Yongjiu Cai

Assessing river water quality using water quality index in Lake Taihu Basin, China

Lake Taihu Basin, one of the most developed regions in China, has received considerable attention due to its severe pollution. Our study provides a clear understanding of the water quality in the rivers of Lake Taihu Basin based on basin-scale monitoring and a water quality index (WQI) method. From September 2014 to January 2016, four samplings across four seasons were conducted at 96 sites along main rivers. Fifteen parameters, including water temperature, pH, dissolved oxygen (DO), conductivity, turbidity (tur), permanganate index (CODMn), total nitrogen, total phosphorus, ammonium (NH4-N), nitrite, nitrate (NO3-N), calcium, magnesium, chloride, and sulfate, were measured to calculate the WQI. The average WQI value during our study period was 59.33; consequently, the water quality was considered as generally moderate. Significant differences in WQI values were detected among the 6 river systems, with better water quality in the Tiaoxi and Nanhe systems. The water quality presented distinct seasonal variation, with the highest WQI values in autumn, followed by spring and summer, and the lowest values in winter. The minimum WQI (WQImin), which was developed based on a stepwise linear regression analysis, consisted of five parameters: NH4-N, CODMn, NO3-N, DO, and tur. The model exhibited excellent performance in representing the water quality in Lake Taihu Basin, especially when weights were fully considered. Our results are beneficial for water quality management and could be used for rapid and low-cost water quality evaluation in Lake Taihu Basin. Additionally, we suggest that weights of environmental parameters should be fully considered in water quality assessments when using the WQImin method.

Water quality assessment based on the water quality index method in Lake Poyang: The largest freshwater lake in China

Twenty-four samplings were conducted every 3 months at 15 sites from January 2009 to October 2014 in Lake Poyang, and 20 parameters were analyzed and classified into three groups (toxic metals, easily treated parameters, and others). The assessment results based on water quality index (WQI) showed that the water quality in Lake Poyang was generally “moderate”, according to the classification of the surface water quality standard (GB3838-2002) in China, but a deteriorating trend was observed at the interannual scale. Seasonally, the water quality was best in summer and worst in winter. Easily treated parameters generally determined the WQI value in the assessment, especially total nitrogen (TN) and total phosphorus (TP), while toxic metals and other parameters in Lake Poyang were generally at low and safe levels for drinking water. Water level (WL) has a net positive effect on water quality in Lake Poyang through dilution of environmental parameters, which in practice means TN. Consequently, local management agencies should pay more attention to nutrient concentrations during the monitoring schedule, as well as during the low-water periods which manifest a relatively bad water quality state, especially with the prevailing low WL observed recently in Lake Poyang.

Spatial correlation analysis of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in sediments between Taihu Lake and its tributary rivers

The residues of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in surface sediments from Taihu Lake basin (THB) and Taihu Lake body (THL) were investigated. Higher concentrations of both PAHs and OCPs were observed for THB than THL. The concentrations of PAHs ranged from 12.1 to 2281.1ngg-1 dw for THB and from 11.4 to 209.9ngg-1 dw for THL, while OCPs ranged from 16.3 to 96.9ngg-1 dw and from 16.8 to 61.9ngg-1 dw for THB and THL, respectively. Spatial distribution of PAHs and OCPs showed a high correspondence with the land use of THB and surrounding anthropogenic activity. Additionally, the Kriging interpolation plots demonstrated that the major upper reaches were more polluted than the lower reaches, indicating the transport of pollutants with the water flow direction. The organic matter contents were responsible for OCP distribution other than PAHs due to the biodegradation capacity difference of chemicals. Similar compositions of pollutants were observed with 3- and 4-ringed PAHs accounting for a total of 78.3% for THB and 85.8% for THL, respectively. HCHs and DDTs were predominant OCPs, which contributed to 31.8% and 21.7% for THB, and 33.6% and 21.9% for THL, respectively. The isomeric and parent substance/metabolite ratios implied fresh inputs of DDTs and chlordanes, while HCHs and endosulfans were mainly from old usage. PAH source identification performed by diagnostic ratios demonstrated the mixed sources of petrogenic and pyrogenic ones dominated by grass, wood and coal combustion. Furthermore, the hazard quotient (HQ) based on the consensus-based sediment quality guidelines (SQGs) was used to evaluate the ecological risks of sediments. Although no frequently adverse effects were observed, potential ecological risks induced by Ant, BaA, γ-HCH, dieldrin, p,p-DDT and chlordanes should also be paid attention to considering the continuous inputs of such pollutants.

Remediation of internal phosphorus loads with modified clays, influence of fluvial suspended particulate matter and response of the benthic macroinvertebrate community

Clay-based phosphorus (P) sorbents have been increasingly used as geoengineering materials for the management sediment-derived internal P loading in eutrophic lakes. However, the long-term behavior of these sorbents has remained elusive along with their response to burial under suspended particulate matter (SPM), and their effect on macroinvertebrate communities occupying dynamic regions at the sediment-water interface of shallow and turbid lakes. In this study, field mesocosm experiments were undertaken in Lake Chaohu, China, to study the effects of the application of lanthanum-modified bentonite (LMB) and thermally-modified calcium-rich attapulgite (TCAP) on sediment internal P loading and to assess their influence on macroinvertebrate community structure. A complementary laboratory core incubation study was also undertaken to investigate the effects of SPM deposition on LMB and TCAP performance. In the field, both LMB and TCAP effectively intercepted P released from sediment for up to five months. A P fractionation analysis indicated that LMB and TCAP application results in a substantial increase in inert P fractions in sediment. Laboratory studies indicated that deposition of SPM may increase in mobile P both in the upper sediment and across the new post-SPM deposition sediment-water interface. Importantly, a comparison of sediment chemical extractions and estimated P fluxes suggests that chemically-defined forms of P in the sediment may be used as a proxy to estimate the net sediment P flux. Significantly, the surficial application of either LMB or TCAP did not cause negative effects on macroinvertebrate communities. This study indicates that to sustain a low P flux across the sediment-water interface in shallow, turbid lakes, repeat dosing of geoengineering materials, temporally aligned to the deposition of fluvial SPM, may be required.

Relative roles of spatial processes, natural factors and anthropogenic stressors in structuring a lake macroinvertebrate metacommunity

Studies of aquatic metacommunities have so far been focused almost entirely on relatively isolated systems, such as a set of streams, lakes or ponds. Here, we aimed to quantify the relative importance of spatial processes, natural factors and anthropogenic stressors in structuring of a macroinvertebrate metacommunity within a large, highly-connected shallow lake system. The roles of different drivers were evaluated for the entire metacommunity, 10 trait-based deconstructed metacommunities and four common species by incorporating extensive sampling and a large number of abiotic explanatory variables. Contrary to our expectations, we found that variation in community structure among sites was mostly correlated to spatial and wind-wave variables rather than anthropogenic disturbance factors even though the lake presented strong environmental gradients associated with long-term human pressures. In addition, the relative importance of the three groups of drivers varied slightly among the deconstructed trait matrices (i.e. based on dispersal ability, feeding mode and degree of occurrence). Importantly, the distributions of the most common species showed significant and strong spatial autocorrelation, indicating the prominent role of high dispersal rate for their distributions. These findings suggest that the influences of high dispersal rates and natural disturbance may even override the roles of anthropogenic stressors in metacommunity organization in highly-connected aquatic systems. Hence, we strongly encourage that spatial processes and natural drivers are taken into account in the development of bioassessment approaches in highly-connected aquatic systems.

Accumulation of microcystins in a dominant Chironomid Larvae ( Tanypus chinensis ) of a large, shallow and eutrophic Chinese lake, Lake Taihu

Although there have been numerous studies on microcystin (MC) accumulation in aquatic organisms recently, the bioaccumulation of MCs in relatively small sized organisms, as well as potential influencing factors, has been rarely studied. Thus, in this study, we investigated the bioaccumulation of three MC congeners (-LR, -RR and -YR) in the chironomid larvae of Tanypus chinensis (an excellent food source for certain fishes), the potential sources of these MCs, and potentially relevant environmental parameters over the course of one year in Lake Taihu, China. MC concentrations in T. chinensis varied temporally with highest concentrations during the warmest months (except August 2013) and very low concentrations during the remaining months. Among the three potential MC sources, only intracellular MCs were significantly and positively correlated with MCs in T. chinensis. Although MC concentrations in T. chinensis significantly correlated with a series of physicochemical parameters of water column, cyanobacteria species explained the most variability of MC accumulation, with the rest primarily explained by extraMC-LR. These results indicated that ingestion of MC-producing algae of cyanobacteria accounted for most of the MC that accumulated in T. chinensis. The high MC concentrations in T. chinensis may pose a potential health threat to humans through trophic transfer.

Heavy metal pollution in reservoirs in the hilly area of southern China: Distribution, source apportionment and health risk assessment

Reservoirs play more and more important role in providing potable water in many developing countries, including the China. In the present study, pollution characteristics, source and health risk of dissolved heavy metals in 19 representative reservoirs in the hilly area of southern China were investigated. The results presented great spatial heterogeneity in heavy metal concentrations among the studied reservoirs due to the disturbances by different anthropogenic activities. Several reservoirs had significantly higher concentrations of heavy metals compared with others, FengTan (FT) reservoir (0.34μg/L in dry season), Cr in reservoirs of HuangShi (HS) and ZheLin (ZL) with values of 4.16μg/L and 3.45μg/L in dry season respectively, and Al in reservoirs of JiaoKou (JK), GuTian (GT) and DouShui (DS) with values of 1011μg/L, 1036μg/L and 1001μg/L in wet season, respectively. Furthermore, there was a great difference in the seasonal variation of heavy metals, especially for Al and Pb in wet season characterized with relatively high values of 643μg/L and 0.67μg/L, respectively. Accordingly, Al was identified with a great health risk to living beings in view of its mean value in wet season, which greatly exceeded the criteria for drinking water of China, WHO and US EPA. Furthermore, As might be the greatest concern of health risk in this region considering its high carcinogenic risk to the local residents around the reservoirs of OuYangHai (OYH), DS, ZhiXi (ZX) and HS. Multivariate statistical analysis suggested that there was great heterogeneity in the sources of these heavy metals in the hilly area of southern China. Therefore, specific measures, such as controls on point source pollution control and tailings, should be taken for maintaining drinking water safety and aquatic ecosystem health.

Substrate degradation and nutrient enrichment structuring macroinvertebrate assemblages in agriculturally dominated Lake Chaohu Basins, China

Rapid agricultural development has induced severe environmental problems to freshwater ecosystems. In this study, we aimed to examine the structure and environmental determinants of macroinvertebrate assemblages in an agriculture dominated Lake Chaohu Basin, China. A cluster analysis of the macroinvertebrate communities identified four groups of sites that were characterized by significantly different macroinvertebrate species. These four groups of sites had concentric spatial distribution patterns that followed the variation in the environmental conditions from the less anthropogenically disturbed headwaters towards the more anthropogenically disturbed lower reaches of the rivers and the Lake Chaohu. Moreover, taxa richness decreased from the headwaters towards the Lake Chaohu. The increasing practice of agriculture has reduced the abundances and richness of pollution sensitive species while opposite effects on pollution tolerant species. The study identified substrate heterogeneity and nutrient concentrations as the key environmental factors regulating the changes in the macroinvertebrate communities. We propose that particular attentions should be paid to reduce the nutrient enrichment and habitat degradation in the Lake Chaohu Basin and similar agriculture dominated basins.

Heavy metal contamination in surface sediments of representative reservoirs in the hilly area of southern China

A study on the characteristics of heavy metals in surface sediments of typical reservoirs in the hilly area of southern China was carried out. The results showed that contents of heavy metals had great temporal and spatial heterogeneity among studied reservoirs. Zn, Pb, and As presented significant enrichment ratio in reservoirs of Dou Shui (DS) and Feng Tang (FT), as well as Ti in reservoirs of DZ and GT. The content of Cd in reservoir of FT reservoirs was characterized with high health risk with the significantly highest value of 52.43xa0mg/kg. Furthermore, Pb was identified with high health risk in reservoirs of SFM, Ouyang Hai (OYH), FT, and DS, and As was in OYH and ZX. Multivariate statistical analysis suggested high consistency in the variations of Cr, Ni, and Cu; moreover, Cd, Zn, and Pb were characterized with great homogeneity in their sources. In addition, agricultural activities might exert less effect on variations of heavy metals in studied reservoirs, considered that there was a weak relationship between heavy metals and nutrients. These results could improve our understanding of the spatial variations of heavy metals and their potential sources in reservoirs in this ecologically fragile region.

Climatically-modulated decline in wind speed may strongly affect eutrophication in shallow lakes

Surface wind speed has declined significantly globally. However, the response of aquatic systems to decreasing wind speeds has received little attention. We examined the effects of a long-term decrease in wind speed on shallow, eutrophic Lake Taihu, Chinas third largest lake, by combining high-frequency monitoring, long-term meteorological and water quality data with short-term laboratory sediment nutrient release experiments. The annual mean wind speed showed a significant decreasing trend and the maximum continuous days with wind speed <3u202fm/s increased significantly from 1996 to 2017. The high-frequency monitoring data showed that bottom water hypoxia occurred occasionally in summer and autumn. The water quality data combined with the experimental results suggest that lower wind speed and longer low wind duration can enhance the release of phosphorus (P) from the sediments and increase nitrogen (N) losses, likely via denitrification, because a longer stability period leads to lower dissolved oxygen concentrations near the lake bottom. The results of Bayesian functional Linear regression with Sparse Step functions (Bliss) indicated that wind speed during spring and summer strongly affected chlorophyll a (Chla) concentrations in the summer by enhancing the release of nutrients from the sediments. The results of the structural equation models indicated that declined wind speed might increase phytoplankton biomass (as Chla) by altering nutrient availability. Increasing water temperatures and decreasing wind speeds synergistically enhance water column stability, which may offset some of the immediate benefits of reductions in external nutrient loading by enhancing internal loading. Given predicted global change, it will become increasingly important to reduce the external nutrient loading for overall improvement of water quality in this and other shallow eutrophic lakes.