Effects Of Eutrophication Research Articles

Effect of river-lake connectivity on ecological stoichiometry of lake and carbon storage status in Eastern Plain, China.

C, N, and P in lake sediment are the basis of material and energy cycle, reflecting the economic development, ecological function, and environmental effect. Current research on the effect of lake eutrophication on carbon storage and the river-lake connectivity on nutrient diffusion is lack. This work investigated the accumulation, distribution, correlations, and stoichiometric ratios of C, N, and P of 82 lakes (≥ 10km2) in Eastern China, analyzed the nutrient limitation, sediment carbon sink, and effect of river-lake connectivity, and discussed the relationships between eutrophication and sediment carbon storage. The average concentrations and ranges of total C, N, and P in lake sediments were (23.26mg/g, 0.08-153.45mg/g), (2.32mg/g, 0.29-14.17mg/g), and (0.86mg/g, 0.23-2.64mg/g), respectively. The ecological stoichiometry of C: N: P in lake sediments was 32: 3.2: 1. P can be easily accumulated in lakes connected from the Yangtze River, while C and N can be easily accumulated in disconnected lakes. The soil-water erosion in runoff is an important factor for P diffusion. The C/N and C/N/P weren't affected by the river-lake connectivity but depended on the plant type. The Eastern Plain Lake Region of China is C and N co-depletion, and P enrichment. The lake eutrophication leading to algal bloom is unfavorable to the goal of carbon storage and carbon neutrality. Outcome of this study will provide a significant reference and strategies for carbon sequestration research, eco-environmental protection, and watershed nutrient management.

A hybrid empirical and parametric approach for managing ecosystem complexity: Water quality in Lake Geneva under nonstationary futures

Severe deterioration of water quality in lakes, characterized by overabundance of algae and declining dissolved oxygen in the deep lake (DOB), was one of the ecological crises of the 20th century. Even with large reductions in phosphorus loading, termed "reoligotrophication," DOB and chlorophyll (CHL) have often not returned to their expected pre-20th-century levels. Concurrently, management of lake health has been confounded by possible consequences of climate change, particularly since the effects of climate are not neatly separable from the effects of eutrophication. Here, using Lake Geneva as an iconic example, we demonstrate a complementary alternative to parametric models for understanding and managing lake systems. This involves establishing an empirically-driven baseline that uses supervised machine learning to capture the changing interdependencies among biogeochemical variables and then combining the empirical modelwith a more conventional equation-based model of lake physics to predict DOB over decadal time-scales. The hybrid model not only leads to substantially better forecasts, but also to a more actionable description of the emergent rates and processes (biogeochemical, ecological, etc.) that drive water quality. Notably, the hybrid model suggests that the impact of a moderate 3°C air temperature increase on water quality would be on the same order as the eutrophication of the previous century. The study provides a template and a practical path forward to cope with shifts in ecology to manage environmental systems for non-analogue futures.

Fluxes of riverine nutrient to the Zhujiang River Estuary and its potential eutrophication effect

Fluxes of riverine nutrient to the Zhujiang River Estuary and its potential eutrophication effect

Amphipod Isotope Composition, Condition and Reproduction in Contrasting Sediments: A Reciprocal Transfer Experiment

Eutrophication is a process that results in excessive phytoplankton blooms, which sink to the sediment and enrich the organic matter (OM). This alters the available resources to benthic organisms and may have consequences for feeding ecology and reproduction strategies of marine populations. While effects of eutrophication on biodiversity are well documented, the more subtle effects of OM on population dynamics and diet plasticity are understudied. We performed a reciprocal transfer experiment with the benthic bioindicator amphipod Monoporeia affinis from two stations in the Baltic Sea with differing sediment OM (low and high) creating four treatments (low control, low transferred, high transferred, and high control). We investigated sediment OM effects on: i) the dietary niche and organism body condition of two different life stages of M. affinis utilizing bulk stable isotopes δ13C and δ15N, and C:N ratio; and ii) M. affinis fecundity and embryo viability. There was no initial significant differences between the females from different stations in terms of δ13C, δ15N, C:N, fecundity or viable embryos. However, we found that moving females from high OM to low OM (where the low OM sediment has higher δ15N and lower δ13C) significantly depleted their 13C values, while amphipods in low OM sediment had always significantly enriched 15N regardless of female origin indicating feeding on the new sediment. Although end-of-experiment females had lower C:N than initial females, individuals in low OM sediment presented significantly higher C:N (indicating higher body condition) than those in high OM sediment. Conversely to adult amphipods, no effects of OM were seen for juveniles δ13C or δ15N, but their individual biomass was larger in high OM sediment treatments and high OM transferred to low OM sediment. Our results indicate that the low range of sediment OM tested here altered female amphipod δ13C, δ15N and C:N ratios, with those in low OM treatments having a better body condition, but those in high OM treatments had a greater reproductive success in terms of offspring biomass. Our findings suggest a tradeoff between female condition and reproduction and indicates that even relatively small levels of sediment organic enrichment will impact female condition. Our study provides valuable information useful to interpret the effects of OM on amphipod populations used as bioindicators for anthropogenic impacts.

Benthic–Pelagic Coupling in the Oligotrophic Eastern Mediterranean: A Synthesis of the HYPOXIA Project Results

Benthic–pelagic coupling studies have shown that the response of the benthic system to eutrophication is subject to complex nonlinear dynamics with specific thresholds beyond which abrupt changes in the response of the ecosystem occur and time lags between inputs and responses. The “HYPOXIA: Benthic–pelagic coupling and regime shifts” project aimed to investigate how nutrient input in the water column results in ecological processes of eutrophication, which may lead to significant, irreversible changes in the eastern Mediterranean marine ecosystems within a short period of time. The project included analysis of historical water and benthic data, field sampling, and mesocosm experiments. From the project results, it can be concluded that nutrient inputs are quickly capitalized by small phytoplankton species in the water column resulting in the bloom of specific species with high nutrient uptake capabilities. When Eutrophic Index values (calculated using nutrient and chlorophyll-a concentrations) cross the moderate-to-poor threshold, the precipitating organic matter can cause observable effects on the benthic system. Depending on eutrophication intensity and persistence, the effects can start from microbenthos, meiofauna, and macrofauna increase in abundance and biomass to significant changes in the community structure. The latter includes the proliferation of macrofaunal opportunistic species, an increase in deposit feeders, and the high risk of ecosystem quality degradation. However, contrary to other regions of the world, no water hypoxia or benthic dead zones were observed as chlorophyll-a and O2 concentrations showed a positive correlation. This is caused by the high photosynthetic activity of the phytoplankton and microphytobenthos, the increased bioturbation of macrofauna, and the increased abundance of sediment deposit-feeding species, which quickly consume the excess organic matter. Eastern Mediterranean coastal ecosystems show high resilience to the adverse effects of eutrophication, preventing hypoxia and azoic conditions when eutrophication is the only source of environmental disturbance.

Increases of opportunistic species in response to ecosystem change: the case of the Baltic Sea three-spined stickleback

Abstract Under rapid environmental change, opportunistic species may exhibit dramatic increases in response to the altered conditions, and can in turn have large impacts on the ecosystem. One such species is the three-spined stickleback (Gasterosteus aculeatus), which has shown substantial increases in several aquatic systems in recent decades. Here, we review the population development of the stickleback in the Baltic Sea, a large brackish water ecosystem subject to rapid environmental change. Current evidence points to predatory release being the central driver of the population increases observed in some areas, while both eutrophication and climate change have likely contributed to creating more favourable conditions for the stickleback. The increasing stickleback densities have had profound effects on coastal ecosystem function by impairing the recruitment of piscivorous fish and enhancing the effects of eutrophication through promoting the production of filamentous algae. The increase poses a challenge for both environmental management and fisheries, where a substantial interest from the pelagic fisheries fleet in exploiting the species calls for urgent attention. While significant knowledge gaps remain, we suggest that the case of the Baltic Sea stickleback increase provides generalisable lessons of value for understanding and managing other coastal ecosystems under rapid change.

The Structuring Effects of Salinity and Nutrient Status on Zooplankton Communities and Trophic Structure in Siberian Lakes

Many continental saline lakes are under the effects of salinity increase and anthropogenic eutrophication exacerbated by global change. The response of the food web to these drivers of change is not straightforward. To understand the consequences of salinity and eutrophication interactive effects on the food web, we studied the seasonal dynamics of zooplankton and phytoplankton and water quality parameters in 20 lakes of different salinity (from freshwater to hypersaline) and nutrient status (from oligotrophic to eutrophic) located in southern Siberia. We observed a pronounced bottom-up effect of nutrients, which induced an increase in the biomass of phytoplankton and zooplankton and a decline in water quality. A significant decrease in the species abundance of zooplankton was observed at a threshold salinity of 3 g L−1 and the disappearance of fish at 10 g L−1. The top-down effect induced by salinity manifested itself in an increase in the biomass of zooplankton with the disappearance of fish, and in the change of the size distribution of phytoplankton particles with an increase in the proportion of cladocerans in the zooplankton. Even though we observed that with the salinity increase the food web in saline lakes transformed from three-trophic to two-trophic without fish, we conclude that in the salinity range from 10 to 20–30 g L−1 this transition in most cases will not increase the ability of zooplankton to control phytoplankton. Interactive effects of salinity and eutrophication strongly depend on the size and depth of the lake, as deep stratified lakes tend to have a better water quality with lower biomasses of both phyto- and zooplankton. Thus, the salinity per se is not the driver of the decline in water clarity or the uncontrolled development of phytoplankton. Moreover, for deep lakes, salinity may be a factor affecting the stability of stratification, which mitigates the consequences of eutrophication. Thus, small shallow lakes will be the most vulnerable to the joint effect of salinity increase and eutrophication with the degradation of ecosystem functioning and water quality at moderate salinities of 3–20 g L−1.

Effects of Warming and Phosphorus Enrichment on the C:N:P Stoichiometry of Potamogeton crispus Organs.

The loss of submerged macrophytes from freshwater ecosystems is accelerating owing to the combined effects of eutrophication and climate change. Submerged macrophytes depend on spring clear water; however, increased water temperatures and excessive phosphorus (P) inputs often lead to the dominance of phytoplankton. It is still not clear how the stoichiometric characteristics of carbon (C), nitrogen (N), and P in different tissues of submerged macrophytes respond to P enrichment and temperature increases. In this study, we established 36 mesocosm ecosystems to explore the effects of warming and P addition on the leaf, turion, stem, and seed stoichiometry of Potamogeton crispus. The results revealed that different functional plant organs show distinct responses to P addition and warming, which demonstrates the importance of evaluating the responses of different submerged macrophyte organs to environmental changes. In addition, interactive effects between P addition and warming were observed in the leaf, turion, and seed C:N:P stoichiometry, which highlights the importance of multifactorial studies. Our data showed that warming caused a decrease in the C content in most organs, with the exception of the stem; P addition increased the P content in most organs, with the exception of seed; N content in the turion and seed were influenced by interactive effects. Collectively, P addition could help P. crispus to resist the adverse effects of high temperatures by aiding growth and asexual reproduction, and asexual propagules were found to be more sensitive to P enrichment than sexual propagules.

Penyisihan Fosfat dan Amonium Pada Air Limbah Menggunakan Presipitasi Struvite Dengan Penambahan Bittern

The fertilizer industry generally produces wastewater with relatively high ammonium and phosphate content, so processing is necessary so as not to cause eutrophication effects that harm the environment. Struvite precipitation with bittern media was an alternative method to remove struvite content in wastewater. This study aimed to analyze the effect of pH and molar ratio [Mg2+] : [NH4+] : [PO43-] on the struvite precipitation process in reducing the ammonium and phosphate content in the artificial wastewater of the fertilizer industry and to characterize the struvite obtained from the precipitation process. The precipitation process was conducted in batches with various pH and molar ratios [Mg2+]: [NH4+]: [PO43-]. The variation of pH used is 8−10. The molar ratios used are 1.5 : 1.0 : 1.0 and 3.0 : 1.0 : 1.0. Struvite characterization was conducted using SEM-EDX and XRD methods. The results showed that pH and molar ratio had an effect on the efficiency of removal ammonium and phosphate using struvite precipitation. The best pH value and molar ratio that can be used to remove content of ammonium and phosphate is at pH 9 with a molar ratio of [Mg2+] : [NH4+] : [PO43-] 3.0 : 1.0 : 1.0 which results in the removal efficiency of 86.50% and 99.96% respectively. The morphology of struvite obtained from precipitation is irregular rod-shaped with an average size of 28.53 μm. XRD results have detected peaks indicating the struvite phase.

Impacts of nutrient reduction on temporal β-diversity of rotifers: A 19-year limnology case study on Lake Wuli, China

There have been many studies on the effects of eutrophication on beta diversity (β-diversity) of species assemblages. However, few studies have focused on the effects of nutrient reduction on β-diversity and community structure, and long-time series analyses are particularly scarce. We conducted a 19-year case study on the impacts of management intervention on the temporal β-diversity of aquatic grazers in a lake at the Yangtze River Basin. In our study, we compared the changes in temporal β-diversity as well as its two components, nestedness and turnover, and the synchrony of the rotifer community after management intervention. Our results showed that while the abundance of some sensitive species increased, there was no trend in species richness. Moreover, both the seasonality and interannual stabilities of rotifer assemblages increased. The species synchrony decreased in both spring and summer after management intervention. We also found that management intervention significantly reduced nutrient concentrations but not water clarity and phytoplankton abundance. The total nitrogen (TN): total phosphorous (TP) ratio was reduced after management intervention, causing an increase in the abundance of cyanobacteria that may contribute to the increase of rotifer synchrony in autumn. Our results imply that stable environmental fluctuations after management intervention may increase temporal β-diversity and stability of herbivorous assemblages. However, imbalanced changes in TN and TP after management intervention may weaken the top-down control of zooplankton on phytoplankton and slow down water clarity improvement.

Adsorption of humic acids to lake sediments: Compositional fractionation, inhibitory effect of phosphate, and implications for lake eutrophication

Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbon and nutrients and thus the trophic state of a lake. The adsorption behavior of HAs to sediments in the absence and presence of phosphate was investigated in this study. Three types of HAs were used, AHA from algae-dominated lake sediments, MHA from macrophyte-dominated lake sediments, and a reference HA (RHA) with terrestrial sources. The adsorption capacity of lake sediments was highest for AHA, which can be explained by that AHA contained more carboxyl-containing molecules, proteinaceous compounds and polysaccharides that were preferentially adsorbed by minerals. Phosphate showed a stronger inhibitory effect on MHA adsorption than on AHA adsorption, suggesting that AHA can more effectively replace phosphate adsorbed to sediments. Our findings show that the functional groups of organic compounds control not only their fractionation and burial but also their ability to replace phosphate in sediments. We propose a novel mechanism to explain the legacy effect of lake eutrophication. That is, as lakes shift from a macrophyte-dominated state to more eutrophic, algae-dominated state, increasing algae-derived organic compounds can promote the release of phosphate from sediments, forming a positive feedback loop that sustains internal phosphorus loading and hence lake eutrophication.

Comparative Analysis of Physiological Responses in Two Ulva prolifera Strains Revealed the Effect of Eutrophication on High Temperature and Copper Stress Tolerance

Climate change directly influences species composition and distribution of macroalgae on a global scale. Meanwhile, eutrophication and heavy metal pollution continue to be major concerns in coastal areas. The objective of this study was to explore interactive effects of these complex environmental conditions (high temperature, eutrophication and heavy metal pollution) in the bloom forming green alga, Ulva prolifera. This study evaluated the physiological characteristics of two strains of U. prolifera (Korean strain and Chinese strain) at two temperature levels (20 and 25°C), two nutrient concentrations (low nutrient: 50 μM of N and 5 μM of P; high nutrient: 250 μM of N and 25 μM of P) and three copper concentrations [Control (0.03 μM); 0.1 μM; 1 μM]. Under the 20°C and low nutrient condition, the Chinese strain grew significantly slower at 1μM copper group compared to copper control group. Whereas there was no significant change in the growth rate of the Korean strain. High nutrient significantly increased the growth rate, photosynthetic and respiration rates, soluble protein and tissue N in both strains at all copper groups under 20°C compared to copper groups under 20°C and low nutrient condition. Both strains grew significantly slower at 1 μM copper group compare to copper control group under high nutrient and 20°C condition. 25°C significantly reduced the growth rate of both strains at each nutrient condition. Under 25°C and low nutrient condition, 1 μM copper had no effects on growth rate and all photosynthetic parameters of both strains. Meanwhile, under 25°C and high nutrient conditions, 1 μM copper significantly inhibited growth and photosynthetic rates and increased soluble protein content in the Chinese strain compared to copper control treatment. These results suggest that the Korean strain had higher tolerance to the copper stress than the Chinese strain. Higher nutrient levels enhanced the temperature tolerance and the copper stress in U. prolifera. Increased temperature reduced the negative effects caused by copper stress in U. prolifera.

Effects of sediment physicochemical factors and heavy metals on the diversity, structure, and functions of bacterial and fungal communities from a eutrophic river

Urbanization has destroyed river ecosystems, leading to eutrophication. Heavy metals are frequently observed in urban rivers, and the joint effects of eutrophication and heavy metals on microbial communities, especially on fungal communities, have not been adequately explored. In this study, we explored the effect of sediment physicochemical factors and heavy metals on the microbial diversity, community structure, and functions of bacterial and fungal communities from a black-odorous river in Wuhu, China. Twenty-four samples were collected, and the diversity and structure of fungal and bacterial communities were determined by high-throughput sequencing. Proteobacteria and Rozellomycota were the main phyla in the bacterial and fungal communities, respectively. The results showed different distribution patterns of bacterial and fungal communities along the river. Physicochemical factors and heavy metals exhibited different effects on microbial variation. Specifically, pH and Cr negatively affected bacterial α-diversity, whereas total phosphorus and Cr significantly affected fungal α-diversity. Variance partitioning analysis revealed that physicochemical factors explained more of the bacterial community structure than heavy metals (49.5% vs. 36.6%), with pH and total phosphorus being the dominant factors. Opposite patterns were observed for fungal community structure, with heavy metals contributing the most (48.0%). A similar influence pattern was observed for the predicted functions of the two communities. This study suggests that heavy metals in eutrophication rivers are essential factors that shift the microbial variation and should be considered in urban river evaluation and remediation.

Distribution and species composition of red algal communities in the northern Baltic Sea

Red algae are an important component of the Baltic Sea rocky shores. Within the Finnish marine area, in the northern Baltic Sea, red algal communities (on habitat level) are currently listed as endangered, due to eutrophication effects and potential future decrease in salinity. At species level, Rhodomela confervoides and Ceramium virgatum are red-listed. Despite their common use in different management contexts within the Baltic Sea, e.g. their depth distribution used as an indicator of the status of the sea areas, we know little about the commonness and more detailed distribution patterns of the red algal species. This limits the reliability of algae-based assessments. The aim of this study was to describe the general occurrence patterns, abundance and prevalence of erect perennial and annual red algae, based on extensive scuba-diving inventories within the Finnish marine area. Furthermore, the most representative areas for the red algal communities were identified. The results show high variation in depth distribution and prevalence across environmental gradients for many red algal species, e.g. for the relatively common perennial species Furcellaria lumbricalis and Vertebrata fucoides. In comparison to older data, reductions in depth penetration and occurrence were identified especially for deep-occurring species such as Rhodomela confervoides. With improved knowledge on the occurrence patterns of red algal species in relation to environmental variation, our results enable more reliable use of red algae as indicators of the status of the sea areas. By identifying areas where red algal communities are currently most representative, the results also allow better targeting of management efforts aiming to improve their status, such as areal protection measures or reducing nutrient input from point sources.

Phytoplankton responses to repeated pulse perturbations imposed on a trend of increasing eutrophication.

While eutrophication remains one of the main pressures acting on freshwater ecosystems, the prevalence of anthropogenic and nature‐induced stochastic pulse perturbations is predicted to increase due to climate change. Despite all our knowledge on the effects of eutrophication and stochastic events operating in isolation, we know little about how eutrophication may affect the response and recovery of aquatic ecosystems to pulse perturbations. There are multiple ways in which eutrophication and pulse perturbations may interact to induce potentially synergic changes in the system, for instance, by increasing the amount of nutrients released after a pulse perturbation. Here, we performed a controlled press and pulse perturbation experiment using mesocosms filled with natural lake water to address how eutrophication modulates the phytoplankton response to sequential mortality pulse perturbations; and what is the combined effect of press and pulse perturbations on the resistance and resilience of the phytoplankton community. Our experiment showed that eutrophication increased the absolute scale of the chlorophyll‐a response to pulse perturbations but did not change the proportion of the response relative to its pre‐event condition (resistance). Moreover, the capacity of the community to recover from pulse perturbations was significantly affected by the cumulative effect of sequential pulse perturbations but not by eutrophication itself. By the end of the experiment, some mesocosms could not recover from pulse perturbations, irrespective of the trophic state induced by the press perturbation. While not resisting or recovering any less from pulse perturbations, phytoplankton communities from eutrophying systems showed chlorophyll‐a levels much higher than non‐eutrophying ones. This implies that the higher absolute response to stochastic pulse perturbations in a eutrophying system may increase the already significant risks for water quality (e.g., algal blooms in drinking water supplies), even if the relative scale of the response to pulse perturbations between eutrophying and non‐eutrophying systems remains the same.

Assessing long-term nutrient and lime enrichment effects on a subtropical South African grassland

Nutrient enrichment influences grassland ecosystem structure, typically manifested by reduced species richness and increased productivity. Quantifying the long-term impacts of nutrient enrichment on grasslands contributes to understanding eutrophication effects on grassland, particularly for grasslands adapted to low soil nutrient status. Overextended time periods, nutrient enrichment may modify soil fertility. The Ukulinga Grassland Nutrient Experiment situated on a natural C4 grassland was set up in 1951 on the Ukulinga research farm, South Africa. Continuously applied treatments on plots measuring 2.7 × 9 m include combinations of nitrogen at 0, 7, 14 and 21 g m−2 per annum, phosphorus at 0 and 2.8 g m−2 per annum and lime at 0 and 225 g m−2 applied every five years. Nitrogen sources included ammonium sulphate (acidifying) and limestone ammonium nitrate (less acidifying). Grass species composition was influenced by both nitrogen forms. In contrast, forb species composition was more sensitive to LAN. We found evidence of nitrogen limitation on aboveground net-primary production. However, species richness (for grass and forbs) declined with increasing ammonium sulphate levels, owing to increased soil acidity and high aluminium concentrations. Aluminium toxicity can affect overall species composition by replacing Al-sensitive species with Al-tolerant species on site.

Benthos response to nutrient enrichment and functional consequences in coastal ecosystems

As land use intensifies, many coastal waters are becoming enriched with otherwise limiting nutrients, leading to eutrophication. While the extreme effects of eutrophication on benthic communities are well documented, there is still a lack of knowledge about how nutrient enrichment alters biogeochemical interactions occurring at the sediment-water interface. Using ex-situ experiments, this study explores the consequences of nutrient enrichment on sediment characteristics, macrofauna community and benthic fluxes. The quantity of sedimentary organic matter and porewater concentration of NH4+, NOx and PO43− increased in enriched treatments. These changes did not affect the macrobenthic community structure. However, macroinfauna buried less deep and increased their ventilation activity. As consequences, nutrient efflux increased, thereby favouring eutrophication processes. These effects were reduced in presence of seagrass, thus illustrating the buffering capacity of seagrass in the context of environmental changes, and particularly, of eutrophication. Overall, this study highlights that the functional consequences of nutrient enrichment involve interconnected processes that are variable in space and time.

The spatiotemporal characteristics of water quality and phytoplankton community in a shallow eutrophic lake: Implications for submerged vegetation restoration

One of the most serious consequences of eutrophication in shallow lakes is deterioration of water quality, proliferation of phytoplankton and disappearance of submerged macrophytes. After removing herbivorous and plankti-benthivorous fish, submerged macrophyte restoration was utilized at the entire lake (82.7 km2) to combat eutrophication and improve water quality in the shallow subtropical aquaculture of Lake Datong. We conducted two years of monitoring, from March 2018 to February 2020. During the first year of restoration, 80% of the area of Lake Datong (approximately 60 km2) was successfully recovered by submerged vegetation, and the water quality was improved. For example, the phosphorous (P) content (including total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP)) and turbidity decreased, and the Secchi depth (SD) increased. However, the submerged vegetation disappeared from autumn 2019 in the intermittent recovery area (MN), while the continuous recovery area (DX) continued to recover with an abundance of submerged vegetation. During the second year, the water quality continued to improve significantly in the DX area, with high biomass and coverage of submerged vegetation. In the MN area, although turbidity and ammonia nitrogen (NH4+-N) increased significantly and SD decreased significantly, the P content (TP, TDP, and DRP) still continued to decrease. The restoration of submerged macrophytes could significantly decrease the density of phytoplankton. Over time, there was a regime shift in Lake Datong. The structural equation model (SEM) results illustrated that the water level and submerged plant coverage were the primary drivers that triggered changes in the state of the lake ecosystem. Our results highlight the potential of restoring submerged vegetation to control water eutrophication at the whole-lake scale. However, the water level in spring was the primary driver that triggered changes in the state of the lake ecosystem. Water level management should be emphasized during the early stages of recovery of submerged plants.

The effects of eutrophication and browning on prey availability and body growth of the three-spined stickleback (Gasterosteus aculeatus)

Shallow coastal areas often have high productivity and diversity, in part due to the high availability of light and nutrients. At the same time, they are exposed to multiple environmental pressures, such as browning and eutrophication. Browning is mainly caused by runoff bringing coloured dissolved organic matter (CDOM), reducing light availability in waters, whereas eutrophication is caused by high nutrient loading, leading to eutrophication symptoms such as algal blooms. Existing variation and further change in light and nutrients of coastal areas could have large implications for aquatic food webs, including fish. For instance, reduced light might alter food availability and reduce foraging abilities, whereas increased nutrient supply might, depending on the extent, increase food availability. In this study, we performed a mesocosm experiment, including benthic and pelagic communities, together with young-of-the-year three-spined stickleback (Gasterosteus aculeatus) as predators. The three-spined stickleback is not only a common model organism but also an increasingly common and important mesopredator in the Baltic Sea. We examined the extent to which browning and nutrient-enrichment, alone and in combination, influenced the density, biomass, and composition of stickleback prey, and diet choice, body growth and condition of the stickleback. Stickleback body growth was positively affected by nutrient-enrichment, probably because of a positive bottom-up effect with increased primary production, as evident in the much higher chlorophyll-a concentrations in the pelagic habitat, and increased food availability. In contrast, there was a marginal negative effect of browning on stickleback body growth and condition, most likely due to negative effects of reduced visibility on feeding rates. We also found that prey availability increased with nutrient-enrichment but not with browning. Interestingly, nutrient-enrichment counteracted the negative effects of browning when combined. Our findings add novel understandings about the potential for both eutrophication and browning to affect coastal food webs and fish body growth in the Baltic Sea.

Eutrophication decrease compositional dissimilarity in freshwater plankton communities

Human activities, such as land use change and eutrophication, threaten freshwater biodiversity and ecosystem function. In this study, we examined both the α- and β-diversity of plankton communities, that is, bacteria/prokaryotic algae, eukaryotic algae, and zooplankton/metazoans, using both classical microscopy and high-throughput sequencing methods across 40 lakes of the Yangtze River Basin. The spatial variations in plankton communities were explained by environmental variables such as trophic status index (TSI) and environmental heterogeneity according to non-metric multidimensional scaling analyses, mantel tests, and structural equation model. Our results showed that the compositional dissimilarities of bacteria, cyanobacteria, eukaryotic algae, and metazoans all decreased with the increasing TSI values, and were significantly positively related to environmental dissimilarity. Both the species richness and compositional dissimilarity of zooplankton had positive effects on zooplankton/phytoplankton biomass ratio. Zooplankton diversity was not directly affected by TSI and environmental dissimilarity; however, it was indirectly affected by the biotic interactions with cyanobacteria or eukaryotic algae. In addition, there were significant positive relationships between bacteria/cyanobacteria and eukaryotic algae dissimilarities. Our results indicated that increased trophic status and decreased environmental dissimilarity as consequences of eutrophication may weaken the trophic cascading effects of planktonic food chain via reducing the top-down effects of zooplankton on phytoplankton.