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Organic carbon (OC) accumulation and storage in lake sediments is considered to be an important component of global C cycling. However, the storage of OC in Chinese lakes is not well constrained, and its role in future global change processes has rarely been considered. Here, we analyzed the OC burial and its correlation with lake catchment properties in Chinese lakes that have experienced heavy anthropogenic influence over the last ∼150 years. We compiled OC data from sixty-four lakes from the literature. The results showed that organic carbon accumulation rates (OCARs) in Chinese lakes ranged between 1.4 and 259.5 g m −2 yr −1 , with a mean of 22 g m -2 yr −1 over the past ∼150 years, consistent with the global estimate of the carbon burial rate in lake sediments (11–26 g m −2 yr −1 ). Extrapolated to the whole country, a total of 269.5 Tg OC (ranging from 138.9 to 690.4 Tg C) was stored in Chinese lakes over the past 150 years. Spearman analysis revealed that OCARs strongly depended on lake and catchment size, precipitation, temperature, longitude, altitude and anthropogenic activities. Moreover, OCARs showed an increasing trend, especially after the 1950s, coinciding with land use changes and lake nutrient level shifts. [ABSTRACT FROM AUTHOR]

Abstract: In 2009, two short sedimentary cores (DJZ and DQG) were collected from the East Taihu Lake at the lower Yangtze River Basin using a gravity corer. Lead isotopes and metals including Pb, Al, Fe, and Ti were measured. Radio nuclides including 210Pb and 137Cs were also analyzed for dating of the sediments at both cores. The averaged sedimentation rate at DQG site was 0.32 cm/a since the early 1960s, while at DJZ it was at least 1 cm/a. Significant decline of 206Pb/207Pb ratios were observed in DQG from the deeper sediments to near-surface sediments, indicating increased anthropogenic lead load to the lake sediments due to human impact since the 1970s. The uppermost sediments' lead contents were 2.3 times of those before the 1950s. Trends of anthropogenic lead in both cores inferred from a lead isotope mixing model were found to be similar to those from Al, Fe, and Ti normalization methods. Ti was found to be the best passive tracer element, highly in accordance with Pb isotope mixing model results. In DQG, anthropogenic lead increased sharply since the 1970s and reached a maximum in 2000s (28 mg/kg from lead isotope mixing model), while at DJZ the highest value was 20 mg/kg. These results revealed significant anthropogenic lead influx into the lake caused by human activities, in good agreement with the economic development in the past three decades in China. [Copyright &y& Elsevier]

Abstract: This study attempted to quantify the lake sedimentation and its role in recording catchment soil erosion in the lower reaches of the Yangtze River basin, using cesium-137 (137Cs, anthropogenic) and lead-210 (210Pb, natural) dating. Six cores taken from five lakes, including the two largest lakes in the region (Taihu, Chaohu), were selected for understanding the change of sedimentation rates. High rates of sediment accumulation between the late 1920s and the late 1960s in the three lakes of the Qinyi-Shuiyang River basin showed good correlation with farmland change in adjacent counties, indicating enhanced human-induced soil erosion in the catchment. Chaohu Lake core to some extent also recorded catchment erosion, e.g., high flux in the late 1960s consistent with catchment disturbance. However, at Taihu Lake, sediment accumulation rates do not generally reflect catchment erosion history. Sediment accumulation rates of large shallow lakes in the lower Yangtze River basin do not accurately record soil erosion, whereas relatively small lakes may be sensitive to catchment disturbance. [Copyright &y& Elsevier]

Abstract: The lakes along the middle-lower Yangtze River Basin have undergone dramatic water quality deterioration and eutrophication during recent decades. The nutrient and metal accumulation in the lake sediments through time were investigated using the sedimentary-geochemical records of the drilling cores from several typical lakes. The results showed a general increase in total organic carbon and total nitrogen concentration with lower depth in the profiles. Increased delivery of organic matter to the lake system could be responsible for the nutrient enrichments in the lake bottom sediments. The general trend of nutrients matter enriched upwards in the core indicated that these lakes had become eutrophic since the mid-1950s (macrophyte-type lake), or late 1980s (algae-type lake). In addition, the results have also shown that human activities have exerted a great influence on the past lake environmental changes since the 1950s, inferred from the changes in the sedimentary rate and the anthropogenic metal accumulation in the sediment cores. Enhanced human activities seem to occur around the early 1970s. [ABSTRACT FROM AUTHOR]

Abstract: Sedimentary cores were collected from Honghu Lake, Guchenghu Lake, Taihu Lake during 2002–2005. The total organic carbon (TOC) and metals (Pb, Al, Fe, and Ti) were analyzed. Combined with 137Cs or 210Pb dating method, average sedimentation rates were calculated to be 0.15cm/a at Honghu core, 0.067cm/a at Guchenghu core and 0.35–0.41cm/a at Taihu core. Regression model between lead and geogenic tracer elements and TOC was established. The relationship between lead and geogenic tracer elements or TOC was significant. Pb contamination was estimated based on the natural contribution using regression model. The results indicated anthropogenic lead in the three lakes. The onset of lead pollution was estimated to be early 1970s based on sedimentations from 137Cs or 210Pb dating method. It means the possibility of using lead as time marker. According to the sediment quality guideline (SQG), the sediment was unpolluted except the surface sediment at Honghu and Guchenghu Lake cores. The lead concentrations of Taihu Lake core were higher than that from the other two lakes, but still lower than heavily polluted level. However, anthropogenic lead load to Guchenghu and Honghu increased which should cause the attention of scientist and lake managers. [Copyright &y& Elsevier]

• δ13C in different tissue components of macrophytes was estimated. • δ13C values differed between cellulose and whole samples. • Dissolved inorganic carbon and pH were the major factors affecting δ13C variability. • δ13C variability in α-cellulose was affected the most by environmental variables. Aquatic plants are essential for maintaining the diversity and stability of a lake ecosystem. Stable carbon isotopes (δ13C) of macrophytes have been widely used as a powerful tool to study ecological processes and paleoenvironmental evolution in lakes. Varying results are obtained when using the δ13C of macrophytes to study the changes in the lake environment at different spatio-temporal scales. Thus, sample preparation and subsequent laboratory analyses are crucial for studying environmental changes using the isotopic signal retained in the macrophytes, and are essential for the interpretation of isotope-environment relationships. This study analyzed the δ13C of different tissue components of macrophytes in three lakes of the lower Yangtze River basin, and a correlation analysis was performed on aquatic environments influencing the δ13C values in the different tissue components of macrophytes. The test results showed the difference between the δ13C values of the whole sample and cellulose. Relative analyses indicated that the major factors contributing to the δ13C variability in macrophytes were pH and the concentration of dissolved inorganic carbon (DIC). The δ13C of α-cellulose (δ13C AC) is more sensitive to environmental variables than that of the whole sample (δ13C W) and holocellulose (δ13C HC). The results of this study imply that extraction of α-cellulose is a prerequisite for research on the changes in lake environment using δ13C of macrophytes. This study aims to provide theoretical and data basis for further research on the environmental and ecological change using stable carbon isotopes of aquatic plants. [ABSTRACT FROM AUTHOR]

Burial in sediments is a crucial way to reduce mobilization and risks of hydrophobic organic contaminants (HOCs), but ability of sediments to bury HOCs may be altered if the environment is changed. Whether the ability of sediments to bury HOCs has been affected by climate change remains largely unclear. We excluded the impacts of anthropogenic emissions and eutrophication from that of climate change, and for the first time found that not only the rising surface air temperature but also the declining wind speed and the reducing days with precipitation had weakened the ability of Chinese lakes to bury 16 polycyclic aromatic hydrocarbon (PAHs) by 69.2% ± 9.4%–85.7% ± 3.6% from 1951 to 2017. The relative contributions of the climatic variables to the reduced burial ability depended on the properties of the PAHs, and lakes. Burial ability of the PAHs responded differently to climate change, and was correlated to their volatilization and aqueous solubility, and lake area, catchment area/lake area ratio, and water depth. Our study suggests that not only the rising surface air temperature but also the declining wind speed and the reducing days with precipitation can undermine global efforts to reduce environmental and human exposure to PAHs. Image 1 • Methodological approach was used to study climate change and burial ability of PAHs. • Temperature, wind speed, and days with precipitation weakened the burial ability. • Contribution of the climatic variables to the reduced burial ability was estimated. • The reduced burial ability was correlated to the properties of PAHs, and the lakes. For the first time we find not only rising surface air temperature but also declining wind speed and reducing days with precipitation weakens the ability of lakes to bury PAHs. [ABSTRACT FROM AUTHOR]

Shengjin Lake is a typical Yangtze River-connected lake, that is also a national nature reserve and a Wetland of International Importance. In order to evaluate the eco-environmental evolution of Shengjin Lake, a210Pb- and 137Cs-dated sediment core collected from the upper part of the lake was analyzed. Based on a biological indicator (subfossil cladoceran) and geochemical indicators (loss on ignition (LOI), total organic carbon (TOC), δ13C of bulk sediments (δ13C org), total phosphorous (TP) and total nitrogen (TN)), we revealed the changes in the cladoceran assemblages and eco-environmental processes of Shengjin Lake. The results showed that there was a healthy ecological environment with low nutrient levels in Shengjin Lake before the 1980s. However, the increasing levels of the eutrophic species B. longirostris , nutrients (TN and TP) and organic matters (LOI and TOC), and the decreasing δ13C org in recent decades indicated that the trophic state of Shengjin Lake has increased since the 1980s. This corresponded with increasing anthropogenic effects, including land reclamation, chemical fertilizer application, and sluice construction. In addition, the droppings of water birds also promoted increases in nutrient and organic matters levels in Shengjin Lake. [ABSTRACT FROM AUTHOR]

Lake level changes respond to variations in regional water balance and thus it has been one of the most important indicators applied to reconstruct paleoprecipitation and paleoclimate. In this study, the effective precipitation and the atmospheric circulation during the past three key periods, i.e., Last Interstadial (30 cal ka B.P.), the Last Glacial Maximum (LGM, 21 cal ka B.P.) and Mid-Holocene (6 cal ka B.P.), were analyzed based on the 76 lake-level records documented in the second version of Chinese Lake Status Data Base (CLSDB 2). The results indicated that the western part of China was characterized by elevated lake levels and expanded lake surfaces at 30 cal ka B.P., resulting from the strength of southwest monsoons. The high water stands appeared at 21 cal ka B.P. for lakes in western China were due to the enhanced intensities of Westerlies as well as the low evaporation, although the distribution extent of high lake-levels was reduced. For the period of Mid-Holocene, the lake stands of western China were relatively lower than those of the Last Interstadial and LGM, mainly as a result of shrunken Westerlies. Lake records from eastern China during the Last Interstadial and LGM were scarce, although there were a few reports showing higher or lower water stands compared to the present. A large number of high lake level records from eastern China were observed at the Mid-Holocene, which may be linked with the enhanced East-Asian summer monsoons. [ABSTRACT FROM AUTHOR]

Studying the response of vegetation to past climate changes may help better predict the potential impacts of future climate changes on the terrestrial ecosystems. Here we present a pollen record that covers the second half of the Holocene from the Nanling Mountains, southern China. Our record reveals six cooling events occurring during 5600−4800, 4400−4100, 3800−3300, 3200−2900, 1600−1400, and 500−380 cal yr BP in this area. These cooling events broadly correspond to the episodic weakening of the Asian summer monsoon and the Bond events in the North Atlantic realm, suggesting a common forcing mechanism. Given that temperature has an important effect on the vertical distribution of alpine vegetation in this area, the projected future warming may lead to a large upward shift of the upper forest line and a threat to the life of alpine tree species on the Nanling Mountains. For example, under the RCP8.5 scenario, mean surface air temperature is projected to increase by 4.9 °C by the end of this century. This magnitude of warming definitely would result in the disappearance of Tsuga chinensis in this area. [ABSTRACT FROM AUTHOR]

Lakes are hotspots for carbon cycling and therefore important in the terrestrial carbon budgets. In this study, 15 sediment cores from Hulun Lake, the largest lake in northern China, were analyzed to determine the spatial and temporal trends of organic carbon (OC) burial during the past 150 years. The most plausible factors controlling OC burial are also discussed. The OC burial rates varied from 8.43 g m −2 yr −1 to 73.98 g m −2 yr −1 among the studied sediment cores and exhibited an overall northwest−southeast gradient, with the higher rates in the northwest part of the lake. The OC burial rate for the entire lake was 9.52 g m −2 yr −1 before 1900 and increased to 27.33 g m −2 yr −1 during the period 1900–1950 and then to 35.68 g m −2 yr −1 after 1950. The ratios of the post-1950 period to the pre-1900 and 1900–1950 periods were 3.53 and 1.68, respectively, which indicates an increasing trend of the OC burial rate over the past 150 years. The changes in the burial rates of OC were positively linked to climate warming rather than human activities in Hulun Lake, implying that Hulun Lake will be an increasingly important carbon pool in the future as global warming proceeds. [ABSTRACT FROM AUTHOR]

• The δ 13C cellulose and geochemical proxies were analyzed in Shengjin Lake. • The δ 13C cellulose probably indicates changes in the productivity of the lake. • There is an urgent need for action to reduce nutrient inputs to lakes. The freshwater lakes in the middle and lower reaches of the Yangtze River (MLYR) have been affected by a multitude of factors, including climate change and human activities, and are currently facing a range of aquatic ecological environment problems. In order to establish restoration goals and paths, it is essential to have a scientific understanding of the historical process and pattern of long-term degradation of the lake ecological environment. This study focused on Shengjin Lake, a representative Yangtze River-connected lake in MLYR. Based on the analysis results of cellulose carbon isotopes (δ 13C cellulose) in modern aquatic macrophytes, the response characteristics of aquatic macrophytes δ 13C cellulose to lake environment evolution were revealed by high-resolution multi-proxy (δ 13C cellulose of plant residues and geochemistry indices) analysis of a sediment core. The study also reconstructed the ecological environment evolution process of Shengjin Lake over the past two hundred years. The primary research findings are as follows: Firstly, the results of the modern process survey demonstrated that the δ 13C cellulose of different modern species exhibited considerable variation. The submerged plants exhibited an enrichment of 13C, while the emergent plants exhibited an enrichment of 12C. Secondly, a comprehensive modern process investigation, coupled with palaeo-limnological records and literature data, led to the conclusion that the large plant residues of sediments were primarily derived from submerged plants. Concurrently, statistical analysis indicated that the content of total organic carbon in lakes was the primary factor influencing the changes in sediment δ 13C cellulose. The composition of δ 13C cellulose may be indicative of changes in lake primary productivity. Finally, the paleo-limnological record revealed that the ecological environment of Shengjin Lake has undergone significant changes over the past two hundred years. In particular, since the 1970 s, the δ 13C cellulose has been significantly enriched by 12C, and the geochemical indexes of elements have shown an increasing trend (p < 0.01). This suggests that the ecological environment of Shengjin Lake is gradually deteriorating as a consequence of human activities such as enclosure aquaculture and the construction of Huangpen Sluice, which have occurred in the context of climate warming and regional wind speed decrease in recent decades. This study presents new indicators and evidence for the reconstruction of the evolutionary process of the nutrient environment of lakes in MLYR. Moreover, it provides a foundation for the protection and restoration of lakes. [ABSTRACT FROM AUTHOR]

In June 2009, two short sedimentary cores, wdlc-3 and wdlc-5, were collected from Wudalianchi Lake (48°40′ N ∼ 48°47′ N, 126°06′ E ∼ 126°15′ E) in the north central of Heilongjiang Province, northeastern China, using a gravity corer. The catchment erosion and trophic status changes were studied by an interpretation of the variations of multi-proxies, including organic matter (loss on ignition (LOI 550°C ) and total organic carbon (TOC)), total phosphorus (TP), total nitrogen (TN), magnetic susceptibilities, organic carbon isotope (δ 13 C org ) and grain size. Sediment accumulation rates (SARs) and ages were determined using a composited model of the 210 Pb or 137 Cs methods, respectively. The results are as follows: 1) the average sediment rate was 0.28 g cm −2 y −1 (0.59 cm y −1 ) in wdlc-3 and 0.25 g cm −2 y −1 (0.55 cm y −1 ) in wdlc-5 over the past 100 years. The interaction of the large-scale land reclamation and rainfall were related to high sediment accumulation rates before the 1980s; after the 1980s, however, the changes of precipitation were most likely the main influencing factor on SARs. 2) The δ 13 C org values ranged from −26.78 to −25.79‰ in wdlc-3 and −25.82 to −21.95‰ in wdlc-5. The TOC and TN showed an upcore increasing tendency, and TN, TOC and TP showed a dramatic increase since the 1980s. Based on the multi-proxies, the sediments recorded the change of the aquatic plant community from macrophyte-dominant to algae-dominant in the third lake and to macrophyte and algae coexistence in the fifth lake, also reflecting the changes of trophic status over the past 100 years. 3) Large-scale reclamation was the main factor impact the lake environment before the 1980s; after the 1980s, enhanced agricultural activities such as extensive use of fertilizers and the discharge of domestic waste water resulted in dramatic changes in the lake environment. [ABSTRACT FROM AUTHOR]

• The δ13C of different components of macrophytes in Taihu Lake were analysed. • The different components of δ13C exhibited significant differences in macrophytes. • The main influencing factor to the δ13C variability was the water pH. • The α-cellulose is more suitable as study carrier for study the evolution of lake. Understanding the fractionation mechanism and factors controlling carbon isotopes (δ13C) in macrophytes is significant for studying the biogeochemical carbon cycle and changes in nutrients within lakes. However, whether the environmental implications of δ13C are different in the different components (α-cellulose, holocellulose and whole sample) of macrophytes is unclear. In this paper, the δ13C composition of different macrophytes tissue components in Taihu Lake was analysed on spatial and temporal scales. The effects of aquatic environmental variables on the δ13C values of macrophytes were also explored. The results showed that emergent plants have the most negative stable carbon isotope signals, with a mean value (±SD) of −27.85‰ ± 0.95‰. Submerged macrophytes have large variations with significantly more positive δ13C values (−15.19‰ ± 3.08‰). The δ13C values of floating-leaved plants (−25.32‰ ± 1.02‰) fall between those of the two groups above. In the one-way analysis of variance (ANOVA), the different components (α-cellulose, holocellulose and whole sample) of δ13C exhibited significant differences (p-value <0.01) among the three groups of macrophytes. However, there was no significant seasonal difference in the δ13C of macrophytes. In addition, the δ13C of macrophytes in rivers were lighter than those in lakes. Correlation analyses indicated that the water pH was the main factor affecting δ13C variability in macrophytes. The δ13C values of α-cellulose showed stronger sensitivity to environmental variation than did those of the whole samples and holocellulose. Hence, it is necessary to extract α-cellulose when using the δ13C of aquatic macrophytes to study the changes in lake ecological environments. These results provided a theoretical reference and experimental data support for a modern process of using δ13C in macrophytes for palaeoenvironmental changes. [ABSTRACT FROM AUTHOR]

Channelization significantly affects soil erosion in river floodplains. The object of this study was to use 137Cs as a tracer to determine the 137Cs inventory and derived soil erosion rates under various land use types in a catchment on channelized river floodplain in the lower reaches of Yangtze River, China. Sampling was carried out to establish a137Cs reference inventory in a 70-year old paddy field located on the shoulder-slope of a local hill. The mean reference inventory of 137Cs was 1275 Bq m−2, whereas the 137Cs inventory within the catchment ranged from 284 to 1150 Bq m−2 and the soil erosion rates from −33.3 to −2.4 t ha−1 yr−1, respectively. The dominated land use of paddy in cultivated soils contributed relative low soil erosion. Bamboo and castanea mollissima were preferential for local land uses in uncultivated soils in comparison with woodland and Pinnus massoniana. The rates of soil erosion rates in old tea garden were higher than that in new tea garden. Overall, severe soil erosion and no deposition in the entire catchment occurred in the entire catchment due to the human-induced channelization in the 1970s. Our results suggest that restricting farmland being returned to tea plantations, thereby maintaining the current land use types would reduce soil erosion in river floodplain in the future. • Quantification of soil erosion on a channelized river floodplain using the 137Cs technique. • Soil erosion was accelerated by man-made channelization of Langchuan River. • Returning farmland to tea plantations should be forbidden. [ABSTRACT FROM AUTHOR]

• The δ13C cellulose and geochemical proxies were analyzed in East Taihu Lake. • The δ13C cellulose probably indicates changes in the productivity of the lake. • There is an urgent need for action to reduce nutrient inputs to lakes. At present, East Taihu Lake has been profoundly affected by human interventions. However, the earlier limnological conditions such as the occurrence of temporal nodes and the cause of eutrophication remain unclear due to the short temporal range covered by the instrumental record. The stable carbon isotope ratio of plant residue α-cellulose (δ13C cellulose) is a sensitive proxy indicator of palaeoproductivity, but this proxy index is rarely used in Chinese lakes. In order to test whether δ13C cellulose can be used as a lake ecological environment changes indicator, we investigated the relationship between the δ13C cellulose and several geochemical proxies from a ∼ 30 cm core extending 100 years obtained from a shallow lake: East Taihu Lake, China. Here, the changes in δ13C cellulose of plant residues in sediments from East Taihu Lake were coupled analysis with geochemistry indexes to identify the response of δ13C cellulose from plant residues to the past environmental changes. Combined with the results of C/N ratios, δ13C cellulose and other related studies, the big plant residues in the sediments of East Taihu Lake may be derived from autochthonous aquatic macrophytes. In addition, the δ13C cellulose showed a significant negative correlation with total organic carbon, probably indicating the changes of primary productivity of the lake. The δ13C cellulose and geochemical proxy records revealed that the environmental changes in East Taihu Lake have undergone three distinct periods. The first period (1900s-1960s) represented a natural state without intensive human disturbance. The acceleration of lake eutrophication from the middle period (1960s-1995s) was a consequence of intensive local human activities. The late stage (1995s-2010s) represented a minor decline in nutrient levels after the implementation of ecological protection and restoration. By comparing the results with historical documents and measurements from East Taihu Lake, we inferred that anthropogenic pressures were the primary cause of the changes in the aquatic macrophyte communities and environments. This study provides a unique approach to the ecological environment evolution of East Taihu Lake. At present, Taihu Lake still suffers from annual cyanobacterial blooms due to economic growth (urbanization and industrialization). There is an urgent need for interventions to reduce nutrient inputs in order to enhance ecosystem resilience. Finally, the results of study of East Taihu Lake in China reveal the potential of combining δ13C cellulose and other geochemical proxies to study palaeoenvironmental change, which provides new perspectives for understanding lake ecological environmental change in lakes. [ABSTRACT FROM AUTHOR]

How eutrophication affects biogeochemical processes of hydrophobic organic contaminants (HOCs) in aquatic environments is a pending challenge. Although the direct influence of eutrophication on biogeochemical processes of HOCs in waters has been well addressed, the indirect influence of eutrophication on biogeochemical processes of HOCs remains largely unknown. Here we take the large shallow eutrophic Lake Taihu in China and polycyclic aromatic hydrocarbons (PAHs) as examples to provide novel knowledge on the indirect influence of eutrophication on air – water exchange fluxes, sinking fluxes, and occurrence of HOCs. The air – water exchange fluxes of individual PAHs varied dramatically at different sites in all studied seasons. The sinking flux of ΣPAH 16 was 14 855.3 ± 1579.9, 3548.9 ± 650.6, and 5588.4 ± 530.7 ng m −2 d −1 in spring, summer, and winter. The corresponding concentration of ΣPAH 16 in surface sediments was 713.1 ± 78.6, 339.7 ± 36.6, and 293.0 ± 35.2 ng g −1 d.w. Our study for the first time suggested that recruitment of cyanobacteria from surface sediments to water column in spring reduced the concentrations of PAHs in surface sediments, but enhanced their concentrations in the bulk water column, and overwintering of cyanobacteria in winter enhanced the concentrations of PAHs in surface sediments. High pH induced indirectly by eutrophication decreased seasonal air – water exchange fluxes (enhanced net volatilization) of PAHs, reduced the aromaticity of surface sediments and the hydrophobicity of phytoplankton cell surface, and reduced the accumulation of PAHs in surface sediments and phytoplankton consequently. Sinking fluxes and daily loss of PAHs from the water column decreased with phytoplankton biomass because the fraction of organic matter sinking from the water column decreased with phytoplankton biomass. Our study provides novel complementary knowledge for the biological pump for HOCs, and has important implications for understanding the coupling between eutrophication and biogeochemical processes of HOCs in subtropical shallow eutrophic waters. [ABSTRACT FROM AUTHOR]

Hydrophobic organic contaminants (HOCs) are toxic and ubiquitous in aquatic environments and pose great risks to aquatic organisms. Bioaccumulation by plankton is the first step for HOCs to enter aquatic food webs. Trophic status is considered to dominate variations in bioaccumulation of HOCs in plankton in temperate and frigid deep oligotrophic waters. However, long-term driving factors for bioaccumulation of HOCs in planktonic food webs of subtropical shallow eutrophic waters have not been well investigated. China has the largest subtropical lake density in the Northern Hemisphere. Due to limited field data, long-term variations in the bioaccumulation of HOCs in these lakes are almost unknown. Here we take Lake Xuanwu as an example to investigate long-term variations in the bioaccumulation, and biomagnification of polycyclic aromatic hydrocarbon (PAHs) in planktonic food webs of subtropical shallow eutrophic lakes in China, and elucidate the driving factors. Our results indicate that temperature rather than nutrients dominates long-term dynamics of planktonic biomass in this lake. Precipitation significantly enhances the concentrations of the PAHs, and total suspended particles, and consequently affects the distribution of the PAHs in the water column. Biomass dilution induced by temperature dominates bioaccumulation of the PAHs by both phytoplankton and zooplankton (copepods and cladocerans). Biomagnification of the PAHs from phytoplankton to zooplankton is positively correlated with temperature. Our study suggests that temperature and precipitation drive long-term variations in the bioaccumulation of the PAHs in the planktonic food webs of this subtropical shallow eutrophic lake. Lake Xuanwu has a similar mean annual temperature, annual precipitation, sunshine duration, and nutrient levels as other subtropical shallow eutrophic lakes in China. This study may also help to understand the bioaccumulation of HOCs in planktonic food webs of other subtropical shallow eutrophic lakes. [ABSTRACT FROM AUTHOR]

Effects of Cu 2+ , Zn 2+ , Cd 2+ , and Ag + on the uptake of phenanthrene, pyrene, and benzo[a]pyrene by Microcystis aeruginosa were investigated. A biomimic passive sampler, triolein embedded cellulose acetate membrane (TECAM) was used to help to study the related mechanisms. The facilitation effects of the metals on the uptake of the PAHs by M. aeruginosa increased with the softness order of the metals (Zn 2+ ≈ Cd 2+ < Cu 2+ < Ag + ) and the π donor strength of the PAHs (phenanthrene < pyrene < benzo[a]pyrene). The cation–π interactions between Cu 2+ , Ag + and the PAHs increased the freely dissolved concentrations of the PAHs, and consequently their uptake by M. aeruginosa . The increase in aromaticity of dissolved organic matter (DOM) caused by Cu 2+ , and Ag + also enhanced the uptake of the PAHs. The facilitation effects of Cu 2+ , and Ag + exceeded their toxic effects, uptake of the PAHs was thereby enhanced. In the presence of Zn 2+ , and Cd 2+ , no cation–π interactions between Zn 2+ , Cd 2+ and the PAHs formed in solutions. Aromaticity of DOM was reduced, the diffusive mass transfer of the PAHs was not enhanced. Uptake of the PAHs was thereby reduced. This study suggests that uptake of PAHs by phytoplankton can be significantly influenced by the properties of both metals and PAHs, which will help to understand the fate and risks of PAHs in eutrophic waters co-contaminated with metals. [ABSTRACT FROM AUTHOR]

Abstract: Influences of pH, two types of ions of transition metals (Cu2+, Cd2+), Na3PO4 and their co-influences on the sorption of pentachlorophenol (PCP) on cyanobacterial biomass derived from natural bloom were studied. Sorption of PCP significantly decreases with pH in the range of 3.25–9.00. Although sorption coefficient of ionized PCP is 8.51 times lower than that of neutral species, it is the dominant species at environmentally relevant pH and contributes more to the total sorption of PCP. In the presence of low concentration of Cu2+ (≤40 μmol L−1), sorption of PCP was much lower than that of the blank. However, it increased gradually with Cu2+, and overpassed the blank when concentration of Cu2+ was higher than 50 μmol L−1. Compared with the sole influence of pH, coexisted Cu2+ inhibited the sorption of PCP at pH of 3.25 and 4.35, but enhanced it in the pH range of 5.00–9.00. In the presence of Cd2+, sorption of PCP first increased then decreased rapidly and finally increased slightly again with Cd2+. Except for at pH of 9.00, sorption of PCP at other pH in the presence of Cd2+ was much lower than that solely affected by pH. In the presence of Na3PO4, sorption of PCP increased rapidly then maintained with Na3PO4. Under the influence of both Na3PO4 and pH, sorption of PCP at pH from 3.25 to 5.00 was lower than that solely affected by pH, while it increased with pH in the range of 5.00–9.00 and was higher than that solely affected by pH in the range of 6.00–9.00. Ion pairs of pentachlorophenolate-metal facilitated the sorption of PCP, which was largely dependent on pH illustrated by UV–visible and FTIR spectra. Speciations of metals and PCP and the stability constants of ion pairs of pentachlorophenolate-metal greatly affected the sorption. Ionic strength also played an important role for the sorption of PCP. [Copyright &y& Elsevier]

• The increases of trophy and water level since the modern 1970 s are recorded by subfossil Cladocera. • The density of Bosminidae and Cladocera sum have strong ties to the change of cultivated land area. • P/L ratio responds to extreme hydrological phenomena happening in Nanyi Lake in the past 200 years. At present, most lakes in the world are facing the threat of eutrophication, especially mesotrophic lakes, which are in a critical period of ecosystem transformation. However, how the internal biological composition and structure of these lakes change accordingly has not yet been explored extensively. Here, a paleolimnological evaluation of subfossil Cladocera was initiated to study ecological and hydrological environmental changes in Nanyi Lake, which is a large (203 km2) shallow freshwater lake in the lower reaches of the Yangtze River Basin, China. In this study, subfossil Cladocera data combined with several geochemical proxies from three well-dated sediment cores were obtained. Both the sedimentary subfossil Cladocera and the modern Cladocera in the water column indicated that Bosminidae was the dominant species in Nanyi Lake. We observed that the changes in the density of Bosminidae and Cladocera had strong ties to changes in the cultivated land area, which could cause the obvious alteration of the sedimentation rate around the lake. In addition, the ratio of planktonic species to littoral species (P/L ratio) in Nanyi Lake responded to the occurrence of several extreme hydrological phenomena, such as flooding corresponding to a high P/L ratio and drought corresponding to a low P/L ratio, during the past 200 years. The analysis of Cladocera assemblages and the geochemical indices of the three cores in Nanyi Lake indicated increases in trophy and water levels, especially since the modern 1970s. [ABSTRACT FROM AUTHOR]

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 (δ13C s-bos) and bulk sediment (δ13C org), total organic carbon (TOC), loss on ignition (LOI), C/N, total nitrogen (TN), and total phosphorous (TP). Stable carbon isotopes of living algae (δ13C alg) and Bosmina (δ13C l-bos) were also measured at the same sampling locations. The δ13C s-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 δ13C alg and δ13C l-bos values further revealed depleted 13C. The changes in the δ13C s-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. Unlabelled Image • Bosmina and its δ13C reflected the transformation of lake eco-environment. • Bosmina and its δ13C recorded the signal of eutrophication issues. • δ13C s-bos was used for the first time in food web dynamics of subtropical lakes. [ABSTRACT FROM AUTHOR]

• TP has a key effect on B. (E.) longispina and Chydorus cf. sphaericus. • The abundances of subfossil Bosminidae has decreased since 1960s. • The eutrophication increased and water level decreased after 1960s. East Taihu Lake (the south-eastern portion of Taihu Lake in China) suffers from eutrophication. The study of lacustrine subfossil zooplankton assemblages can be used to reconstruct the long-term evolution of lake water environments. In particular, the analysis of subfossil Cladocera can indicate historical changes in aquatic plants, water level, trophic states, and human disturbance in lakes. In this study, we correlated downcores changes in cladoceran assemblages with several geochemical proxies to identify the response of Cladocera to environmental change in East Taihu Lake over the past one hundred years. Redundancy analysis (RDA) and Pearson correlation analysis identified significant correlations between total phosphorus (TP) and Bosmina spp. (total), B. (E.) longispina , and Chydorus cf. sphaericus (correlation coefficients: −0.720 (P < 0.01), −0.646, and 0.667 (P < 0.05), respectively). We observed decreasing abundances of subfossil Bosminidae and increases in littoral cladoceran species and TP after the 1960s, coinciding with the introduction of land reclamation for fish and crab farming. These anthropogenic pressures exacerbated eutrophication, which led to the rapid growth of submerged vegetation and subsequently altered the zooplankton assemblage. [ABSTRACT FROM AUTHOR]