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Ni Z.,Chinese Research Academy of Environmental Sciences | Ni Z.,Yunnan Key Laboratory of Pollution Process and Management of Plateau Lake Watershed | Ni Z.,Dongting Lake Ecological Observation and Research Station | Wang S.,Chinese Research Academy of Environmental Sciences | And 3 more authors.
Science of the Total Environment

Total hydrolysable amino acids (THAAs) constitute the most important fraction of labile nitrogen. Anthropogenic activities directly influence various biogeochemical cycles and then accelerate lake ecosystem deterioration. This is the first study that has established the relationship between sediment THAAs and anthropogenic activities using dated sediment cores, and evaluated the possibility of THAAs release at the sediment interface based on changes in environmental conditions in Erhai Lake. The results showed that historical distribution and fractions of THAAs could be divided into three stages: a stable period before the 1970s, a clear increasing period from the 1970s to 1990s, and a gradually steady period that started after the 1990s. The chemical fraction, aromatic and sulfur amino acids (AAs) accounted for only ≤. 3% of THAAs. Basic AAs accounted for 5-17% of THAAs, and remained at a relatively stable level. However, acidic and neutral AAs, which accounted for 19-44% and 35-69% of THAAs, respectively, were the predominant factors causing THAAs to increase due to rapid agricultural intensification and intensification of contemporary sedimentation of phytoplankton or macrophytes since the 1970s. These trends were closely related to both anthropogenic activities and natural processes, which implied that sediment THAAs could act as an effective indicator that reflects anthropogenic activities and aquatic environmental characteristics. The current contributions of sediment THAAs on TN and TOC were <. 5% and 1.5%, respectively. However, the dramatic increase in THAAs in the sediment cores indicated that there was a huge potential source of labile nitrogen for the overlying water under certain environmental conditions. Correlation analysis suggested that the release of THAAs was negatively correlated with pH, whereas positively correlated with bacterial number and degree of OM mineralization, which particularly depend on the stability of HFOM. Therefore, the risk of sediment THAAs release might increase when the sediment environment continuously changes. © 2016 Elsevier B.V. Source

Ni Z.,Chinese Research Academy of Environmental Sciences | Ni Z.,Dongting Lake Ecological Observation and Research Station | Wang S.,Chinese Research Academy of Environmental Sciences | Wang S.,Dongting Lake Ecological Observation and Research Station
Ecological Engineering

The release of endogenous nutrients from sediments significantly affects water quality and accelerates eutrophication. In general, lakes from the Yungui Plateau of China are characterized by high sediment nutrient contents and relatively good water quality. Thus, the risk of nutrient release from sediments may be enhanced under certain environmental conditions, and this enhanced risk would become a general concern during eutrophication. Knowledge about historical nutrient accumulation and effect of environmental parameters on nutrient dynamics at the sediment-water interface in the lakes from this region is important to understand the eutrophication processes for these lakes. Hence, this study reconstructs the historical accumulation of nutrient and the effects of environmental parameters on possible release risk of nutrient at the sediment interface for Erhai Lake in the Yungui Plateau region. This study also analyzes historical changes in environmental conditions to predict the future release of nutrient from sediment. In the past decades, the burial fluxes (BFs) of nitrogen (N) in the sediments have continuously increased, whereas those of phosphorus (P) have not or only slightly increased, except in highly polluted areas. These situations may be attributed to the long-term fertilization practices of farmers in the watershed, where the application of N fertilizers is much higher than that of P fertilizers. The mentioned phenomena can also be ascribed to the different biogeochemical behaviors of N and P. Nutrient pollution started in the 1970s and worsened from the 1990s. Before the 1970s, nutrients were relatively low and stable. Thereafter, N in the entire area and P in seriously polluted areas (northern area) dramatically increased because of natural and anthropogenic processes, such as excessive artificial N and P fertilization. After the early 1990s, the BFs of nutrients were steady but high because of the degradation of aquatic vegetation and the implementation of pollution control policies. The burial efficiencies (BEs) of TN range between 44% and 85%, with a mean value of 71%. Combined with the high increase rate of BFs during the past decade, this relative low BE indicates that the release of sediment N into overlying water has increased yearly. The BEs of TP range between 98% and 102%, with a mean value of 99%, and the increase rate of historical BFs is small. This result suggests that the sediment generally serves as a sink for P. In addition, the diffusion fluxes of nutrients is an important factor because their forms and environmental conditions (dissolved oxygen (DO), pH, etc.) influence water quality. However, the risk of nutrient release from sediment source might increase if these environmental conditions change (i.e., decreased DO and increased pH). © 2015 Elsevier B.V. Source

Ni Z.,Chinese Research Academy of Environmental Sciences | Ni Z.,Dongting Lake Ecological Observation and Research Station | Wang S.,Chinese Research Academy of Environmental Sciences | Wang S.,Dongting Lake Ecological Observation and Research Station | And 2 more authors.
Environmental Pollution

This study aims to establish the relative importance of sediment organic phosphorus (Po) to the total P and the major classes of organic molecules that contribute to sediment Po, determined by measuring their susceptibility to enzymatic hydrolysis, across a suite of lakes ranging from oligotrophic to eutrophic status. The results showed that Po accounted for 21-60% of total P, and bioavailable Po accounted for 9-34% of Po in the sediments. The bioavailable Po includes mainly labile (H2O-Po) and moderately labile (NaOH-Po) P forms. For H2O-Po (accounting for only1.4% of Po), 53% (average) was labile monoester P, 28% was diester P and 17% was phytate-like P. For NaOH-Po (accounting for 9-33% of Po), 32% was labile monoester P, 33% was phytate-like P and 18% was diester P. The composition of bioavailable Po, determined by enzyme assays, was related to the lake nutrient levels, which implies that sediment bioavailable Po could act as an effective indicator for lake eutrophic status. With the increase of lake nutrient levels, bioavailable Po content and alkaline phosphatase activity in the sediment all increased, indicating that Po represents an important and bioavailable source of P that increases with eutrophication, and could contribute to internal loading and resistance of eutrophic lakes to remediation. This implies that eutrophic lakes would maintain long-term eutrophic status and algal bloom phenomena even after the external input of P was controlled and the total P concentration of water has declined. Thus, in order to reduce the release risk of sediment P more efficiently and effectively, sediment P control technique should focus not only on reducing the total P and inorganic P, but should also pay close attention to the removal of bioavailable Po. © 2016 Elsevier Ltd. Source

Ni Z.,Chinese Research Academy of Environmental Sciences | Ni Z.,Dongting Lake Ecological Observation and Research Station | Wang S.,Chinese Research Academy of Environmental Sciences | Wang S.,Dongting Lake Ecological Observation and Research Station
Environmental Science and Pollution Research

China has been confronted with serious water quality deterioration concurrent with rapid socioeconomic progress during the past 40 years. Consequently, knowledge about economic growth and lake water quality dynamics is important to understand eutrophication processes. Objectives were to (i) reconstruct historical nutrient accumulation and the basin economic progress on burial flux (BF); (ii) determine forms and structures of nitrogen (N) and phosphorus (P) in sediment and water using six cores in three of the most severely eutrophic lake areas in China (i.e., Eastern Plain, Yunnan-Guizhou Plain, and Inner Mongolia–Xinjiang regions). Results suggest that BFs of total nitrogen (TN) continued to increase in sediment, whereas total phosphorus (TP) levels were consistent or only slightly increased, except in highly polluted lakes during the past decades. Similar results were observed for concentrations of nutrients in water (i.e., increased N/P). This historical distribution pattern was correlated to long-term fertilization practices of farmers in the watershed (N fertilization exceeds that of P) and was contingent upon pollution control policies (e.g., emphasized P whereas N was ignored). Vertical profiles of BFs indicated that lake nutrient accumulation included three stages in China. Nutrient accumulation started in the 1980s, accelerated from the 1990s, and then declined after 2000. Before the 1980s, nutrients were relatively low and stable, with nutrient inputs being controlled by natural processes. Thereafter, N- and P-bound sediments dramatically increased due to the increasing influence of anthropogenic processes. Nutrients were primarily derived from industries and domestic sewage. After 2000, BFs of nutrients were steady and even decreased, owing to implementation of watershed load reduction policies. The decreasing NaOH-extracted P (Fe/Al–P) and increasing organic phosphorus (OP) indicated that the source of exogenous pollution underwent a shift. Inputs of nutrients were predominantly from agricultural and domestic sewage, whereas industrial pollution has been gradually controlled in most of the watersheds. Historical nutrient dynamics suggest that the economy of China is growing at the expense of its aquatic ecological environments. Therefore, more attention to nutrient export to groundwater resulting from economic development is important for further aquatic ecosystem deterioration and eutrophication in China. © 2015 Springer-Verlag Berlin Heidelberg Source

Ni Z.,Chinese Research Academy of Environmental Sciences | Ni Z.,Dongting Lake Ecological Observation and Research Station | Wang S.,Chinese Research Academy of Environmental Sciences | Wang S.,Dongting Lake Ecological Observation and Research Station | And 3 more authors.
Environmental Science and Pollution Research

Biogeochemical cycling of internal bioavailable organic phosphorus (OP) is an important source for algal bloom after exogenous P inputs are controlled. Biogeochemical cycling may be affected by hydrological processes and the water cycle and eventually result in water quality deterioration and accelerated lake eutrophication. Poyang Lake is the largest freshwater lake in China. The hydrological condition of the lake has significantly changed since 2003, thereby causing a continuous decline in water level. In this study, sediments were obtained from different elevations and different hydrological conditions in Poyang Lake. The sediments were subjected to sequential extraction and enzymatic hydrolysis to determine the transformation of OP into various chemical forms, their bioavailability, and the exchange between the sediments and overlying water. Results suggested that the descending water level caused by the changes in hydrological conditions was one of the major factors affecting OP dynamics. Long exposure of sediments resulted in high OP content and increased availability. The increased OP content in exposed sediments was primarily derived from H2O-Po and NaOH-EDTA-Po. Moreover, the increased OP availability in exposed sediments was mainly attributed to the increasing amount of orthophosphate caused by processes governing sediment exposure, promotion of OP release, and transformation of chemical forms from nonlabile to labile. Sediment exposure time and area have considerably expanded since 2003; hence, the amounts of OP and orthophosphate in the sediments have increased by as much as 600 and 120 tons in the lake every year, respectively. Although the increase in orthophosphate only accounted for 6 % of the external total phosphorus, the local region may exhibit higher risk for OP release from the sediments, thereby accelerating quality deterioration. Therefore, maintaining reasonable hydrological conditions is important to protect Poyang Lake water. © 2015, Springer-Verlag Berlin Heidelberg. Source

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