Nutrient Load Reduction Research Articles

Evaluating best management practices for nutrient load reductions in tile-drained watersheds of the Laurentian Great Lakes Basin: A literature review.

Tile drainage systems are extensively implemented across the Laurentian Great Lakes Basin (GLB) to enhance agricultural productivity on poorly drained soils. However, these systems substantially contribute to excess nutrient runoff, particularly phosphorus (P) and nitrogen (N), exacerbating eutrophication and harmful algal blooms in the Great Lakes. This literature review synthesized current knowledge on nutrient loadings from tile-drained agricultural watersheds and evaluated the effectiveness of various agricultural best management practices (BMPs) in mitigating nutrient losses in the GLB. Through a meta-synthesis of field and watershed scale monitoring and modeling studies and statistical analysis using Box-Whisker plots and Monte Carlo simulations, we assessed the nutrient reduction potential of representative BMPs, including cover cropping, nutrient management, controlled drainage, and constructed wetlands in tile-drained landscapes. Findings indicated that individual BMPs substantially reduced nutrient loadings, but the effectiveness of these BMPs depended on site-specific factors, including climate conditions, soil type, and drainage system design. Integrated approaches at field, edge-of-field, and watershed scales with a combination of multiple BMPs enhanced nutrient reduction benefits, aligning with regional water quality targets. The review also highlighted the challenges of climate change that may undermine BMP performance by altering precipitation patterns and increasing extreme weather events. To address these complexities, we proposed a framework for developing adaptive BMP scenarios tailored to specific watershed conditions, emphasizing the need for long-term monitoring and hydrologic model enhancements. This framework was designed to help policymakers, stakeholders, and farmers protect water quality and balance agricultural productivity in the GLB and similar agricultural regions globally.

The Role of Internal Phosphorus Loading in the Archipelago Sea Ecological Status

In eutrophic aquatic ecosystems like the Archipelago Sea in the northern Baltic, the role of the sediment as a sink and source of nutrients is especially important. Based on previous research on the Archipelago Sea, it can be concluded that the amount of stored phosphorus that can be released with time from sediments is large, and internal phosphorus recycling processes may thus play a key role in phosphorus fluxes in the coastal zone. The release of nutrients from the sediment has been suggested as an explanation for the fact that a substantial reduction in the external nutrient load does not always result in a corresponding reduction in nutrient concentrations and phytoplankton biomass in recipient waters. However, the magnitude of the actual internal phosphorus load in the Archipelago Sea has not been successfully estimated, or the estimates have been evidently too high. In this study, calculations were performed based on the measured water quality data to estimate how much phosphorus has been transported from the bottom water layer to the surface layers during the biological production season for use in algal production. In other words, the magnitude of the effective internal phosphorus load in the Archipelago Sea was determined. The calculations resulted in a summer internal net phosphorus load in the surface layer of approximately 270 tons over 5 months. The other total phosphorus load in the Archipelago Sea, which mainly (60%) originates from the catchment area, was 575 t/a. A permanent way to mitigate internal loading has been thought to be to reduce external loading. However, a decrease in internal loading occurs with an unknown delay, making it impossible to predict the recovery rate.

Nutrient loading as a key cause of short- and long-term anthropogenic ecological degradation of the Salton Sea

The Salton Sea (SS), California’s largest inland lake at 816 square kilometers, formed in 1905 from a levee breach in an area historically characterized by natural wet-dry cycles as Lake Cahuilla. Despite more than a century of untreated agricultural drainage inputs, there has not been a systematic assessment of nutrient loading, cycling, and associated ecological impacts at this iconic waterbody. The lake is now experiencing unprecedented degradation, particularly following the 2003 Quantification Settlement Agreement—the largest agricultural-to-urban water transfer in the United States. Combined with high evaporation rates, reduced inflows have led to rapid lake shrinkage, with current maximum depths of only 10 m. Here we report distinct temporal and spatial patterns for nutrient dynamics at the SS for two decades spanning the period before and after major water transfer agreement. While external nutrient loading remains relatively consistent year-round, internal cycling varies seasonally. Winter exhibits high total phosphates and nitrate levels due to reduced primary productivity, with lower ammonium concentrations from increased oxygenation. Summer conditions shift to decreased phosphate and nitrate levels from enhanced primary production, sustained partly by internal phosphorus release from sediments during anoxic periods. Although N:P molar ratios can exceed 50:1 to 100:1 (far above the Redfield ratio of 16:1), phosphorus consistently remains at hypereutrophic levels (> 0.05 mg/L) challenging previous assumptions of phosphorus limitation. Post-2020 data show disrupted stratification patterns. Despite higher oxygen levels in bottom waters compared to 2004–2009, overall water column oxygenation has declined, reflecting altered hydrodynamics in the shallowing lake. These changes have intensified environmental challenges stemming from cultural eutrophication including harmful algal blooms, threatening both ecosystem and public health. Effective remediation will require significant reduction in external nutrient loading through constructed wetlands and/or treatment facilities at tributary mouths to reduce the lake’s overall nutrient inventory over time.

Geography, Trajectories, and Controls of Coastal Water Quality: More Rapid Improvement in the Shallow Zone of the Chesapeake Bay.

Many coastal ecosystems have suffered from cultural eutrophication and dead zones. In the Chesapeake Bay, water quality degradation is manifested in low dissolved oxygen, poor water clarity, and decreased submerged aquatic vegetation acreage. This research combines long-term monitoring data, science-based assessment methods, and novel data analysis approaches (i.e., machine learning) toward understanding the geography, trajectories, and controls of water quality in the Chesapeake Bay, which provides an example for the assessment and management of complex coastal ecosystems. Results showed that the attainment of water quality standards has improved in both the deep zone and the shallow zone since 1985, but the shallow zone has improved more rapidly. In addition, the attainment trajectory has been affected by mainly external drivers (i.e., nutrient reductions) and, to a lesser extent, internal drivers (i.e., water temperature and stratification). Reductions in nutrient loads would improve attainment, whereas warming and stratification would decrease attainment. Furthermore, scenario analyses demonstrated the importance of managing both nitrogen and phosphorus loads. Overall, the deep zone and the shallow zone showed different trajectories and controls, emphasizing the importance of geographical targeting with management actions.

Evaluation of drain quality and nutrient load management scenarios by using QUAL2kw model.

The examination of wastewater and effluents flowing into receiving water bodies is crucial for identifying pollutant sources and implementing scenarios to reduce them. In this study, QUAL2kw was used to identify, assess, and predict the pollutant load of a drainage canal located 6 km away from Anzali Wetland. Initially, the model was calibrated and validated with data collected in 2017. The NRMSE of the values was mostly less than 20%, except for flow accounting for 37% during calibration. The model did well in simulating EC and ammonium levels, but there is room for improvement in predicting nitrate and inorganic P concentrations. Field visits and sampling were done during the rice growth period in April-June 2021. The model was simulated for a three-time series in 2021; the simulation showed that May was the most critical, as the levels of nitrates, ammonium, and phosphates were at their highest. This study focused on the employment of QUAL2kw to drainage canals, emphasizing its suitability for regions with limited data availability. Scenarios were employed to explore ways to enhance water resource quality, showcasing how targeted interventions can effectively mitigate nutrient loads. Scenarios were considered to reduce nutrient loads. Reducing the amount of fertilizer led to a 9-27% while applying water stress resulted in a 0.1-1% reduction in the discharge outflow from the drain and less than 1% reduction in the amount of ammonium and nitrate. It is concluded that reduction in fertilization is more efficient in reducing concentrations and pollutant loads at the exit point of the canal to water resources compared to applying water stress since urea fertilizer contains a high percentage of nitrogen, and declining water application can enhance the soil's nutrient retention ability but only to a small degree.

Simulating water balance and nutrient losses in a pastoral catchment using the SWAT+ model: added value of isotope data

ABSTRACT New Zealand’s freshwater is under increasing pressure from intensified dairy farming. This study assesses agricultural nitrogen loads from small pastoral catchments contributing to eutrophication and periodic algae blooms in a lake. Using the Soil and Water Assessment Tool (SWAT+), we simulated hydrological processes and nutrient loads, incorporating water (δ2H, δ18O) and nitrate (δ15N, δ18O) isotope data to improve model performance. The SWAT+ model was calibrated and validated with flow and nitrate data, achieving R2 values of 0.65–0.90, Nash-Sutcliffe efficiency (NSE) of 0.46–0.82, and percent bias (PBIAS) between 10.24% and 33.48%. The study demonstrates that stable isotope insights can enhance SWAT+ modelling accuracy and highlight the need for better fertilizer management to reduce nutrient loads.

Bioremediation of nitrate in agricultural drainage ditches: Impacts of low-grade weirs on microbiomes and nitrogen cycle gene abundance

Artificial drainage is essential for the success of modern agriculture, but it can also accelerate the movement of nutrients, especially nitrate, from soil to surrounding and downstream water bodies. Removal of nitrate from agricultural drainage by using controlled drainage systems, such as ditches installed with low-grade weirs, has been shown to help reduce nutrient loading into watersheds. However, the effect of low-grade weirs varies greatly, likely due to the differences in climate, system designs (e.g., hydraulic characteristics), and the resulting variation in microbial structures and functions in the ditch. In this study, we analyzed the temporal and spatial dynamics of microbiomes in a paired ditch system with weir-installed and uninstalled (control) channels over two years by using the 16S rRNA gene amplicon sequencing and the high-throughput quantitative PCR targeting various N cycle-associated genes [the Nitrogen Cycle Evaluation (NiCE) chip]. The installation of the low-grade weir had a significant impact on the microbiome structure and the distribution of denitrifiers. Microbiome structures also differed significantly between the ditch inlets and the outlets. Denitrification functional genes were more abundant in the inlets than in the other locations and in the channel installed with a low-grade weir. Additionally, oxygenic denitrifiers that use nitric oxide dismutase (nod) to produce N2 and O2 gases from nitric oxide were detected in the ditch channels, suggesting the occurrence of nitrate removal process that bypasses the production of nitrous oxide (N2O). The ditch microbiomes sampled during high-flow seasons (i.e., spring and fall) exhibited greater similarity to each other than microbiomes sampled during low-flow seasons (i.e., summer). Taken together, this study indicates that the low-grade weirs have the potential to foster a more favorable environment for denitrifiers, resulting in an increase in the abundance of denitrification functional genes. These findings could offer valuable insights into system management and optimization strategies.

Lake Restoration Improved Ecosystem Maturity Through Regime Shifts—A Case Study of Lake Baiyangdian, China

Lake ecosystems are impacted by anthropogenic disturbances and have become vulnerable worldwide. Highly disturbed lake ecosystems are not well understood due to the lack of data on changes in the structures and functions of ecosystems. In this paper, we focus on Lake Baiyangdian (BYDL), the largest shallow lake in North China. Following the establishment of the Xiong’an New Area (XNA) in 2017, concerted efforts to restore BYDL’s aquatic environment have been undertaken, which has led to significant changes in the structures and functions of the ecosystems. We evaluated the biomass dynamics of main biological communities and detected the regime shifts of environmental factors in BYDL from 2016 to 2023. Further, we constructed a food web model for the BYDL ecosystem in 2023 by using Ecopath with Ecosim (EwE) and made a comparison with the reported results in 2018. The results showed significant changes in the ecosystem structure of BYDL over the last 6 years. In 2023, the submerged macrophytes biomass in the system increased by 4.2 times compared to 2018, leading to an increase in total system throughput. We found that BYDL changed from an algal-type lake to a macrophyte-dominated lake. In addition, we found TN, NH4+-N, and CODMn were significantly decreased in BYDL during the restoration. TN and NH4+-N had a change point in approximately 2021, indicating that a regime shift had occurred during restoration. Overall, the BYDL ecosystem was in an immature but developing state, as indicated by ecological network analysis indicators. Nutrient-loading reduction, hydrological regulation, and rational biomanipulation may be the potential driving factors of change in the BYDL ecosystem. We strongly recommend the timely harvesting of submerged macrophytes, the proliferation and release of herbivorous fishes, and the assessment of the ecological capacity of carnivorous fishes in the future ecological restoration of BYDL.

Water quality–fisheries tradeoffs in a changing climate underscore the need for adaptive ecosystem–based management

Changes driven by both unanticipated human activities and management actions are creating wicked management landscapes in freshwater and marine ecosystems that require new approaches to support decision-making. By linking a predictive model of nutrient- and temperature-driven bottom hypoxia with observed commercial fishery harvest data from Lake Erie (United States-Canada) over the past century (1928-2022) and climate projections (2030-2099), we show how simple, yet robust models and routine monitoring data can be used to identify tradeoffs associated with nutrient management and guide decision-making in even the largest of aquatic ecosystems now and in the future. Our approach enabled us to assess planned nutrient load reduction targets designed to mitigate nutrient-driven hypoxia and show why they appear overly restrictive based on current fishery needs, indicating tradeoffs between water quality and fisheries management goals. At the same time, our temperature results show that projected climate change impacts on hypoxic extent will require more stringent nutrient regulations in the future. Beyond providing a rare example of bottom hypoxia driving changes in fishery harvests at an ecosystem scale, our study illustrates the need for adaptive ecosystem-based management, which can be informed by simple predictive models that can be readily applied over long time periods, account for tradeoffs across multiple management sectors (e.g., water quality, fisheries), and address ecosystem nonstationarity (e.g., climate change impacts on management targets). Such approaches will be critical for maintaining valued ecosystem services in the many aquatic systems worldwide that are vulnerable to multiple drivers of environmental change.

Individual and combined effects of sodium dichloroisocyanurate and isothiazolinone on the cyanobacteria-Vallisneria natans-microbe aquatic ecosystem

The use of algaecides to control high-density cyanobacterial blooms is often complicated by secondary pollution and the toxicity to non-target organisms. This study investigates the individual and combined effects of sodium dichloroisocyanurate (NaDCC, 5, 50, and 100 mg/L) and isothiazolinone (0.1, 0.5, and 1.5 mg/L) on a cyanobacteria-Vallisneria natans-microbe aquatic ecosystem, focusing on their interactions and ecological impacts. Results indicate that NaDCC could achieve a higher algae removal rate than isothiazolinone within 15 days, but has a greater negative effect on Vallisneria natans. Both algaecides disrupt nutrient and secondary metabolite balances at low and high concentrations, increasing nutrient loads and harmful substances. Optimal results were obtained with low concentrations of NaDCC (5 mg/L) and isothiazolinone (0.1 mg/L), effectively controlling cyanobacteria while minimizing harm to Vallisneria natans and reducing nutrient loads and microcystin accumulation. Algaecide application enhanced microbial diversity in water and leaves, shifting the dominant community from cyanobacteria to organisms adapted to the post-cyanobacterial decay environment. Metabolomic analysis indicated increased secretion of lipids and organic acids by cyanobacteria in response to algaecide stress. High concentrations of NaDCC and isothiazolinone disrupted nitrogen metabolism in cyanobacteria and induced ROS overproduction, affecting unsaturated fatty acid synthesis and other metabolic pathways. These findings highlight the importance of exploring different combinations of algaecides to reduce their concentrations, balance algal control with ecological stability, and offer insights for effective eutrophication management.

Disaster avoided: current state of the Baltic Sea without human intervention to reduce nutrient loads

Disaster avoided: current state of the Baltic Sea without human intervention to reduce nutrient loads

Mitigating inland waters’ greenhouse gas emissions: current insights and prospects

ABSTRACT Natural and constructed inland waters emit globally significant amounts of greenhouse gasses (GHGs) into the atmosphere. As a result of human-induced alterations in the landscape, these emissions tend to increase. While proper management of waterbodies is fundamental to reaching the global sustainable development goals as well as the Paris Agreement, insights on climate-smart inland water management are still underexplored. Here we review and discuss physical, chemical, and biological management measures applied in a wide range of inland waters to (1) reduce external loads of compounds fueling aquatic GHG emissions, (2) reduce the aquatic production of GHG-fueling compounds, and (3) minimize GHG production and stimulate GHG consumption. Some measures are well studied and others are in the exploration phase, resulting in a varying degree of confidence with respect to their effectiveness. Climate-smart water management (e.g., through the reduction of organic matter and nutrient loading) generally not only reduces GHG production and emission but also improves the ecological state of aquatic environments. Reductions in GHG emissions from 5% (fish effect) to ∼90% (salinization effect) were observed among the climate-smart measures discussed here. Certainly, the global effect of the different measures also depends on the application scale. Depending on the local context, the implementation of one or more of these measures can be considered in a GHG mitigation program.

Ex-situ restoration of the Mediterranean forest-forming macroalga Ericaria amentacea: Optimizing growth in culture may not be the key to growth in the field

Evidence of local and regional declines in the canopy-forming alga Ericaria amentacea, a foundation species of diverse marine forest communities on exposed Mediterranean coasts, have spurred restoration efforts focused on sustainable ex-situ techniques. The need to balance the costs of culture maintenance and the susceptibility of early life stages to stressors in the native habitat, including rapid, often extreme shifts in temperature, hydrodynamics and nutrient availability, have driven current efforts to create a culture environment that primes seedlings for outplant, increasing their resilience rather than maximizing growth. We tested the effects of 1) higher culture temperature (25 °C) combined with wave simulation and 2) reduced nutrient loads (10% of standard protocol) with wave simulation on post-culture and post-outplant outcomes relative to optimal growth conditions in established protocols (20 °C, no waves, high-nutrient culture medium). While increased temperature and water motion negatively affected seedling growth in culture, and higher nutrients caused oxidative stress likely associated with enhanced epiphyte overgrowth, these effects were not clearly translated into patterns of long-term growth in the field. Instead, survival in the initial days post-outplant appeared to be the bottleneck for restoration potential, where substrates with persisting seedlings at one month were generally found with flourishing juveniles at four months. Larger clumps of seedlings, in turn, were strongly associated with both initial survival and future growth. These results underscore the importance of the zygote settlement phase to establish high seedling densities, which may be optimized by phenological monitoring of the donor population. They also suggest that less-controlled, more environmentally-realistic culture conditions involving the introduction of mild stress may enhance the survival of early life stages of E. amentacea during the transition to the native environment, providing a means to simultaneously reduce human resource costs in culture and move toward scaling up.

Long-term responses of internal environment dynamics in a freshwater lake to variations in external nutrient inputs: A model simulation approach

Lake restoration usually focuses on reducing external nutrient sources. However, when sediments contain nutrients accumulated over multiple years, internal nutrient release can delay restoration progress. In lake restoration and management, it is important to understand the dynamic relationship between nutrient concentrations in a lake and internal and external nutrient sources. In this study, we quantified external nutrient inputs through measurements and compared them with internal sediment release from simulation using the PCLake+ model. Additionally, we evaluated alterations in the internal nutrient release, lake nutrient concentrations, and algae biomass (chlorophyll-a) within the lake following varying degrees of reduction in external nutrient loads. The results demonstrate that the PCLake+ effectively simulated the lake's nutrient concentration and algae biomass. Based on the PCLake+ estimates, internal nutrient loads accounted for 51 % of the total nitrogen (N) and 80 % of the total phosphorus (P) loadings in Lake Erhai in 2019. In 2020, the total contributions were 43 % for TN and 72 % for TP. We simulated four scenarios where external nutrient inputs were reduced to 25 %, 50 %, 75 %, and 99.99 % of their original levels. The 40-year simulation showed that the lake's ecological system initially exhibited a fast internal response but reached equilibrium after eight years. P concentrations took longer to reach equilibrium compared to N concentrations, probably due to the stronger binding characteristics of P. To meet the water quality target in the future, it is necessary to reduce external N and P inputs into Lake Erhai by at least 23 % and 15 %, respectively, under current conditions. Although reducing external nutrient loads can indirectly lower internal nutrient loads, water management should address both external and internal loads simultaneously, as internal release cannot be effectively reduced by external reductions alone. Additionally, the lake's internal release may continue for several years, even with reductions in external inputs.

Hysteretic and asynchronous regime shifts of bacterial and micro-eukaryotic communities driven by nutrient loading

Nutrient pollution is pervasive in many urban rivers, while restoration measures that reduce nutrient loading but fail to improve biological communities often lack effectiveness due to the indispensable role of biota, especially multi-taxa, in enhancing ecosystem stability and function. The investigation of the response patterns of multi-taxa to the nutrient loading in urban rivers is important for the recovery of biota structure and thus ecosystem function. However, little is known about the response patterns of multi-taxa and their impact on ecosystem structure and function in urban rivers. Here, the study, from the perspective of alternative stable states theory, showed the hysteretic response of both bacterial and micro-eukaryotic communities to nutrient loading based on the field investigation and environmental DNA metabarcoding. Bistability was shown to exist in both bacterial and micro-eukaryotic communities, demonstrating that the response of microbiota to nutrient loading was a regime shifts with hysteresis. Potential analysis then indicated that the increased nutrient loading drove regime shifts in the bacterial community and the micro-eukaryotic community towards a state dominated by anaerobic bacteria and benthic Bacillariophyta, respectively. High nutrient loading was found to reduce the relative abundance of metazoan, but increase that of eukaryotic algae, which made the trophic pyramid top-lighter and bottom-heavier, probably exacerbating the degradation of ecosystem function. It should be noted that, in response to the reduced nutrient loading, the recovery threshold of micro-eukaryotic communities (nutrient loading = ∼0.5) was lower than that of bacterial communities (nutrient loading = ∼1.2), demonstrating longer hysteresis of micro-eukaryotic communities. In addition, the markedly positive correlation between the status of microbial communities and N-related enzyme activities suggested the recovery of microbial communities probably will benefit the improvement of N-cycling functionality. The obtained results provide a deep insight into the collapse and recovery trajectories of multi-trophic microbiota to the nutrient loading gradient and their impact on the N transformation potential, therefore benefiting the restoration and management of urban rivers.

Low-dose natural clay Kaolin promotes the growth of submerged macrophytes and alters the rhizosphere microorganism community: Implications for lake restoration

Sediment properties have a crucial effect on the growth and recovery of aquatic plants in lakes. Addition of various chemical substances has been proposed to reinforce the recovery of plants after a nutrient loading reduction. However, the effects of such sediment amendments on plant growth, especially those from rhizosphere microorganisms, is limited. We added Kaolin clay to sediments in different concentrations to explore its impact on the growth of Vallisneria natans and Ottelia acuminate and the concurrent shift in rhizosphere microorganisms using high-throughput sequencing technology. We found that the addition of low doses (10 % and 20 % in mass ratio) of Kaolin significantly modified sediment conditions (oxidation reduction potential and pH), with implications also for the composition, diversity, and stability of rhizosphere microorganisms. LEfSe analysis revealed that low-dose addition of Kaolin increased the abundances of functional microbial groups that benefit plant nutrient absorption and enhance plant stress resistance, such as Spirillaceae, Rhodocyclaceae, and Burkholderiales. Moreover, low doses of Kaolin significantly promoted the photosynthesis and nutrient absorption of submerged macrophytes, thereby facilitating plant growth. A structural equation model (SEM) indicated that the direct impact of Kaolin on the growth of submerged plants was relatively minor, while the indirect effect through modulation of rhizosphere microorganisms was important. Our study suggests that low doses of Kaolin may be used to promote the growth of submerged macrophytes when lakes with a high organic content in the sediment are recovering after nutrient loading reduction.

Marked interannual variability in the relative dominance of phytoplankton over submerged macrophytes rather than regime shifts in a shallow eutrophic lake: Evidence from long-term observations

The theory of regime shift is rooted in the concept of fold catastrophe and posits the existence of alternative stable states, such as a lake dominated by phytoplankton or macrophytes under similar environmental conditions. Although regime shifts have been reported in many shallow lakes, recent evidence has revealed that a linear rather than dual relationship between chlorophyll-a (Chla) and nutrients is more common, indicating that regime shifts are rare in nature. Here, long-term field observations and the coverage of the submerged macrophyte area (SMA) retrieved from remote sensing (RS) images of Yilong Lake, in which regime shifts have been reported, were used to re-examine the presence or absence of regime shifts and to explore the drivers of abrupt changes. During the past three decades, Yilong Lake has experienced three abrupt changes in water quality, phytoplankton biomass (Chla) and the SMA. However, the relationship between Chla and nutrients was significantly linear, and the state variables (Chla, Secchi depth and SMA) changed along the gradient of environmental stress, which demonstrates the absence of regime shifts and instead highlights the presence of marked interannual changes. Moreover, we found that nutrients and water depth are the main environmental factors driving the establishment/collapse of the SMA and shaping the relative dominance of phytoplankton over the SMA, further inducing rapid changes in nutrient cycling and water quality in Yilong Lake. The significant interannual variability in the SMA and Chla in Yilong Lake reflects a pronounced weakening of resilience. To enhance resilience, an adaptive strategy involving external nutrient loading reduction, water level management and biodiversity restoration is proposed.

Geographically driven shifts in land use influence phytoplankton community patterns in the Inner Mongolian Plateau lakes

Abstract Phytoplankton play an irreplaceable role as producers in maintaining lake ecosystems. Nevertheless, scant attention has been given to investigating the dispersion of phytoplankton communities and the factors influencing them across expansive areas. In this study, we present the results of a survey on the distribution of phytoplankton community and the effects of different driving factors in 11 lakes along Inner Mongolia in July–August 2020. Non-metric multidimensional scaling analysis and variance decomposition (VPA) were used to elucidate the distribution of phytoplankton communities and the response of drivers. A total of 169 species of phytoplankton from 8 phyla were detected. Both the abundance and diversity of phytoplankton in the Inner Mongolia lakes showed a trend of high in the east and low in the west (with Daihai Lake as the boundary). The Margalef index of phytoplankton significantly negatively correlated with salinity (r = −0.707, P < 0.05) and total dissolved solids (r = −0.720, P < 0.05), and both density and biomass highly significantly positively correlated with the suspended solids, Chlorophyll a and trophic level index. The VPA explained 38.9% of the changes in the phytoplankton community with the highest rate of explanation of land use. Therefore, preventing anthropogenic impacts, as well as reducing nutrient loads, can effectively ensure the ecological diversity of lake phytoplankton in lake populations with large geographical spans and varying levels of nutrients.

Cross-watershed leakage of agricultural nutrient runoff

Agricultural nutrient runoff has been a major contributor to hypoxia in many downstream coastal ecosystems. Although programs have been designed to reduce nutrient loading in individual coastal waters, cross watershed interdependencies of nutrient runoff have not been quantified due to a lack of suitable modeling tools. Cross-watershed pollution leakage can occur when nutrient runoff moves from more to less regulated regions. We illustrate the use of an integrated assessment model IAM that combines economic and process-based biophysical tools to quantify Nitrogen loading leakage across three major US watersheds. We also assess losses in consumer and producer surplus from decreased commodity supply and higher prices when nutrient delivery to select coastal ecosystems is restricted. Reducing agricultural N loading in the Gulf of Mexico by 45% (a) increases loading in the Chesapeake Bay and Western Lake Erie by 4.2% and 5.5%, respectively, and (b) results in annual surplus losses of $7.1 and $6.95 billion with and without restrictions on leakage to the Chesapeake Bay and Lake Erie, respectively.

Seagrass recovery trajectories and recovery potential in relation to nutrient reduction

Abstract Seagrass recovery has been reported across the globe where previously eutrophied waters have become less nutrient‐rich. In the European Wadden Sea, different recovery trajectories were found after riverine nutrient loads decreased, namely full, temporary and no recovery. We compiled intertidal seagrass presence (Zostera noltei and Z. marina) and eutrophication data for 1930–2020, to relate the seagrass trajectories and regional eutrophication differences to riverine nutrient loads, and inferred prospects for seagrass recovery. Seagrass fully recovered in the less eutrophic North Frisian region. The recovery trajectory was tightly coupled to riverine nutrient load reduction. Relative seagrass area (meadow area/region area) dropped from 10% prior to eutrophication to 2% during the eutrophication peak, increased to 7% during the nutrient reduction period and subsequently expanded to 13%. Colonization of marginal habitats was observed, indicating propagule spillover from neighbouring meadows. The more eutrophic southern regions showed no or only temporary seagrass recovery. Prospects for (limited) recovery are good in only two out of four southern regions, provided that riverine nutrient loads are further reduced by ~40% (reference: 2010–2017). Without this reduction, seagrasses may only temporarily recover and will remain vulnerable to erratic disturbances like macroalgae accumulation or storms. Historical evidence and application of habitat suitability models suggest that the potential relative seagrass area in the southern regions is low: less than 0.2% in the western Dutch region and maximum 2.4% in the Ems‐Jade region. Synthesis and applications. Within a large seascape (15,000 km2) the least eutrophicated region showed seagrass recovery upon nutrient reduction. We translated the critical riverine nutrient loads for this recovery, via regional eutrophication indicators, to loads that may enable a sustained recovery in the other regions. This technique is applicable in other complex systems, provided sufficient historical data are available. Propagule spillover exerts a positive feedback at metapopulation scale leading to acceleration of recovery. Occupied and potential seagrass habitat (e.g. assessed by the maximum recorded area in the past) are thus important landscape selection criteria for restoration, particularly when eutrophication is not yet sufficiently reduced.