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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 210 Pb-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 (δ 13 C s-bos ) and bulk sediment (δ 13 C org ), total organic carbon (TOC), loss on ignition (LOI), C/N, total nitrogen (TN), and total phosphorous (TP). Stable carbon isotopes of living algae (δ 13 C alg ) and Bosmina (δ 13 C l-bos ) were also measured at the same sampling locations. The δ 13 C 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 δ 13 C alg and δ 13 C l-bos values further revealed depleted 13 C. The changes in the δ 13 C 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., (Copyright © 2020 Elsevier B.V. All rights reserved.)

As the largest polycyclic aromatic hydrocarbons (PAHs) emission country, China is suffering from severe PAHs pollution. Twenty-eight lakes in the middle and lower reaches of the Yangtze River region (MLYR), where numerous lakes are located in and play very important roles in the development of the local economy and society, were selected to investigate the levels and sources of the PAHs in this region and the related influence factors. Concentrations of the 16 PAHs (∑PAHs) in the sediments ranged from 221.0 to 2418.8 ng g(-1) (dry weight). The mean ∑PAHs was higher in the lower reaches than in the middle reaches. ∑PAHs in the sediments was positively correlated with the local gross domestic product (GDP), which implies that GDP was the key factor to affect the PAHs level in the sediments of study area. According to the composition of 16 PAHs, the 28 lakes were grouped into 3 clusters. Major PAHs sources for the three types of lakes were significantly different, which were biomass combustion, coal combustion, and vehicle/coal source, respectively. The total toxic benzo(a)pyrene equivalent (TEQ(carc)) of the carcinogenic PAHs in the sediments varied from 12.9 to 472.9 ng TEQ(carc) g(-1). Benzo(a)pyrene (BaP) and dibenzo(a,h)anthracene (DaA) were the two main contributors to total TEQ(carc).

To date no passive sampler has been used to predict bioavailability of contaminants to macrophytes. Here a novel passive sampler, linoleic acid embedded cellulose acetate membrane (LAECAM), was developed and used to in situ measure the freely dissolved concentrations of ten polycyclic aromatic hydrocarbons in the sediment porewaters and the water columns of two lakes in both winter and summer and predict their bioavailability to the shoots of resident submerged macrophytes (Potamogeton malainus, Myriophyllum spicata, Najas minor All., and Vallisneria natans (Lour.) Hara). PAH sampling by LAECAMs could reach equilibrium within 21 days. The influence of temperature on LAECAM-water partition coefficients was 0.0008-0.0116 log units/°C. The method of LAECAM was comparable with the active sampling methods of liquid-liquid extraction combined with fDOC adjustment, centrifugation/solid-phase extraction (SPE), and filtration/SPE but had several advantages. After lipid normalization, concentrations of the PAHs in LAECAMs were not significantly different from those in the macrophytes. In contrast, concentrations of the PAHs in the triolein containing passive sampler (TECAM) deployed simultaneously with LAECAM were much higher. The results suggest that linoleic acid is more suitable than triolein as the model lipid for passive samplers to predict bioavailability of PAHs to submerged macrophytes.

Although numerous studies have addressed sequestration of hydrophobic organic compounds (HOCs) in laboratory, little attention has been paid to its evaluation method in field at large temporal scale. A biomimetic tool, triolein embedded cellulose acetate membrane (TECAM), was therefore tested to evaluate sequestration of six PAHs with various hydrophobicity in a well-dated sediment core sampled from Nanyi Lake, China. Properties of sediment organic matter (OM) varying with aging time dominated the sequestration of PAHs in the sediment core. TECAM-sediment accumulation factors (MSAFs) of the PAHs declined with aging time, and significantly correlated with the corresponding biota-sediment accumulation factors (BSAFs) for gastropod (Bellamya aeruginosa) simultaneously incubated in the same sediment slices. Sequestration rates of the PAHs in the sediment core evaluated by TECAM were much lower than those obtained from laboratory study. The relationship between relative availability for TECAM (MSAF(t)/MSAF(0)) and aging time followed the first order exponential decay model. MSAF(t)/MSAF(0) was well-related to the minor changes of the properties of OM varying with aging time. Compared with chemical extraction, sequestration reflected by TECAM was much closer to that by B. aeruginosa. In contrast to B. aeruginosa, TECAM could avoid metabolism and the influences from feeding and other behaviors of organisms, and it is much easier to deploy and ready in laboratory. Hence TECAM provides an effective and convenient way to study sequestration of PAHs and probably other HOCs in field at large temporal scale.

The middle and lower reaches of the Yangtze River, a primary region for freshwater lakes in China, have undergone significant transformations throughout the Holocene. These changes, driven by factors such as sea-level rise, climate change, and human activities, have led to the progressive elevation of water levels in this area. As a result, a floodplain has emerged, characterized by the formation of numerous shallow lakes along the river course. However, the pattern of water-level changes in the main channel of the Yangtze River during the Holocene remains unclear. This gap in knowledge poses challenges for understanding sediment transport dynamics, the interactions between the river and its adjacent lakes, and the prevention and control of flood disasters in the Yangtze River basin. To shed light on these issues, our study compiled data on the surface elevation and water depth of 81 lakes in the mid-lower reaches of the Yangtze River basin. Additionally, we analyzed historical water-level records from the 1900s to the 1970s at eight gauging stations from Shashi to Jiangyin along the river's main stream. Our findings reveal that, particularly along the Jingjiang section, the basal elevation of most lakes is lower than the Yangtze River's water level during the dry season. Conversely, the water level of the main stream exceeds that of both the floodplain and the lakes enclosed by the Jingjiang embankment. In the tidal reach, especially within the Taihu Lake basin, the basal elevation of lakes typically falls below sea level. Meanwhile, lakes located along the section from Chenglingji to Wuhu exhibit basal elevations that correspond with the Yangtze River's annual average and dry season water levels. Given the widespread presence of lakes along the middle and lower reaches of the Yangtze River, our study introduces a new proxy for reconstructing the mean water level of the mid-lower Yangtze River in the Holocene. By analyzing sediments from Nanyi Lake and Chenyao Lake in the lower Yangtze River, we attempted to reconstruct the water level of the Yangtze River's main channel since 8 ka BP. [ABSTRACT FROM AUTHOR]

Purpose: Sediments are natural archives to record the occurrence and sources of organochlorine pesticides (OCPs). Most previous studies on historical occurrence and sources of OCPs in China only focused on DDTs and HCHs. Comprehensive knowledge of historical occurrence and sources of persistent OCPs in China are scarce. Materials and methods: One 20-cm sediment core was collected from the third largest freshwater lake (Lake Taihu) in China, then sliced every 1 cm, dated with 137Cs and 210Pb, and used for the analysis of 21 OCPs. Isomer ratios and principal component analysis (PCA) were applied to apportion the historical sources of the OCPs in this lake. Results and discussion: Three concentration peaks of OCPs were observed in the middle-late 1950s, early-middle 1980s, and the middle 2000s. The average concentration of ΣDDX was 238.55 ± 55.43 ng gdw−1 from 1948 to 2012. p,p′-DDT was the dominant congener of DDX, mostly derived from the legacy technical DDT. The average concentration of ΣHCHs, aldrin, heptachlor epoxide, endosulfan sulfate, methoxychlor, heptachlor, trans-chlordane, cis-chlordane, endosulfan I, endrin, diendrin, endosulfan II, diendrin aldehydrate, and diendrin ketone were 24.56 ± 6.90, 10.35 ± 3.26, 9.51 ± 1.88, 7.37 ± 1.81, 7.01 ± 2.82, 2.60 ± 0.81, 0.63 ± 0.24, 3.21 ± 1.25, 1.04 ± 0.29, 3.89 ± 2.61, 5.67 ± 1.59, 1.07 ± 0.19, 1.09 ± 0.22, and 1.32 ± 0.33 ng gdw−1. Conclusions: Dicofol and p,p′-DDT-containing anti-fouling paints may be responsible for the current input of p,p′-DDT. Most of the HCHs were derived from the legacy technical HCHs, but there was input of lindane as well. PCA indicated that the legacy technical DDTs, HCHs, heptachlor, chlordane, aldrin, and endrin, the current input of p,p′-DDT, methoxychlor, and endosulfan, and microbial transform of γ-HCH to α-HCH were the dominant sources for the 21 OCPs in Lake Taihu. [ABSTRACT FROM AUTHOR]

Lakes are important source of atmospheric methane (CH4). Especially for large and shallow lakes, accurate CH4 emission budgets must consider the spatial and seasonal heterogeneity which characterize these ecosystems. CH4 concentrations in sediment and lake water and CH4 fluxes from sediment were analysed in selected open water areas of Lake Taihu, the third largest freshwater lake in China, to test the hypothesis that CH4 concentrations and fluxes differ both spatially and temporally in relation to biological and environmental features. The results showed that Lake Taihu was a source of CH4 throughout the year. The observed CH4 concentrations and fluxes were higher in the north-western and south-eastern areas of the lake, and lower in the central area. This spatial heterogeneity in methane emissions was mainly related to local organic matter content, plant characteristics, deposition rate and sediment features. Seasonally, CH4 showed stronger emissions in summer. These results suggest that the analysis of CH4 dynamics in shallow lakes should consider the habitat heterogeneity and the different sources of organic matter. Furthermore, the CH4 emission budget should at least include high and low temperature periods to decrease temporal bias. [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: 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]

Metals in lacustrine sediment have both anthropogenic and natural sources. Because of intensified human activities, the anthropogenic input of metal elements has exceeded the natural variability. How to distinguish the anthropogenic sources in lake sediments is one of the tasks in environmental management. The authors present a case study, which combined the geochemical and statistical methods to distinguish the anthropogenic sources from the natural background. A 56 cm core (core DJ-5) was collected from Dongjiu Lake, Taihu Lake catchment, China. The concentration distributions of Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Sr, Ti, V and Zn in core DJ-5 indicated that Dongjiu Lake had serious Cd pollution, and the concentrations of Cr, Cu, Pb, Mn and Zn had also exceeded the Chinese State Standards of Soil Environmental Quality in the upper layer of the core. Using Al as a reference element, the other metals were normalized and compared with their baselines to calculate the enrichment factors (EFs). The principal component analysis (PCA) of metal concentrations was performed using ViSta6.4. The results of EFs and PCA indicated that the concentration variations of Cd, Cu, Pb, Mn and Zn were mainly caused by the anthropogenic sources, and the concentration variations of Cr and Ni were influenced by both the anthropogenic and natural factors, while the other metals were mainly derived from the natural sources. Intensified human activities within the lake catchment area resulted in the increase of heavy metal inputs directly and the acceleration of erosion which caused other metal elements to deposit in the aquatic environment. The results of this work will be useful in probing changes forced by humans in the lake environment and in adjusting human activity in restoring the lake environment. [ABSTRACT FROM AUTHOR]

• 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]

• 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]

• 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]

• Cladocera assemblages shifted from littoral to planktonic species since 1970s. • Ecological turnover of changing sedimentary environment and increasing nutrition occurred in 1970s. • Periodical changes of eco-environment modulating by human activities and climate change occurred in Wulanpao Lake. The ecological environment of grassland lakes is closely related to water security and human health in both arid and semiarid regions. The protection of freshwater and wetland ecological environments in grasslands promotes the stable and healthy development of ecosystems in arid and semiarid areas. In the present study, we investigated the long-term eco-environmental evolution of a typical grassland lake: Wulanpao Lake, located in the Hulun Lake Basin of northern China. This region represents the junction of areas subject to monsoons and those that are not and is arid or semiarid. We used the biological indicator of subfossil Cladocera, geochemical indices, and grain size from a well-dated sediment core. The ecological environment of Wulanpao Lake was influenced by climate change, consistent with a low trophic status, and the site developed aquatic vegetation between the 1860s and 1970s. However, the observed shift from predominantly littoral to planktonic Cladocera species was accompanied by ecological turnover (changes in the sedimentary environment and increases in trophic status and organic matter) when human activities began to impact the lake environment in the 1970s. This research provides an empirical foundation for managers and policymakers to protect similar grassland freshwater eco-environments. [ABSTRACT FROM AUTHOR]

• 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]

• 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]