Shallow Chinese Lake Research Articles

Solar radiation transfer in an ice-covered lake at different snow thicknesses

ABSTRACT Field observations were performed in Lake Nanhai, a shallow Chinese lake, to investigate the impact of variations in snow thickness (0–7.0 cm) on solar radiation transfer. As the snow thickness increases from 0 to 7.0 cm, the albedo increases from 0.27 to 0.96. The bulk extinction coefficients of snow, snow-ice, and congelation ice are 9.47, 9.69, and 2.18 m−1, respectively. The peak of the transmission spectrum shifts from the blue to green light waveband compared to the solar radiation spectrum. The proportion of incident radiation at surface penetrating to the under-ice water ranges from 0.5% to 19.7% associated with snow depth from 7 cm to 0 cm. Fresh snow influences the under-ice light condition crucially, and therefore the seasonal evolution of the lake phytoplankton community is affected.

Multimedia distribution, partitioning, sources, comprehensive toxicity risk and co-occurrence network characteristics of trace elements in a typical Chinese shallow lake with high antibiotic risk

Although the combined pollution of trace elements and antibiotics has received extensive attention, the fate and toxicity risk of trace elements with high antibiotic risk are still unclear. The multimedia distributions, partitioning, sources, toxicity risks and co-occurrence network characteristics of trace elements in surface water (SW), overlying water (OW), pore water (PW) and sediment (Sedi) samples of 61 sites from Baiyangdian (BYD) Lake were investigated. The trace elements in the SW and OW are derived mainly from traffic and agricultural sources, and those in PW and Sedi samples are primarily from lithogenic and industrial sources. The total toxicity risk index (TRI) of nine trace elements (ΣTRI) in Sedi samples showed a very high toxicity risk (18.35 ± 8.84), and a high combined pollution toxicity risk (ΣΣTRI) was observed in PW (149.17 ± 97.52) and Sedi samples (46.37 ± 24.00). The co-occurrence network from SW to PW became more vulnerable. Generally, total antibiotics and TP may be keystones of trace elements in water and sediment. The high antibiotic risk significantly influenced ΣΣTRI in water samples but not in Sedi samples. The findings provide new implications for the monitoring and control of combined antibiotic-trace element pollution in shallow lakes.

Antibiotics affected the bacterial community structure and diversity in pore water and sediments with cultivated Phragmites australis in a typical Chinese shallow lake.

The migration of antibiotics and bacterial communities between sediments and pore water occurring in the lake, which is affected by aquatic vegetation. However, the differences in bacterial community structure and biodiversity between pore water and sediments with plants in lakes under antibiotic stress are still poorly understood. We collected pore water and sediments in both wild and cultivated Phragmites australis regions in the Zaozhadian (ZZD) Lake to explore the characteristics of the bacterial community. Our results showed that the diversity of bacterial community in sediment samples were significantly higher than those in pore water samples in both P. australis regions. Due to higher antibiotic levels in sediments from the cultivated P. australis region, the composition of bacterial communities showed a difference, which reduced the relative abundance of dominant phyla in pore water and increased that in sediments. The higher bacterial variations in pore water could be explained by sediment in the cultivated P. australis region than that in wild P. australis region, therefore plant cultivation might change the source-sink pattern between sediments and pore water. The dominant factors shaping the bacterial communities in the wild P. australis region pore water or sediment were NH4-N, NO3-N, and particle size, while cultivated P. australis region pore water or sediment were oxytetracycline, tetracycline, etc. The findings of this work indicates that the antibiotic pollution caused by planting activities has a greater impact on the bacterial community, which will provide a reference for the use and management of antibiotics in lake ecosystems.

Fate and ecological risks of antibiotics in water-sediment systems with cultivated and wild Phragmites australis in a typical Chinese shallow lake

River carrying antibiotics from upstream posed serious threats to receiving lake, and plants might had effects on antibiotics. Therefore, samples of waters, sediments and tissues of cultivated and wild Phragmites australis were collected to analyse antibiotics fate and ecological risks (RQs) in Zaozhadian Lake. Our results revealed that the total antibiotics showed an increasing tendency in surface/pore water and P. australis tissues and a decreasing tendency in overlying water and sediments from the lake entrance to the centre. The bioaccumulation factors (BAFs) of two sulfonamides (SAs) and three quinolones (QNs) increased in sediments and decreased in those of erythromycin in pore water from Site 1 to Site 11. Three QNs and two tetracyclines (TCs) were dominant antibiotics in pore water/sediment and surface/overlying water respectively. Higher levels of two SAs in surface/pore water and two macrolides (MAs) in overlying/pore water and sediments were observed in the wild P. australis region, while higher values of two TCs in overlying/pore water and three QNs in sediment were observed in the cultivated P. australis region. Higher BAFs of SAs and QNs in sediments were observed in the cultivated and wild P. australis region respectively. The RQs of oxytetracycline and two MAs posed moderate risks in surface/overlying water from more than 50% of sampling sites. Norfloxacin exhibited moderate RQ and low ∑RQ levels in sediments, and showed high risk in pore water. Our findings imply that much more attention should be given to the antibiotics from river inputs and management normatives to control antibiotic pollution.

Temporal dependence of chlorophyll a–nutrient relationships in Lake Taihu: Drivers and management implications

Eutrophication and its associated algal blooms are principal environmental challenges confronting lakes worldwide. The empirical relationships between nutrient (total nitrogen, TN; total phosphorus, TP) and chlorophyll a (Chla) level are widely used as a theoretical basis for lake eutrophication management. Here, seasonal environmental variables and Chla from 2005 to 2020 in Chinese shallow eutrophic Lake Taihu were examined and Chla-nutrient equations in the entire period and annually from 2005 to 2020 were explored using 95% quantile regression model. The results showed robust linear relationships of logChla-logTN and logChla-logTP in the vast majority of cases. Based on Chla-nutrient equations in the entire study period, 0.69 mg/L TN and 52 μg/L TP are recommended as nutrient threshold in Lake Taihu. Furthermore, the results revealed increasing Chla sensitivity to nutrient for each study month (i.e. February, May, August, and November) from 2005 to 2020, whose drivers included increase in water temperature and water level, decrease in wind speed, mass ratio of nitrogen to phosphorus, and grazing effect. It is noteworthy that atmospheric stilling is likely to be the key climatic factor promoting annual peak Chla in Lake Taihu. For one, the deviations of the sub-index of Trophic State Index indicated that light is a critical limiting factor of summer Chla in Lake Taihu. For another, calmer water mainly due to atmospheric stilling decreased near 40% non-algal turbidity and a substantially increased buoyant cyanobacteria during the study period, improving phytoplankton “light niche”. Thus, increasing algal sensitivity to nutrient occurred until the additional algal-turbidity induce further light limitations or the exhaustion of TN (or TP) cause nutrient limitation. Given atmospheric stilling is a global phenomenon, this study would affect future algal bloom mitigation efforts in shallow lakes as temperature is always the focus in the recent literatures on global climate change.

Spatial-temporal dynamics, ecological risk assessment, source identification and interactions with internal nutrients release of heavy metals in surface sediments from a large Chinese shallow lake

The surface sediment concentrations of heavy metals (Cu, Zn, Pb, Cd, Cr, Hg, and As), major metals (Fe and Mn), and the nutrient concentrations in the interstitial water of Lake Houguan, a large eutrophic shallow lake, were surveyed for three years. The results showed that Cu, Zn, and Fe were significantly higher in the east lake parts, and Cd in November was significantly higher than April. 19% of Hg and all of As were larger than the probable effect concentrations (PECs) according to the consensus-based sediment quality guidelines (SQGs), and the geo-accumulation index (Igeo) indicated As, Hg, and Cd were slightly polluted to severely polluted. The RI value (average 704.2) of the potential ecological risk index (PERI) suggested that heavy metals posed very high ecological risks with most of the contributions induced by Cd and Hg. The consequence of hierarchical clustering analysis (HCA) and principle component analysis (PCA) identified Cd, As, and Pb might originate from urbanization, industrial pollution, and agricultural activity; Hg might be from atmospheric deposition and anthropogenic sources above; Cu, Zn, Cr, Fe, and Mn might be from both natural and anthropogenic sources. The Spearman correlation analysis indicated Pb and As were significantly positively correlated with total nitrogen, while Cd significantly negatively correlated with sulfate; As was significantly correlated with ammonia, sulfate, and nitrate in the interstitial water. These results suggested eutrophication might affect sedimental heavy metals by increasing organic matter or influencing the redox potentials in the sediment.

Response of traditional and taxonomic distinctness diversity indices of benthic macroinvertebrates to environmental degradation gradient in a large Chinese shallow lake.

A variety of biodiversity metrics are available to assess the quality of aquatic ecosystems. However, different types of metrics perform with considerable variation and provide various information involved in ecosystem conditions. Taxonomic distinctness (TD) indices have been recommended as desirable measures for assessing environmental degradation, but their utility based on lake macroinvertebrates is still largely unknown. Here, we evaluated the response of traditional and taxonomic distinctness diversity indices (the average taxonomic distinctness, Δ+, and variation in taxonomic distinctness, Λ+) of benthic macroinvertebrates to environmental degradation gradient in Lake Taihu, the third largest freshwater lake in China. Benthic assemblages responded markedly to human disturbances, with significance among-region differences in community composition throughout four seasons. The traditional biodiversity indices (Shannon-Wiener diversity and Pielou's evenness) showed high sensitivity in discriminating anthropogenic impacts, with highest values in macrophytic region but lowest values in eutrophic region. In contrast, Δ+ and Λ+ did not perform well in distinguishing sites subjected to different disturbance levels. The Pearson correlation and multiple regression analysis both indicated that traditional biodiversity metrics (Shannon-Wiener diversity, taxon richness, and Pielou's evenness) responded more readily to water quality variables (Secchi depth, electrical conductivity, and comprehensive trophic level index) than Δ+ and Λ+. Despite the weak correlations between TD indices of benthic macroinvertebrates and water quality in the present study, we suggest that the TD indices should still be considered in bioassessment programs because they provide useful complementary information on traditional diversity indices.

Comparison of Community and Function of Dissimilatory Nitrate Reduction to Ammonium (DNRA) Bacteria in Chinese Shallow Lakes with Different Eutrophication Degrees

Dissimilatory nitrate reduction to ammonium (DNRA) plays an important role in controlling nitrogen (N) loading in lake ecosystems. However, studies on the linkage between DNRA bacterial community structure and lake eutrophication remain unclear. We examined the community and abundance of DNRA bacteria at six basins of four shallow lakes with different degrees of eutrophication in China. Measurements of the different forms of N and phosphorus (P) in the water column and interstitial water as well as total organic carbon (TOC) and sulfide in the sediments in summer (July 2016) were performed. The nutritional status of Lake Chaohu was more serious than that of the lakes in Wuhan, including Lake Qingling, Lake Houguan, and Lake Zhiyin by comparing geochemical and physical parameters. We found a higher abundance of the nrfA gene, which is a function gene of DNRA bacteria in sediments with higher contents of TOC and sulfide. Moreover, nitrate was a significant factor influencing the DNRA bacterial community structure. A significant difference of the DNRA bacterial community structure between Lake Chaohu and the lakes in Wuhan was discovered. Furthermore, DNRA bacterial abundance and community positively correlated with NH4+ and Chl a concentrations in Lake Chaohu, in which a percent abundance of dominant populations varied along eutrophication gradients. Overall, the abundance and community structure of the DNRA bacteria might be important regulators of eutrophication and cyanobacteria bloom in Lake Chaohu.

Coupling between Nitrification and Denitrification as well as Its Effect on Phosphorus Release in Sediments of Chinese Shallow Lakes

The coupling of nitrification and denitrification has attracted wide attention since it plays an important role in mitigating eutrophication in aquatic ecosystems. However, the underlying mechanism is largely unknown. In order to study the coupling relationship between nitrification and denitrification, as well as its effect on phosphorus release, nutrient levels, functional gene abundance and potential rates involved in nitrification and denitrification were analyzed in three shallow urban lakes with different nutrient status. Trophic level was found positively related to not only copy numbers of functional genes of nitrosomonas and denitrifiers, but also the potential nitrification and denitrification rates. In addition, the concentrations of different forms of phosphorus showed a positive correlation with the number of nitrosomonas and denitrifiers, as well as potential nitrification and denitrification rates. Furthermore, the number of functional genes of nitrosomonas exhibited positive linear correlations with functional genes and rate of denitrification. These facts suggested that an increase in phosphorus concentration might have promoted the coupling of nitrification and denitrification by increasing their functional genes. Strong nitrification–denitrification fueled the nitrogen removal from the system, and accelerated the phosphorus release due to the anaerobic state caused by organic matter decomposition and nitrification. Moreover, dissolved organic nitrogen was also released into the water column during this process, which was favorable for balancing the nitrogen and phosphorus ratio. In conclusion, the close coupling between nitrification and denitrification mediated by nitrifier denitrification had an important effect on the cycling mode of nitrogen and phosphorus.

Biotic factors drive distinct DNRA potential rates and contributions in typical Chinese shallow lake sediments

Dissimilatory nitrate reduction to ammonia (DNRA) is an important nitrate reduction pathway in lake sediments; however, little is known about the biotic factors driving the DNRA potential rates and contributions to the fate of nitrate. This study reports the first investigation of DNRA potential rates and contributions in lake sediments linked to DNRA community structures. The results of 15N isotope-tracing incubation experiments showed that 12 lakes had distinct DNRA potentials, which could be clustered into 2 groups, one with higher DNRA potentials (rates varied from 2.7 to 5.0 nmol N g−1 h−1 and contributions varied from 27.5% to 35.4%) and another with lower potentials (rates varied from 0.6 to 2.3 nmol N g−1 h−1 and contributions varied from 8.1% to 22.8%). Sediment C/N and the abundance of the nrfA gene were the key abiotic and biotic factors accounting for the distinct DNRA potential rates, respectively. A high-throughput sequencing analysis of the nrfA gene revealed that the sediment C/N could also affect the DNRA potential rates by altering the ecological patterns of the DNRA community composition. In addition, the interactions between the DNRA community and the denitrifying community were found to be obviously different in the two groups. In the higher DNRA potential group, the DNRA community mainly interacted with heterotrophic denitrifiers, while in the lower DNRA potential group, both heterotrophic and sulfur-driven autotrophic denitrifiers might cooperate with the DNRA community. The present study highlighted the role of the sulfur-driven nitrate reduction pathway in C-limited sediments, which has always been overlooked in freshwater environments, and gave new insights into the molecular mechanism influencing the fate of nitrate.

Spatial and Historical Occurrence, Sources, and Potential Toxicological Risk of Polycyclic Aromatic Hydrocarbons in Sediments of the Largest Chinese Deep Lake.

Lake sediments are important reservoirs for polycyclic aromatic hydrocarbons (PAHs) in catchments. Knowledge of occurrence, sources, and toxicological risk of PAHs is crucial to abate their pollution and risk. We investigated the spatial and temporal occurrence, sources, and potential toxicological risks of 12 PAHs in the surface sediments and one sediment core of the largest deep lake (Lake Fuxian) of China. Our results indicated the average ΣPAH12 in the surface sediments of this lake was 1550.6 ± 231.4ngg dw -1 , much higher than those of most Chinese shallow lakes. The average ΣPAH12 in the lake area was higher than that in the estuaries. The average ΣPAH12 in the estuaries of influent rivers was higher than that of the outlet river. Coal combustion, gasoline combustion, and diesel combustion were the major sources, which contributed 68.5%, 19.8%, and 11.8% to the ΣPAH12. The average total benzo[a]pyrene toxic equivalent concentration (TEQcarc) of the six most carcinogenic PAHs was 317.1 ± 86.3ngTEQcarcg-1 in the surface sediments. The ΣPAH12 increased from 301.7 to 1964.4ngg dw -1 from 1945 to 2011 and significantly increased with the GDP and population of the catchment. The contribution of coal combustion to the concentrations of PAHs increased gradually with time. The total TEQcarc, and the percentage of ΣPAHcarc to ΣPAH12 in the sediment core increased from 5.0 to 84.6ngTEQcarcg-1 and from 5.7 to 23.3%, respectively. Our study highlights the importance of such deep waters in burying PAHs and the increasing risk of PAHs from human activities.

Tissue-based assessment of hazard posed by mercury and selenium to wild fishes in two shallow Chinese lakes.

Total (all forms of inorganic and organic) concentrations of mercury (Hg) and selenium (Se) were measured in dorsal muscle and eggs of wild fishes from two shallow lakes in China: Tai Lake (Ch: Taihu; TL) and Baiyangdian Lake (BYDL). Hazard quotients (HQs) were calculated by dividing concentrations of Se or Hg in muscle or eggs of fishes by threshold concentrations for effects expressed as tissue residue toxicity reference values (TR-TRVs). Concentrations of Hg in whole bodies of fishes were estimated by concentrations in muscle. Based on concentrations of Hg in whole body, HQs for fishes in TL and BYDL were less than 1.0, which suggests little to moderate potential for effects on these fishes and unaccepted adverse effects of Hg are unexpected for adult fishes. HQs of Se in muscle of common carp from TL were closed to 1.0, and 27% of HQs based on concentrations of Hg in eggs of fishes from BYDL exceeded 1.0. Potential hazard due to Hg on common carp in TL and reproductive effects of Se on fishes from BYDL exhibited need for concern. Ratios of molar concentrations of Se to Hg were greater than 1.0. Thus, there might be some protective effects of Se on effects of Hg on fishes in TL and BYDL.

An enzymatic mechanism for balancing the stoichiometry of nitrogen and phosphorus in a shallow Chinese eutrophic lake

The over-enrichment of lake waters with nitrogen (N) and phosphorus (P) has become a serious environmental problem, but modes of change in stoichiometry and enzymatic regeneration along trophic gradients are largely unknown. Seasonal variations in the kinetics of extracellular aminopeptidase (LAP) and alkaline phosphatase (AP), together with the composition of phytoplankton and concentrations of N and P, were examined from Jun 2013 to September 2014 in a Chinese shallow lake in which two basins had contrasting trophic states. The turbid basin had a significantly higher concentration of chlorophyll a and lower ratios of N to P. In parallel, the turnover time of organic N mediated by LAP (LAPT) was significantly shorter, and its maximum velocity (Vmax) was significantly higher compared to those in the clear basin. Considering data from both basins, there were linear decreases in N/P and the ratios between dissolved inorganic N and total N with an increasing trophic state index, coupled with a significantly positive relationship between N/P and LAPT. Additionally, with decreasing TN/TP, the Michaelis constant (Km) of the AP increased linearly, reducing the efficiency of P regeneration. In contrast, the Km value of LAP decreased, and Vmax increased, which enhanced N mineralization by simultaneously increasing the reaction velocity and improving the affinity for substrate. Additionally, the Km value of LAP was significantly related to that of AP and the ammonium concentration. Thus, substrate affinity acted as a key factor modifying the pathways of enzymatic degradation of organic N and P according to their stoichiometry in the water column. Phytoplankton composition was directly linked to LAPT. Overall, this study seemed to be the first to connect a stoichiometric shift of N and P with kinetics of extracellular enzymes responsible for their regeneration along trophic gradients, presenting an additional pathway to overcome nitrogen deficiency in eutrophic lakes.

Interactive effects of environmental factors on phytoplankton communities and benthic nutrient interactions in a shallow lake and adjoining rivers in China

Shallow lakes are vulnerable to eutrophication because of abundant phytoplankton and significant nutrient input from sediments. Previous studies have researched the effect of environmental factors on phytoplankton and phosphorus release from sediment. However, few studies have simultaneously evaluated the interactive effects of environmental factors on phytoplankton communities and the interactions among different sediment nutrients. This paper reports on a 2016 investigation that examined the phytoplankton community and physical and chemical factors in both the water column and sediments in a Chinese shallow lake and its adjoining rivers. Our results indicated that rivers with water gates and lake areas had greater Chlorophyll a concentrations (Chl a) than natural rivers with similar total phosphorus (TP) concentrations; this indicates the importance of residence time on phytoplankton biomass. Although temperature impacted Chl a less than nutrients, its effects were highly species-specific, modulating relationships between nutrients and the abundance of different phytoplankton taxa. The effects of nutrients changed based on phytoplankton biomass and community composition, suggesting that different phytoplankton taxa have different nutrient demands. We predict that increasing residence time, temperature, and nutrients will increase phytoplankton biomass and increase the future dominance of Chlorophyta and Cyanophyta. In the interstitial water, there were no significant seasonal differences in TP, total nitrogen, and soluble reactive silica concentrations. However, ammonia concentrations were higher in the spring and lower in other seasons; nitrate and sulfate were abundant when the ammonia concentration was low. The total iron level in sediments was significantly negatively related with TP at low ammonia and silica concentrations and at high nitrate and sulfate concentrations in the interstitial water. These results indicated that nutrients are closely coupled in the sediments, highlighting the importance of oxidation-reduction potentials on internal nutrient balance.

Characteristics of phosphorus components in surface sediments from a Chinese shallow eutrophic lake (Lake Taihu): new insights from chemical extraction and 31P NMR spectroscopy.

As a primary factor responsible for lake eutrophication, a deeper understanding of the phosphorus (P) composition and its turnover in sediment is urgently needed. In this study, P species in surface sediments from a Chinese large eutrophic lake (Lake Taihu) were characterized by traditional fractionation and 31P nuclear magnetic resonance (NMR) spectroscopy, and their contributions to the overlying water were also discussed. Fractionation results show that NaOH-P predominated in the algal-dominated zone, accounting for 60.1% to total P in Zhushan Bay. Whereas, refractory fractions including HCl-P and residual-P were the main P burial phases in the macrophyte-dominated zone, the center and lakeshore. Recovery rates of the total P and organic P were greatly improved by using a modified single-step extraction of NaOH-EDTA, ranging from 22.6 to 66.1% and from 15.0 to 54.0%. Ortho-P, monoester-P, and pyro-P are identified as the major P components in the NaOH-EDTA extracts by 31P NMR analysis. Trace amount of DNA-P appeared only in sediments from algal- and macrophyte-dominated zones, ascribing to its biological origin. The relative content of ortho-P is the highest in the algal-dominated zone, while the biogenic P including ester-P and pyro-P is the highest in the macrophyte-dominated zone. Moreover, ortho-P and pyro-P correlated positively with TP and chlorophyll a in the overlying water, whereas only significant relationships were found between monoester-P, biogenic P, and chlorophyll a. These discrepancies imply that inorganic P, mainly ortho-P, plays a vital role in sustaining the trophic level of water body and algal bloom, while biogenic P makes a minor contribution to phytoplankton growth. This conclusion was supported by the results of high proportion of biogenic P in algae, aquatic macrophytes, and suspended particulate from the published literature. This study has significant implication for better understanding of the biogeochemical cycling of endogenous P and its role in affecting lake eutrophication.

Bisphenol analogues in surface water and sediment from the shallow Chinese freshwater lakes: Occurrence, distribution, source apportionment, and ecological and human health risk

Compared to Bisphenol A (BPA), current knowledge on the spatial distribution, potential sources and environmental risk assessment of other bisphenol analogues (BPs) remains limited. The occurrence, distribution and sources of seven BPs were investigated in the surface water and sediment from Taihu Lake and Luoma Lake, which are the Chinese shallow freshwater lakes. Because there are many industries and living areas around Taihu Lake, the total concentrations of ∑BPs were much higher than that in Luoma Lake, which is away from the industry-intensive areas. For the two lakes, BPA was still the dominant BPs in both surface water and sediment, followed by BPF and BPS. The spatial distribution and principal component analysis showed that BPs in Luoma Lake was relatively homogeneous and the potential sources were relatively simple than that in Taihu Lake. The spatial distribution of BPs in sediment of Taihu Lake indicated that ∑BPs positively correlated with the TOC content. For both Taihu Lake and Luoma Lake, the risk assessment at the sampling sites showed that no high risk in surface water and sediment (RQt < 1.0, and EEQt < 1.0 ng E2/L).

Restoration of Shallow Lakes in Subtropical and Tropical China: Response of Nutrients and Water Clarity to Biomanipulation by Fish Removal and Submerged Plant Transplantation

Fish removal has been used to restore temperate lakes, and positive effects on ecological state and water clarity have frequently been recorded in many lakes. Recently, a supplementary measure, transplantation of submerged macrophytes after fish removal, has been applied to restore warm Chinese shallow lakes in order to compensate for the expected lack of increasing grazing control of phytoplankton after the biomanipulation. These measures have successfully shifted turbid warm lakes to a clear water state, but little is known about the responses to restoration of key physico-chemical variables. We analyzed the seasonal variation in nutrient concentrations in two subtropical and one tropical biomanipulated shallow Chinese lakes subjected to restoration. In all three lakes, a marked decline occurred in the concentrations of lake total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), and chlorophyll a (Chl a), while the transparency (SD:WD ratio, Secchi depth to water depth ratio) increased. A clear water state was established, lasting so far for 7 to 23 months, and TN, TP, Chl a, and TSS levels in the three restored lakes decreased to, on average, 49%, 58%, 41%, and 18% of the level prior to restoration and/or the level in a reference lake, respectively, while the annual mean SD:WD ratio exhibited a 1.5–4 fold increase. In conclusion, lake restoration by transplantation of submerged macrophytes after fish removal had major positive effects on the physico-chemical variables in our study lakes. However, continuous control of omnivorous and herbivorous fish biomass is recommended as the fish typically present in warm, shallow lakes to some extent feed on submerged macrophytes, when available.

Hydrological regulation drives regime shifts: evidence from paleolimnology and ecosystem modeling of a large shallow Chinese lake.

Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such 'regime shifts' can be driven by human activities which degrade ecological stability including water level control (WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when implementing hydrological regulation for aquatic ecosystems around the globe.

Sediment–water interaction in phosphorus cycling as affected by trophic states in a Chinese shallow lake (Lake Donghu)

Lake sediment substantially accumulates nutrients, while little is known regarding the conditions under which it tends to be a sink or source of phosphorus. It is postulated that the above functions were largely dependent on trophic state. To test this hypothesis, composition, abundance, and size-spectrum of phytoplankton were studied in a Chinese shallow lake (Lake Donghu), together with concentrations and sorption behaviors of phosphorus in water column and sediment. Relationships among these variables were also examined by structural equation model. In the basins with the lowest phosphorus concentration, sediment was a phosphorus source as judged by equilibrium phosphorus concentration, directly affecting the abundance of phytoplankton with smaller size. Contrastingly, in the basins with the highest phosphorus concentration, sediment tended to uptake phosphorus, companied by the lowest ratio of nitrogen to phosphorus, diversity, and evenness of phytoplankton with the smaller size one dominating. Oscillatoria sp. was directly affected by ammonia and phosphorus. Moreover, with a balanced exchange of phosphorus between sediment and water column, phytoplankton increased markedly with the highest diversity and evenness in the basins having intermediate phosphorus concentration. Overall, trophic state modulated sediment functions to supply nutrient and was in turn greatly affected by the sediment in shallow lakes.

Functions of Calcium-bound Phosphorus in Relation to Characteristics of Phosphorus Releasing Bacteria in Sediment of a Chinese Shallow Lake (Lake Wabu)

ABSTRACTSediment phosphorus (P) release accelerates lake eutrophication, while retention capacity and release potential of different P fractions, calcium-bound P (CaCO3∼P) in particular, still remains unclear. Fractionation and sorption behaviors of phosphorus were studied in sediment of a Chinese shallow lake (Lake Wabu) and two inflowing rivers from December 2011 to December 2012. Abundance of P releasing bacteria was analyzed, and their main species were isolated using a culture-dependent method and identified by their 16S rDNA sequences. CaCO3∼P release abilities of these bacteria were also tested. In sediments of both the lake and rivers studied, the rank order of the different P extracts was CaCO3∼P > iron-bound P > acid-soluble organic P > hot NaOH-extractable organic P. At the same time, CaCO3∼P content and equilibrium P concentration (EPC0) values in river sediments were significantly higher than those in the lake. Additionally, EPC0 changes non-monotonically with increasing CaCO3∼P content, forming a V-shaped curve, with the lowest EPC0 at an intermediate CaCO3∼P content (around 180 mg kg−1). Below this threshold, CaCO3∼P was a component strengthening P retention; moreover, CaCO3∼P became an active species responsible for P release. Noticeably, between the two parts divided by this threshold, the differences in abundance of inorganic phosphorus solubilizing bacteria (IPB) and organic phosphorus mineralizing bacteria (OPB) were insignificant and the dominant IPB species clustered together. By contrast, OPB was distinguished from each other, whose dominant species isolated from the part with higher CaCO3∼P content, namely Novosphingobium sp., exhibited a stronger ability to solubilize CaCO3∼P. Shortly, with lower content, CaCO3∼P tends to stabilize P in sediment; while with higher content or under eutrophic condition, it shifted into P source, with some OPB species becoming the main factors to drive its release.