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Simple Summary: Ecological fishery management is one of the predominant approaches to lake ecological management in China; it involves the stocking of filter-feeding fish species to mitigate algal blooms. This strategy not only enhances water quality but also yields ecological benefits by fostering the growth of fish populations, thereby offering both ecological and economic advantages. Nonetheless, there is a scarcity of works in the literature addressing the effects on fish community dynamics and diversity in lakes subsequent to the cessation of ecological fishing practices. This study focuses on the initial changes observed in fish community composition and diversity following the cessation of an ecological fishery project in Qilu Lake, an eutrophic shallow lake situated in China. Ecological fishery projects aim to improve the water quality of eutrophication lakes by stocking filter-feeding fish species that feed on algae. The findings indicate a significant decline in the number of fish species, average individual size, and species diversity index following the cessation of fisheries-related activities (including fish stocking and fishing activities) due to the termination of the ecological fishery project in the lake. To preserve fish biodiversity and enhance water quality in Qilu Lake, it is recommended that policies be implemented to sustain the implementation of ecological fisheries projects, restore habitats for native fish species, and regulate the proliferation of small fish populations. The Qilu Lake is an eutrophic shallow lake located in Yunnan Province, China. An ecological fishery project was initiated in the lake from 2011 to 2021 to introduce filter-feeding fish species that feed on algae, with the aim of improving water quality. In January 2022, when the ecological fishery project expired, all fisheries-related activities (including fish stocking and fishing activities) ceased in the lake. To comprehensively evaluate the initial alterations in fish community structure and diversity resulting from the fishing cessation in the Qilu Lake, the present study conducted field surveys within the one year before the fishing cessation (referred to as BFC) and the one year after the fishing cessation (referred to as AFC). A total of twenty-one fish species were collected, including four native species. Four species were recorded in the lake for the first time, including Pelteobagrus fulvidraco, Pelteobagrus vachelli, Paramisgurnus dabryanus, and Hyporhamphus intermedius. The number of fish species decreased from 21 to 13 following the fishing cessation. The fishes collected in both BFC and AFC are mainly omnivorous-feeding and of bottom-dwelling habits. The mean size of the fishes in the AFC sample shows a significant decrease compared to those in BFC. After the fishing cessation, the Shannon–Wiener diversity index and Margalef richness index of the fish slightly declined. The fish community structure of the Qilu Lake exhibits a high degree of similarity to adjacent lakes in central Yunnan. Our study demonstrates a significant shift in the fish community of the Qilu Lake following the fishing cessation, one which may adversely impact the stability of the lake ecosystem. To enhance fish species diversity in the Qilu Lake, it is recommended that policies be implemented to promote the ecological fishery project and improve habitat restoration for native fish species, while also regulating fish community structure. [ABSTRACT FROM AUTHOR]

Global warming can affect biomass accumulation and the dynamics of periphytic communities, potentially altering their role in aquatic ecosystem functioning. We conducted a 38-day mesocosm experiment to investigate the effects of an increase in winter temperature on periphyton biomass accumulation under eutrophic conditions. We evaluated the warming effect on colonization phases, identifying the most affected phase. The experiment had two treatments (control: current winter temperature of 23.5 ℃, warming: + 5.7 ℃ under IPCC scenario). It was carried out in growth chambers under controlled temperature, light, and humidity. Periphyton and water samplings were performed on days 3, 6, 9, 13, 17, 21, 27, and 38. The increase in temperature did not affect the organic matter accrual rate of the periphyton. However, it negatively affected the net and gross accrual rate of the algal biomass. Ash-free dry mass and chlorophyll-a ratio in the periphyton increased at higher temperatures, indicating a decrease in autotrophic components in the periphyton in the warming treatment. We detected losses in algal biomass during the intermediate and advanced colonization phases. Our results showed a decrease in periphytic algal biomass with an increase in average temperature in winter. In conclusion, a warming scenario can negatively influence periphyton biomass in eutrophic ecosystems, where algal growth in the community is generally unfavorable. [ABSTRACT FROM AUTHOR]

Nitellopsis obtusa is a large invasive freshwater macroalgae that forms extensive, monotypic beds which have altered habitat and impacted littoral communities in lakes across North America. N. obtusa is native to Eurasia including the UK but is considered to be cryptogenic and likely introduced in Ireland, where it was first recorded in 2016. Recent evidence of its spread prompted this hydroacoustic survey which investigated the distribution and abundance of N. obtusa in two large interconnected lakes, Loughs Ree and Derg, within the Shannon River system. Using a consumer grade depth finder and a simplistic approach, we propose an accessible method of hydroacoustic surveying for macrophytes such as N. obtusa which form dense, often monotypic beds. Nitellopsis obtusa beds quantified within three bays in Lough Ree covered 254.4 hectares with a total biovolume of ~ 2.7 million m3, indicating that it may be one of the most aggressive macrophytes introduced to Ireland. The hydroacoustic survey methodology proved to be cost and time efficient. Measurements of plant height and lake depth gathered from the hydroacoustic survey were comparable to diver gathered measurements which provides confidence in the methodology. The rapid expansion of N. obtusa within Loughs Ree and Derg is a concern for other alkaline waterbodies in Ireland, especially marl lake systems, and warrants monitoring. There is no feasible method to eliminate the extensive populations of N. obtusa in Lough Ree and therefore management interventions should aim to limit the spread of this species to other waterbodies. [ABSTRACT FROM AUTHOR]

The Qilu Lake is an eutrophic shallow lake located in Yunnan Province, China. An ecological fishery project was initiated in the lake from 2011 to 2021 to introduce filter-feeding fish species that feed on algae, with the aim of improving water quality. In January 2022, when the ecological fishery project expired, all fisheries-related activities (including fish stocking and fishing activities) ceased in the lake. To comprehensively evaluate the initial alterations in fish community structure and diversity resulting from the fishing cessation in the Qilu Lake, the present study conducted field surveys within the one year before the fishing cessation (referred to as BFC) and the one year after the fishing cessation (referred to as AFC). A total of twenty-one fish species were collected, including four native species. Four species were recorded in the lake for the first time, including Pelteobagrus fulvidraco, Pelteobagrus vachelli, Paramisgurnus dabryanus, and Hyporhamphus intermedius. The number of fish species decreased from 21 to 13 following the fishing cessation. The fishes collected in both BFC and AFC are mainly omnivorous-feeding and of bottom-dwelling habits. The mean size of the fishes in the AFC sample shows a significant decrease compared to those in BFC. After the fishing cessation, the Shannon–Wiener diversity index and Margalef richness index of the fish slightly declined. The fish community structure of the Qilu Lake exhibits a high degree of similarity to adjacent lakes in central Yunnan. Our study demonstrates a significant shift in the fish community of the Qilu Lake following the fishing cessation, one which may adversely impact the stability of the lake ecosystem. To enhance fish species diversity in the Qilu Lake, it is recommended that policies be implemented to promote the ecological fishery project and improve habitat restoration for native fish species, while also regulating fish community structure.

This study investigates the decomposition process of algal blooms (ABs) in eutrophic lakes and its impact on the labile endogenous nitrogen (N) cycle. In situ techniques such as diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper) were employed to decipher the vertical distribution of N fractions within the sediment–water interface (SWI) in Taihu, China. Additionally, an annular flume was used to simulate regional differences in lake conditions and understand labile nitrogen transformation during AB decomposition. This study reveals that the NH4+-N fraction exuded from algae is subsequently converted into NO3-N and NO2-N through nitrification, resulting in a significant increase in the concentrations of NO3−-N and NO2−-N at the SWI. The decomposition of algae also induces a significant increase in dissolved organic matter (DOM) concentration, referring to humic acid and humus-like components; a seven-millimeter decrease in dissolved oxygen (DO) penetration depth; as well as a significant decrease in the pH value near the SWI, which consequently promotes denitrification processes in the sediment. Moreover, the decomposition process influences nitrogen distribution patterns and the role conversion of sediments between a "source" and a "sink" of nitrogen. This investigation provides evidence on the migration and/or transformation of N fractions and offers insights into the dynamic processes across the SWI in eutrophic lakes. [ABSTRACT FROM AUTHOR]

With increasing anthropogenic activities, freshwater ecosystems around the world are becoming increasingly affected by various pressures, including eutrophication, overfishing, and irrational stocking, which may have a negative impact on the food web structure. Despite the extensive research and proposed management measures for eutrophic lakes, there are only few analysis on long-term monitoring data regarding fishery resources. Additionally, there is a lack of evaluation and prediction of the effectiveness of current fish management policies. To remedy this, we analyzed long-term monitoring data from Lake Taihu, China, a severely eutrophicated lake with a skewed fish size structure exhibiting dominance of small individuals. We first constructed 14 Ecopath models to investigate how trophic interactions and biomass fluxes changed from 2007 to 2020. Subsequently, the Ecosim model was used to predict how the biomass of fish and the ecosystem network respond to the initiated 10-years fishing ban. Our results demonstrate long-term changes in fish biomass and ecosystem stability. The analyses revealed that 1) the biomass development in different feeding types of fish is controlled by human activities (mainly catches and stocking) and trophic interactions and 2) the rate of decline in ecosystem network stability slows down during the fishing ban. The primary focus of this study was to fill the gap in long-term serial studies of fish monitoring data and ecosystem stability in the lake and, for the first time, to predict the outcome of the fishing ban from an ecosystem perspective using the Ecosim model. Overall, our results emphasize the importance of rational stocking and fishing policies and provide a better understanding of the changes in the ecological dynamics in Lake Taihu of relevance for the management and restoration of the lake.

This study investigates the decomposition process of algal blooms (ABs) in eutrophic lakes and its impact on the labile endogenous nitrogen (N) cycle. In situ techniques such as diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper) were employed to decipher the vertical distribution of N fractions within the sediment–water interface (SWI) in Taihu, China. Additionally, an annular flume was used to simulate regional differences in lake conditions and understand labile nitrogen transformation during AB decomposition. This study reveals that the NH4+-N fraction exuded from algae is subsequently converted into NO3-N and NO2-N through nitrification, resulting in a significant increase in the concentrations of NO3−-N and NO2−-N at the SWI. The decomposition of algae also induces a significant increase in dissolved organic matter (DOM) concentration, referring to humic acid and humus-like components; a seven-millimeter decrease in dissolved oxygen (DO) penetration depth; as well as a significant decrease in the pH value near the SWI, which consequently promotes denitrification processes in the sediment. Moreover, the decomposition process influences nitrogen distribution patterns and the role conversion of sediments between a “source” and a “sink” of nitrogen. This investigation provides evidence on the migration and/or transformation of N fractions and offers insights into the dynamic processes across the SWI in eutrophic lakes.

Organic matter (OM) and nutrient inputs generated by human activities promote the development of eutrophication. Amino acids (AAs) are an integral part of OM, and studying their patterns will provide new insights into organic matter dynamics in lakes. Four seasonal field campaigns in eutrophic Lake Taihu and a 14-day phytoplankton degradation experiment were carried out to determine the variability and bioavailability of amino acids. The quality and quantity of AAs varied among different seasons and lake types. The concentrations of particulate (PAA) and dissolved (DAA) AA were 14.67 ± 13.25 μM (carbon- and nitrogen-normalized PAA yields: PAA-C%, 23.8 ± 13.5%; PAA-N%, 22.8 ± 2.1%) and 2.95 ± 1.05 μM (carbon- and nitrogen-normalized DAA yields: DAA-C%, 3.7 ± 1.1%; DAA-N%, 12.6 ± 11.2%) in Lake Taihu, respectively. PAA and DAA showed high mean values in the algal-dominated northern area in summer. Glutamic acid (Glu), alanine (Ala), aspartic acid (Asp) and glycine (Gly) contributed to nearly 50% of PAA, while Gly, accounting for 17–24%, was the main component of DAA. During a 14-day phytoplankton degradation period, 98% of Chl a, 63% of POC and 92% of PAA were removed in the dark treatment, and a more obvious downward trend was recorded than in the light treatment. Principal component analysis of the indices of PAA indicated that Glu, arginine (Arg) and histidine (His) were dominant on day 0, while Gly and lysine (Lys) were dominant on day 14. There were notable serine + threonine (Ser + Thr [mol%]) and aspartic acid/glycine ratio (Asp/Gly [mol%]) end-member divisions among different organic matter sources. DAA had higher Ser + Thr [mol%] and lower Asp/Gly [mol%] values than PAA. The amino acid degradation index (DI) of PAA and DAA was 0.97 ± 0.28 and − 1.04 ± 0.43, respectively. The fresh DAA from the algae degradation incubation also had DI values similar to those of field DAA in the northern algae–dominated lake region. Amino acid parameters (AA-C%, DI values, Ser + Thr [mol%] and Asp/Gly [mol%]) were calculated to indicate the source, freshness and bioavailability of organic matter in eutrophic shallow Lake Taihu. [ABSTRACT FROM AUTHOR]

Lakes are important natural sources of atmospheric methane (CH4), which should be considered in global CH4 budget estimations. However, the CH4 emissions from lakes can be highly variable, and the emissions from the river inlet region were less studied, which seriously hamper our understanding of CH4 budget estimates of lakes. Here, field measurements from over six years (2012 to 2017) at Lake Taihu, a large eutrophic shallow lake with a complicated river network, were conducted to address the issue. Results show that the river inlet region of the lake was a hot spot of CH4 emission. The CH4 emission at the river inlet region with an annual mean value of 0.183 mmol m−2 d−1 was seven times higher than that at pelagic region (0.028 mmol m−2 d−1). Peak CH4 emission occurred in warm seasons, and the lowest in cold seasons at the pelagic region, but peak emission occurred in cold seasons at the river inlet region. The seasonal CH4 emission at the pelagic region can be explained by water temperature; however, less temperature dependency of CH4 emission at the river inlet region was found. The variability of CH4 emission was linked to pollution loadings, and CH4-rich water in the inflowing river likely sustained the large CH4 emission of river inlet region. [ABSTRACT FROM AUTHOR]

The aim of the investigation was to study the current structure of the parasitic fauna of the gibel carp (Carassius gibelio) population in the Georgian part of Jandari Lake. In total, 423 young gibel carp collected during 2014-2018 years from Jandari Lake have been subject to parasitological examination. The 20.3% (n=86) of examined fish were invaded by 11 species of parasites belonging to 5 taxonomic groups. The dominant taxonomic groups were discovered to be Protozoa and Monogenea. The eight species were registered for the first time in the gibel carp of freshwater reservoirs in Georgia. In general, young fish were more invaded by the monoxenic species of the direct life cycle. None of the revealed parasites were specific to gibel carp. The parasitic fauna of Jandari Lake is relatively poor, though it is comparatively rich and diverse in spring. Trichodina sp. from Protozoa, Ancyrocephalus sp., Dactylogyrus vastator, Gyrodactylus elegans from Monogenea, and Contracaecum sp. from Nematoda were revealed as the species most sensitive to annual changes. The main factor determining the parasite fauna of gibel carp in Lake Jandari is anthropogenic eutrophication, which changes the qualitative and quantitative composition of zooplankton, the main food source of juvenile fish and intermediate hosts of helminths. The difference in invasion indices between female and male gibel carp was insignificant. The synergetic relationship between some parasitic protozoans and monogeneans was marked. [ABSTRACT FROM AUTHOR]

Warming has been affecting carbon cycling in freshwater ecosystems throughout recent decades. However, how the co-metabolism effect (CE) during the decomposition of sediment organic carbon (SOC) in eutrophic lakes responds to warming remains understudied. A 33-day experiment was conducted to examine the mechanisms that underpin the CE in lacustrine sediments. The results indicated that warming increased the co-metabolism intensity of sedimentary organic matter. At the beginning of the experiment (0–9 d), the co-metabolism intensity increased rapidly at both 25℃ and 35℃. However, at the end of the experiment (33 d), the cumulative co-metabolism intensity was highest at 25℃, which was 33.75% and 153.74% higher than the intensities at 15℃ and 35℃, respectively. By enhancing the co-metabolism intensity of the SOC, warming would weaken lakes "carbon sink" functions. Thus, our study provides novel evidence that microorganisms regulate SOC turnover and effectively maintain a balance between resources and microbial requirements. [ABSTRACT FROM AUTHOR]

Context: Sulfate (SO42−) concentrations in eutrophic lakes are continuously increasing. Aims: This study aimed to explore the effects on nitrogen and their limiting factors in eutrophic lakes. Methods: We constructed a series of microcosms with different initial SO42− concentrations (0–180 mg L−1) to simulate the SO42− concentration in eutrophic lakes. Key results: The NO3−-N concentration rapidly decreased in all treatments. The respective 2.21 and 2.77 mg L−1 concentrations of NO3−-N recorded on Day 5 in the initial 150 and 180 mg L−1 SO42− concentration treatments were higher than in other treatments. The highest N2O concentrations in all treatments showed insignificant differences. The existence of free Fe2+ that was released from iron reduction resulted in an insignificant effect of increased SO42− concentration on nitrogen dynamics. With a decrease in Fe2+, the acid volatile sulfate (AVS) increased, and the highest AVS concentrations were positively correlated with the initial SO42− concentration (7.20–12.88 mg kg−1). Conclusion: This effect could be ascribed to the fact that the rapid combination of sulfide (∑S2−) and Fe2+ prevents ∑S2− from producing a toxic effect on the denitrification. Implications: Our study highlighted the role of iron in eutrophic lakes, especially in the coupling of sulfate reduction and nitrogen dynamics. Increasing concentrations of sulfate in eutrophic lakes has gained a lot of attention. Cyanobacteria decomposition enhances sulfate reduction leading to the release of sulfide, which inhibits the activities and abundance of microorganisms because of its toxicity. However, in a system with high iron ion concentrations, reducing sulfide is rapidly bound, and its toxic effect on microorganisms is significantly inhibited, thereby eliminating its significant influence on the nitrogen dynamics and nitrogen oxide production. [ABSTRACT FROM AUTHOR]

Aquatic ecosystems are globally significant sources of greenhouse gases (GHG) to the atmosphere, offsetting the terrestrial sinks. A one-year field study was carried out in a shallow eutrophic Lake Wuliangsuhai, Inner Mongolia (draining waters from one of the largest irrigation areas in China), to estimate diffusive GHG fluxes and their relative importance in global warming potential (GWP). Our results showed high spatiotemporal variation in dissolved CO2, CH4 and N2O concentrations, while they did not differ significantly between the bottom and surface layers of the shallow waterbody. In general, GHG concentrations and diffusive fluxes were higher in the north part of the lake than in the south. GHG concentrations in the water under the ice were significantly higher than those during the open-water period. Spatial variability of GHG concentrations varied with the bathymetry of the lake. The location of study sites relative to the main inflow and abundance of submerged macrophytes were the main controlling factors of GHG concentrations, as indicated by the consistency of GHG concentrations at the sampling sites, particularly for N2O. The total diffusive GHG emission from Lake Wuliangsuhai was 76.9 ± 5.4 Gg CO2 equivalents yr−1, with CO2, CH4 and N2O contributing 16 %, 83 %, and 1 %, respectively. Overall, the results suggest that shallow lakes in mid-latitude arid areas with cold winters can be potentially important GHG sources. However, those lakes are insufficiently represented in the scientific literature, and therefore they deserve more research attention.

Several studies have suggested the pivotal roles of eutrophic lakes in carbon (C) cycling at regional and global scales. However, how the co-metabolism effect on lake sediment organic carbon (OC) mineralization changes in response to integrated inputs of labile OC and nutrients is poorly understood. This knowledge gap hinders our ability to predict the carbon sequestration potential in eutrophic lakes. Therefore, a 45-day microcosm experiment was conducted to examine the dominant mechanisms that underpin the co-metabolism response to the inputs of labile C and nutrients in lacustrine sediments. Results indicate that the labile C addition caused a rapid increase in the positive co-metabolism effect during the initial stage of incubation, and the co-metabolism effect was positively correlated with the C input level. The positive co-metabolism effect was consistently higher under high C input, which was 152% higher than that under low C input. The higher β-glucosidase activity after nutrient addition, which, in turn, promoted the OC mineralization in sediments. In addition, different impacts of nutrients on the co-metabolism effect under different C inputs were observed. Compared with the low nutrient treatments, the largest co-metabolism effect under high C with high nutrient treatment was observed by the end of the incubation. In the high C treatment, the intensity of the co-metabolism effect (CE) under high nitrogen treatment was 1.88 times higher than that under low nitrogen condition. However, in the low C treatment, the amount of nitrogen had limited impact on co-metabolism effect. Our study thus proved that the microorganisms obviously regulate sediment OC turnover via stoichiometric flexibility to maintain a balance between resources and microbial requirements, which is meaningful for evaluating the OC budget and lake eutrophication management in lacustrine sediments. [ABSTRACT FROM AUTHOR]

The aim of this study was to reveal the variation in dissolved organic matter (DOM) components, bacterial community composition, and their co-relationships during groundwater migration. A well-studied shallow eutrophic lake, Lake Taihu, was selected to explore the DOM components and bacterial communities during groundwater replenishment from the lake using three-dimensional fluorescence-parallel factor analysis and high-throughput sequencing, respectively. Six fluorescent components of DOM were identified, including four humic-like components (C1: λ E x / E m = 330 / 400 n m , C2: λ E x / E m = 260 , 350 / 450 n m , C3: λ E x / E m = 270 , 380 / 480 n m , and C6: λ E x / E m = 220 / 410 n m ) and two protein-like components (C4: λ E x / E m = 230 , 280 / 320 n m , C5: λ E x / E m = 230 , 290 / 340 n m ). With increasing distance to Lake Taihu, the fluorescence intensity of C1, C3, C4, and C5 decreased within 15 km away from lake shore and then tended to be stable. Thirty-three phyla of bacteria were identified in the aquifer, including Proteobacteria (61.9% of total bacteria), Bacteroidetes (15.0%), Planctomycetes (4.8%), Verrucomicrobia (3.4%), and Actinobacteria (3.3%). The relative abundance of Proteobacteria was significantly positively correlated with the fluorescence intensity of C1–C3, while the relative abundance of Actinobacteria showed the opposite relationship with the fluorescence intensity of C1–C3. The relative abundances of Novosphingobium and Limnohabitans were positively correlated with the fluorescence intensity of C4–C6. Our work suggests that the influence of groundwater replenishment from a eutrophic lake on DOM in the surrounding aquifer may extend to within 15 km from the lake shore. A large amount of DOM inputs (especially humic acid-like components) can induce variation in groundwater bacterial community composition and thus affects the groundwater biogeochemistry. [ABSTRACT FROM AUTHOR]

Eutrophication is a critical environmental challenge affecting lakes globally. Mitigating trophic level under endogenous phosphorus release is an unsolved problem in eutrophic lakes. However, understanding the dynamics and assembly of microbial communities encoding the alkaline phosphatase (phoD community) and their responses during trophic transitions in eutrophic lakes is limited. In this study, we compared the composition and assembly mechanisms of phoD communities in four seasons in the Yilong Lake, a shallow lake of the Yunnan-Guizhou Plateau. The lake exhibits slightly eutrophic conditions in summer and mesotrophic conditions in spring, autumn, and winter. By analyzing seasonal variations, we observed that during summer, the relative abundance of Pseudomonas in the water had the highest value, while the Shannon-Wiener index of phoD communities was lowest. Mantel tests showed an increased Bray-Curtis dissimilarity of phoD communities in the water with rising eutrophication, a trend not observed in sediment. Notably, eutrophication heightened the homogeneity selection governing the assembly of phoD communities in water. The co-occurrence networks showed that the OTUs in the summer exhibited closer interconnections than those in other seasons. Additionally, the topological parameters from networks indicated that eutrophication is poised to instigate changes and modulate the dynamics of the microbial phoD community, resulting in markedly distinct seasonal behaviors. pH was identified as a critical factor directly influencing phoD community diversity via partial least squares path modeling (PLS-PM). This study shed light on our understanding of the seasonal dynamics of phoD communities and their pivotal role in phosphorus cycling in eutrophic lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

This document is an editorial published in Frontiers in Plant Science titled "The performance and adaptation of aquatic plants under global changes." The editorial discusses the impact of global changes, such as intensified human activities and climate change, on aquatic plants. These changes can lead to habitat disturbances, including eutrophication, algal blooms, pollution, habitat fragmentation, extreme hydrological events, warming, and biological invasions. These disturbances can result in plant loss, expansion of harmful algal blooms, and loss of vulnerable species, affecting the ecosystem's capacity to support ecological functions and services. The editorial emphasizes the need for further research to assess the impact of global change disturbances on aquatic plant performance and adaptation strategies and their cascading effects on freshwater ecosystems. [Extracted from the article]

Sediment microbial fuel cells (SMFCs) have served as an alternative technique to suppress phosphorus release from lake sediments to water bodies and thus mitigate eutrophication. However, the phosphorus regulation mechanism remains unclear. The purpose of this research was to understand the electrochemical influence of an SMFC on the phosphorus concentration in interstitial water. In this study, a lab-scale SMFC was applied to acetate-spiked sediments (ace+) and unspiked sediments (sed) with closed-circuit (CC)/open-circuit (OC) columns, and the circuitry was switched to investigate the relationship between electron transfer and phosphorus concentration. The dissolved total phosphorus (DTP) concentration in the sediment interstitial water in CC columns significantly decreased to below 0.1 mg/L, whereas the DTP in OC columns remained high for nine weeks. After switching the circuit, the DTP in OC→CC columns dropped but that in CC→OC columns increased within one week. At the end of the experimental period, the DTP concentrations in CC/sed, CC/ace+, OC/sed, and OC/ace+ columns were 0.10 ± 0.02, 0.03 ± 0.00, 0.82 ± 0.01, and 1.66 ± 0.12 mg/L, respectively. The respective estimated anode capacitances of those columns were 2.05 ± 0.49, 5.15 ± 0.14, 0.72 ± 0.19, and 0.71 ± 0.12 nF. We concluded that the phosphorus may have been electrochemically attracted and retained on the anode in the sediment because the adsorbed DTP contents and the increased anode capacitances were strongly correlated. Thus, SMFCs can be used for suppressing phosphorus release from eutrophic lake sediments. [ABSTRACT FROM AUTHOR]

Little is known about the distribution and risk levels of nutrients and organic matter (OM) in the surface sediment of shallow submerged macrophyte-dominated lakes. In the current study, sixty surface sediment samples were collected from Xukou Bay, a typical submerged macrophyte-dominated zone in Lake Taihu, China. A 60-day degradation experiment of Potamogeton malaianus , a dominant species in the bay, was done in the laboratory. The results demonstrated that the ranges of total nitrogen (TN) and total phosphorus (TP), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), and OM in the surface sediment of the bay were 262.2–2,979.6 mg/kg, 41.2–728.7 mg/kg, 8.6–150.0 mg/kg, 4.4–36.4 mg/kg, and 3.7–50.2 g/kg, respectively. The spatial distributions of TN, OM, and AN concentrations showed similar trends: The highest concentrations were present in the northeastern and southwestern zones, while the TP and AP concentrations were high in the northeastern, central, and southwestern zones. The heterogeneity in the spatial distribution of nutrients and OM in the surface sediment of the bay was associated with aquatic vegetation and anthropogenic activities. The comprehensive risk index and organic nitrogen index revealed that the surface sediment was moderately, interactively contaminated by TN and TP and by organic nitrogen. TN and OM in the northeastern zone were mainly derived from endogenous residues due to the decomposition of aquatic plants, while TN in the southwestern zone was primarily derived from agricultural wastewater. Consequently, targeted measures should be implemented to reduce TN and OM in the surface sediment of macrophyte-dominated lakes. [ABSTRACT FROM AUTHOR]

Water resource management and lake rehabilitation are global interest, to overcome the acute water scarcity facing most urban areas, especially in developing countries. Lake Mariut (LM) is an Egyptian lake that lies south of the Mediterranean Sea, and its management had a great interest in Alexandria's future development and as a part of the environmental sustainability of the Mediterranean basin. LM consists of 4 major basins, namely, main (MB), northwest (NWB), southwest (SWB), and fishery (FB). The MB has deteriorated as it consistently received (sewage and industrial) wastewaters till 2010. This was the date of diversion of the polluting sources as a rehabilitation step. The present work is made after elapsing 8 years from the diversion and aims at monitoring and assessing the status of the water quality not only of MB but also for the other 3 basins too. This was carried out twice, one in cold winter and the other in warm summer. The parameters studied were physico-chemical including water temperature, pH, dissolved oxygen/hydrogen sulfide (DO/H2S), salinity, and chlorophyll a besides nutrient salts (nitrogen, N and phosphorus, P compounds). The results revealed that the waters of both MB and SWB basins were depleted in DO to a level difficult to sustain fish life and showed elevated levels of most nutrient salts. Trophically, all the studied basins were in eutrophic-hypereutrophic condition. As a result of pollution source diversion away from MB to be discharged in the downstream part of Umum Drain (UD), the levels of TN and TP entering Mex Bay through UD were slightly higher than the permissible limit and lower than dangerous loading. The applying of principle component analysis (PCA)-based classification approach, for obtaining the WQI on the current study, revealed that the FB, NWB, and SWB2000 showed a relatively good water quality when compared with MB. The depletion in the vital DO is catastrophic and needs urgent solution/s. One of the proposed solutions is the dredging of bottom spoiled organic-rich sediments. This and other suggested solutions are, however, discussed, evaluated, and presented. [ABSTRACT FROM AUTHOR]

• Eutrophication enhanced CH 4 and CO 2 solubility and emissions in lakes. • Influx of cyanobacteria-derived carbon created detritus mat on the sediment surface. • Isotopic tracers reveal downward migration of cyanobacteria-derived carbon in sediments. • Cyanobacteria-derived carbon dictate CH 4 and CO 2 emission capacity of sediments. • Cyanobacteria decay altered CH 4 and CO 2 produced hotspots along vertical sediment profiles. Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH 4 and CO 2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH 4 and CO 2 , this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH 4 and CO 2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m2·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH 4 and CO 2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH 4 and CO 2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH 4 and CO 2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH 4 and CO 2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH 4 and CO 2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions. [Display omitted] [ABSTRACT FROM AUTHOR]

Volatile organic sulfur compounds (VOSCs) function as a water–atmosphere link in the global sulfur cycle. It is generally believed that the vast majority of VOSCs are released from the ocean. However, due to the pervasive eutrophication and pollution of inland waters, the VOSC production and emission in rivers, lakes and reservoirs are attracting more attention. In this study, the temporal and spatial distributions of three VOSCs, including methanethiol, Dimethyl sulfide, and dimethyl disulfide in Yangcheng Lake, a eutrophic shallow lake, are investigated monthly and seasonally. Results show that VOSCs are higher in summer and autumn, with the western region as a hotspot. Our results show a positive correlation between VOSC and phytoplankton biomass (p < 0.05). Interestingly, from algal phylum composition, all the phylum, except those with low biomass, played a positive effect on VOSCs' concentration. We did not find any specific phylum or species of cyanobacteria that contributed solely to the VOSCs. The water-air effluxes of Dimethyl sulfide (DMS) are estimated by a stagnant film model. The DMS effluxes from Yangcheng Lakes were higher than deep lakes and similar to the ocean, indicating that VOSCs, particularly DMS, in those eutrophic shallow lakes were non-negligible. [ABSTRACT FROM AUTHOR]

The external nutrient loading significantly affects large shallow lakes, particularly those with intricate rive networks. In Lake Taihu, pollutant discharge standards have traditionally been quantified based on water environmental capacity, while neglecting the response characteristics of algal growth in different regions to boundary inputs. For that analysis, this study first estimated the river pollutant loadings of 16 most significant inflow and outflow rivers of Lake Taihu from 2008 to 2020 and explored the correlations between inflow water quality parameters and lacustrine chlorophyll-a levels. Results highlighted the significant influence of high river input of permanganate values in spring on the chlorophyll-a levels in the lake. Based on this, this study proposed the hypothesis that reducing the inflow concentration of permanganate in spring would inhibit algal growth, which was further validated using coupled hydrodynamic and ecological models. The simulation results indicated that the reduction of permanganate inflow concentration during spring would significantly decrease chlorophyll-a concentration in spring and summer, especially leading to a notable impact on peak values. However, due to variations in background concentrations among rivers, the extent of reduction in lake chlorophyll-a levels showed significant spatial differences. Additionally, analysis of extracted algal bloom areas revealed that there still remained a relatively high risk of algal blooms occurring in the main regions, particularly during autumn when inflow pollutant concentrations increased rapidly. These findings emphasized the importance of formulating reasonable exogenous reduction schemes, which should consider the concentration and variation trend of inflow pollutants, as well as the response characteristics of algal bloom growth in different lake zones to the boundary.

Lakes are important natural sources of atmospheric methane (CH4), which should be considered in global CH4 budget estimations. However, the CH4 emissions from lakes can be highly variable, and the emissions from the river inlet region were less studied, which seriously hamper our understanding of CH4 budget estimates of lakes. Here, field measurements from over six years (2012 to 2017) at Lake Taihu, a large eutrophic shallow lake with a complicated river network, were conducted to address the issue. Results show that the river inlet region of the lake was a hot spot of CH4 emission. The CH4 emission at the river inlet region with an annual mean value of 0.183 mmol m−2 d−1 was seven times higher than that at pelagic region (0.028 mmol m−2 d−1). Peak CH4 emission occurred in warm seasons, and the lowest in cold seasons at the pelagic region, but peak emission occurred in cold seasons at the river inlet region. The seasonal CH4 emission at the pelagic region can be explained by water temperature; however, less temperature dependency of CH4 emission at the river inlet region was found. The variability of CH4 emission was linked to pollution loadings, and CH4-rich water in the inflowing river likely sustained the large CH4 emission of river inlet region.

Lake Alboraj, located in southeast Spain, was declared natural Microreserve and included into European Natura-2000 Network due to its contribution to environmental heritage. Unfortunately, the ecological status of the lake has changed dramatically, mainly due to the lowering of water table caused by groundwater abstractions for irrigation. It is a permanent small karstic lake whose surface has reduced in the last decades to nearly the third part of its historical water level. The water column shows a marked seasonal oxycline, that splits an aerobic upper layer (epilimnion) from an anaerobic layer below (hypolimnion). Sequencing 16S rRNA gene amplicons and applying chemical tools at epilimnion, hypolimnion and sediment, showed a clear gradient in the bacterial community structure, which support the co-existence of assimilatory and dissimilatory microbial mediated reactions. Results allows to infer that microbial stratification could provide various physical and chemical environments at different depths in the water column related to biogeochemical reactions providing N-S-C- recycling processes. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) plays a crucial role in both the carbon cycle and geochemical cycles of other nutrient elements, which is of importance to the management and protection of the aquatic environments. To achieve a more comprehensive understanding the characteristics of DOM in the Changjiang (Yangtze) River basin, water samples from four natural lakes (Xiandao, Baoan, Daye, and Qingshan) in southeastern Hubei Province in China with different eutrophication levels were collected and analyzed. The optical characteristics were analyzed using ultraviolet-visible spectrophotometry and excitation-emission matrix spectroscopy coupled with parallel factor analysis. The results show that: (1) two humic-like components (C1 and C2) and two protein-like substances (C3 and C4) of DOM were identified in all waterbodies; (2) C3 originated primarily from the degradation of microalgae and contributed substantially to humic-like components during transformation. C4 was widely present in the Changjiang River basin and its formation was related to microbial activity, rather than algal blooms or seasons. Influenced by the water mixing, the protein-like components were more likely to be transformed by microorganism, whereas humic-like components were more easily to be photobleached; (3) the concentration of DOM and the fluorescence intensity of humic-like components gradually increased with rising lake eutrophication levels. With respect to protein-like components, only C3 showed changes along the eutrophication gradients; (4) DOM showed a high affinity with permanganate index (CODMn) and chlorophyll a (chl a) while the relationship was variable with phosphorus. This study helps us systematically understand the DOM characteristics, microbial activities, and pollutant transformation in the Changjiang River basin and provides reference to the ecological restoration of aquatic environments. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs), in particular those consisting of the cyanobacteria Microcystis, are becoming increasingly more common across the globe. Despite the growing body of evidence that suggests vertical heterogeneity of Microcystis can be a precursor to HAB formation, the abiotic drivers of vertical distribution of Microcystis are poorly understood in the field environment. The prediction of subsurface cyanobacteria is also pertinent because subsurface concentrations are not easily recognizable to the public or lake system managers, creating a risk of exposure to harmful algal toxins. High‐frequency temporal and vertical data were collected from a research station anchored in a stratified and eutrophic lake for five months. Using a combination of dimensional analysis and machine learning approaches, data show that the magnitude of the subsurface Microcystis concentration peak and the center of gravity of the deep cyanobacteria layer are statistically significantly mediated by the thermal structure of the lake. The peak subsurface cyanobacteria biovolume is related to the thermocline depth and temperature, whereas the center of gravity of the subsurface cyanobacteria biovolume is related to the mixed layer depth and temperature. Furthermore, our data suggest there is a seasonal evolution of the subsurface cyanobacteria center of gravity that could potentially indicate timing of HAB onset. Based on easily measured parameters associated with the vertical lake temperature profile and meteorological conditions, we provide evidence of predictable trends in subsurface cyanobacteria variables. Key Points: A high frequency, long‐duration field study reveals diurnal and seasonal trends in cyanobacteria vertical distribution dynamicsIn a stratified lake environment, magnitude of subsurface cyanobacteria peak concentration is driven primarily by the depth and temperature at the thermoclineIn a stratified lake environment, center of gravity of subsurface cyanobacterial biomass is driven primarily by the width and temperature of the surface mixed layer [ABSTRACT FROM AUTHOR]

Quantifying and predicting the drawdown of dissolved oxygen (DO) in lakes is important to ensuring healthy ecosystems and safe water sources. The characterization of DO depletion using available definitions and models requires extensive monitoring to obtain reliable results. These approaches have been mostly developed for seasonally stratified monomictic and dimictic lakes, limiting their applicability for polymictic systems which stratify and mix repeatedly. We compared the predicted duration of hypoxic events in the three basins of a large eutrophic polymictic lake (Clear Lake, CA, USA) by using three different one‐dimensional (1‐D) analytical approaches; two being original and requiring minimal input variables. Data on meteorology, lake temperature, and DO were all measured at multiple locations for one year and used to develop a novel method, named the Birge‐Winkler method. The daily net surface heat fluxes provided an energy term from which estimates of the onset and length of hypoxic periods could be made with minimal calibration. We used the Lake Number method to evaluate the level of accuracy of the Birge‐Winkler method. Finally, we estimated DO values next to the sediments using a Buoyancy Frequency method. Our results from the two original methods provided simple and effective tools for early warning of onset and duration of hypoxia, with a maximum of ±3–5 days uncertainty in the predictions. These indices can become powerful decision support tools for addressing aquatic ecological challenges triggered by hypoxia, including fish kills, internal nutrient loading, heavy metals release, and harmful algal blooms. Key Points: We present a new one‐dimensional method to estimate onset and duration of hypoxic events in eutrophic polymictic lakesThe model only requires basic meteorological variables, lake surface temperatures, and dissolved oxygen at the lake bottom for calibrationThe method can be a cost‐effective decision‐making tool for management actions affecting ecosystem health and water quality [ABSTRACT FROM AUTHOR]

Arsenic (As) is a metalloid that can accumulate in eutrophic lakes and cause adverse health effects to people worldwide. However, the seasonal process and dynamic mechanism for As mobilization in eutrophic lake remains effectively unknown. Here we innovatively used the planar optodes (PO), high-resolution dialysis (HR-Peeper) combined with fluorescence excitation-emission matrix coupled with parallel factor (EEM-PARAFAC) analysis technologies. We synchronously investigate monthly O 2 , As, iron (Fe), manganese (Mn), and naturally occurring dissolved organic matter (DOM) changes in sediments of Lake Taihu at high resolution in field conditions. We find high As contamination from sediments with 61.88–327.07 μg m−2 d−1 release As fluxes during the algal bloom seasons from May to October 2021. Our results show that an increase in DOM, mainly for humic-like components, resulting in high electron transfer capacity (ETC), promoted the reductive dissolution of Fe and Mn oxides to release As. Partial least square-path modeling (PLS-PM) and random forest modeling analysis identified that Mn oxide reductive dissolution directly accelerated sediments As contamination, which is the crucial factor. Understanding crucial factor controlling As release is especially essential in areas of eutrophic lakes developing effective strategies to manage As-rich eutrophic lake sediments worldwide. [Display omitted] • Monthly monitoring revealed high sediment As pollution during algal bloom seasons. • High DOM triggers the Mn/Fe redox cycle by increasing sediment ETC to release As. • PLS-PM analysis identified Mn redox cycle accelerating sediment As contamination. [ABSTRACT FROM AUTHOR]

The environmental risks resulting from the increasing antivirals in water are largely unknown, especially in eutrophic lakes, where the complex interactions between algae and drugs would alter hazards. Herein, the environmental risks of the antiviral drug arbidol towards the growth and metabolism of Microcystis aeruginosa were comprehensively investigated, as well as its biotransformation mechanism by algae. The results indicated that arbidol was toxic to Microcystis aeruginosa within 48 h, which decreased the cell density, chlorophyll-a, and ATP content. The activation of oxidative stress increased the levels of reactive oxygen species, which caused lipid peroxidation and membrane damage. Additionally, the synthesis and release of microcystins were promoted by arbidol. Fortunately, arbidol can be effectively removed by Microcystis aeruginosa mainly through biodegradation (50.5% at 48 h for 1.0 mg/L arbidol), whereas the roles of bioadsorption and bioaccumulation were limited. The biodegradation of arbidol was dominated by algal intracellular P450 enzymes via loss of thiophenol and oxidation, and a higher arbidol concentration facilitated the degradation rate. Interestingly, the toxicity of arbidol was reduced after algal biodegradation, and most of the degradation products exhibited lower toxicity than arbidol. This study revealed the environmental risks and transformation behavior of arbidol in algal bloom waters. [Display omitted] • The environmental risks of arbidol (ARB) in eutrophic lakes were firstly investigated. • ARB was hazardous to the growth and metabolism of M. aeruginosa within 48 h. • The synthesis and release of MCs by M. aeruginosa were promoted by ARB exposure. • ARB can be degraded by intracellular enzymes via loss of thiophenol and oxidation. • The toxicity of the ARB solution was decreased after M. aeruginosa biodegradation. [ABSTRACT FROM AUTHOR]

Lake eutrophication mitigation measures have been implemented by ecological water diversion, however, the responses of carbon cycle to the human-derived hydrologic process still remains unclear. With a famous river-to-lake water diversion activity at eutrophic Lake Taihu, we attempted to fill the knowledge gap with integrative field measurements (2011–2017) of gas carbon (CO 2 and CH 4) flux, including CO 2 -equivalent, and dissolved carbon (DOC and DIC) at water-receiving zone and reference zone. Overall, results showed the artificial water diversion activity increased gas carbon emissions. At water-receiving zone, total gas carbon (expressed as CO 2 -equivalent) emissions increased significantly due to the occurring of water diversion, with CO 2 flux increasing from 9.31 ± 16.28 to 18.16 ± 12.96 mmol C m−2 d−1. Meanwhile, CH 4 emissions at water-receiving zone (0.06 ± 0.05 mmol C m−2 d−1) was double of that at reference zone. Water diversion decreased DOC but increased DIC especially at inflowing river mouth. Temporal variability of carbon emissions and dissolved carbon were linked to water temperature, chlorophyll a , and nutrient, but less or negligible dependency on these environment variables were found with diversion occurring. Water diversion may increase gas carbon production via stimulating DOC mineralization with nutrient enrichment, which potentially contribute to increasing carbon emissions and decreasing DOC at the same time and the significant correlation between CO 2 flux and CH 4 flux. Our study provided new insights into carbon biogeochemical processes, which may help to predict carbon fate under hydrologic changes of lakes. • The river-to-lake water diversion increased the gas carbon emissions from lake. • Low DOC occurred especially at inflowing river mouth with the water diversion. • Temperature and eutrophication dependency of carbon efflux decrease with diversion. • Diversion-induced changes in N and eutrophication led to enhanced carbon emissions. [ABSTRACT FROM AUTHOR]

Inland shallow lakes are recognized as an important source of greenhouse gases (GHGs), and their contribution is expected to increase due to global eutrophication. The generation and release of GHGs involved multiple variables, leading to many uncertain potential factors. This study examined the emission characteristics of GHGs at the water-air interface in 12 shallow lakes categorized into four eutrophic levels in the Yangtze River basin. The average emission rates of CH 4 , CO 2 and N 2 O were 1.55, 3.43, 18.13 and 30.47 mg m−2 h−1, 4.12, 14.64, 25.11 and 69.84 mg m−2 h−1, and 0.2, 0.25, 0.43 and 0.79 mg m−2 day−1 in the oligotrophic, mesotrophic, eutrophic and hypereutrophic lakes, respectively. There were significant correlations between eutrophic levels and the emission rates of CH 4 and CO 2 (p < 0.05). Redundancy analysis and Mantel test were conducted to further examine the key factors influencing carbon emissions from eutrophic water. It was found that the presence of algae and nutrients in the overlying water played a crucial role in the release of GHGs, indicating the importance of ecosystem productivity in the carbon budget of the lake. In order to assess the bioavailability of organic matter, a new indicator called R (P/H) was proposed. This indicator represents the ratio of protein and humus-like components, which were obtained through EEMs-PARAFAC modeling. The relationship between R (P/H) and CH 4 was found to be exponential (R2 = 0.90). Additionally, R (P/H) showed a linear relationship with CO 2 and N 2 O (R2 = 0.68, R2 = 0.75). Therefore, it is crucial to consider R (P/H) as an important factor in accurately estimating global GHG emission fluxes in the future, especially with advancements in the database. [Display omitted] • Greenhouse gas emissions along trophic level gradients were investigated in lakes. • Source and components of dissolved organic matter varied in different trophic lakes. • Greenhouse gas emission rates were positively correlated with trophic level index. • A new indicator of R (P/H) was defined to evaluate dissolved organic matter composition. • High correlations between R (P/H) and greenhouse gases were observed to improve prediction methods. [ABSTRACT FROM AUTHOR]

Clonal fragmentation (CF), caused by various disturbances, significantly affects the growth performance of plants. However, little is known about how CF affects the growth of submersed macrophytes facing light limitation and nutrient enrichment, a typically situation found in eutrophic lakes. To examine the effects of CF on Vallisneria natans (Lour.) Hara, a common submersed macrophyte species in warm lakes, we combined three different light intensities (4%, 15%, and 30% natural light) with three different nutrient levels in the water and kept the stolons severed or intact. We found that CF negatively affected the growth of V. natans and that the effect strongly depended on light and nutrient levels. Our comparison between severed and intact plants showed that CF decreased the biomass accumulation under moderate-light conditions, whereas no significant difference appeared at low and high light levels. The negative effect of CF on plant biomass tended to be more significant at moderate and high nutrient levels. The total chlorophyll content decreased with CF at moderate and high nutrient levels when light availability was high. Our study adds new information about the role of CF on the survival and growth of submersed macrophytes in eutrophic lakes. [ABSTRACT FROM AUTHOR]

Volatile organic sulfur compounds (VOSCs) function as a water–atmosphere link in the global sulfur cycle. It is generally believed that the vast majority of VOSCs are released from the ocean. However, due to the pervasive eutrophication and pollution of inland waters, the VOSC production and emission in rivers, lakes and reservoirs are attracting more attention. In this study, the temporal and spatial distributions of three VOSCs, including methanethiol, Dimethyl sulfide, and dimethyl disulfide in Yangcheng Lake, a eutrophic shallow lake, are investigated monthly and seasonally. Results show that VOSCs are higher in summer and autumn, with the western region as a hotspot. Our results show a positive correlation between VOSC and phytoplankton biomass (p < 0.05). Interestingly, from algal phylum composition, all the phylum, except those with low biomass, played a positive effect on VOSCs’ concentration. We did not find any specific phylum or species of cyanobacteria that contributed solely to the VOSCs. The water-air effluxes of Dimethyl sulfide (DMS) are estimated by a stagnant film model. The DMS effluxes from Yangcheng Lakes were higher than deep lakes and similar to the ocean, indicating that VOSCs, particularly DMS, in those eutrophic shallow lakes were non-negligible.

Lacustrine sediment played important roles in migration and transformation of its water soluble organic matter (WSOM), and the source and composition of WSOM would affect water trophic status and the fate of pollutants. However, we know little about the pathway of WSOM transformation and its driving bacterial communities in lacustrine sediment. In the present study, we investigated the spatial distribution patterns of sediment WSOM and its fluorescent fractions across Lake Chaohu using fluorescence spectroscopy, and explored WSOM compositional structure through our proposed calculated ratios. In addition, we also analyzed sediment bacterial community using Illumina sequencing technology, and probed the possible pathway of sediment WSOM transformation under the mediate of indigenous bacteria. Our results showed that the inflowing rivers affected the spatial distribution patterns of WSOM and its five fractions (including tyrosine-, tryptophan-, fulvic acid-, humic acid-like substances and soluble microbial productions), and sediment WSOM originated from fresh algae detritus or bacterial sources. In parallel, we also found that Proteobacteria (mainly γ-Proteobacteria and δ-Proteobacteria), Firmicutes (mainly Bacilli), Chloroflexi, Acidobacteria, Planctomycetes and Actinobacteria dominate sediment bacterial community. Furthermore, these dominant bacteria triggered sediment WSOM transformation, specifically, the humic acid-like substances could be converted into fulvic acid-like substances, and further degraded into aromatic protein-like and SMP substances. In addition, our proposed ratios (P-L:H-L, Ar-P:SMP and H-L ratio), as supplementary tool, were effective to reveal WSOM composition structure. These results figured out possible pathway of WSOM transformation, and revealed its microbial mechanism in lacustrine sediment. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Coexisting floating-leaved and submerged plants experience similar environmental changes but may evolve different patterns of genetic variation. To compare local-scale genetic variation, we collected samples of floating-leaved Nymphoides peltata and submerged Myriophyllum spicatum coexisting in a disturbed urban lake in China. At the subpopulation level, using microsatellites, M. spicatum had higher clonal diversity than N. peltata. M. spicatum had 28.4% multilocus genotypes (MLGs) shared between subpopulations, but N. peltata had only one MLG shared between two adjacent subpopulations. N. peltata displayed more genetic variation between subpopulations than within subpopulations, but the reverse was true for M. spicatum. Principal components and Bayesian cluster analyses showed that individuals from each subpopulation of N. peltata tended to have relatively close genetic relationships. For M. spicatum, individuals from each subpopulation were genetically scattered with those from other subpopulations. Our results imply that in unpredictable adverse environments M. spicatum may be less subjected to local-deme extinction than N. peltata because of genetically diverse clones at the subpopulation level. This characteristic means that following adverse events, M. spicatum may rapidly restore subpopulation distributions via re-colonization and intense gene flow among subpopulations. [ABSTRACT FROM AUTHOR]

Environmental controls on methane (CH4) emission from lakes are poorly understood at subdaily time scales due to a lack of continuous data, especially for ebullition. We used a novel technique to partition eddy covariance CH4 flux observed in the littoral zone of a midlatitude shallow lake in Japan and examined the environmental controls on diffusion and ebullitive CH4 flux separately at a subdaily time scale in different seasons. Using the high‐frequency data, we investigated how CH4 accumulation in the water and sediment layers alters the dynamics and environmental controls of fluxes. The contribution of ebullitive flux to total flux was 57% on average. Environmental controls of diffusive and ebullitive fluxes known in the literature were confirmed. We further found that the environmental controls were different in different seasons and suggested that additional consideration of CH4 accumulation could explain the variability. The transfer of accumulated dissolved CH4 from the bottom water layer to the surface in summer and the accumulation of dissolved CH4 under surface ice in winter were suggested to be important for explaining the variability of diffusive flux. In summer, a higher ebullitive flux tended to occur following triggers such as a decrease in hydrostatic pressure. In winter, the impact of triggers was not obvious, and a higher ebullitive flux tended to occur in the morning. We suggested that the low CH4 production rate in winter slowed the replenishment of bubbles in the sediment, negating the effect of triggers on ebullition. Plain Language Summary: Lakes are one of the main natural sources of methane (CH4). Methane is emitted from lake sediments to the atmosphere via diffusion through the water column and episodic emission of bubbles (ebullition). Currently, environmental controls at subdaily time scales are poorly understood due to a lack of continuous data, especially for ebullition. We applied a new technique to partition continuous CH4 flux data obtained with the eddy covariance technique in a midlatitude shallow lake into diffusive and ebullitive fluxes and examined their environmental controls separately. We confirmed that the diffusive flux increased with increasing wind speed and increasing dissolved CH4 concentrations in the surface water as known in the literature. We further suggested that for this shallow lake, the transfer of accumulated dissolved CH4 from the bottom water layer to the surface under thermally stratified conditions was important for explaining the variability in diffusive flux. In summer, a higher ebullitive flux tended to occur following a decrease in hydrostatic pressure. In winter, however, the impact of triggers was not obvious. We suggested that, in winter, the low CH4 production rate slowed the replenishment of bubbles in the sediment, negating the effect of triggers on ebullition. Key Points: Partitioned diffusive and ebullitive methane fluxes from a shallow lake were examined for their subdaily environmental controlsThe subdaily environmental controls of diffusive and ebullitive fluxes were different in different seasonsThe accumulations of methane in the water and sediment were suggested to alter the environmental controls of fluxes between seasons [ABSTRACT FROM AUTHOR]

The water quality of Lake Mariut has been deteriorated for about 5 decades due to continuous discharge of agricultural, municipal, and industrial wastes from Alexandria City and the adjacent land. During the past two decades, some steps were taken for rehabilitation of the lake through primary treatment of the discharged wastes and insulation of the polluted wastewater of QD from the water body in the main basin of the lake. Several parameters of water quality at the surface and near bottom were measured at twelve locations during winter (January) and summer (August) of 2013 and 2014. The present study revealed that the lake water appeared to be well aerated but still containing high concentrations of N and P and suffering hyper-eutrophic conditions. The water quality index (WQI) reflected medium condition in the lake and bad condition in the diverted drains. The P-budget calculation displayed that TP input into the LMMB from UDus and resuspension process from sediments exceeded the output by out flowing at UDds and settling. [ABSTRACT FROM AUTHOR]

Understanding the biogeochemical controls on the partitioning between nitrogen (N) removal through denitrification and anaerobic ammonium oxidation (anammox), and N recycling via dissimilatory nitrate (NO3–) reduction to ammonium (DNRA) is crucial for constraining lacustrine N budgets. Besides organic carbon, inorganic compounds may serve as electron donors for NO3– reduction, yet the significance of lithotrophic NO3– reduction in the environment is still poorly understood. Conducting incubation experiments with additions of 15N-labeled compounds and reduced inorganic substrates (H2S, Fe2+, Mn2+), we assessed the role of alternative electron donors in regulating the partitioning between the different NO3–-reducing processes in ferruginous surface sediments of Lake Lugano, Switzerland. In sediment slurry incubations without added inorganic substrates, denitrification and DNRA were the dominant NO3–-reducing pathways, with DNRA contributing between 31 and 46% to the total NO3– reduction. The contribution of anammox was less than 1%. Denitrification rates were stimulated by low to moderate additions of ferrous iron (Fe2+ ≤ 258 μM) but almost completely suppressed at higher levels (≥1300 μM). Conversely, DNRA was stimulated only at higher Fe2+ concentrations. Dissolved sulfide (H2S, i.e., sum of H2S, HS– and S2−) concentrations up to ∼80 μM, strongly stimulated denitrification, but did not affect DNRA significantly. At higher H2S levels (≥125 μM), both processes were inhibited. We were unable to find clear evidence for Mn2+-supported lithotrophic NO3– reduction. However, at high concentrations (∼500 μM), Mn2+ additions inhibited NO3– reduction, while it did not affect the balance between the two NO3– reduction pathways. Our results provide experimental evidence for chemolithotrophic denitrification or DNRA with Fe2+ and H2S in the Lake Lugano sediments, and demonstrate that all tested potential electron donors, despite the beneficial effect at low concentrations of some of them, can inhibit NO3– reduction at high concentration levels. Our findings thus imply that the concentration of inorganic electron donors in lake sediments can act as an important regulator of both benthic denitrification and DNRA rates, and suggest that they can exert an important control on the relative partitioning between microbial N removal and N retention in lakes. [ABSTRACT FROM AUTHOR]

Epizoic diatom communities were studied on four turtle species (Chelonia mydas L., Eretmochelys imbricata L., Lepidochelys olivacea Eschscholtz and Dermochelys coriacea Vandelli) from the Eastern Caribbean, the Equatorial West Atlantic and the South Pacific. In the present study, we focused on one taxon of Navicula Bory de Saint-Vincent, described here as a new taxon, which was found on seven individuals of Dermochelys coriacea and one individual of Lepidochelys olivacea in French Guiana. The new Navicula taxon was found neither on Chelonia mydas (83 specimens examined) nor Eretmochelys imbricata (13 specimens examined). Furthermore, the new taxon appears to have a restricted biogeography, as so far it has only been reported from French Guiana. A species of Navicula is reported for the first time as a supposedly exclusive epizoic taxon. Navicula dermochelycola sp. nov. is characterized in detail; its ultrastructure is described and compared with other members of Navicula. [ABSTRACT FROM AUTHOR]

We have determined how Crustacea, zebra mussels (Dreissena polymorpha), fish and nutrients affect the trophic state in mesocosms filled with water collected from the pelagic zone of a eutrophic lake. We hypothesized that the pool of nutrients would increase both directly due to the input of phosphorus and nitrogen and/or indirectly due to the introduction of animal biomass. We used trophic state indices based on the abundance and species structure of rotifers to assess changes in the trophic state in mesocosms. The role of small detritophages in rotifer communities increased as a result of treatments. Our results clearly demonstrated that D. polymorpha was able to reduce the trophic status of mesocosm waters as indicated by reduced rotifer trophic state indices regardless of interactions with other treatment factors. Contrary to our expectations, neither the nutrients added at the beginning of the experiment nor the introduction of crustaceans or fish affected the rotifer trophic indices. [ABSTRACT FROM AUTHOR]

A good understanding of lead (Pb) mobilization in eutrophic lakes is a key to the accurate assessment of Pb pollution. In this work, dissolved and labile Pb was determined by both high resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) in sediment-water profiles of the hyper-eutrophic Meiliang Bay of Lake Taihu on a monthly basis during one year. The drinking water standards for dissolved Pb of the World Health Organization (10 μg/L) and those of China were exceeded in the overlying water (20.79–118.5 μg/L). Out of which, a total of five months even exceeded the fisheries water quality limitation (50 μg/L) in China. The algal blooms created an anaerobic environment in the surface sediments in July. The reductive conditions led to the dissolution of Fe/Mn and this caused the release of Pb, followed by organic matter complexation. This was supported by the coincident changes of dissolved Pb with dissolved organic matter (DOM) in sediments under anaerobic incubation. Algae residue decomposition in October caused another distinct release of Pb, but this process should be considerably suppressed by increased sulfide precipitation and pyrite adsorption of Pb ion. These results indicated that Pb mobilization in sediments can be significantly enhanced by algal blooms in eutrophic lakes, indicating that further attention should be paid to Pb pollution in waters with harmful algal blooms. Unlabelled Image • Mobile Pb was studied using high-resolution techniques in eutrophic lake sediment. • Soluble Pb concentrations in overlying water in summer and autumn exceeded EPA-CMC. • Fe/Mn oxide reduction and DOC complexation induced high Pb mobility in summer. • Algal bioaccumulation and decomposition induced high Pb mobility in autumn. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fish biomass were driven by fish stocking, catches, and ecological effects. • The ecosystem was unstable and showed a decreasing trend in maturity. • The ten-year fishing ban may fail to achieve the expected goal of restoration. • Fish of different feeding types require different targeted policies. With increasing anthropogenic activities, freshwater ecosystems around the world are becoming increasingly affected by various pressures, including eutrophication, overfishing, and irrational stocking, which may have a negative impact on the food web structure. Despite the extensive research and proposed management measures for eutrophic lakes, there are only few analysis on long-term monitoring data regarding fishery resources. Additionally, there is a lack of evaluation and prediction of the effectiveness of current fish management policies. To remedy this, we analyzed long-term monitoring data from Lake Taihu, China, a severely eutrophicated lake with a skewed fish size structure exhibiting dominance of small individuals. We first constructed 14 Ecopath models to investigate how trophic interactions and biomass fluxes changed from 2007 to 2020. Subsequently, the Ecosim model was used to predict how the biomass of fish and the ecosystem network respond to the initiated 10-years fishing ban. Our results demonstrate long-term changes in fish biomass and ecosystem stability. The analyses revealed that 1) the biomass development in different feeding types of fish is controlled by human activities (mainly catches and stocking) and trophic interactions and 2) the rate of decline in ecosystem network stability slows down during the fishing ban. The primary focus of this study was to fill the gap in long-term serial studies of fish monitoring data and ecosystem stability in the lake and, for the first time, to predict the outcome of the fishing ban from an ecosystem perspective using the Ecosim model. Overall, our results emphasize the importance of rational stocking and fishing policies and provide a better understanding of the changes in the ecological dynamics in Lake Taihu of relevance for the management and restoration of the lake. [ABSTRACT FROM AUTHOR]

Lake Alboraj, located in southeast Spain, was declared natural Microreserve and included into European Natura-2000 Network due to its contribution to environmental heritage. Unfortunately, the ecological status of the lake has changed dramatically, mainly due to the lowering of water table caused by groundwater abstractions for irrigation. It is a permanent small karstic lake whose surface has reduced in the last decades to nearly the third part of its historical water level. The water column shows a marked seasonal oxycline, that splits an aerobic upper layer (epilimnion) from an anaerobic layer below (hypolimnion). Sequencing 16S rRNA gene amplicons and applying chemical tools at epilimnion, hypolimnion and sediment, showed a clear gradient in the bacterial community structure, which support the co-existence of assimilatory and dissimilatory microbial mediated reactions. Results allows to infer that microbial stratification could provide various physical and chemical environments at different depths in the water column related to biogeochemical reactions providing N-S-C- recycling processes.

Increasing amount of aluminum (Al) gets into aquatic ecosystem through anthropogenic activity, but the knowledge about Al migration and relationships with sediments possessing different physico-chemical properties in eutrophic lakes is limited. Here, the Al migration rule and relationships with sediment nutritions in the Hangzhou West Lake, China was investigated, where a certain amount of residual Al-salts can enter because of the pre-treatment of the Qiantang River diversion project every day. Results revealed the obvious spatial distribution heterogeneity of Al in sediment vertical direction and horizontal direction following water flow. The Al content in sediment ranged 0.463–1.154 g kg−1 in Maojiabu Lake, and ranged 9.862–40.442 g kg−1 in Xiaonanhu Lake. Higher Al content distributed in upper layer sediment in lake with more disturbance. Total nitrogen (TN) contents were higher 0.917–3.387 mg g−1 and 0.627–0.786 mg g−1 in upper layer sediment than that in lower layer in Maojiabu Lake and Xiaonanhu Lake, respectively. Total phosphorus (TP) content ranged 0.779–2.580 mg g−1, in which IP and Fe/Al-P contributed 24.9–80.8% and 17.0–51.6%, respectively. Correlations between Al content with nutrition, humic acid (HA) etc. of sediment regionally varied in Maojiabu and Xiaonanhu Lake. Spatial distribution of Al-salt in eutrophic lakes closely related with the physico-chemical characteristics of nutrients, humus, human disturbance and water division parameters. Results provides new insight into Al-salts migration and references for Al-risk evaluating in eutrophic lakes. Image 1063 • Increasing amount of Al gets into water bodies due to human activities. • Spatial distribution heterogeneity of Al contents in sediment in eutrophic lake. • Higher Al contents distributed in upper layer sediment for disturbance. • Al contents positive correlated with TN, IP, HA, ORP, negative with OP, pH in sediment. • Conjugation of P-Al, HA-Al may passivate Al-salts entering eutrophic lake. Capsule: Al contents present spatial distribution heterogeneity in sediment in eutrophic lake, and correlate with nitrogen, phosphorus, humic acid content, etc. [ABSTRACT FROM AUTHOR]

A leaf-bag field experiment was conducted to investigate the decomposition and release of nutrients from leaves of two aquatic macrophytes (floating-leaved Trapa bispinosa and submerged Vallisneria natans) deposited in the four vertical locations (i.e. air-water interface, AW; sediment-water interface, SW; buried at a depth of 10 cm, B10; buried at a depth of 20 cm, B20) of littoral zone in Nanhu Lake, China, for 60 days from July to August 2015. Leaf initial quality significantly influenced mass loss and nutrient release except TN (total nitrogen) remaining. Compared to V. natans, T. bispinosa leaves decomposed faster under the same treatments. The decomposition was greatly affected by both leaf chemical quality and the location of deposition. With the increasing depth of vertical locations, leaf biomass loss and nutrient release of both T. bispinosa and V. natans decreased. In addition, initial N:P ratio and cellulose were the major determinants for decomposition in AW and SW treatments while total phenol in B10 and B20. Our results suggest that the combined effect of leaf chemical quality and burial could mediate macrophyte mass loss and release of nutrients and carbon, which in turn can influence organic matter accumulation and nutrient cycling in shallow freshwater lakes. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) has been assumed to play an important role in nitrogen removal from ecosystems. This study assessed the potential role of Feammox in nitrogen transformation in eutrophic lake sediment using an isotope tracing technique in sediment slurry incubation experiments. Feammox was discovered in eutrophic lake sediment. A significant correlation was found between Feammox rates and iron-reducing rates. Furthermore, the positive correlations between the abundance of iron-reducing bacteria (FeRB), such as Geobacteraceae spp. and Shewanella spp., and Feammox rates indicate that Feammox was mediated by FeRB. The potential rate of Feammox in the isotopic tracer incubation treatment was 0.23–0.43 mg N kg−1 day−1. The estimated nitrogen loss caused by Feammox accounts for 5.0–9.2% of the human-induced N input annually into the eutrophic lake. Feammox alone or coupled with anaerobic ammonium oxidation (anammox) and/or denitrification may have an essential role in the nitrogen cycle within eutrophic lake sediment. [ABSTRACT FROM AUTHOR]