Taihu Watershed Research Articles

Shift of major driver for chemical weathering from the natural control to human dominance since 1980s in the Taihu watershed, China.

Anthropogenic acidification has become a concerned problem in the Taihu region; however, how it affected the regional weathering rate, especially at the different sub-watershed levels has hardly been studied. To reveal the impact of human activities on watershed weathering and water chemistry in Taihu sub-watersheds, historical water chemistry data (1950s-1970s) and recent water samples (2018-2021) of the local river systems, as well as sediment samples of Taihu lake were collected and analyzed, and a linear addition mass balance method was used to determine the weathering rate at the sub-watershed level. The results indicated that, compared with 60years ago, the current weathering rate of carbonates and silicates in the Taoge water system (TG) was the highest, reaching 67.2 and 11.4 t·km-2·a-1, increasing by 4.1 and 2.7-folds, respectively; and meanwhile the carbonate and silicate weathering rates increased by 3.1 and 4.9-folds in the Nanhe water system (NH), and 5.2 and 3.4-folds in the Tiaoxi water system (TX), respectively. The increasing rate was significantly correlated to the atmospheric SO2 concentration in different sub-watersheds and was affected by the sub-watershed lithology, e.g., TX had a higher increase rate of silicate weathering due to the wider distribution of silicates in this sub-watershed than the other two. The sediment evidence of Na/K and Ca/Al on the profile in different lake parts, which was influenced by different influx river systems, confirmed that the overall intensity of watershed weathering was higher in TG than in the TX sub-watershed and was higher in the recent decade than 50-60years ago. The accelerated weathering rate was found to present a definite consistency with the social and economic development in the watershed. Combined analyses of the accelerated weathering rate in the watershed and sedimentation evidence indicated that the major driving force for the watershed weathering has shifted from carbonic acid under the natural condition to human-induced sulfuric acid since 1980s.

Accelerated carbonate dissolution caused by anthropogenic acidification - contrast of watershed soils to lake sediments in Taihu Region, China.

Although Taihu watershed is an "acid-insensitive" region, anthropogenic acidification has greatly changed the water chemistry in Taihu Lake. However, how soil carbonates responded to the long-term human-induced acidification received less attention. In this work, we investigated soil carbonate concentrations from different land uses in the upstream of the lake and sediment carbonate profiles in the lake, to explore the linkage of carbonates dissolution in the land and sedimentation in the lake. The result showed that the wheat-rice surface soil, the most acidification-impacted by fertilization and acid deposition, had significantly lower pH than vegetable and wetland soils (p < 0.05). Meanwhile, the carbonate concentration in wetland soils, only impacted by acid deposition, was significantly higher than that in wheat-rice and vegetable soils (p < 0.05). The pH profile of fertilized soils, with an increasing trend from the surface to bottom, further indicated the acidifying effect of fertilization. Although the average soil pH across all land uses was 6.6 in the upstream of the lake, remaining carbonate buffering system, the significant carbonate decrease especially in surface soils evidenced the definite carbonate dissolution by acidification, which is cumulative and irreversible. Contrary to the topsoils, the sediment carbonate concentration presented an increasing trend from the depth of 15cm (denoting around the early 1980s) to the surface, indicating that lake sediment is a major sink of carbonate Ca and Mg from the watershed, particular under an alkaline lake environment caused by frequent algae blooms in the past decades. In addition, Ca/Mg ratio in the sediment, having higher values in a higher pH environment, was quite different from the watershed soil pattern, suggesting different biogeochemical processes Ca and Mg underwent during their transportation and sedimentation. The effects of acidification-altered re-distribution of carbonate Ca and Mg and Ca/Mg ratio in the terrestrial and aquatic environments deserve wider considerations of ecosystem consequence.

Distinctive Microbial Processes and Controlling Factors Related to Indirect N2O Emission from Agricultural and Urban Rivers in Taihu Watershed.

Inland rivers are hotspots of anthropogenic indirect nitrous oxide (N2O) emissions, but the underlying microbial processes remain poorly understood. This study measured N2O fluxes from agricultural and urban rivers in Taihu watershed and investigated the microbial processes driving N2O production and consumption. The N2O fluxes were significantly higher in agricultural rivers (140.1 ± 89.1 μmol m-2 d-1) than in urban rivers (25.1 ± 27.0 μmol m-2 d-1) (p < 0.001). All wind-based models significantly underestimated N2O flux in urban rivers (p < 0.05) when using the Intergovernmental Panel on Climate Change method because they underestimated the N2O emission factor (EF5r). Wind speed and nitrate were the key factors affecting N2O fluxes in agricultural and urban rivers, respectively. NirK-type denitrifiers produced N2O in urban river water, while nirS-type denitrifiers consumed N2O in the sediments of all rivers. Co-occurrence network analysis indicated organics from Microcystis served as electron donors for denitrifiers (dominated by Flavobacterium) in water, while direct interspecies electron transfer between Thiobacillus and methanogens and between Dechloromonas and sulfate-reducing bacteria enhanced N2O reduction in sediments. This study advances our knowledge on the distinctive microbial processes that determine N2O emissions in inland rivers and illustrates the need to revise EF5r for N2O estimation in urban rivers.

Surface Water Quality Assessment and Contamination Source Identification Using Multivariate Statistical Techniques: A Case Study of the Nanxi River in the Taihu Watershed, China

Understanding the spatiotemporal patterns of water quality is crucial because it provides essential information for water pollution control. The spatiotemporal variations in water quality for the Nanxi River in the Taihu watershed of China were evaluated by a water quality index (WQI) and multivariate statistical techniques; additionally, the potential sources of contamination were identified. The data set included 22 water quality parameters collected during the monitoring period from 2015 to 2020 for 14 monitoring stations. WQI assessment revealed that approximately 85% of monitoring stations were classified as “medium-low” water quality, and most showed continuous improvement in water quality. Cluster analysis divided the 14 monitoring stations into three clusters (low contamination, medium contamination and high contamination). Discriminant analysis identified pH, petroleum, volatile phenol, chemical oxygen demand, total phosphorus, F, S, fecal coliform, SO4, Cl, NO3-N, total hardness, NO2-N and NH3 as important parameters affecting spatial variations. Factor analysis identified four potential contamination source types: nutrient, organics, feces and oil. This study demonstrated the usefulness of multivariate statistical techniques in assessing large data sets, identifying contamination source types, and better understanding spatiotemporal variations in water quality to restore and protect water resources.

Mutual environmental drivers of the community composition, functional attributes and co-occurrence patterns of bacterioplankton in the composite aquatic ecosystem of Taihu watershed in China.

This study aimed to determine the environmental and ecological factors influencing the planktonic prokaryotic community profiles in the composite ecosystem comprising Taihu Lake, Taipu River and Jinze Reservoir in the Taihu Watershed in China. A total of 42 water samples were intermittently collected from different sites in 6 months across four seasons. Physicochemical characteristics of the ecosystem, bacterioplankton diversity and composition, the presence of co-occurrence patterns, and environmental predictors of ecological modules in the bacterioplankton network were determined. The central species played a more important role in regulating the structure and function of the bacterioplankton community and in responding to environmental contamination than the entire community. The relative abundance of the phylum Proteobacteria and the class Betaproteobacteria varied significantly between months and locations, which were identified as core functional taxa. A non-random co-occurrence pattern and function-driven modular structure were observed in the bacterioplankton co-occurrence network. Dissolved oxygen and ammonium nitrogen were the major and mutual environmental predictors of the bacterioplankton community composition, functional attributes and relative abundance of ecological modules. The results improve our understanding of the impact of anthropogenic contamination on bacterioplankton diversity and biogeochemical cycles and the formulation of strategies for bioremediation of the Taihu Watershed.

Stream loss in an urbanized and agricultural watershed in China

Stream losses are extensively observed due to human activities in the world, and the patterns of stream loss vary in different land use types. However, relationship between stream loss pattern and land use covers is poorly understood. We select the lower Taihu watershed (LTWS) within Yangtze River Delta (YRD), which is dominated by agricultural and urban covers and a typical case of most urbanized watersheds in China. In this study, we measured the stream loss of LTWS from 1960s to 2010s and investigated its relation to different land use covers and impervious area percentage (IAP) in order to figure out the main factor of stream loss in this area. The results show that urban area has tripled with fractional contribution from 10.3% to 33.18% in the form of conversion from agriculture to urban area during 1990–2015. 12.5% of all the streams are lost and 1st-order streams contribute most (91.8%) to the total stream loss. Urban cover contribute most (76%) to total streams loss compared to other land use types. We find that 1st-order streams have highest stream loss intensity, which is mainly caused by urban expansion, but preferred protections are given to highest-order streams. The linear model of correlation of pixel-level streams loss and IAP shows that the streams loss is statistically significant positive with IAP of cells (R2 = 0.91). Tradeoffs between city expansion and river network make small channels sacrifice for the urbanization. Urgent measures including legislation must be taken to protect small streams during urbanization nowadays and in future.

Spatial and seasonal distributions of Feammox from ecosystem habitats in the Wanshan region of the Taihu watershed, China

Anaerobic ammonium oxidation coupled to Fe(III) reduction, termed Feammox, is a newly identified microbial process that occurs in nitrogen and iron cycles. As the seasonal distribution of Feammox in different ecosystem habitats has not been fully explored, this study investigated the potential Feammox rates and the diversity and abundance of iron reducing bacteria (IRB) in three habitats during two seasons by using isotope tracing technique and molecular analysis, respectively. Results showed that potential Feammox rates vary both seasonally and spatially, having relatively higher rates in summer (0.05–0.19 mg N kg−1 d−1) and lower rates in winter (0.02–0.09 mg N kg−1 d−1). In addition, relatively higher and lower rates were observed in farmland soils (0.09–0.19 mg N kg−1 d−1) and river sediments (0.02–0.05 mg N kg−1 d−1), respectively. The abundance and diversity of IRB were also found to vary both spatially and seasonally. Furthermore, the results show that Feammox may transform nitrogen at a rate of approximately 2.4–22.5 kg N ha−1 yr−1 within the investigated area. It is considered that the soil moisture, the Fe(III) content, and the total organic carbon are important factors controlling Feammox and IRB. Overall, these results extend current scientific knowledge about nitrogen and iron cycles in ecosystem habitats.

Quantification of Microbial Source Tracking and Pathogenic Bacterial Markers in Water and Sediments of Tiaoxi River (Taihu Watershed).

Taihu Lake is one of the largest freshwater lakes in China, serving as an important source of drinking water; >60% of source water to this lake is provided by the Tiaoxi River. This river faces serious fecal contamination issues, and therefore, a comprehensive investigation to identify the sources of fecal contamination was carried out and is presented here. The performance of existing universal (BacUni and GenBac), human (HF183-Taqman, HF183-SYBR, BacHum, and Hum2), swine (Pig-2-Bac), ruminant (BacCow), and avian (AV4143 and GFD) associated microbial source tracking (MST) markers was evaluated prior to their application in this region. The specificity and sensitivity results indicated that BacUni, HF183-TaqMan, Pig-2-Bac, and GFD assays are the most suitable in identifying human and animal fecal contamination. Therefore, these markers along with marker genes specific to selected bacterial pathogens were quantified in water and sediment samples of the Tiaoxi River, collected from 15 locations over three seasons during 2014 and 2015. Total/universal Bacteroidales markers were detected in all water and sediment samples (mean concentration 6.22 log10 gene copies/100 ml and 6.11 log10 gene copies/gram, respectively), however, the detection of host-associated MST markers varied. Human and avian markers were the most frequently detected in water samples (97 and 89%, respectively), whereas in sediment samples, only human-associated markers were detected more often (86%) than swine (64%) and avian (8.8%) markers. The results indicate that several locations in the Tiaoxi River are heavily polluted by fecal contamination and this correlated well with land use patterns. Among the five bacterial pathogens tested, Shigella spp. and Campylobacter jejuni were the most frequently detected pathogens in water (60% and 62%, respectively) and sediment samples (91% and 53%, respectively). Shiga toxin-producing Escherichia coli (STEC) and pathogenic Leptospira spp. were less frequently detected in water samples (55% and 33%, respectively) and sediment samples (51% and 13%, respectively), whereas E. coli O157:H7 was only detected in sediment samples (11%). Overall, the higher prevalence and concentrations of Campylobacter jejuni, Shigella spp., and STEC, along with the MST marker detection at a number of locations in the Tiaoxi River, indicates poor water quality and a significant human health risk associated with this watercourse. GRAPHICAL ABSTRACTTracking fecal contamination and pathogens in watersheds using molecular methods.

Long-term trends of acid anion in the rain water in Lake Taihu watershed and the lake water, and its environmental implications

为揭示太湖流域降雨和湖水酸根阴离子长期变化特征及环境意义，通过历史数据收集和采样分析，对太湖流域降雨和湖水中的SO₄^2-、NO₃^-变化特征和来源进行了研究.结果表明：自1990s以来太湖流域降雨中SO₄^2-呈显著下降趋势，年平均下降率为0.28 mg/（L·a）；NO₃^-浓度却呈显著上升趋势，年平均增长率为0.05 mg/（L·a），降雨中氮污染呈现加重的趋势.与之相反，湖水中SO₄^2-呈显著上升趋势，年平均增长率为1.24 mg/（L·a）；NO₃^-浓度却呈显著下降趋势，年平均下降率为0.02 mg/（L·a）.30年以来，太湖水体SO₄^2-/NO₃^-比值不断升高，远高于降水SO₄^2-/NO₃^-比值.研究认为：流域SO₂排放引起的酸沉降是湖水SO₄^2-浓度增长的最重要原因，但氮氧化物排放并未引起湖水NO₃^-浓度升高，说明太湖流域对大气沉降的氮氧化物有滞留作用，而太湖水体是流域大气沉降硫酸盐的重要汇.综合治理太湖流域酸性物质排放对防止太湖水体酸化和治理富营养化都具有重要意义.;To explore long-term trends of acid anions in the rain water in Lake Taihu watershed, the lake water and their environmental implications, the variation characteristics, sources and the relationships of SO₄^2-, NO₃^- in the rain water and the lake water were studied via historical data collection and sampling analysis. The results indicated that SO₄^2- in the rainwater showed a significant decreasing trend since 1990s with an annual average decrease rate of 0.28 mg/(L·a), and the NO₃^- showed a significant increasing trend with an annual average increase rate of 0.05 mg/(L·a), which suggests an aggravating trend of nitrogen pollution in the rain water. In contrast, SO₄^2- in the lake water showed a significant increasing trend with an annual average increase rate of 1.24 mg/(L·a), and the NO₃^- showed a significant decreasing trend with an annual average decrease rate of 0.02 mg/(L·a). During the past 30 years, the ratio of SO₄^2-/NO₃^- in Lake Taihu water continuously increased, much higher than that of the rain water. The research indicated that the acid deposition caused by SO₂ emissions in the watershed was mainly responsible for the increased concentration of SO₄^2- in the lake water. However, the nitrogen oxides emissions did not cause an increase concentration of NO₃^- in the lake water, indicating that Lake Taihu watershed plays a significant role in the retention of nitrogen deposition, while the lake water is an important sink for sulfate deposition. The regional nitrogen deposition has an important impact on Lake Taihu water eutrophication. It is of great significance to prevent the acidification and eutrophication in Lake Taihu via comprehensive management of acid emissions in Lake Taihu watershed.

Spatial Distributions of Transferable Nitrogen Forms and Influencing Factors in Sediments from Inflow Rivers in Different Lake Basins

It is necessary to investigate the distribution of nitrogen forms in river sediments to recognize the water environment quality. In this study, ion exchangeable form nitrogen(IEF-N), weak acid extractable form nitrogen (WAEF-N), strong alkali extractable form nitrogen (SAEF-N) and strong oxidation extractable form nitrogen (SOEF-N) in sediments were obtained by means of sequential extraction procedures.We analyzed the spatial variations of nitrogen forms in sediments from Taihu watershed (Dongtiaoxi River and Xitiaoxi River) and Hongzehu watershed (Anhe River and Suihe River), and expounded the influence factors of nitrogen form distribution. The results showed that the physicochemical properties of sediments from different watersheds varied in space. The concentrations of total nitrogen and nitrogen fractions also showed obvious changes in river sediments. As a whole, the concentrations of total nitrogen and transferable nitrogen in Taihu rivers were higher than those in Hongzehu rivers, but the former showed smaller spatial changes. Sediments from Taihu rivers showed the different concentration order of total nitrogen and transferable nitrogen comparing with those from Hongzehu rivers. The former followed the order of SOEF-N > SAEF-N > IEF-N > WAEF-N, and the latter followed the order of SOEF-N > SAEF-N > WAEF-N > IEF-N.The spatial varitions of transferable nitrogen fractions in Hongzehu rivers were prominent, which was associated with nitrogen sources. The spatial distributions of transferable nitrogen in sediments were obviously affected by their physicochemical properties, especially for organic matter and grain size.

Assessment of Water Quality and Identification of Pollution Risk Locations in Tiaoxi River (Taihu Watershed), China

Taihu Lake is the third largest freshwater lake in China and serves as a drinking water source for ~30 million residents. Tiaoxi River is one of the main rivers connected to this lake and contributes &gt;60% of the source water. Taihu Lake has been facing various environmental issues; therefore, it is important to study the water quality of its inflow rivers. This study aimed to evaluate the physico-chemical and microbiological characteristics of Tiaoxi River and to determine the spatial and seasonal variations in the water quality. Water samples were collected from 25 locations across the Tiaoxi River in three seasons in 2014–2015. Fourteen water quality parameters including multiple nutrients and indicator bacteria were assessed, and the data analyzed by multivariate statistical analyses. The physico-chemical analysis showed high levels (&gt;1 mg/L) of total nitrogen (TN) in all locations for all seasons. Total phosphorus (TP), nitrite-N (NO2-N), and ammonium-N (NH4-N) exceeded the acceptable limits in some locations and fecal coliform counts were high (&gt;250 CFU/100 mL) in 15 locations. Hierarchical cluster analysis showed that the sampling sites could be grouped into three clusters based on water quality, which were categorized as low, moderate, and high pollution areas. Principal component analysis (PCA) applied to the entire dataset identified four principal components which explained 83% of the variation; pH, conductivity, TP, and NO3-N were found to be the key parameters responsible for variations in water quality. The overall results indicated that some of the sampling locations in the Tiaoxi River are heavily contaminated with pollutants from various sources which can be correlated with land use patterns and anthropogenic activities.

Application of a Load Duration Curve for Establishing TMDL Programs Upstream of the Tiaoxi River within the Taihu Watershed, China

ABSTRACT Luo, Y. and Zhang, J., 2017. Application of a load duration curve for establishing TMDL programs upstream of the Tiaoxi River within the Taihu Watershed, China. In: Zhi, Y. and Guido Aldana, P.A. (eds.), Sustainability of Water Resources and the Development of Coastal Environments: Select Proceedings from the 2016 International Conference on Water Resource and Environment (WRE2016). Journal of Coastal Research, Special Issue No. 80, pp. 80–85. Coconut Creek (Florida), ISSN 0749-0208. The impairment of water quality is a major concern for streams and rivers in China. Total Maximum Daily Loads (TMDLs) can be used to establish a framework and propose a series of techniques and tools to assess water quality at the watershed scale. While TMDLs have been developed for water quality management by the U.S. Environmental Protection Agency, scientists and stakeholders, the development of TMDLs in China is hindered due to the lack of comprehensive data collection system and by the difficulties in incorporat...

Spatio-Temporal Patterns and Source Identification of Water Pollution in Lake Taihu (China)

Various multivariate methods were used to analyze datasets of river water quality for 11 variables measured at 20 different sites surrounding Lake Taihu from 2006 to 2010 (13,200 observations), to determine temporal and spatial variations in river water quality and to identify potential pollution sources. Hierarchical cluster analysis (CA) grouped the 12 months into two periods (May to November, December to the next April) and the 20 sampling sites into two groups (A and B) based on similarities in river water quality characteristics. Discriminant analysis (DA) was important in data reduction because it used only three variables (water temperature, dissolved oxygen (DO) and five-day biochemical oxygen demand (BOD5)) to correctly assign about 94% of the cases and five variables (petroleum, volatile phenol, dissolved oxygen, ammonium nitrogen and total phosphorus) to correctly assign &gt;88.6% of the cases. In addition, principal component analysis (PCA) identified four potential pollution sources for Clusters A and B: industrial source (chemical-related, petroleum-related or N-related), domestic source, combination of point and non-point sources and natural source. The Cluster A area received more industrial and domestic pollution-related agricultural runoff, whereas Cluster B was mainly influenced by the combination of point and non-point sources. The results imply that comprehensive analysis by using multiple methods could be more effective for facilitating effective management for the Lake Taihu Watershed in the future.

Study on Regional Environment Social Economic System near Hangzhou Bay in China - The Case of the Jiaxing City

Water shortage due to deterioration of water quality is quite serious near Hangzhou Bay. Jiaxing city is near the Shanghai and Hangzhou city, located at Zhejiang province in the South China, which belongs to the typical area of network of rivers in the Taihu watershed. The research provides a primary consideration of methodology to comprehensively evaluate regional environment social economic system, focuses on regional environment social economic system of Jiaxing city, including its location and transportation status, and summary to improve the water environment for the future generations are given.

Satellite data application for the assessment of water balance in the Taihu watershed, China

With the development of population and economy, the problems of deficit in water resources and degradation in water environment are increasingly serious in the Taihu watershed of China. The information on spatial and temporal availabilities of water will be helpful for the optimum utilization of water resources. In this study, we apply precipitation (P) from the Tropical Rainfall Measuring Mission (TRMM) products, evapotranspiration (ET) derived from MODIS data, and ground-observed runoff. Then annual water budgets in the Taihu watershed from 2005 to 2007 and the variation of water budget components in spatial and temporal (monthly and annually) scales were evaluated. The results indicated that ET was the most notable component of water consumption in the watershed. The annual mean ratio of the ET to the precipitation was 0.73 to 0.89 in the watershed and 1.1 to 1.3 in Lake Taihu area from 2005 to 2007. The analysis of water balance in the watershed indicated that the amount of water input and output were approximately equal for the watershed and the lake areas with imbalance percentages of 1.4% to 4.4% and 0.1% to 4.0%, respectively.

Environmental factors regulating cyanobacteria dominance and microcystin production in a subtropical lake within the Taihu watershed, China

Understanding the pattern of phytoplankton and their dependence on water quality variables, can help the management of eutrophic lakes. The aim of this study was to determine water quality and environmental factors associated with cyanobacteria dominance and microcystin production in Qingshan Lake, a subtropical lake located in the headwater of the Taihu watershed, China. Water samples collected monthly from 10 study sites in Qingshan Lake were analyzed for the species distributions of freshwater algae and physico-chemical parameters including total nitrogen (TN), ammonia (NH4 + -N), nitrate (NO3 − -N), total phosphorus (TP), and chlorophyll a (Chl-a) from June, 2008 to May, 2009. Qingshan Lake was found to be eutrophic, based on the calculated trophic state index (TSI). The average TN of 4.33 mg/L during the study period exceeded the Surface Water Quality Standards of China. TP was significantly correlated with relative abundance of cyanobacteria and Microcystis biovolume, indi- cating its important role in regulating cyanobacteria. Microcystis, Anabaena, and Oscillatoria were dominant cyanobacteria in Qingshan Lake from June to November, 2008. Cyanobacteria dominance was regulated by water temperature and TP. Principal component analysis further indicated that microcystin production was most affected by water temperature, TP, and cyanobacteria biomass. Results suggest that the control of TP in summer can mitigate cyanobacteria dominance and microcystin production in Qingshan Lake, and close monitoring should be undertaken in summer.

Effects of anthropogenic activities on chemical contamination within the Grand Canal, China

Contamination of nutrients and heavy metals within aquatic system is of great concern due to its potential impact on human and animal health. The Grand Canal of China, the largest artificial river in the world, is of great importance in supplying water resource, transporting cargo, and recreating resident, as well as great historical heritage. This study assessed and examined the impact of human activities on characters of contamination distribution within the section of the Canal in Taihu watershed. Physicochemical parameters of surface water quality were determined monthly from the year 2004 to 2006 at 11 sites that were influenced by different anthropogenic activities along the Canal. Moreover, contaminations at surface sediments (20 cm) at the same locations were also analyzed in September 2006. Results showed that the Canal had been seriously polluted, which was characterized with high spatial variations in contaminations distribution. The sites influenced mainly by industry and urbanization showed higher contents of nutrients and lower levels of dissolve oxygen than other sites. Concentrations of nitrogen at all studied sites exceeded the worst level of surface water quality according to the National Criterion of Surface Water Quality, China, with the average values varying from 2.27 to 10.34 mg/L. Furthermore, the site influenced mainly by industry (i.e., Site 4) presented the highest contents of cadmium (3.453 mg/kg), chromium (196.87 mg/kg), nickel (87.12 mg/kg), zinc (381.8 mg/kg), and copper (357.32 mg/kg). While sites in vicinity to cities had presented relatively higher contents of metals, especially for the site located downstream of Changzhou City (Site 3) had presented the highest contents of mercury (1.64 mg/kg) and lead (197.62 mg/kg). Copper at Sites 2 to 6, Nickel at Sites 2 to 9 except for Site 7, chromium, lead, and zinc at Sites 3 to 6 had exceeded New York State Department of Environmental Conservation (NYSDEC) Severe Effect Level (SEL). By multivariate statistical, nutrient variables, companied with V-phen, had contributed the most variation of water quality, while nutrient and metals had explained the most part of total variance of contaminations in sediment. This study indicated that the canal had been polluted severely and urgently need to control.

Response of freshwater algae to water quality in Qinshan Lake within Taihu Watershed, China

Although frequent algal blooms in Taihu Lake in China have become major environmental problems and have drawn national and international attention, little is understood about the relationship between algal blooms and water quality. The goal of this study was to assess the growth and species responses of freshwater algae to variation in water quality in Qinshan Lake, located in headwaters of the Taihu watershed. Water samples were collected monthly from ten study sites in the Qinshan Lake and were analyzed for species distribution of freshwater algae and physiochemical parameters such as total nitrogen (TN), NH 4 + –N, NO 3 - –N, total phosphorus (TP), chemical oxygen demand (COD Mn) and Chl-a. The results showed that average TN was 4.47 mg/L, with 92.2% of values greater than the TN standard set by the Chinese Environmental Protection Agency; average TP was 0.051 mg/L, with 37.9% of values above the TP national standard; and average trophic level index (TLI) was 53, the lower end of eutrophic condition. Average Chl-a concentration was 12.83 mg/m 3. Green algae and diatom far outweighed other freshwater algae and were dominant most time of the year, with the highest relative abundances of 96% and 99%, respectively. Blue-green algae, composed mainly toxic strains like Microcystis sp ., Nostoc sp. and Oscillatoria sp., became most dominant in the summer with the maximum relative abundance of 69%. The blue-green algae sank to the lake bottom to overwinter, and then dinoflagellates became the dominant species in the winter, with highest relative abundance of 89%. Analysis indicated that nutrients, especially control of ammonia and co-varying nutrients were the major restrictive factor of population growth of blue-green algae, suggesting that control in nutrient enrichments is the major preventive measure of algal blooms in Qinshan Lake.

Influence of N fertilization rates, rainfall, and temperature on nitrate leaching from a rainfed winter wheat field in Taihu watershed

Cropland derived nitrate leaching was a major reason for groundwater pollution. The objective of this study was to on-farm investigate the behavior of nitrate leaching affected by N fertilization rates, rainfall, and temperature in a rainfed winter wheat field in Taihu watershed. The experiment had five urea-N rates (0–360 kg N ha −1 in 90-kg increments), and nitrate-N in leachate was daily collected by wedge-shaped fiberglass wick lysimeters during four stages (seeding stage, SS; tillering stage, TS; booting stage, BS; harvesting stage, HS). Results showed that: (1) higher potential of leachate would be engendered when the rainfall intensity was over 5.9 mm d −1; (2) variations of nitrate concentrations in leachate were well responsed to three split fertilizations, which increased with the increase of urea-N applied rates. A similar variation pattern of nitrate concentrations was observed in −0.3 m and −0.6 m soil leachate. Besides, the nitrate concentrations in leachate could be raised with the sharply increase of air temperature, especially in the SS and TS stages; (3) the fluxes of nitrate leaching were significantly affected by N rates ( P < 0.05) with the loss ratio varied from 4.0% to 8.5% for five treatments, and the fluxes in four wheat growing stages followed the order of TS > HS > BS > SS. The N application rate of 180 kg N ha −1 optimized wheat production, but N application over that rate greatly increased nitrate leaching potential. Therefore, options other than lowering the N application rate need to be considered to reduce environmental impacts while maintain winter wheat production.

Development and application of an integrated surface runoff and groundwater flow model for a catchment of Lake Taihu watershed, China

Severe pollution in Lake Taihu in the lower reach of the Yangtze River has led to the need to evaluate transport pathways and the overall water balance of the catchment. This paper describes the development of a grid-based spatially distributed hydrological model for integrated simulations of surface runoff and groundwater flow at catchment scales. Surface water flow is modeled based on rainfall-runoff transformation and stream flow routing, while the saturated groundwater is modeled by MODFLOW-2005. Surface water flow is coupled to the groundwater flow regime through the soil layer. Relatively simple equations are used to describe the soil storage and soil water percolation. These equations are computationally inexpensive and overcome some of the limitations in existing models for coupled simulation of surface and subsurface domains, such as either multiple soil layer data are needed in the vertical direction or numerical difficulties are encountered in dealing with the high non-linearity of the equations representing the variably-saturated subsurface. The model was verified against the V-catchment benchmark problem and was compared to existing models to demonstrate its accuracy and capability. The model was applied to Xitiaoxi catchment of Lake Taihu watershed. The accuracy of the model was satisfactory with daily and monthly efficiencies of 0.80 and 0.92, respectively for stream discharge comparison, and an absolute error of 0.144 m for groundwater level comparison. The model indicated that for Xitiaoxi catchment, a percentage of 37.4% of rainfall transferred to surface overland flow, and a percentage of 16% infiltrated as groundwater recharge, of which 81% returns to rivers as base flow and the rest is lost to the system via evapotranspiration. The model can be used as an alternative to more complex methods to assess impacts of land use or/and climate changes on water resources availability, and the interactions between surface and subsurface flow domains.