Shallow Eutrophic Lake Research Articles

Field observation and simulation experiments on nutrient transformation during phytoplankton-derived particulate matter deposition.

Phytoplankton-derived particulate matter (PPM) is the active component of the solid particles in eutrophic shallow lakes. To date, understanding of the degradation characteristics of PPM and the effect of degradation products on nutrient cycling in water are limited. In this study, field observations and simulation experiments were carried out to elaborate the nutrient transformation during phytoplankton-derived particulate matter deposition in the cyanobacterial blooming area of Lake Taihu. Results showed that the deposition of the PPM was strongly facilitated by the cyanobacterial bloom and the sediment resuspension. The main variation characteristics of phosphorus (P) species in PPM are shown in the increase of Ortho-P and the decrease of biodegradable phosphorus (Poly-P, DNA-P) during the deposition of PPM. The degradation of the PPM resulted in the release of dissolved nitrogen (N) and P to the water body. The conversion of easily degradable particulate N and P in the PPM to ammonium nitrogen (NH3-N) and soluble reactive phosphorus were believed to be responsible for this phenomenon. The cycling of nutrients and the cyanobacterial bloom status might therefore be altered because of the deposition and degradation of PPM. More considerations should be given on this process in future works.

Application of subfossil Bosmina and its δ13C values in tracing the long-term food web dynamics of shallow eutrophic lakes: A case in Taihu Lake, southeast China

Cladoceran subfossil assemblages have been used successfully to trace the signals of long-term changes in lake eutrophication. However, their potential for reconstructing food webs has not yet been explored extensively. Here, we assess whether the stable carbon isotope analysis (SCIA) of subfossil Bosmina can be used to reconstruct the eutrophication and food web history of a shallow lake in southeast China. Two 210Pb-dated sediment cores were collected from the western and central parts of Taihu Lake, one of the largest eutrophic lakes in the region. Multiproxy analyses of the cores were performed, including of the subfossil Bosmina assemblages, stable carbon isotopes of subfossil Bosmina (δ13Cs-bos) and bulk sediment (δ13Corg), total organic carbon (TOC), loss on ignition (LOI), C/N, total nitrogen (TN), and total phosphorous (TP). Stable carbon isotopes of living algae (δ13Calg) and Bosmina (δ13Cl-bos) were also measured at the same sampling locations. The δ13Cs-bos gradually declined over time with reciprocal increases in the assemblages of subfossil Bosmina and total cladocerans and in the TOC, LOI, TN and TP in both cores. The δ13Calg and δ13Cl-bos values further revealed depleted 13C. The changes in the δ13Cs-bos in relation to the other proxies indicated rapid nutrient enrichment and a possible shift in the food web in Taihu Lake, providing new insight into the reconstruction of food webs and eutrophication in shallow lakes in southeast China.

Suspended particles phoD alkaline phosphatase gene diversity in large shallow eutrophic Lake Taihu

The bacterial phoD gene encodes alkaline phosphatase plays an important role in the release of bioavailable inorganic phosphorus (P) from organic P in environmental systems. However, phoD gene diversity in suspended particles in shallow freshwater lakes is poorly understood. In this study, we explored the potential relationship between environmental factors and phoD phosphatase gene in suspended particles in different ecosystem types (lake zones) in Lake Taihu, a large shallow eutrophic lake in China. Quantitative PCR and high-throughput sequencing were used to analyze phoD gene abundance and the phoD-harboring bacterial community composition. Our results indicate that the distribution of phoD gene abundance in suspended particles had a high spatiotemporal heterogeneity. The phoD gene abundance in each lake zone decreased significantly from June to September. The dominant phoD-harboring phylum in all samples was Actinobacteria, followed by Proteobacteria, Cyanobacteria and Gemmatimonadetes. The first predominant phoD-harboring genera varied among samples, but most of them belonged to phylum Actinobacteria. Driven by different environmental factors, the phoD-harboring bacterial community structure varied with sampling month and ecosystem type. Nitrate and ammonia nitrogen were the main environmental drivers of phoD-harboring bacterial community in suspended particles in the river mouth zone, while water pH and dissolved oxygen were important factors for the algae-dominated, macrophyte-dominated and central lake zones.

Diel variation of CH4 and CO2 dynamics in two contrasting temperate lakes

ABSTRACT The concurrent short-term fluctuations of methane (CH4) and carbon dioxide (CO2) concentrations and emissions in lakes are not well studied. Quantifying the differences in daytime versus nighttime dynamics may provide information about the controls over greenhouse gas production and may have relevance to lake carbon budgets. In this study, the diel variation of CH4 and CO2 emissions and concentration patterns were determined along the water column of 2 temperate lakes with different trophic states during July 2015. The results showed that the shallow eutrophic lake had significantly higher CH4 and CO2 releases than the deep oligo-mesotrophic lake. No significant diel fluctuations were observed in atmospheric CH4 emissions from either lake or in CO2 emission from the oligo-mesotrophic lake, but significantly higher CO2 emission from the eutrophic lake occurred during the daytime compared to nighttime. Based on a diffusion–reaction model, it was possible to estimate the diel variation of the sources and sinks of dissolved CH4 throughout the water column, suggesting lateral transport is a potential source of CH4 in oxygenated water layers in the oligo-mesotrophic lake. Sources and sinks throughout the water column should be considered in future studies for a better understanding of CH4 dynamics within the lakes.

Spatiotemporal patterns and environmental drivers of total and active bacterial abundances in Lake Taihu, China

• 120 samples were seasonally sampled to identify bacterial patterns in Lake Taihu. • Total and active bacterial abundances (TB-AB) varied dramatically among seasons. • On average, active bacteria accounted for ~10% of the total bacterial abundance. • Nitrogen, phosphorus, organic carbon and temperature mostly shaped AB variation. • AB is a more sensitive bioindicator of environmental changes than total bacteria. Bacteria are a key component in lake ecosystems, playing a crucial role in driving biogeochemical and energy fluxes. In lake biomonitoring, false alarms have often been triggered due to the presence of abundant dead or dormant bacterial cells. Thus, quantification of the metabolically active and dormant cells is required for effective biomonitoring. In this study, 120 sites were seasonally sampled in a large, shallow, eutrophic lake (Taihu, China) to quantify the total bacterial (TB) and active bacterial (AB) abundances and explore their spatiotemporal distribution. Generalized additive models (GAMs) were used to identify the major environmental drivers of TB and AB dynamics. TB ranged from 7.57 × 10 4 to 1.84 × 10 8 cells mL −1 , while AB ranged from 4.42 × 10 3 to 5.56 × 10 6 cells mL −1 . The proportion of AB was significantly higher in May (mean: 18.7%; cyanobacterial bloom thriving season) than in January or September (6.8% and 4.7%, respectively). GAMs indicated that dissolved oxygen, total dissolved nitrogen (TDN), total dissolved phosphorus and turbidity explained 47.8% of the TB variation, while TDN, dissolved organic carbon, water temperature and total phosphorus explained 72.7% of the AB variation. Our study showed that nutrients and physical factors are the major drivers of the TB and AB abundance variations in Lake Taihu. Bacterial responses to environmental variation were mostly non-linear. The high proportion of AB variation (72.7%) explained by environmental parameters indicates that active bacteria are more sensitive to environmental changes and could be more effective bioindicators for long-term monitoring in shallow eutrophic lakes.

How many submerged macrophyte species are needed to improve water clarity and quality in Yangtze floodplain lakes?

Successful re-establishment and maintenance of submerged macrophytes is a pivotal problem for the restoration of shallow eutrophic lakes, since submerged macrophytes can facilitate a shift of lake ecosystems from a turbid water state to a clear water state through their structuring roles. However, little is known about the optimal number of macrophyte species (species richness) needed for the recovery of shallow eutrophic lakes. Here, we investigated 19 shallow eutrophic lakes along the mid-lower reaches of the Yangtze River to reveal the underlying interrelations among water clarity, water quality and species richness. Our results showed positive correlations of water nutrients (TN and TP) with Kd and Red/Blue light ratio, suggesting that bad water quality can significantly lower water clarity. The results of path analysis indicated that the underwater light climate directly affects morphological and physiological traits and species richness of submerged macrophytes. Changes in functional traits also affected significantly the species richness of submerged macrophytes. Moreover, the presence of submerged macrophytes not only had positive effects on the underwater light climate (water clarity), but also on water quality. Most importantly, the assemblage of three or more submerged macrophyte species can significantly improve water clarity in these sampled eutrophic lakes, but not water quality. Additionally, the basic species assemblage of Myriophyllum spicatum and Vallisneria natans can be used for restoration of submerged macrophytes in shallow eutrophic Yangtze floodplain lakes. It is concluded that species richness and species assemblage are critical for recovery of submerged macrophytes in shallow eutrophic lakes.

Characteristics and Source of Dissolved Organic Matter in Lake Hulun, A Large Shallow Eutrophic Steppe Lake in Northern China

Lake Hulun, the fifth largest lake in China, is a typical eutrophic steppe lake located in the Hulun Buir Prairie. The dissolved organic matter (DOM) in the water of Lake Hulun has a high concentration. However, little is known about the occurrence characteristics and source of the DOM in Lake Hulun. The spatial and temporal distribution characteristics of DOM concentration in Lake Hulun were thoroughly surveyed, and the optical characteristics, fluorescence components and sources of DOM were analyzed by excitation emission matrix (EMM) and parallel factor analysis (PARAFAC) technology. The DOM concentration was 6.46–42.87 mg C/L, and was highest in summer and lowest in winter. The difference in the spatial distribution of DOM in winter was significant due to the ice over, and showed a trend where the concentration near the shore was higher than that in the center of the lake. Three humic-like components and one component consisting of a mixture of humic-like and protein-like substances of DOM were identified, with the former being prevalent. The humification index of DOM was 2.22–9.92, indicating that the DOM has a high degree of humification. The DOM is mainly derived from terrestrial sources, with the highest proportion (91.0% ± 8.1%) found in winter and the lowest (66.2% ± 7.7%) in summer. Given that the DOM in Lake Hulun is mainly dominated by humic-like components with a high degree humification, the DOM may have low bioactivity. However, this is just a preliminary analysis and judgment, and it is necessary to conduct other experiments such as biodegradation experiments to further study the bioavailability of DOM in Lake Hulun.

How warming and other stressors affect zooplankton abundance, biomass and community composition in shallow eutrophic lakes

We aimed to investigate the influence of environmental factors and predict zooplankton biomass and abundance in shallow eutrophic lakes. We employed time series of zooplankton and environmental parameters that were measured monthly during 38 years in a large, shallow eutrophic lake in Estonia to build estimates of zooplankton community metrics (cladocerans, copepods, rotifers, ciliates). The analysis of historical time series revealed that air temperature was by far the most important variable for explaining zooplankton biomass and abundance, followed, in decreasing order of importance, by pH, phytoplankton biomass and nitrate concentration. Models constructed with the best predicting variables explained up to 71% of zooplankton biomass variance. Most of the predictive variables had opposing or antagonistic interactions, often mitigating the effect of temperature. In the second part of the study, three future climate scenarios were developed following different Intergovernmental Panel on Climate Change (IPCC) temperature projections and entered into an empirical model. Simulation results showed that only a scenario in which air temperature stabilizes would curb total metazooplankton biomass and abundance. In other scenarios, metazooplankton biomass and abundance would likely exceed historical ranges whereas ciliates would not expand. Within the metazooplankton community, copepods would increase in biomass and abundance, whereas cladocerans would lose in biomass but not in abundance. These changes in the zooplankton community will have important consequences for lake trophic structure and ecosystem functioning.

Using Microcystin Gene Copies to Determine Potentially-Toxic Blooms, Example from a Shallow Eutrophic Lake Peipsi.

Global warming, paired with eutrophication processes, is shifting phytoplankton communities towards the dominance of bloom-forming and potentially toxic cyanobacteria. The ecosystems of shallow lakes are especially vulnerable to these changes. Traditional monitoring via microscopy is not able to quantify the dynamics of toxin-producing cyanobacteria on a proper spatio-temporal scale. Molecular tools are highly sensitive and can be useful as an early warning tool for lake managers. We quantified the potential microcystin (MC) producers in Lake Peipsi using microscopy and quantitative polymerase chain reaction (qPCR) and analysed the relationship between the abundance of the mcyE genes, MC concentration, MC variants and toxin quota per mcyE gene. We also linked environmental factors to the cyanobacteria community composition. In Lake Peipsi, we found rather moderate MC concentrations, but microcystins and microcystin-producing cyanobacteria were widespread across the lake. Nitrate (NO3−) was a main driver behind the cyanobacterial community at the beginning of the growing season, while in late summer it was primarily associated with the soluble reactive phosphorus (SRP) concentration. A positive relationship was found between the MC quota per mcyE gene and water temperature. The most abundant variant—MC-RR—was associated with MC quota per mcyE gene, while other MC variants did not show any significant impact.

Algal Accumulation Decreases Sediment Nitrogen Removal by Uncoupling Nitrification-Denitrification in Shallow Eutrophic Lakes.

In eutrophic lakes, the decay of settled algal biomass generates organic carbon and consumes oxygen, favoring sediment nitrogen loss via denitrification. However, persistent winds can cause algae to accumulate into dense mats, with uncertain impacts on sediment nitrogen removal. In this study, we investigated the effects of algal accumulation on sediment nitrogen removal in a shallow and eutrophic Chinese lake, Taihu. We found that experimental treatments of increased algal accumulation were associated with decreased sediment nitrogen losses, indicating the potential for a break in coupled nitrification-denitrification. Likewise, field measurements indicated similar decreases in sediment nitrogen losses when algal accumulation occurred. It is possibly caused by the decay of excess algal biomass, which likely depleted dissolved oxygen, and could have inhibited nitrification and thereby denitrification in sediments. We estimate that if such algal accumulations occurred over 20% or 10% of lake area in Taihu, sediment nitrogen removal rates decreased from 835.6 to 167.2 and 77.2 μmol N m-2h-1, respectively, during algal accumulation period. While nitrogen removal may recover later, the apparent nitrogen removal decrease may create a window for algal proliferation and intensification. This study advances our knowledge on the impacts of algal blooms on nitrogen removal in shallow eutrophic lakes.

The influence of ship wave on turbulent structures and sediment exchange in large shallow Lake Taihu, China

Turbulent burst plays a key role in momentum transfer and sediment movement in large shallow lakes. This study addresses the quantitative influence of ship wave on turbulent structures, momentum and sediment fluxes in Lake Taihu, a large, shallow eutrophic lake that experiences heavy shipping traffic. Acoustic Doppler Velocimeter (ADV) and Optical Backscatter Sensor (OBS) were used to obtain high-frequency flow velocities and suspended sediment concentration (SSC) data before and when a cargo ship passed by. We found that ship waves mainly propagate along the horizontal direction. The near-bed turbulent bursting events with ship disturbance increased by 8.42%. Consequently, the vertical momentum and sediment fluxes were increased by 3.4 times and 8 times, respectively. In terms of bursting processes, ejection and sweep possess much stronger capacity in carrying sediment and are largely controlled by the disturbance in the vertical direction, while inward and outward interactions are mainly affected by horizontal disturbance. These findings represent an important step towards understanding the mechanism and effect of turbulent bursting under ship disturbance, and pave the way to future research in order to manipulate turbulent dynamics.

Sediment internal nutrient loading in the most polluted area of a shallow eutrophic lake (Lake Chaohu, China) and its contribution to lake eutrophication

It is well known that sediment internal loading can worsen lake water quality for many years even if effective measures have been taken to control external loading. In this study, a 12-month field study was carried out to reveal the relationship between sediment phosphorus (P) and nitrogen (N) forms as well as their fluxes across sediment-water interface from the most polluted area of Lake Chaohu, a large shallow eutrophication lake in China. The possible contribution of mobile fraction of P and N to lake eutrophication is also analyzed. The results indicate that the content of total P and N and their forms in water and sediment were rather dynamic during the year-long field investigation. Low concentrations of P and N from sediment and overlying water were observed in the winter but increased sharply in summer. The phosphate and ammonium fluxes showed evident seasonal variation, and higher fluxes can be observed in warmer seasons especially during the period of algal bloom with high sedimentation. The reduction of ferric iron and degradation of organic matter could be responsible for the increased P flux from sediment in algal bloom seasons, which is consistent with the seasonal variation of P forms in sediment. A comparison of the mole ratio of P flux:N flux to both the P:N mole ratio in sediments and the Redfield ratio was used to further distinguish the dominant sediment P forms’ release during seasonal variation. Moreover, the anoxic condition and enhanced microbial activity in warmer seasons contribute a lot to the ammonium release from sediment. Consequently, the nutrient fluxes seasonally influence their corresponding nutrient concentrations in the overlying water. The results of this study indicate that sediment internal loading plays an important role in the eutrophication of Lake Chaohu.

Studies of eutrophication in shallow lakes and the future

Studies of eutrophication in shallow lakes and the future

Water column nutrient concentrations are related to excretion by benthic invertebrates in Lake Taihu, China

Internal release of nutrients is an important contributor to the nutrient dynamics in shallow eutrophic lakes. Zoobenthic organisms may contribute to this release by excreting nutrients to the overlaying water. Based on experiments and using results from previous experimental studies as well as field monitoring density data from 2007 to 2017, we calculated the annual and seasonal nutrient excretions of the two most common macroinvertebrates (Corbicula fluminea and Limnodrilus hoffmeisteri) in Lake Taihu, China. We compared these rates with the concentrations of NH4–N, total nitrogen (TN), PO4–P and total phosphorus (TP) in the lake water as well as with previous results of release rates from undisturbed sediments collected in the lake. The spatial distribution of nutrient excretion by the two invertebrate species varied markedly among sites and years. Regression analyses revealed significant relationships between total nutrient excretions by these two species and the concentrations of NH4–N, TN, PO4–P and TP in the lake, but with seasonal differences. The relationship was overall strongest in winter, followed by spring, and weakest in summer and autumn. The flux of NH4–N and PO4–P released by the two macroinvertebrate species were equivalent to as much as 50% and 66%, respectively, of the sediment release recorded in lab experiments under undisturbed conditions; however, the percentages would be somewhat lower under field conditions where the sediment is subjected to frequent wind-induced resuspension and fish disturbance, enhancing the release rates. The release declined during the study period due to a reduction in the density of macroinvertebrates, perhaps indicating increasing stocking of fish since 2007. Our results indicate that benthic invertebrates are important contributor to the internal loading in shallow eutrophic lakes.

Driving factors of phytoplankton functional groups in the shallow eutrophic lakes of lowland areas of Huaihe River (China).

In this study, we want to clarify the driving factors of phytoplankton community in a set of eutrophic lakes in the lowland areas of Huaihe River, one of seven biggest rivers in China. We analyzed the phytoplankton community of five lakes located in the lowland areas of Huaihe River using Reynolds functional groups (RFG) approach, with simultaneous measurement of several environmental variables in monthly sampling campaigns during 2years. The annual average phytoplankton biovolume of the five lakes ranged from 3.7 to 9.9mm3/L, with the highest values occurring during warm seasons. The shallow eutrophic lakes primarily contained mixing and low-light adaptive species with C and D groups as dominant all-round the year. Representatives of X2, Y, and W1 were predominant during the spring and the autumn with high nutrients and organic matter concentrations. Cyanobacteria were mainly represented by group S1 especially during the summer. Mixing, temperature, together weak light caused by phytoplankton biomass, could shape phytoplankton assemblage more than nutrients in the shallow eutrophic lakes with warm-temperate climate.

Reconstructing Six Decades of Surface Temperatures at a Shallow Lake

Lake surface water temperature (LSWT) plays a fundamental role in the lake energy budget. However, direct observations of LSWT require considerable effort for acquisition and hence are rare relative to a large number of lakes. In lakes where LSWT has not been covered sufficiently by in situ measurements, remote sensing and lake modeling can be used to produce a fine spatio-temporal record of LSWTs. In our study, the Moderate-Resolution Imaging Spectroradiometer (MODIS) LSWT was used to compare with in situ data at the overpass times over the six sites in Lake Chaohu, a large shallow lake in China. MODIS-derived LSWT reflected the variation of lake surface temperature well, with a correlation coefficient of 0.96 and a cool bias of 1.25 °C. The bias was modified by an “Upper Envelop” smoothing method and then employed to evaluate the general lake model (GLM) performance, a one-dimensional hydrodynamic model. The GLM simulations showed good performance compared with MODIS LSWT data at an interannual time scale. A 57-year record of simulated LSWT was hindcast by the well-calibrated GLM for Lake Chaohu. The results showed that LSWT decreased by 0.08 °C/year from 1960 to 1981 and then increased by 0.05 °C/year. These trends were most likely caused by a cooling effect of decreased surface incident solar radiation and a warming effect of reduced wind speed. Our study promoted the use of MODIS-derived LSWT as an alternative data source, and then combined with a numerical model for inland water surface temperature, and also further provided an understanding of climate warming effect on such a shallow eutrophic lake. Key points: (1) Moderate-Resolution Imaging Spectroradiometer (MODIS) lake water surface temperature (LSWT) was validated with real-time in situ data collected at Lake Chaohu with high accuracy; (2) MODIS LSWT was modified by the bias correction and employed to evaluate a one-dimensional lake model at interannual and intraannual scale; The LSWT hindcast by a well-calibrated model at Lake Chaohu decreased by 0.08 °C/year from 1960 to 1981 and increased by 0.05 °C/year from 1982 to 2016.

The Role of Top-Down and Bottom-Up Control for Phytoplankton in a Subtropical Shallow Eutrophic Lake: Evidence Based on Long-Term Monitoring and Modeling

Lake ecosystems are exposed to a range of anthropogenic pressures, particularly eutrophication, and in some cases also stocking and/or overfishing of top-predator fish species, all factors that have implications for the food web structure and which could lead to dominance of nuisance cyanobacteria. Restoration of degraded lakes demands insight into the relative role of top-down for bottom-up regulating forces. While knowledge about these forces in temperate lakes is extensive, comparatively little is known of their role in subtropical lakes where the importance of herbivorous and benthic feeding fish is higher. Here, we analyzed a long-term monitoring data set on subtropical, shallow Lake Taihu, China, and applied random forests regression to examine how phytoplankton was related to environmental variables and biotic assemblages. Our results indicate that the biomass and density of phytoplankton increased with increasing biomass of benthivorous and zooplanktivorous fish and decreased with increases in ammonium concentrations, the nitrogen to phosphorus ratio, and zooplankton biomass, while the response to climate fluctuations and changes in the biomass of piscivores was weak. Effects of higher trophic levels explained as much of the variance in phytoplankton biomass as did nutrients and climatic factors. Moreover, the remarkably reduced ratio of zooplankton to phytoplankton biomass and the decline in cladoceran individual biomass emphasized the increasing importance of top-down control in regulating the phytoplankton following extensive stocking. Our findings offer insight into how fish management may be combined with catchment-level restoration measures to conserve and enhance water quality.

Factors related to aggravated Cylindrospermopsis (cyanobacteria) bloom following sediment dredging in an eutrophic shallow lake

In recent years, Cylindrospermopsis raciborskii blooms have been widely found worldwide. Topics dealing with the mitigation of C. raciborskii bloom is of great importance for toxins produced could threaten public health. The paper first investigated C. raciborskii dynamics over three years following sediment dredging in a shallow eutrophic Lake Dongqian (China). Based on rpoC1 gene copies, C. raciborskii bloom formed with average density of 1.30 × 106 cells/L on July 2009. One year later after sediment dredging, C. raciborskii cell density decreased below 1.17 × 105 cells/L or under detected limits during summer days on 2010. While two years later, the C. raciborskii bloom period was returned with markedly increased cell density reaching up to 4.15 × 107 cells/L on October 2011, and the maximum peak density was shown at 20.3 °C that was much lower than reported optimal growth temperature. Inferred from Spearman correlation analysis, linear regression showed C. raciborskii density was significant and positive with pH and SD, whereas they were significant and negative with TP and DO. Multiple regression analysis further demonstrated that TN, TP, SRP, pH and DO provided the best model and explained 53.1% of the variance in C. raciborskii dynamics. The approaches managing nutrients reduction might not control C. raciborskii bloom as extremely low TN (avg. 0.18 mg/L) and TP concentrations (avg. 0.05 mg/L) resulted in the highest C. raciborskii cell density after sediment dredging.

Effects of sediment oxidation on phosphorus transformation in three large shallow eutrophic lakes in China.

Oxidation of surface sediments is an important means for altering phosphorus (P) exchanges across sediment-water interface (SWI) in shallow lakes. In this study, the potential and composition of regenerated oxidation capacity (OC) of surface sediments were evaluated in three large shallow lakes (Tai Lake, Chao Lake, and Dianchi Lake) in China; the transformation of sedimentary P was quantified through P fractionation scheme. The composition of the regenerated OC differed among these three lakes, with Fe(III) and SO42- dominant in Dianchi Lake, Mn(IV) and Fe(III) in Chao Lake and Tai Lake. Oxidation of sediments enhanced the transformation of sedimentary P and altered P exchanges across the SWI. In Chao Lake, the HCl-P was transformed to BD-P; in Tai Lake, the NaOH-P was involved too, and transformed to BD-P; whereas in Dianchi Lake, an increase in NH4Cl-P was also observed except for the transformation from HCl-P to BD-P. The sediment-to-water flux of P was enhanced with 0.17mg/g DW in Dianchi Lake and 0.08mg/g DW in Chao Lake, while a contrary water-to-sediment flux of P was observed in Tai Lake, reaching 0.01mg/g DW. This study advances our knowledge on the impacts of sediment oxidation on P cycles in lakes, which will be beneficial to eutrophication control.

The influences of eutrophication for the carbon and nitrogen sources for aquatic consumer communities—A case study in Lake Baiyangdian

富营养化对湖泊生态系统能流和物流的影响具有不确定性，多数研究仅关注富营养化对浅水湖泊食物网结构和功能的影响，而富营养化对消费者群落碳源和氮源的影响及其时空分异特征较少关注.鉴于此，本研究选取华北平原最大的浅水富营养化湖泊——白洋淀为研究区，依据生境理化参数将白洋淀划分为3类生境（生境1（Ⅰ和Ⅱ区）主要遭受上游府河废水排放影响；生境2（Ⅴ、Ⅶ和Ⅷ区）主要遭受水产养殖和生活污水的影响；生境3（Ⅲ、Ⅳ和Ⅵ区）遭受人为干扰较小）.在2018年4月和8月分别收集了浮游生物、底栖生物和鱼类样品，运用碳、氮稳定同位素技术定量估算3类生境中底栖和浮游生物对消费者群落碳源和氮源贡献百分比的时空分异特征；同时收集水体和沉积物样品进行常规理化参数分析，明晰富营养化对白洋淀消费者群落碳源和氮源贡献百分比的影响.结果表明：1）就水体和沉积物理化参数季节变化而言，除pH相对稳定外，化学需氧量（COD）、沉积物氨氮（NH₃-Ns）、总氮（TN）和沉积物总磷（TPs）4月高于8月，而其他理化参数则8月高于4月；就空间分布而言，温度（T）、水深（WD）、溶解氧（DO）和沉积物总碳（TCs）值在生境3中最高，而其他理化参数的值则在生境1中最高；2）就δ¹³C和δ¹⁵N空间分布而言，对于同一群落，δ¹³C和δ¹⁵N在3类生境中富集程度呈现显著差异；就时间分布而言，不同季节消费者群落的δ¹³C值存在显著差异，而δ¹⁵N值未呈现显著差异，且消费者群落的δ¹³C和δ¹⁵N呈显著负相关；3）就消费者营养级的空间分布而言，3类生境存在显著差异，同一消费者营养级在生境1中最高，在生境3中最低；就时间分布而言，消费者营养级未呈现显著差异；4）浮游生物对消费者群落碳源和氮源贡献百分比4月高于8月，生境1高于其他生境；而底栖生物对消费者群落碳源和氮源贡献百分比则8月高于4月，生境3高于其他生境；5）通过相关分析，结果表明白洋淀消费者群落的δ¹³C与总磷（TP）、TCs、沉积物总氮（TNs）、总有机碳（TOCs）、TPs呈现负相关关系；δ¹⁵N值与TP、TCs、TNs、TOCs、TPs呈正相关关系.因此，湖泊富营养化会影响消费者群落的碳源和氮源，进而改变湖泊生态系统的能流和物流.;The effects of eutrophication on the energy flow and material flow for lake ecosystems need to be studied. Most of previous studies showed the impacts of eutrophication on the structure and function of lake food web, while the influences of eutrophication on the nitrogen and carbon sources for consumer communities were limited. In view of this, the largest shallow eutrophic lake in North China Plain—Lake Baiyangdian was selected as the study area. According to the physical-chemical parameters in water and sediment, the Lake Baiyangdian was subdivided into three habitats(Habitat 1 strongly influenced by wastewater discharge(Sites Ⅰ and Ⅱ), Habitat 2 influenced by aquaculture and densely populated villages(Sites Ⅴ, Ⅶ and Ⅷ), and Habitat 3 influenced the least by human disturbances (Sites Ⅲ, Ⅳ and Ⅵ)). In April and August 2018, the samples for pelagic organisms, benthic organisms and fish were collected, respectively. Carbon and nitrogen stable isotope techniques were used to quantitatively calculate the contribution percentage of benthic and pelagic organism for the carbon and nitrogen sources of consumer communities. The results showed that: 1) according to the seasonal variation of water and sediment parameters, except pH, the values of chemical oxygen demand (COD), Ammonia nitrogen in sediments (NH₃-Ns), total nitrogen (TN), and total phosphorus in sediment (TPs) in April were higher than that in August, while the other parameters were existed higher values in August; in terms of spatial distribution, temperature (T), water depth (WD), dissolved oxygen (DO), total carbon in sediments (TCs) were showed the highest values in Habitat 3, while the other parameters were showed the highest values in Habitat 1; 2) According to the spatial distribution of δ¹³C and δ¹⁵N, for the same populations, the degree of enrichment were appeared significantly different at three habitats; while for the seasonal variation, the values of δ¹³C for the consumer communities showed significant difference, while the values of δ¹⁵N without significant difference; furthermore, the δ¹³C and δ¹⁵N of the consumer communities were existed the negatively correlated; 3) According to the spatial distribution of consumer trophic level (TL), the TL was appeared significantly different at three habitats; for the same consumer community, the highest values were appeared in Habitat 1, while the lowest values were appeared in Habitat 3; in terms of the temporal variation, the TL was not existed the significantly difference; 4) For the pelagic organisms, the contribution percentage for the carbon and nitrogen sources of consumer communities were appeared higher values in April, and the highest values were existed in Habitat 1; while for the benthic organisms, the contribution percentage for the carbon and nitrogen sources of consumer communities were appeared higher values in August, and the highest values were existed in Habitat 3; 5) Through correlation analysis, the results showed that the δ¹³C of consumer communities were appeared the negatively correlated with TP, TCs, TN in sediment (TNs), total organic carbon in sediment (TOCs), TPs; while the δ¹⁵N were existed the positive correlation with TP, TCs, TNs, TOCs, TPs. Therefore, the eutrophication can influence the carbon and nitrogen sources for consumer communities, and change the energy flow and material flow for the lake ecosystem.