus, particularly from agriculture, are a major contributor to phosphorus levels in riverine sediments, where it can be utilised by benthic algae and rooted plants. This phosphorus can also be released into the water column by a variety of processes. As point sources are brought under control, the relative contribution from diffuse sources becomes increasingly important. An integrated programme of control, involving proactive action on both point and diffuse sources, will be required in most circumstances to bring phosphorus levels in the water column and sediment down to near background levels.

An ecological engineering was conducted for eutrophication control in the Nanhu Lake of Changchun. In 1996, the removal of phosphorus by harvesting aquatic macrophytes and fishes was 149.6 kg and 189.9 kg, respectively, and the phosphorus fixed in molluscs was 153.4 kg. The total output was 492.9 kg, which amounted approximately to the annual phosphorus input to the lake. After ecological engineering, the water quality turned better, the TP concentration in lake water decreased, the phytoplankton density reduced, and the number of phytoplankton species increased. The roles of molluscs and fish in controlling lake eutrophication should be further studied. Ecological engineering is an ideal method to control the eutrophication of urban lakes.

Ecological and health problems posed by microalgal blooms (red tides) occurring in the Southern part of Chile are reviewed. Out of the six human illnesses provoked by microalgal toxins, paralytic shellfish poisoning is the most important, because of its high mortality rate and the high levels of phycotoxins found in contaminated molluscs. Saxitoxin and its analogues bind to a receptor in the voltage-gated sodium channel of neural membranes. The most important toxin-producer microalgae are Alexandrium catenella and Dinophysis acuta. Phycotoxins become concentrated by filter-feeding shellfish, like Mytilus chilensis. Highly sensitive methods available for detection of microalgal toxins are analyzed.

Many surface waters in the world are impounded by eutrophication due to the global warming phenomenon. This study analyzed the trophic level in the Bangka Strait, a busy pathway that connects two provinces (Bangka and South Sumatra) of Indonesia, using MODIS-Terra chlorophyll-a (Chl-a) data from the 2020 year. We applied the GIS analysis to generate Chl-a concentration and trophic state maps over the study area. The results of the study revealed that the mesotrophic, eutrophic, and oligotrophic status encompass 50%, 43%, and 7% of the Bangka Strait region, respectively. The highest concentration of Chl-a was observed in May (5.38 g/L), while the lowest was observed in September (3.02 g/L). Our study revealed that the high Chl-a concentration was primarily due to nutrient contributions from South Sumatra rivers. On the other hand, the COVID-19 restriction policy significantly reduced Chl-a from July to October. The trophic state of the Bangka Strait was at a mesotrophic level, and the major contributors to the trophic condition in the strait came from the coasts of South Sumatra, which mostly consisted of agricultural and aquacultural activities. These findings will be useful in developing an effective policy for monitoring and protecting surface waters from eutrophication events.

Coastal waters are currently receiving anthropogenic impacts from the mainland that caused the natural conditions to change to higher nutrient content. This study was conducted to examine the spatial and temporal dynamics of trophic status and how zone location and rainfall category affect the distribution of trophic status. Water quality data were collected for 6 months with different rainfall intensities at 16 observation stations. Trophic status was determined using the TRIX index which combines biological, physical, and chemical water variables. Rainfall had no significant effect on the TRIX index with a p-value of 0.223 (>0.05), but the distance from the land had a significant effect with a p-value of (

Chlorophyll-a (Chl a) is an important indicator of algal biomass frequently used to evaluate the severity of cultural eutrophication. Identifying the key covariates of Chl a concentrations is essential to understand the mechanisms that drive eutrophication and to develop forecasting tools that guide the restoration process. In this study, we present a novel ensemble modeling framework founded upon the complementary features of Random Forest (RF) and Generalized Additive modeling (GAMs). A series of RF models are first developed to forecast Chl a concentrations based on the antecedent values of a multitude of environmental predictors. GAMs are then used to explore the presence of non-linearities in the seasonal relationships between Chl a and the identified predictors. The optimal RF models using a 0–8 day time lag displayed high predictive skills with adjusted R2 values consistently above 0.80. Analyses of the RF models revealed that the modulating factors of Chl a display significant seasonality. Dissolved oxygen (DO) and turbidity were the key covariates of Chl a in the spring, while the water level fluctuations predominantly regulated phytoplankton biomass in the summer and winter. The occurrence and severity of algal blooms in the summer and autumn were associated with threshold levels of 0.06 and 1.50 mg/L for total phosphorus (TP) and total nitrogen (TN) concentrations, respectively. These results reveal the potential of the introduced modeling framework to shed light on the regulatory factors of algal biomass as well as to establish real-time predictions in the Nanji wetland waters of Poyang Lake.

Assessments of lake ecosystem health, based on indicators of physical–chemical water quality, ecological conditions, and human health risks, are needed to apprise the public and facilitate lake management. While unrefereed lake water quality reports exist, this is the first peer-reviewed study to report data processing and analysis methods and results for current state and recent trends in multiple environmental indicators in monitored lakes across Aotearoa New Zealand. Lake grading based on national criteria indicated that many lakes are failing to achieve statutory bottom lines for phytoplankton chlorophyll a, total nitrogen, and total phosphorus concentrations. In contrast, most monitored lakes had high grades for two human health risk indicators, E. coli and cyanobacteria concentrations, and for potential toxicity of ammonia for biological communities. We included 166 lakes and considered indicator state and trends for two lake classifications based on geomorphology and land cover. Elevated scores for an indicator of trophic state (the trophic level index; TLI) in most shoreline, riverine, peat, landslide, dam, and aeolian lakes indicated eutrophic conditions or worse. Lower TLI scores were indicative of oligotrophic conditions in most glacial lakes. Nutrient, E. coli and suspended sediment concentrations and TLI scores were positively correlated, and Secchi depths negatively correlated, with high-intensity agricultural land cover. Ten-year trend analyses indicated that lakes with increasing Secchi disk depth, chlorophyll a, dissolved reactive phosphorus, E. coli, ammoniacal nitrogen, TLI, total nitrogen, and total suspended solids trends outnumbered those with decreasing trends. Twenty-year trend analyses indicated that the numbers of lakes with increasing and decreasing trends in most of the indicators we assessed were comparable, but lakes with increasing 20-year trends in total nitrogen outnumbered those with decreasing trends, and lakes with decreasing 20-year trends in ammoniacal nitrogen, dissolved reactive phosphorus, total phosphorus, and nitrate nitrogen outnumbered those with increasing trends. This study presents clear data processing steps and trend analysis methods as applied to a nationwide dataset for Aotearoa New Zealand, while acknowledging data limitations. For example, the choice of trend periods is challenging and can greatly affect conclusions. The results of this empirical study and the collective results of preceding studies of lake ecosystem health indicate that eutrophication poses a threat to the ecological health of many if not most lakes in Aotearoa New Zealand. Recommendations include monitoring network expansion especially for the indicators bottom dissolved oxygen and cyanobacteria (toxic and total cyanobacteria biovolumes) and judicious selection of trend periods in lake-specific trend analyses to determine causes for increasing or decreasing trends in environmental indicators.

Abstract Deep lakes are critical for freshwater storage, yet they are struggling against major ecological issues from climate change and nutrient pollution. A comprehensive understanding of internal feedback mechanisms is crucial for regulating nutrients in these lakes. A five‐year study was conducted on the diatom community and environment in Lake Fuxian, China's largest deep freshwater lake, which is becoming eutrophic. The results indicate a shift in the diatom community from a stable state dominated by a single species to a rapid seasonal fluctuation, and there is a significant increase in diatom biomass. Specifically, stable stratification and low nutrient concentrations are limiting the growth of diatom biomass and maintaining the dominance of Cyclotella. Nutrients in the hypolimnion were replenished in the epilimnion during the extreme cold of winter, triggering a shift in the diatom community. This shift may imply that future climate change will exacerbate the positive feedback of hypoxia‐nutrient release of algal blooms, potentially triggering a regime shift in the ecosystem of the entire lake. This study underscores the fact that climate change alters the internal feedback mechanisms of deep lakes, reducing ecosystem stability, and provides a scientific basis for further clarification of protection measures for deep lakes.

Chlorophyll-a (Chl-a) and algal cell density (ACD) are vital for assessing algal proliferation and eutrophication in aquatic ecosystems. Although Chl-a is often used as a proxy for ACD, its accuracy requires validation, and studies on their linear correlation are scarce. Additionally, Chl-a and ACD are influenced by various factors, including nutritional, economic, biochemical, physicochemical, and meteorological factors. However, the relative importance of these factors on Chl-a and ACD remains insufficiently studied. This study analyzed data from 57 lakes and reservoirs across China from March 2021 to February 2023, investigating the distribution patterns of Chl-a and ACD across different regions and seasons. The study employed a linear regression model to explore the correlation between Chl-a and ACD in various regions and seasons throughout China. Furthermore, Mantel test and generalized linear model were used to evaluated the relative importance of nutritional factors (total nitrogen (TN), total phosphorus (TP), TN/TP ratio (TN/TP), and ammonia nitrogen (NH3-N)), economic factors (gross domestic product), meteorological factors (surface pressure, net solar radiation, air temperature, wind speed (WS), and rainfall (RF)), as well as biochemical and physicochemical factors (turbidity (TUR), pH value, water temperature (WT), permanganate index, and dissolved oxygen) on Chl-a and ACD. Results showed that the average concentrations of Chl-a and ACD in South China were highest, at 12 μg/L and 19.5 × 106 cells/L, respectively. Seasonally, Chl-a peaked in spring and was lowest in winter, while ACD peaked in summer and was lowest in winter. Significant seasonal and regional variations in the Chl-a and ACD correlation were observed, with spring showing the strongest relationship. In Central China, Chl-a and ACD were significantly correlated throughout the four seasons, whereas correlations were less distinct in Eastern and Western regions. Therefore, Chl-a as a proxy for ACD requires caution. Nutrient factors (TN, TP, TN/TP, NH3-N) were identified as the primary drivers of Chl-a and ACD. Meteorological factors (WS, RF), along with biochemical and physicochemical factors (WT, TUR) also emerged as critical predictors of Chl-a and ACD, with spatial variations. This study validates Chl-a as a proxy for ACD, analyzes their spatiotemporal distribution, and assesses the influence of various factors on Chl-a and ACD, enhancing our understanding of algal dynamics in Chinese lakes and reservoirs.

Abstract Anthropogenic eutrophication of ecosystems is an important driver of biodiversity loss. Even protected areas (PAs) may be impacted by anthropogenic nutrients, for example, from atmospheric deposition or the provision of supplementary feeding. However, the resultant nutrient patterns, and the role of local wildlife in shaping them, remain poorly understood. We investigated anthropogenic influences on the role that red deer (Cervus elaphus) play in the nutrient balance of a PA in Denmark. We used habitat selection modeling and theoretical scenarios where we varied the proportion of energy the deer obtained from supplementary versus natural forage and compared it with the nutrients removed due to hunting. We show that the movement and distribution of the red deer population within the PA are very heterogeneous and likely influenced by the need for shelter. Moreover, depending on their reliance on supplementary feeding, deer can potentially import large amounts of nutrients to the PA, and concentrate them in localized hotspots. However, we also explore the potential for nutrient loss due to hunting activities. Such indirect anthropogenic impacts on nutrient landscapes may counteract restoration and conservation efforts. We therefore recommend incorporating anthropogenic influences on zoogeochemistry and the animal‐mediated connectivity between PAs and anthropogenically dominated landscapes into future management plans.

The spatiotemporal distribution of harmful algal blooms (HABs) in rivers remains poorly understood, and there is an urgent need to develop a consistent set of metrics to better document HAB occurrences and forecast future events. Using data from seven sites in the Illinois River Basin, we computed metrics focused on HAB conditions related to excess algal growth and hypoxia. Daily mean chlorophyll and dissolved oxygen (DO) concentrations, gross primary productivity (GPP), and net ecosystem productivity (NEP) rates, focused on water quality status, identifying the timing of the transition from a clear-water to an algal dominated state. Early warning indicators (EWIs), the first-order autoregressive process (Ar1) and standard deviation (SD) of chlorophyll concentrations, focused on future events, forecasting blooms. Metrics were compared to either literature-derived or statistical-based thresholds and were normalized by total number of daily samples for an exceedance rate. Exceedances of a daily mean chlorophyll concentration averaged 50 % across all sites using a 10 µg L−1 threshold but increasing the threshold to 50 μg L−1 reduced the average exceedance rate to 5 %. The average exceedance rate for GPP (∼8 g O2 m2d−1 threshold) was 15 %, similar to the daily amplitude DO concentration (∼3 mg L−1 threshold), but the average for NEP (0 g O2 m2 d−1 threshold) was higher, at 28 %. The number of days with at least 1 continuous DO concentration below the threshold of 5, 3, or 2 mg L−1, had basin wide exceedance rates of 9 %, 3 %, and 2 %, respectively. Thresholds for EWIs, Ar1 and SD, were exceeded at 5 of the 7 sites with high chlorophyll concentrations and GPP rates. The correlation between proxies for algal biomass (chlorophyll concentration) and productivity (GPP) was strongest for sites in the middle region of the basin, with R2 values between 0.54 and 0.74. Although, cyanotoxin concentrations are the most commonly used metrics by states to define an inland water HAB, there is a paucity of publicly available data. The wider availability of chlorophyll and oxygen data combined with the results from this study suggest that biomass and productivity state and event-based metrics may be a promising way to assess and predict the vulnerability of rivers to some of the deleterious effects of HABs at broad spatial scales.

Eutrophication is a major problem currently affecting sediment biodiversity in different kingdoms. Surveys at different spatial scales have suggested that nutrient enrichment drove the congruence in biodiversity across different kingdoms. In this study, we examined the diversity indexes of bacteria, fungi, and zoobenthos in Dongting Lake, which is undergoing different trophic levels. The species richness and Shannon index of bacteria, fungi, and zoobenthos were all consistent with the intermediate disturbance hypothesis along the content of TN and TP, with the hysteresis of fungal group. Significant cross-taxon congruence was found in species richness between bacteria and zoobenthos, and Shannon index between bacteria and fungi. Also, the strength of congruence in biodiversity among bacteria, fungi and zoobenthos would decrease along nutrient enrichment. Multi- and single-kingdom networks found that bacterial group contained more nodes and edges compared to fungal and zoobenthos groups, and bacterial removal led to the lowest natural connectivity. And highest positive interaction proportion and lowest absolute value of natural connectivity slope were observed in zoobenthos group. These results highlighted the importance of bacteria as stabilizer in sediment ecosystem, and the most sensitive feature of zoobenthos to nutrient enrichment. Taken together, our results confirmed the cross-taxon congruence between multi-kingdoms, and the effectiveness of bacteria as a potential bioindicator of ecological change.

Abstract Background Eutrophication and acid rain are two threats that many water bodies must contend with. Eutrophication and climate change have accelerated widespread outbreaks of cyanobacterial blooms as both have become more severe. Pontederia cordata, a garden ornamental plant, can inhibit some algae growth and remove total nitrogen (TN) and total phosphorus (TP) from the water. In this study, we investigated how simulated acid rain and eutrophication co-pollution affected P. cordata's growth physiology and ability to inhibit algae growth. Results Under mild eutrophication (2 mg·L−1 TN, 0.4 mg·L−1 TP, and 15 mg·L−1 CODMn) or weak acid rain (pH = 5.0), P. cordata alleviated the degree of cell membrane lipid peroxidation by stabilizing superoxide dismutase (SOD) and catalase (CAT) activities in the leaves, allowing for normal plant growth. Under mild eutrophication and acid rain conditions, cultured P. cordata water samples maintained strong algae inhibition by reducing the Chl a content and SOD activity of Microcystis aeruginosa cells. Compound stress where acid rain was the primary inhibitory factor along with moderate or severe eutrophication inhibited P. cordata growth, which probably reduced the input of algae-inhibiting allelochemicals, thus reducing its ability to inhibit algae. Conclusions In summary, P. cordata has application potential in mild eutrophic water and acid rain (pH ≥ 4). These findings provide guidance for further research on phytoremediation and algae control in scenarios of compound pollution.

Abstract Wetland habitats are changing under multiple anthropogenic pressures. Nutrient leakage and pollution modify physico‐chemical state of wetlands and affect the ecosystem through bottom‐up processes, while alien predators affect the ecosystems in a top‐down manner. Boreal wetlands are important breeding areas for several waterbird species, the abundances of which potentially reflect both bottom‐up and top‐down ecosystem processes. Here, we use long‐term national monitoring data gathered from c. 130 waterbird breeding sites in Finland from the 1980s to the 2020s. We hypothesised that the physico‐chemical state of the waters and increasing alien predator abundance both play a role in steering the waterbird population trends. We set out to test this hypothesis by relating population changes of 17 waterbird species to changes in water chemistry and to regional alien predator indices while allowing species‐specific effects to vary with foraging niche (dabblers, invertivore divers, piscivorous divers, herbivores), nesting site, female mass and habitat (oligotrophic, eutrophic). We found niche and nesting site‐specific, habitat‐dependent changes in waterbird numbers. While the associations with higher phosphorus levels and browning water were in overall positive at the oligotrophic lakes, the numbers of invertivore and piscivore diving ducks were most strongly negatively associated with higher phosphorus levels and browning water at the eutrophic lakes. Furthermore, increased pH levels benefitted piscivores. Invertivore diving duck species nesting on the wetlands had declined most on sites with high alien predator indices. Large herbivorous species and species preferring oligotrophic lakes seem to be successful. We conclude that the large‐scale breeding waterbird decline in Finland is closely connected to both bottom‐up and top‐down processes, where negative associations are emphasised especially at eutrophic lakes. Niche‐, nest site‐ and habitat‐specific management actions are required to conserve declining waterbird populations. Managing wetlands on catchments level together with alien predator control may provide important approaches to future wetland management.

Eutrophication has become prominent in many lakes of the world, resulting in a continuous rise of suspended particulate organic matter (POM) that can be of vital consequence for water quality and carbon cycling. While the accumulation and decomposition of POM can enhance nutrient cycling at a rate depending on the property of lake-water organic carbon, it is important to identify the source of suspended POM for evaluating eutrophication and carbon burial. Here we analyzed the distribution of stable isotopic ratios (δ13C and δ15N) and the carbon/nitrogen ratio (C/N) in suspended POM in a shallow eutrophic lake of subtropical China, for apportioning the POM sources using Bayesian mixing model. Specifically, we collected seasonal samples of lake-water POM (>0.7 μm) from 20 sites in Yilong Lake from September 2020 to June 2022, as well as six types of modern samples covering the main carbon sources in the catchment. The spatial surveys showed that in the dry year (low water level) the δ13C of POM was more enriched in the western basin than those in the central and eastern basins, while the seasonal surveys showed the most enriched δ13C of POM in September. However, this spatio-temporal heterogeneity disappeared in the wet year (high water level). It was also found that the δ13C, δ15N and C/N values of POM varied significantly with those of phytoplankton across sites and seasons. Application of the MixSIAR model further showed that phytoplankton was the predominant source of POM in Yilong Lake (79.8 ± 13.4 %), but with large annual difference, 68.9 ± 10.3 % in the dry year and 90.7 ± 3.7 % in the wet year. In comparison, the contribution of the other five endmembers was much more moderate. In particular, the proportion of allochthonous organic carbon in POM was relatively low, with terrestrial plants and soils contributing 6.1 ± 4.8 % and 4.3 ± 2.5 % of POM, respectively. Our quantitative evidence for the dominance of the autochthonous source (i.e., phytoplankton) in lake-water POM over time and space suggested a determining role of eutrophication in the composition of lake organic carbon. Therefore, the coupling of algal blooms with organic carbon cycling in inland waters can be enhanced with continuous catchment development and regional warming.

Coastal marine ecosystems are integral in providing numerous ecosystem functions and services. However, intense and chronic anthropogenic stressors often impact marine ecosystems surrounding highly urbanized, densely populated coastal megacities. The associated reduction of water quality and biodiversity of these ecosystems potentially erodes ecosystem functions and provision of services. While there is general consensus that greater biodiversity supports a multitude of ecosystem functions, evidence from marine ecosystems in real-world settings is lacking. In this study, we evaluated the influence of water quality on benthic and fish assemblages, as well as quantified six key ecosystem functions in coastal waters of Hong Kong. Hong Kong’s marine ecosystems are marred with long-term damage that is directly linked with rapid economic growth and anthropogenic activities. We found that water quality significantly affected community composition and clustered assemblages into separate groups related to strength of impact: high impact sites were generally dominated by bivalves and small, opportunistic organisms such as damselfish (Pomacentrinae) and cardinalfish (Apogonidae); low impact sites were dominated by macroalgae, bryozoa, and commercially important piscivores such as groupers (Epinephelinae) and seabreams (Sparidae). Ecosystem function tests showed that low impact sites were much more productive than high impact sites, with 15-times greater macroalgal cover and 5-times higher fish biomass. On the other hand, herbivory and predation rates were context-dependent due to underlying biodiversity effects such as selection, complementarity, and competition. Eutrophication increased decomposition and reduced carbon sequestration, but excessive nutrient input could have suppressed decomposer activities via hypoxia. Therefore, we show that in high impact sites where top-down control is removed, resilient and opportunistic organisms such as cardinalfishes and sea urchins may expand to fulfill functional roles, effectively maintaining ecosystem functions such as predation and herbivory in degraded habitats. Contrary to general consensus, this study demonstrates the merit in conserving even highly impacted marine habitats due to their persistent ecosystem functionality despite chronic water quality issues and shifts in benthic and fish assemblages.

Abstract Eutrophication, increased temperatures and stratification can lead to massive, filamentous, N2‐fixing cyanobacterial (FNC) blooms in coastal ecosystems with largely unresolved consequences for the mass and energy supply in food webs. Mesozooplankton adapt to not top‐down controlled FNC blooms by switching diets from phytoplankton to microzooplankton, resulting in a directly quantifiable increase in its trophic position (TP) from 2.0 to as high as 3.0. If this process in mesozooplankton, we call trophic lengthening, was transferred to higher trophic levels of a food web, a loss of energy could result in massive declines of fish biomass. We used compound‐specific nitrogen stable isotope data of amino acids (CSIA) to estimate and compare the nitrogen (N) sources and TPs of cod and flounder from FNC bloom influence areas (central Baltic Sea) and areas without it (western Baltic Sea). We tested if FNC‐triggered trophic lengthening in mesozooplankton is carried over to fish. The TP of cod from the western Baltic (4.1 ± 0.5), feeding mainly on decapods, was equal to reference values. Only cod from the central Baltic, mainly feeding on zooplanktivorous pelagics, had a significantly higher TP (4.6 ± 0.4), indicating a strong carry‐over effect trophic lengthening from mesozooplankton. In contrast, the TP of molluscivorous flounder, associated with the benthic food web, was unaffected by trophic lengthening and quite similar reference values of 3.2 ± 0.2 in both areas. This suggests that FNC blooms lead to a large loss of energy in zooplanktivorous but not in molluscivorous mesopredators. If FNC blooms continue to trigger the detour of energy at the base of the pelagic food web due to a massive heterotrophic microbial system, the TP of cod will not return to lower TP values and the fish stock not recover. Monitoring the TP of key species can identify fundamental changes in ecosystems and provide information for resource management.

Microbial eukaryotes play critical roles in maintaining the health and stability of lake ecosystems. Consequently, investigating the spatial and temporal evolution of microbial eukaryotic community structures and associated environmental drivers can inform water ecology studies and water environmental protection efforts. In this study, sediment core samples were collected from Lakes Chaohu, Erhai, Lugu and Fuxian in China to reconstruct lake microbial eukaryotic community succession using sediment DNA profiling methods. Mantel tests were used to identify the key factors influencing community succession and explore the mechanisms underlying ecological network changes. Statistical analyses revealed that community structures and diversity in Lakes Chaohu and Erhai shifted in the 2000s and 1980s, respectively, while the communities of Lakes Fuxian and Lugu did not exhibit significant changes during the study period, which may be due to the oligotrophic state of these two lakes. Ciliophora and Chlorophyta were the primary eukaryotic microbial taxa in the four lakes during the study period, with overall relative abundances of 27.2 % and 22.3 %, respectively. The diversities of microbial eukaryotic communities in the lakes were significantly correlated with nutrient enrichment and meteorological factors. Lastly, the ecological niche gap of microbial eukaryotes gradually overlapped after community shifts in Lake Chaohu, while biased interactions strengthened. Overall, this study reveals the impacts of long-term human activities and climate change on lake ecosystems from multiple perspectives of microbial eukaryotic community structure, diversity and ecological network, these findings will contribute to integrate microbial indicators in freshwater environmental monitoring in the future.

Remote sensing is a promising technology for global water eutrophication monitoring, and the quantity and representativeness of the observed samples influence its accuracy. Due to limitations in high costs in situ monitoring, current remote sensing of lakes often relies on models trained with water quality samples from a single season. However, the generalization ability of these single-season trained models to other seasons has not been extensively studied. In this study, focusing on 38 major lakes in the Yangtze River Basin, we utilized monthly chlorophyll-a (Chla) monitoring data and Sentinel-2 image datasets from 2016 to 2021 to assess the impact of different seasonal data-trained models on the performance of Chla concentration retrieval in lakes. The results indicate that: (a) The sampling time for lake Chla significantly affects the performance of the retrieval model. Based on the seasonal data, the trained models show an R2 range of 0.523 to 0.699, with a Bias ranging from −7.06 % to 7.74 %, while the models trained with full-season samples perform between the various seasonal models. (b) When models built with seasonal data are applied to full-season data retrieval, there is a noticeable decrease in performance. The R2 of the spring-winter data trained model drops by 18.2 %, with RMSL and MAPE increasing by 11.4 % and 4.2 %, respectively. Similarly, the model trained from summer-autumn data shows a 4.02 % decrease in R2, with RMSLE and MAPE rising by 2.76 % and 13.56 %, respectively. This suggests that using models established from seasonal samples to infer full-season Chla concentrations can amplify errors. (c) Compared to seasonal models, full-season models based on different seasonal sampling exhibit better performance (R2 = 0.585, RMSLE = 0.337, Bias = -3.12 %, MAPE = 34.71 %). R2, RMSLE, and MAPE are all superior to seasonal models. Therefore, when performing full-time and long-term retrieval of Chla concentrations in water bodies, it is necessary to use data sampled in different seasons to reduce the errors introduced by seasonal sampling. (d) Chla retrieval models were established for 38 typical lakes and reservoirs in the Yangtze River Basin using the full-time dataset, revealing that 25 % (7/28) of the lakes and 20 % (2/10) of the reservoirs showed significant alteration trends. The number of lakes with increasing Chla concentrations exceeded those with decreasing concentrations, indicating that there is still a substantial risk of eutrophication in the lakes and reservoirs of the Yangtze River Basin.

The article is devoted to the disclosure of the effect on the vital activity of cyanobacteria by changes in the nutrients in the chemical composition of artificial aquatic biotopes. The research results allowed us to establish that the dissolution of complex mineral fertilizer (nitrogen, phosphorus and potassium) in the range of up to 10 g/L contributes to the active development of cyanobacteria, which is accompanied by complete binding of mineral additives and absorption of oxygen. The addition of fertilizers in the amount of more than 1 g/L contributes to a sharp increase in the growth rate of the cyanobacteria population, which provokes the conditions for the blooming of the solutions. Enrichment of the nutritive base of biotopes ensures rapid growth of biocenosis and accelerated consumption of dissolved substances. The recorded average absorption rate of phosphorus reached more than 17 g/(L*day), and nitrogen – 30 g/(L*day). The formation of sediment and foam in the test vessels was associated with the depletion of nutrients and the death of hydrobionts. This phenomenon can serve as an indicator of oxygen decrease in the water. The results of the experiment confirmed the ability of cyanobacteria to transform nitrogen and phosphorus dissolved in water into bound organic forms with high intensity. This opens up the prospect of creating biological methods and means of wastewater demineralization.

Temporal patterns of biodiversity are often difficult to interpret because of our limited understanding of how communities vary through time and how processes drive this variation. A further challenge with dynamic systems is choosing an appropriate baseline against which biodiversity change is judged. We used abundance time series of breeding waterbirds in eutrophic lakes in Finland for 1946–2022 to study the dynamics of biodiversity change in local communities and the relative role of two presumed main drivers, i.e. eutrophication and alien predators, in contributing to historical and recent trends in local abundances and biodiversity. We set the cut-off for the historical and recent study periods in the mid-1980 s, because the systematic monitoring of breeding waterbirds in Finland started in 1986 and recent analyses of biodiversity change and population trends in European boreal waterbird communities are mainly based on time series and data gathered since 1986. Both species richness and the total abundance of waterbirds in local communities showed contrasting trends between historical (gathered before the mid-1980 s) and current (gathered after the mid-1980 s) community time series, with the current time series indicating a decline and the historical time series indicating an increase. The abundances of habitat specialists (species preferring eutrophic lakes) and habitat generalists (species using both eutrophic and oligotrophic lakes) showed a corresponding difference between the current and historical time series. The local extinction rates were higher among habitat specialists than among habitat generalists. The trend indices for wetland-nesting species (highly vulnerable to predation by two alien species (the raccoon dog, Nyctereutes procyonoides, and American mink, Neovison vison) in terms of nest site) abundances were more negative than the trend indices of species nesting further away from waterbodies (less vulnerable to predation by two alien species). In addition, bottom-feeding species (presumably more sensitive to negative impacts of eutrophication) did not show more negative population trends than surface-feeding species (presumably less sensitive to negative impacts of eutrophication). Regardless of equal sensitivity to negative impacts of eutrophication, two species highly vulnerable to two alien predators showed more negative population trends than a less vulnerable species. The results suggest that increased predation has been an important driver of the population and biodiversity declines in the studied waterbird communities. The mid-1980 s may not provide an ecologically appropriate baseline against which changes in the populations and biodiversity of boreal waterbird communities are judged.

Urbanization causes immense eutrophication pressure on small urban wetlands, which play a vital role in urban ecosystems. However, our comprehension of the prolonged impacts of eutrophication on these types of wetlands continues to be significantly limited. To address this knowledge gap, we analyzed monthly physical–chemical variables and seasonal phytoplankton and zooplankton communities at the Taipa-Coloane wetland in Macau, China, from 2013 to 2019. Through the generalized additive model (GAM) and principal component analysis (PCA), we found that the aquatic system mainly exhibited interannual variations instead of seasonal variations, with nutrient loads and river discharge (turbidity and salinity) being the most prominent features affected by anthropogenic activities and climate change. Over the years, the increasing turbidity and phytoplankton showed that bottom-up effects predominated the aquatic systems. Under the bottom-up effects of eutrophication and turbidity, the phytoplankton communities showed high adaptation that MP and S1 occupied more dominance after 2016, with higher abundance but lower diversity. Moreover, the bottom-up effects further affected the structure of zooplankton communities. The dominance of rotifers filter feeders (RF) decreased over the years while middle copepods and cladocerans filter feeders (MCF) increased, implying a trend of zooplankton toward large size over time. Overall, our result reveals the bottom-up control pattern in the aquatic systems of small urban wetlands. This research provides valuable insights into the dynamics and responses of plankton communities to environmental changes in small urban wetlands, providing valuable information for future conservation efforts.

Coastal nutrient loading has been linked to a decline in the capacity of seagrass ecosystems to sequester carbon (‘blue carbon’); however, the mechanisms are unclear. Here we investigated how nutrient loading can affect the contribution that seagrass plant material makes to blue carbon stocks by investigating plant quality-decomposition dynamics. Specifically, we used a combination of laboratory and field experiments to account for various changes in biogeochemical cycling from seagrass meadows, ranging from changes in leaf quality to CO2 fluxes. It was found that nutrient loading increased the ‘labile’ content of seagrass (i.e. increased levels of leaf nitrogen, phosphorus and soluble organic carbon (amino acid and soluble sugar content), and at the same time decreased levels of ‘recalcitrant’ carbon (i.e. materials that are harder for microbes to break down, such hemicellulose, cellulose and lignin contents). Nutrient-enriched leaves decomposed ∼ 18 % faster than non-enriched leaves (i.e. greater biomass loss from nutrient-affected seagrass), resulting in ∼ 80 % more CO2 emissions from nutrient-enriched seagrass. We also found that seagrass that naturally contained high levels of labile carbon at the start of the experiment were affected to a greater degree (i.e. higher CO2 emissions) by nutrients addition than seagrass that had high proportions of recalcitrant carbon to begin with. Overall, these findings suggest that nutrient loading can weaken the capacity of seagrass ecosystems to act as blue carbon sinks through its effect on seagrass leaf decomposability.

The Indian River Lagoon (IRL) on Florida’s east-central coast is a highly developed eutrophic estuary, experiencing harmful algal blooms (HABs). Beginning in 2011, the IRL experienced multiple phytoplankton HABs that were followed by widespread seagrass losses and expanding blooms of the rhizophytic macroalga Caulerpa prolifera. To better understand factors related to the changing benthic cover, long-term monitoring data spanning 2011–2020 for seagrass and C. prolifera percent cover at six locations in the northern IRL and Banana River Lagoon were considered in multivariate analyses with environmental parameters (temperature, salinity, pH, dissolved oxygen, etc.), dissolved nutrient and chlorophyll-a concentrations, and macroalgal carbon (δ13C) and nitrogen (δ15N) stable isotopes, elemental composition (%C, %N, %P), and nutrient ratios (C:N:P). Data reduction using the global Bio-Env + STepwise (BEST) procedure followed by linkage tree (LINKTREE) analyses indicated the variable most correlated to annual differences in benthic cover was macroalgal C:P. Following seagrass losses, P availability increased, as the result of heavy rainfall, increased sediment flux, and/or more bioavailable P due to seagrass losses. The most correlated variables among differences in location were C:P, δ13C, and salinity, which could be related to less urbanization at the northernmost sites that had lower percent cover of C. prolifera. While not identified as a significant variable, the increase in C. prolifera was associated with four years (2016–2019) of high ammonium concentrations (6.26 µM) and macroalgal δ15N values (+8.67 ‰), linking the blooms to the influence of human waste. The variables identified in this work as related to benthic cover suggest that reducing stormwater runoff and inputs of human waste will promote the recovery of seagrasses in the IRL. These findings have implications for urbanized estuaries experiencing seagrass loss globally.