Eutrophic Lake Research Articles

Analysing the spatiotemporal variation and influencing factors of Lake Chaohu's CDOM over the past 40 years using machine learning

AbstractChromophoric dissolved organic matter (CDOM) in aquatic environments is an important component of the biogeochemical cycle and carbon cycle. The aim of this study is to investigate the long‐term changes in CDOM in shallow and eutrophic Chaohu Lake, as well as its relationship with climate, environment and social factors. Using long time series Landsat image data and machine learning technology, the spatiotemporal evolution of Chaohu CDOM since 1987 was reconstructed. A total of 180 samples were collected, which were divided into three parts based on regional and hydrological characteristics. The results show that the water quality in different regions were significantly different, and TN may be the key factor driving the change of CDOM in Chaohu Lake. Machine learning algorithms including random forest (RF), support vector regression (SVR), neural network (NN), multimodal deep learning (MDL) model and Extreme Gradient Boosting (XGBoost) were used, among which XGBoost model performed best (R2 = 0.955, mean absolute error [MAE] = 0.024 mg/L, root mean square error [RMSE] = 0.036 mg/L, bias = 1.005) and was used for CDOM spatiotemporal variation retrieval. The change of CDOM was seasonal, highest in August (0.67 m−1) and lowest in December (0.48 m−1), and the western lake is the main source of CDOM. Annual variability of the CDOM indicates that it began to decline after the completion of water pollution control in 2000. Temperature changes were closely related to CDOM (P < 0.01) and agricultural non‐point source pollution plays an important role in Chaohu Lake. This study will provide feasible methods and scientific basis for the long‐term remote sensing supervision of CDOM.

Are increasing roosting waterbird numbers responsible for eutrophication of shallow lakes? Examples from a Danish Ramsar site

AbstractThe Water Framework Directive (WFD) requires actions from European Union Member States to reduce external nutrient loading in lakes of moderate/poor/bad ecological status and restore their good ecological status. Several poor-quality Danish lakes have been exempted from WFD criteria (and more proposed), due to suspected major imported nutrient contributions from waterbirds, without supporting evidence. Here, we estimated relative nutrient contributions from increasing numbers of roosting waterbirds compared to total nutrient loadings in four brackish lakes (43–491 ha) at an internationally important Ramsar site/EU Birds Directive Special Protection Area. Combining night- and daytime counts of roosting numbers of the most numerous species with intake and faecal output models, we estimated roosting birds (mostly geese) contributed 0.2–0.4% of all N inputs (0.3–1.2 kg N/ha/year) and 0.6–2.0% of all P inputs (0.04–0.12 kg P/ha/year) in three lakes (one of which has been proposed exempted from WFD criteria), but potentially as high as 14% and 76%, respectively, at a fourth clearwater lake without direct inflow or outlets. These results confirm the need for case-by-case assessments of avian nutrient import relative to total nutrient balance before exempting lakes from WFD conditions due to supposed natural loading from waterbirds.

Periphyton bioaccumulation and biosorption potential: in-situ experiment in a eutrophic, mixohaline lake ecosystem (Tierra del Fuego, Argentina)

Periphyton is gaining relevance in bioremediation of polluted aquatic ecosystems because of its ubiquity and cost-effectiveness. The aim of this work was to study phosphorus and nitrogen bioaccumulation by periphyton grown on artificial substrata as a remediation strategy in two points (EB1 and EB2) in the Encerrada Bay, a mixohaline, eutrophic lake ecosystem in the City of Ushuaia (Tierra del Fuego, Argentina). In addition, the biosorption potential of the harvested periphytic biomass was assessed, using several organic molecules, including an emerging pollutant. Maximum nitrogen (N) accumulation was achieved after 4 months of colonization of the substrata for EB1 and 2 months for EB2 (1185.9 and 645.9 mg N m−2, respectively). Also, maximum phosphorous (P) accumulation was achieved after 4 months of colonization of the substrata for EB1 and 2 months for EB2 (34.4 and 17.5 mg P m−2, respectively). Once harvested, the dried biomass could be used in biosorption processes for different organic pollutants, as removal efficiencies were above 80% and 60% for dyes methylene blue and crystal violet, respectively, and almost 40% for the emerging pollutant oxytetracycline. These biosorption results are particularly interesting because it would suggest that it is a promising biomass reutilization strategy in the framework of circular economy.

Purification Efficiency of Two Ecotypes of Wetland Plants on Subtropical Eutrophic Lakes in China

Purification Efficiency of Two Ecotypes of Wetland Plants on Subtropical Eutrophic Lakes in China

Anatomical hooking location and bleeding occurrence in northern pike (Esox lucius) caught in recreational catch-and-release angling in a lake with reduced prey fish availability

Catch-and-release (C&R) is a common practice in recreational angling for northern pike (Esox lucius), whereby the angler releases the fish back into the water after capture with the expectation that it will survive with negligible stress and physical injuries. This may not always be the case, as hooking in critical anatomical locations, such as gills, esophagus, and stomach, increases the frequency of bleeding at the hook wound and has been recognized as a key determinant of post-release mortality in pike. Several factors (e.g. bait type and size, hook characteristics, and fish length) can influence the risk of hooking in critical locations, and the fish’s willingness to strike the fishing lure/bait may largely depend on previous feeding history and associated motivation to feed. In this respect, food deprivation and greater feeding motivation can be expected to result in an intensified response and more forceful attacks on fishing lures/baits, which could increase the risk of hooking injuries in sensitive tissues, as the fish may ingest the hook more deeply. Here, we assess the hooking location and bleeding occurrence in pike caught on soft plastic shads and baitfish in a shallow eutrophic lake. The prey fish density of this lake, primarily common roach (Rutilus rutilus), has been substantially reduced by seining as part of a lake restoration project. Experimental angling sessions took place at the end of 2020 and 2022, approximately 1–2 months and 25–26 months after the initial reduction in prey fish density, respectively. Removal of roach from the lake was also done regularly by seining after the angling sessions in 2020. Pike angled in 2022 had significantly lower body condition than individuals caught in 2020, indicating that mass removal of roach from the lake resulted in food shortage. The risk of hooking in critical locations (herein defined as hooking in gills and back of mouth) was not associated to angling year, body condition, or length of the pike. However, across the two angling years, the incidence of hooking in critical locations was higher for soft plastic shads compared to baitfish (24.2% versus 7.4%). Pike caught on soft plastic shads also bled more frequently than individuals caught on baitfish (19.7% versus 6.2%), most likely due to the fact that hooking in the gills almost exclusively occurred with soft plastic shads. Bleeding propensity was also not related to angling year, body condition, or fish length. Hence, the present study found no evidence that long-term reductions in food availability and resulting declines in body condition influence how pike strike and ingest fishing lures/baits, at least not in a manner that increases the risk of hooking injuries in sensitive locations. Instead, bait type seems to play the largest role for the observed bleeding patterns. We recommend that future studies investigate the potential effects of C&R angling on the post-release survival of pike with reduced body condition due to limited food availability.

What's good for fish is good for fishes: Interspecific consistency of growth, condition, and abundance among glacial lakes

AbstractObjectiveFish abundance and growth are regulated by a combination of bottom‐up and top‐down forces, but many management techniques depend more heavily on the latter. Here, we evaluated whether intersystem variation in nutrient loading and bottom‐up forces play more dominant roles in the control of abundance and growth of species across similar lakes than intra‐ and interspecific compensatory effects. We aimed to assess whether patterns of abundance and growth are consistent among fish species across lakes.MethodsWe tested this by evaluating pairwise comparisons of catch‐per‐unit‐effort, condition, and length‐at‐age data for 11 common warmwater fish species from 184 mesotrophic and eutrophic glacial lakes in Indiana, United States. We characterized the environmental conditions of each lake using limnological measurements (e.g., chlorophyll‐a concentration and surface temperature), lake morphology descriptions (e.g., depth and size), catchment characteristics (e.g., percent agricultural land cover), and nutrient load modeling using the Long‐Term Hydrologic Impact Analysis model. Taking a meta‐analysis approach, we used effect size calculation from pairwise correlations among lakes to identify environmental and community impacts on species abundance, condition, and length at age.ResultWe demonstrated that there were positive associations among most species comparisons (i.e., multiple species experiencing relatively fast growth in the same lake). Evaluations of environmental conditions among systems suggested that differences in estimated phosphorus input and the limnological measurements of total phosphorus, Secchi depth, and chlorophyll‐a concentration were good predictors of length at age and catch per unit effort for fish.ConclusionOur results indicated that there is a strong and consistent influence of environmental conditions and bottom‐up processes in determining species abundance and growth. This suggests that bottom‐up forces and environmental conditions linked to nutrient loading likely determine the upper boundary of fish abundance and growth in these lakes.

Impacts of microplastic contamination on the rheology properties of sediments in a eutrophic shallow lake

Microplastic (MP) contamination is a growing global concern, with lake sediments serving as a significant sink for MP due to both anthropogenic and natural activities. Given the increasing evidence of MP accumulation in sediments, it was crucial to assess their influence on sediment erosion resistance, which directly affected sediment resuspension. To fill this gap, this study focused on the effect of MP on the sediments rheological properties. After 60-day experiments, it was found that MP addition into sediments reduced sediment viscosity, yield stress, and flow point shear stress. Meanwhile, MPs also significantly altered sediment properties and extracellular polymer composition. MP addition reduced extracellular polymeric substances production and cation exchange capacity, which then worked together and led to a weak sediment structure. Seemingly, MPs changed fluid sediment characteristics and caused stronger fluidity under less shear force. Consequently, the accumulation of MP might facilitate the resuspension of sediments under smaller wind and wave disturbances. This study provided novel insights into the direct impact of MPs on sediment physical properties using rheology, thereby enhancing our understanding of the environmental behavior of MPs in lake ecosystems.

Organic matter content and source is associated with the depth‐dependent distribution of prokaryotes in lake sediments

Abstract Aquatic sediments harbour a diverse array of microorganisms that drive organic matter recycling, carbon sequestration and greenhouse gases (e.g., CO2, CH4, N2O) emissions. Although largely studied in water columns, vertical profiles of the diversity and composition of prokaryotic communities (i.e., Bacteria and Archaea) in aquatic sediments are still rare. More specifically, much remains to be learnt about their vertical distribution in lake sediments and how environmental conditions at the time of burial have impacted their diversity and composition. We investigated the vertical distribution of prokaryotic community with 16S rRNA gene quantitative (q)PCR and metabarcoding approaches applied to 93 sediment layers collected in a 2‐m‐long sediment core from the eutrophic alkaline Lake Chenghai in subtropical China. We aimed to study the diversity, composition and structure distribution of the prokaryotic community as well as environmental factors influencing it. Bacterial abundance was found to decrease with sediment depth although the richness of both bacterial and archaeal assemblages slightly increased with sediment depth. In terms of composition, a strongly stratified sediment–depth pattern was observed in which Proteobacteria, Desulfobacterota, Bacteroidota and Verrucomicrobiota dominated the inventories in the surface sediment layers, whereas Chloroflexi, Spirochaetota, Planctomycetota, Crenarchaeota were more abundant in the deep sediment layers. Organic matter contents and sources were identified as major factors shaping the structure of the prokaryotic community. Overall, our study provides new evidence about how lake sediment's prokaryotic community are linked to external sources of energy. This complement existing data from other lake systems towards a better understanding of sediment prokaryotic community's contribution to biogeochemical cycle in lakes.

Effects of exotic detritus input on native litter breakdown in a eutrophic lake: investigating the home-field advantage

Effects of exotic detritus input on native litter breakdown in a eutrophic lake: investigating the home-field advantage

Seasonal changes in N-cycling functional genes in sediments and their influencing factors in a typical eutrophic shallow lake, China.

N-cycling processes mediated by microorganisms are directly linked to the eutrophication of lakes and ecosystem health. Exploring the variation and influencing factors of N-cycling-related genes is of great significance for controlling the eutrophication of lakes. However, seasonal dynamics of genomic information encoding nitrogen (N) cycling in sediments of eutrophic lakes have not yet been clearly addressed. We collected sediments in the Baiyangdian (BYD) Lake in four seasons to explore the dynamic variation of N-cycling functional genes based on a shotgun metagenome sequencing approach and to reveal their key influencing factors. Our results showed that dissimilatory nitrate reduction (DNRA), assimilatory nitrate reduction (ANRA), and denitrification were the dominant N-cycling processes, and the abundance of nirS and amoC were higher than other functional genes by at least one order of magnitude. Functional genes, such as nirS, nirK and amoC, generally showed a consistent decreasing trend from the warming season (i.e., spring, summer, fall) to the cold season (i.e., winter). Furthermore, a significantly higher abundance of nitrification functional genes (e.g., amoB, amoC and hao) in spring and denitrification functional genes (e.g., nirS, norC and nosZ) in fall were observed. N-cycling processes in four seasons were influenced by different dominant environmental factors. Generally, dissolved organic carbon (DOC) or sediment organic matter (SOM), water temperature (T) and antibiotics (e.g., Norfloxacin and ofloxacin) were significantly correlated with N-cycling processes. The findings imply that sediment organic carbon and antibiotics may be potentially key factors influencing N-cycling processes in lake ecosystems, which will provide a reference for nitrogen management in eutrophic lakes.

Effects of water quality on fish parasite biodiversity and physiological responses in the host fish Clarias gariepinus from a eutrophic lake subjected to acid mine drainage in South Africa.

Elevated concentrations of contaminants have negative impacts on aquatic organisms and their parasites. Changes in parasite infections have been proposed as a technique for monitoring the health of aquatic ecosystems. Furthermore, alterations in physiological responses (biomarkers) of organisms have also been used to delineate ecosystem quality. Lake Heritage is situated along the Crocodile River in Muldersdrift, Gauteng, South Africa, and is subject to contamination by acid mine drainage. Clarias gariepinus is a well-studied bioindicator species and host to numerous endoparasites and ectoparasites. The aims of this study were to delineate the health status of Lake Heritage through a multifaceted approach by comparing the water quality, biomarker responses, and parasite biodiversity of C. gariepinus, compared to unexposed laboratory-reared fish. Physical and chemical water quality parameters were determined using a hand-held probe, test kits, and element analysis with inductively coupled plasma-mass spectrometry. Biomarker responses in the gill, liver, and muscle tissues from C. gariepinus were assessed for total protein, metallothioneins, superoxide dismutase (SOD), and reduced glutathione (GSH) concentrations and activities of acetylcholinesterase and catalase. Results for water quality variables showed higher pH, nitrate, hardness, and copper levels compared with the South African Target Water Quality Guidelines. Catalase activity and concentrations of SOD and reduced GSH showed a response in C. gariepinus to the water quality. Ectoparasites had lower prevalence and mean intensity than endoparasites. However, there were no differences in the physiological responses between infected and uninfected hosts. The study shows that the eutrophic conditions in Lake Heritage cause biomarker responses in the host when compared to host fish in laboratory conditions. Integr Environ Assess Manag 2024;20:1539-1553. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Combining dredging with modified zeolite thin-layer capping to control nitrogen release from eutrophic lake sediment

Dredging is widely used to control internal sediment nitrogen (N) pollution during eutrophic lake restoration. However, the effectiveness of dredging cannot be maintained for long periods during seasonal temperature variations. This study used modified zeolite (MZ) as a thin-layer capping material to enhance dredging efficiency during a year-long field sediment core incubation period. Our results showed that dredging alone more effectively reduced pore water N, N flux, and sediment N content than MZ capping but showed more dramatic changes during the warm seasons. The N flux in dredged sediment in summer was 1.8 and 2.5 times that in spring and autumn, respectively, indicating a drastic N regeneration process in the short term. In contrast, the combination method reduced the extra 10% pore water N, 22% N flux, and 8% sediment organic N content compared with dredging alone and maintained high stability during seasonal changes. The results indicated that the addition of MZ to the surface of dredged sediment not only enhanced the control effect of dredging by its adsorption capacity but may also smooth the N regeneration process via successive accumulation (in the channel of the material) and activation of bacteria for months, which was evidenced by the variation in microbial diversity in the MZ treatment. As a result, the combination of dredging with modified zeolite simultaneously enhanced the efficiency and stability of the single dredging method in controlling sediment N content and its release, exhibiting great prospects for long-term application in eutrophic lakes with severe pollution from internal N loading.

Overview of the Eutrophication in Romanian Lakes and Reservoirs

In this paper, attention is drawn to the deterioration of Romanian surface water ecosystems due to eutrophication, an important environmental issue both at national and international levels. An inventory of existing studies dealing with the issue of the eutrophication of lakes and reservoirs in Romania is made, aiming to identify the main problems Romania is facing in monitoring, classifying, and managing eutrophic ecosystems. On Web of Science, the keyword “Eutrophication”, with “Romania” as country/region, leads to 50 publications, which are analyzed in this review. The number of articles found does not reflect the real environmental issue represented by eutrophic lakes and reservoirs in Romania. At a national level, only 126 lakes and reservoirs have been monitored and assessed between 2018 and 2020, in terms of ecological status/ecological potential. Thus, at a global evaluation, 77% of natural lakes and 33% of artificial ones do not reach the quality objectives. The results of this study showed that the frequency of measurements taken by water quality indicators is not the strongest point of measurement campaigns, as it is not sufficient for the diagnosis of eutrophic lakes, and supplementary measures must be undertaken to better understand and mitigate this phenomenon.

Assessing long-term diatom changes in sub-Arctic ponds receiving high fluxes of seabird nutrients.

Algal bioindicators, such as diatoms, often show subdued responses to eutrophication in Arctic lakes because climate-related changes (e.g., ice cover) tend to be the overriding factors influencing assemblage composition. Here, we examined how sub-Arctic ponds historically receiving high nutrient inputs from nesting seabirds have responded to recent climate change. We present diatom data obtained from 12 sediment cores in seaduck-affected ponds located on islands through Hudson Strait, Canada. All study cores show consistently elevated values of sedimentary ẟ15N, an established proxy for tracking marine-derived nutrients, indicating seabirds have been present on these islands for at least the duration of the sediment records (~100 to 400 years). We document diverse epiphytic diatom assemblages to the base of all sediment cores, which is in marked contrast to seabird-free Arctic ponds-these oligotrophic sites typically record epilithic diatom flora prior to recent warming. Diatoms are likely responding indirectly to seabird nutrients via habitat as nutrients promote the growth of mosses supporting epiphytic diatom communities. This masks the typical diatom response to increased warming in the Arctic, which also results in habitat changes and the growth of mosses around the pond edges. Changes in sedimentary chlorophyll a were not consistently synchronous with large changes in ẟ15N values, suggesting that primary production in ponds is not responding linearly to changes in seabird-derived nitrogen. Across all ponds, we recorded shifts in diatom epiphytic assemblages (e.g., increases in % relative abundance of many Nitzschia species) that often align with increases in chlorophyll a. The changes in diatoms and chlorophyll a, although variable, are most likely driven by climate change as they are generally consistent with longer ice-free conditions and growing seasons. Together, our results show that to effectively use diatoms in animal population reconstructions across the sub-Arctic and Arctic, a strong understanding of eutrophication and climate change, based on supplementary proxies, is also required.

Composition, Distribution, and Biodiversity of Zooplanktons in Tropical Lentic Ecosystems with Different Environmental Conditions

A study was conducted to evaluate zooplankton species composition, abundance, and diversity in both natural and artificial lakes with varying trophic levels and to determine the relationship between zooplankton community structure and lake environmental conditions. This study hypothesized that correlations exist between zooplankton community structures and environmental parameters associated with eutrophication in natural and artificial lakes. Sampling was conducted across 16 distinct freshwater lentic ecosystems in Malaysia, including natural lakes/swamps, reservoirs, constructed lakes/ponds, and old mining lakes, spanning a range of trophic levels from mesotrophic to hypereutrophic conditions. Physicochemical parameters were measured in situ, while water and zooplankton samples were collected for nutrient analyses, as well as for zooplankton identification and enumeration. Throughout this study, a total of 58 zooplankton species, consisting of 36 species of rotifers, 12 species of cladocerans, and 10 species of copepods, were recorded. The highest zooplankton density (365.7 ± 13.7 ind L−1) was recorded in constructed lakes/ponds while the lowest density was recorded in natural shallow lakes/swamps (200.5 ± 25.5 ind L−1). On the other hand, significantly higher (p < 0.05) mean species diversity was observed in natural lakes/swamps (H’ = 2.2 ± 0.0); whereas, the lowest diversity was in old mining lakes (H’ = 1.5 ± 0.1). The canonical correspondence analysis (CCA) scores indicated that Polyarthra vulgaris and Chydorus ventricosus were the discriminating species in natural shallow lakes/swamps associated with high water transparency. Meanwhile, the small-sized cladocerans (Ceriodaphnia cornuta) and rotifers (Keratella spp., Brachionus spp., and Trichocerca spp.) were the most discriminating species in lakes with high turbidity, nutrients, and chlorophyll a concentrations, which are the main features of reservoirs and constructed lakes/ponds. Low density and diversity in old mining lakes were due to a low species number and the dominance of two species, Lophocharis curvata (38.8%) and Ptygura libera (39.7%). Overall, the high dominance of a specific zooplankton species resulted in lower biodiversity in artificial ecosystems compared to natural ecosystems. This study elucidated that zooplankton community structure in lakes was significantly influenced by the environmental conditions related to the lake trophic status.

The combined effects of lanthanum-modified bentonite and Vallisneria spiralis on phosphorus, dissolved organic matter, and heavy metal(loid)s

The use of lanthanum-modified bentonite (LMB) combined with Vallisneria spiralis (V∙s) (LMB + V∙s) is a common method for controlling internal phosphorus (P) release from sediments. However, the behaviors of iron (Fe) and manganese (Mn) under LMB + V∙s treatments, as well as the associated coupling effect on P, dissolved organic matter (DOM), and heavy metal(loid)s (HMs), require further investigations. Therefore, we used in this study a microelectrode system and high-resolution dialysis technology (HR-Peeper) to study the combined effects of LMB and V∙s on P, DOM, and HMs through a 66-day incubation experiment. The LMB + V∙s treatment increased the sediment DO concentration, promoting in-situ formations of Fe (III)/Mn (IV) oxyhydroxides, which, in turn, adsorbed P, soluble tungsten (W), DOM, and HMs. The increase in the concentrations of HCl-P, amorphous and poorly crystalline (oxyhydr) oxides-bound W, and oxidizable HMs forms demonstrated the capacity of the LMB + V∙s treatment to transform mobile P, W, and other HMs forms into more stable forms. The significant positive correlations between SRP, soluble W, UV254, and soluble Fe (II)/Mn, and the increased concentrations of the oxidizable HMs forms suggested the crucial role of the Fe/Mn redox in controlling the release of SRP, DOM, and HMs from sediments. The LMB + V∙s treatment resulted in SRP, W, and DOM removal rates of 74.49, 78.58, and 54.78 %, which were higher than those observed in the control group (without LMB and V∙s applications). On the other hand, the single and combined uses of LMB and V·s influenced the relative abundances of the sediment microbial communities without exhibiting effects on microbial diversity. This study demonstrated the key role of combined LMB and V∙s applications in controlling the release of P, W, DOM, and HMs in eutrophic lakes.

Lake surface cooling drives littoral-pelagic exchange of dissolved gases.

The extent of littoral influence on lake gas dynamics remains debated in the aquatic science community due to the lack of direct quantification of lateral gas transport. The prevalent assumption of diffusive horizontal transport in gas budgets fails to explain anomalies observed in pelagic gas concentrations. Here, we demonstrate through high-frequency measurements in a eutrophic lake that daily convective horizontal circulation generates littoral-pelagic advective gas fluxes one order of magnitude larger than typical horizontal fluxes used in gas budgets. These lateral fluxes are sufficient to redistribute gases at the basin-scale and generate concentration anomalies reported in other lakes. Our observations also contrast the hypothesis of pure, nocturnal littoral-to-pelagic exchange by showing that convective circulation transports gases such as oxygen and methane toward both the pelagic and littoral zones during the daytime. This study challenges the traditional pelagic-centered models of aquatic systems by showing that convective circulation represents a fundamental lateral transport mechanism to be integrated into gas budgets.

A new model to estimate shallow lake nitrogen removal rate based on satellite derived variables

Lake nitrogen (N) removal, mainly resulting from bacterial denitrification that converts nitrate (NO3 −) to gaseous N (N2), is important for lake water quality and eutrophication control. However, quantifying lake N removal is challenging due to the high background atmosphere N2 concentration and the heavy burden of field surveys, leading to a decoupling of watershed N management and water quality improvement. Here, we developed and validated an innovative nonlinear model for lake N removal rate estimation by linking the N removal rates with remote sensing-derived variables (chlorophyll-a, chromophoric dissolved organic matter, and lake surface water temperature). The model was validated in shallow eutrophic Lake Taihu in the Yangtze River basin and at the global scale. Based on the new N removal model, we estimated that an annual average of 3.21 × 104 t N yr‒1 was removed in Lake Taihu from 2011 to 2020, accounting for 53%–66% of the total lake N loading. The remaining N loading after denitrification removal in Lake Taihu would be approximately 2.37 mg N l‒1, and 0.79 × 104 t N y‒1 of lake N loading still needs to be removed to meet the target of class IV water quality (1.5 mg N l‒1). This is the first study linking lake N removal in sediment microcosm incubations with reach-scale remote sensing derived variables, providing timely-much insights into lake N removal. This approach can be easily applied in other lakes with satellite derived data, to better understand lake N budget, drivers of eutrophication control, and watershed N management.

Organic matter, eutrophication, and increased mass accumulation rates in the Anthropocene are the main drivers of mercury concentrations and historical enrichment in Canadian lake sediments

AbstractMercury (Hg) contamination in the environment is a persistent issue as emissions from industry are ongoing and legacy cycling is prolonged. To quantify total mercury (total Hg) and methylmercury (MeHg) concentrations in lake sediments across a wide suite of temperate to subarctic lakes, measurements and modeling were conducted for 320 sites across Canada. Total Hg varied from 7 to 567 ng g−1 dry sediment with a mean (median) value of 148 (128) ng g−1 dry sediment, with lowest concentrations observed in eutrophic lakes of the Prairies and Boreal Plains. Average total Hg concentrations have increased twofold in contemporary sediments relative to their preindustrial pair. MeHg concentrations were generally low, with a mean of 0.8 ng g−1 dry sediment and this form representing on average 0.6% of the total contemporary mercury concentrations. Water column variables related to eutrophication were among the strongest predictors of contemporary total Hg, MeHg, and total Hg enrichment in the sediments. In lakes where sediment radiometric data were collected, contemporary total Hg accumulation rates were strongly related to longitude(+) and Hg atmospheric deposition(+). Latitude(−) and Hg atmospheric deposition(+) were the best predictors of MeHg accumulation rates. Chromophoric dissolved organic matter optical properties were key predictors of both total Hg concentrations and accumulation rates. Our work highlights the paramount importance of lake trophic state and the nature of organic matter as key predictors of lake sediment mercury metrics.

Exploring nonlinear responses of lake nutrients and algal blooms to restoration measures: A three-dimensional flux network modelling approach

Excessive anthropogenic nitrogen (N) and phosphorus (P) inputs accelerate harmful algal blooms (HABs) and pose a significant global threat to lake ecosystems. Despite the adoption of extensive restoration measures to improve water quality, their effects on nutrient cycles and the underlying pathways remain unclear. In this study, a three-dimensional nutrient flux modelling approach was developed based on a validated Environmental Fluid Dynamics Code (EFDC) model and the Spatiotemporal Integral for Nutrient Networks (SINN) to compute nutrient storages and fluxes in lakes. We then conducted a scenario analysis, composed of 10 schemes, to assess the eight restoration measures in Lake Dianchi, China. The results showed that our model exhibited a high level of agreement with observed data and fluxes reported in previous studies. Of all the measures implemented, pollution interception by lakeshore wastewater treatment plants (WWTPs) accounted for the largest historical improvements in water quality, with reductions of total nitrogen (TN) by 9.3%, total phosphorus (TP) by 36.4%, and chlorophyll a (Chla) by 18.2%. Furthermore, combined implementation of transboundary water transfer and wastewater diversion contributed to a reduction of 13.3% in TN, 11.5% in TP, and 6.2% in Chla. To achieve greater improvements in water quality, efforts must be made to improve the emission standard of WWTPs and ensure compliance with water quality standard of inflow rivers. The cyanobacteria biomass catch can only be used as a supplementary approach to restrict the HAB peaks. The nonlinear responses of lakes were characterized by large loading abatement but slight changes in water quality. Through the SINN approach, we revealed that weakened internal cycling was the primary driver of water quality improvements in all restoration measures. Further analysis demonstrated that measures targeting reducing external loadings significantly weakened internal cycling processes. In contrast, measures targeting the internal loadings, such as sediment dredging, exhibited limited effectiveness in reducing the intensity of internal cycling and Chla in the lake. For eutrophic lakes with substantial legacy nutrients, the abatement of external loadings remains the principal strategy. The approach presented in this study can be used to assess and optimize lake restoration measures.