Zhushan Bay Research Articles

Mercury distribution, speciation and potential ecological risk assessment in sediments from Lake Taihu, China

Twenty-one surface sediments collected from seven surroundings areas of Lake Taihu in two different years were analyzed for total mercury (THg) concentrations, physicochemical characteristics and speciation using a sequential extraction method to assess spatial distribution, sources, and potential ecological risk. Surface sediments from Lake Taihu contained elevated levels of Hg in two sampling years with THg levels ranging from 77 to 346 ng/g (mean 145 ng/g) in October 2010 and ranging from 122 to 573 ng/g (mean 266 ng/g) in November 2012, respectively. The mean THg concentrations in all studied surface sediments exhibited an increasing trend over time. The oxidizable fraction (F3) and residual fraction (F4) were the predominant Hg species in sediments, while more mobile Hg phases of acid-soluble fraction (F1) and reducible fraction (F2) made up less than 0.5% THg. Significant relationships were found between total organic carbon (TOC) and THg and geochemical speciation indicating an important role for organic matter in affecting distribution, mobility, and bioavailability of Hg in sediments. As evidenced by Hakanson’s potential risk index the total ecological risk of Hg was low in the entire Lake Taihu in 2010 but considered moderate in Zhushan Bay, West Coast, and Meiliang Bay in 2012. These findings provide conservation managers with information needed to more effectively regulate the environment of Lake Taihu.

Community Structure and Influencing Factors of Bacterioplankton in Spring in Zhushan Bay, Lake Taihu

In order to investigate the characteristics of bacterioplankton in the spring in Zhushan Bay, Lake Taihu, the 16S rRNA gene of the bacterioplankton at four sampling sites in Zhushan Bay was sequenced by high-throughput sequencing using water samples collected from Yapugang, Shatanggang, Zhushanhunan, and Jiaoshan. The results showed that the coverage of the sequencing library was very high and could accurately represent the bacterioplankton community in the samples. The species richness of Jiaoshan was the highest, but the species evenness was lower. Cyanobacteria, Actinobacteria, Proteobacteria, and Bacteroidetes were the dominant phylum in Zhushan Bay. The average abundance of Cyanobacteria was as high as 64.73%, which indicated an outbreak of cyanobacteria bloom in the water. At the genus level, Anabaena, hgcI_clade, CL 500-29 _marine_group, Microcystis, Synechococcus, and Mycobacterium were predominant. The results of redundancy analysis (RDA) for the relationship between bacterioplankton and environmental factors showed that water temperature, chlorophyll a (Chl-a), ammonia nitrogen(NH4+-N), dissolved oxygen (DO), and phosphate (PO43--P)were the main environmental factors affecting the bacterioplankton community. Dissolved oxygen could significantly affect Microcystis; nutrient and water temperature also had an effect.

Spatial distribution and diversity of organohalide-respiring bacteria and their relationships with polybrominated diphenyl ether concentration in Taihu Lake sediments.

It is acknowledged that organohalide-respiring bacteria (OHRB) can degrade polybrominated diphenyl ethers (PBDEs); however, very little is known about the distribution of OHRB or their response to PBDE contamination in natural sediments. We collected sediments from 28 sampling sites in Taihu Lake, China, and investigated the spatial distribution and diversity of OHRB, and the relationships between the PBDE contamination levels and the PBDE removal potential. The abundances of five typical OHRB genera, namely Dehalobacter, Dehalococcoides, Dehalogenimonas, Desulfitobacterium, and Geobacter, ranged from 0.34×104 to 19.4×107 gene copies g-1 dry sediment, and varied significantly among different areas of Taihu Lake. OHRB were more abundant in sediments from Meiliang and Zhushan Bay, where the PBDE concentrations were higher, and the phylotype diversity of the OHRB belonging to the family Dehalococcoidaceae was lower, than reported for other areas. While the sulfate concentrations explained much of the spatial distribution of OHRB, PBDE concentrations were also a strong influence on the abundance and diversity of OHRB in the sediments. For Dehalococcoides, Dehalogenimonas and Geobacter, the abundance of each genus was positively related to its own potential to remove PBDEs. The dominant OHRB genus, Dehalogenimonas, may contribute most to in situ bioremediation of PBDEs in Taihu Lake.

Characteristics of phosphorus components in surface sediments from a Chinese shallow eutrophic lake (Lake Taihu): new insights from chemical extraction and 31P NMR spectroscopy.

As a primary factor responsible for lake eutrophication, a deeper understanding of the phosphorus (P) composition and its turnover in sediment is urgently needed. In this study, P species in surface sediments from a Chinese large eutrophic lake (Lake Taihu) were characterized by traditional fractionation and 31P nuclear magnetic resonance (NMR) spectroscopy, and their contributions to the overlying water were also discussed. Fractionation results show that NaOH-P predominated in the algal-dominated zone, accounting for 60.1% to total P in Zhushan Bay. Whereas, refractory fractions including HCl-P and residual-P were the main P burial phases in the macrophyte-dominated zone, the center and lakeshore. Recovery rates of the total P and organic P were greatly improved by using a modified single-step extraction of NaOH-EDTA, ranging from 22.6 to 66.1% and from 15.0 to 54.0%. Ortho-P, monoester-P, and pyro-P are identified as the major P components in the NaOH-EDTA extracts by 31P NMR analysis. Trace amount of DNA-P appeared only in sediments from algal- and macrophyte-dominated zones, ascribing to its biological origin. The relative content of ortho-P is the highest in the algal-dominated zone, while the biogenic P including ester-P and pyro-P is the highest in the macrophyte-dominated zone. Moreover, ortho-P and pyro-P correlated positively with TP and chlorophyll a in the overlying water, whereas only significant relationships were found between monoester-P, biogenic P, and chlorophyll a. These discrepancies imply that inorganic P, mainly ortho-P, plays a vital role in sustaining the trophic level of water body and algal bloom, while biogenic P makes a minor contribution to phytoplankton growth. This conclusion was supported by the results of high proportion of biogenic P in algae, aquatic macrophytes, and suspended particulate from the published literature. This study has significant implication for better understanding of the biogeochemical cycling of endogenous P and its role in affecting lake eutrophication.

Spatiotemporal Distribution of Eutrophication in Lake Tai as Affected by Wind

One common hypothesis is that wind can affect concentrations of nutrients (i.e., nitrogen and phosphorus) and chlorophyll-a (Chl-a) in shallow lakes. However, the tests of this hypothesis have yet to be conclusive in existing literature. The objective of this study was to use long-term data to examine how wind direction and wind speed affect the spatiotemporal variations of total nitrogen (TN), total phosphorus (TP) and Chl-a in Lake Tai, a typical shallow lake located in east China. The results indicated that the concentrations of nutrients and Chl-a tended to decrease from the northwest to the southeast of Lake Tai, with the highest concentrations in the two leeward bays (namely Meiliang Bay and Zhushan Bay) in the northwestern part of the lake. In addition to possible artificial reasons (e.g., wastewater discharge), the prevalent southeastward winds in warm seasons (i.e., spring and summer) and northwestward winds in cool seasons (i.e., fall and winter) might be the major natural factor for such a northwest-southeast decreasing spatial pattern. For the lake as a whole, the concentrations of TN, TP and Chl-a were highest for a wind speed between 2.1 and 3.2 m·s−1, which can be attributed to the idea that the wind-induced drifting and mixing effects might be dominant in the bays while the wind-induced drifting and resuspension effects could be more important in the other parts of the lake. Given that the water depth of the bays was relatively larger than that of the other parts, the drifting and mixing effects were likely dominant in the bays, as indicated by the negative relationships between the ratios of wind speed to lake depth, which can be a surrogate for the vertical distribution of wind-induced shear stress and the TN, TP and Chl-a concentration. Moreover, the decreasing temporal trend of wind speed in combination with the ongoing anthropogenic activities will likely increase the challenge for dealing with the eutrophication problem of Lake Tai.

Lipid biomarker evidence for determining the origin and distribution of organic matter in surface sediments of Lake Taihu, Eastern China

Lipid biomarkers from surface sediments of Lake Taihu (Eastern China) were analyzed in order to determine the origin and spatial distribution of sediment organic matter (OM), which is necessary to understand the regional carbon cycles and design environmental management strategies for lake systems. The results indicated significant heterogeneity in the distribution of autochthonous (algae-, photosynthetic bacteria- and macrophyte-based) and allochthonous (terrestrial plant-based) OM in sediments across the lake. Allochthonous OM inputs, indicated by long-chain n-alkane and long-chain n-alkanol biomarkers, generally declined in abundance from northwestern (Zhushan Bay and Meiliang Bay) to southeastern (East Bays) parts of the lake, suggesting a critical influence of hydrology, and in particular of inflowing rivers, which mainly enter the lake from the west and drain from the east. Autochthonous OM, on the other hand, appeared to reflect variations in overall nutrient status and habit type across the lake. Cyanobacterial OM inputs, identified by short-chain n-alkanes, were most abundant in sediment from the most severely polluted zones in Lake Taihu, namely Zhushan Bay and Meiliang Bay. OM derived from diatoms, indicated by brassicasterol and highly branched isoprenoids (HBIs), was most abundant in sediments from the East Bays, a clear-water zone with relatively low levels of nutrient input. Macrophyte OM input, indicated by the middle-chain n-alkanes and Paq ((n-C23+n-C25)/(n-C23+n-C25+n-C29+n-C31)), was only identified in sediments from the East Bays. The lowest recorded inputs for both autochthonous and allochthonous OM were in sediments from open areas with significant sediment resuspension, including Gonghu Bay, Central and Western Region. This finding might reflect degradation mineralization of OM in the water column during sediment resuspension.

Temporal and Spatial Dynamics of Phytoplankton Primary Production in Lake Taihu Derived from MODIS Data

We investigated the long-term variations in primary production in Lake Taihu using Moderate Resolution Imaging Spectroradiometer (MODIS) data, based on the Vertically Generalized Production Model (VGPM). We firstly test the applicability of VGPM in Lake Taihu by comparing the results between the model-derived and the in situ results, and the results showed that a strong significant correlation (R2 = 0.753, p < 0.001, n = 63). Then, VGPM was used to map temporal-spatial distributions of primary production in Lake Taihu. The annual mean daily primary production of Lake Taihu from 2003 to 2013 was 1094.06 ± 720.74 mg·C·m−2·d−1. Long-term primary production maps estimated from the MODIS data demonstrated marked temporal and spatial variations. Spatially, the primary production in bays, especially in Zhushan Bay and Meiliang Bay, was consistently higher than that in the open area of Lake Taihu, which was caused by chlorophyll-a concentrations resulting from high nutrient concentrations. Temporally, the seasonal variation of primary production from 2003 to 2013 was: summer > autumn > spring > winter, with significantly higher primary production found in summer and autumn than in winter (p < 0.005, t-test), primarily caused by seasonal variations in water temperature. On a monthly scale, the primary production exerts a clear character of bimodality, increasing from January to May, decreasing in June or July, and finally reaching its highest value during August or September. Wind is another important factor that could affect the spatial variations of primary production in the large, eutrophic and shallow Lake Taihu.

Effects of abiotic factors on ecosystem health of Taihu Lake, China based on eco-exergy theory

A lake ecosystem is continuously exposed to environmental stressors with non-linear interrelationships between abiotic factors and aquatic organisms. Ecosystem health depicts the capacity of system to respond to external perturbations and still maintain structure and function. In this study, we explored the effects of abiotic factors on ecosystem health of Taihu Lake in 2013, China from a system-level perspective. Spatiotemporal heterogeneities of eco-exergy and specific eco-exergy served as thermodynamic indicators to represent ecosystem health in the lake. The results showed the plankton community appeared more energetic in May, and relatively healthy in Gonghu Bay with both higher eco-exergy and specific eco-exergy; a eutrophic state was likely discovered in Zhushan Bay with higher eco-exergy but lower specific eco-exergy. Gradient Boosting Machine (GBM) approach was used to explain the non-linear relationships between two indicators and abiotic factors. This analysis revealed water temperature, inorganic nutrients, and total suspended solids greatly contributed to the two indicators that increased. However, pH rise driven by inorganic carbon played an important role in undermining ecosystem health, particularly when pH was higher than 8.2. This implies that climate change with rising CO2 concentrations has the potential to aggravate eutrophication in Taihu Lake where high nutrient loads are maintained.

Insight into the spatial distribution of nutrient elements and sediments fraction analysis in Taihu Lake

Lake eutrophication in China is a serious issue and has raised urgent attention, which is required for a better understanding of the eutrophic status. Particularly, the eutrophication of shallow lakes has received public attention for shallow lakes are vulnerable to changes in eutrophic status due to the closer proximity with bottom lake sediments. Herein, a comprehensive investigation on the spatial distribution of nutrient elements (including carbon, nitrogen and phosphorus) was conducted in a typical large shallow lake Taihu Lake, and the internal patterns between the distribution and eutrophic status were analyzed. The results showed that the distributions of nutrient elements in surface sediment displayed spatial diversity in different regions. Zhushan Bay, East Taihu Lake and Dongjiaozui Bay hold distinguished pattern of nutrient contents due to the different geographical locations and economic pattern of adjacent areas. Specifically, the concentrations of total carbon and total nitrogen in East Taihu Lake were significantly higher than other areas, and total phosphorus content in Zhushan Bay was the highest. Furthermore, different phosphorus fractions in sediment and eutrophic indicators of water column were further analyzed to reveal the potential contribution of sediments to nutrient loadings of overlying water. The phosphorus fraction analysis suggested that calcium bounded phosphorus accounted for the main component. Correlation analysis revealed the internal relations among various characteristics in sediment or water, which indicated that microcystis blooms were accompany with excessive COD and phosphorus and depletion of dissolved oxygen. The results offered a comprehensive understanding of the lake eutrophic status and benefited further the study on the ecological status assessment.

Distributions of Arsenic Species in Different Eutrophic Waters of Lake Taihu and Their Relations to Environmental Factors

A detailed field survey of arsenic species and water quality parameters was conducted in different eutrophicated regions of Lake Taihu (Zhushan Bay, Meiliang Bay, Gonghu Bay and Southern Taihu) in summer and winter. Furthermore, spatial and seasonal distributions of arsenic species and their relations to water quality parameters were investigated with multivariate analysis techniques. Higher average contents of total arsenic (TAs), arsenate[As(Ⅴ)], arsenite[ As(Ⅲ)] and methylarsenicals [sum of monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA)] were observed in northern regions (including Zhushan Bay, Meiliang Bay, and Gonghu Bay) (TAs:2.58-3.34 μg·L-1, As(Ⅴ):1.37-2.34 μg·L-1, As(Ⅲ):0.53-0.64 μg·L-1, methylarsenicals:0.16-0.36 μg·L-1), compared to those in Southern Taihu (1.73, 1.10, 0.31, 0.10 μg·L-1). The results exhibited obvious spatial characteristics of arsenic species in the surface water of Lake Taihu. Besides, average values of TAs, As(Ⅴ), As(Ⅲ) and methylarsenicals in summer were 3.40, 2.06, 0.73 and 0.25 μg·L-1, respectively, higher than those in winter (1.78, 1.10, 0.30, 0.17 μg·L-1), reflecting significant seasonal characteristics of arsenic distribution. Factor analysis revealed the significant relationships of TAs and As(Ⅴ) with several water quality parameters, which suggested that spatial and seasonal distributions of TAs and As(Ⅴ) in Lake Taihu were affected by external pollution and internal arsenic release from sediments. Redundancy analysis further indicated significant effects of total phosphorus (TP) and total iron (TFe) on the distributions of TAs and As(Ⅴ). At the mean time, the above statistical analyses exhibited that As(Ⅲ) and methylarsenicals were positively correlated with chlorophyll-a (Chl-a). A large amount of microalgae could accumulate As(Ⅴ) and transform it more strongly to As(Ⅲ) and methylarsenicals in eutrophic regions when compared to mesotrophic region,especially in summer, reflecting the regulation of microalgae on arsenic biotransformation.

Spatial, Temporal Distribution Characteristics and Potential Risk of PPCPs in Surface Sediments from Taihu Lake

Fourteen sediment samples from 15 river estuaries and six sediments from 6 drinking water resource were collected from Taihu Lake. Nine pharmaceutical and personal care products(PPCPs) in the sediments samples were measured by using the HPLC-MS/MS technique. The ranges of geometric mean values were 1.60-129 ng·g-1 and 1.36-22.0 ng·g-1, respectively. Caffeine was the dominant pollutant in fourteen sediments near the river estuary, the content of which covered 52% of amounts of 9 PPCPs. Lincomycin, trimethoprime, azithromycin, sulfamethoxazole and tylosin were the dominant pollutants in six sediments near the drinking water resource, the contents of which covered 79% of amounts 9 PPCPs. From the point of spatial distribution, the results of PPCPs in Zhushan bay and East of Yixing in the northwest and west of Taihu Lake showed higher concentration than those in other sample sites. From the composition, the origin of PPCPs was different. Municipal sewage, stock farming and aquaculture were the main sources of PPCPs in Taihu Lake. Pharmaceuticals of human use showed the dominant pollution in fourteen sediments near the river estuary and drugs of veterinary use showed the dominant pollution in six sediments near the water resource. The concentrations of PPCPs in fourteen sediments of river mouth showed high level. It suggested that PPCPs pollutants were discharged to Taihu Lake continuously. Further risk assessment results showed that the overall risk was not high except for some PPCPs compounds. The RQ exceeded 1 for acetaminophen, azithromycin and sulfamethoxazole in the surface sediments of 15 river estuaries and 6 water resources, which showed high risk. The RQ was between 0.01 to 0.1 for carbazepine in the surface sediments of 15 river estuaries and 6 water resources, which showed medium risk. The RQ was below 0.01 for caffeine, lincomycin, trimethoprim, diltiazem and tylosin in the sediments of 15 river estuaries and 6 water resources, which showed low risk.

Fluorescent components and spatial patterns of chromophoric dissolved organic matters in Lake Taihu, a large shallow eutrophic lake in China.

Water samples at both surface and bottom layers were taken from 102 sites in Lake Taihu to study the fluorescent components and spatial patterns of chromophoric dissolved organic matters (CDOM). Three-dimensional excitation-emission matrix data obtained from the samples were analyzed by parallel factor approach in which four humic-like and two protein-like fluorescent components (named C1-C6) were identified. The results showed that fluorescence intensities were higher in the northern and western lake regions, and notable declines of fluorescence maxima (F max) were observed from the northwest to the center and then to the southeast of the lake. Calculated biological index (BIX) values ranged from 0.88 to 1.44 and humification index (HIX) values from 0.64 to 3.37 for all the samples. The spatial variations of BIX and HIX values suggested stronger allochthonous CDOM characteristics in Zhushan Bay and the western area and autochthonous characteristics in the southern and eastern areas. Vertically, the average F max value of the surface samples was about 6% less than that of the bottom samples, but noticeable variations existed among different sampling sites and components. These distribution characteristics of CDOM were mainly attributed to the spatial heterogeneity of sources and wind-induced transportation process. Interestingly, the C6 component (Exmax/Emmax=250/455nm) seemed to be unique in samples from Zhushan Bay and probably resulted from the discharge of the Taige River. Therefore, it could be used as an indicator of point-source discharge and a tracer to study the fate of CDOM in the lake.

Construction and analysis of the EWE model of the wetland ecosystem in lake buffering zone of Zhushan Bay, China.

Lake buffering zones play a special role in spatial arrangement of the lake watershed, and the wetland in buffering zones also is of great significance in basin ecological health and lake water environmental quality. Taking Zhushanhu wetland ecosystem in the area of lake buffering zone of Zhushan Bay, Lake Taihu as the research object, the biotic components were divided into 16 functional groups to construct the Ecopath with Ecosim (EWE) model, and the characteristics and state of the ecosystem and the interrelation between the functional groups were analyzed. The results showed that the range of effective trophic level in Zhushanhu wetland ecosystem was 1-3.72, tro-phic flows were mainly concentrated in the first 4 trophic levels, and most of the food chains started from submerged plants and detritus. The total energy conversion efficiency of the wetland ecosystem was 5.1%, being lower than the "1/10 law", indicating that the current energy conversion efficiency was low. The average transmission efficiency of material throughput in the ecosystem was 4.3%. The sum of all production in the ecosystem was 2496.66 t·km-2·a-1, and the total system throughput was 10145.2 t·km-2·a-1. The characteristic parameters of ecosystem showed that the current ecosystem was at the immature stage.

Dominant genera of cyanobacteria in Lake Taihu and their relationships with environmental factors.

Cyanobacterial blooms in freshwaters have become one of the most widespread of environmental problems and threaten water resources worldwide. Previous studies on cyanobacteria in Lake Taihu often collected samples from one site (like Meiliang Bay or Zhushan Bay) and focused on the variation in patterns or abundance of Microcystis during the blooming season. However, the distribution of cyanobacteria in Lake Taihu shows differing pattern in various seasons. In this study, water samples were collected monthly for one year at five sites in Lake Taihu with different trophic status and a physicochemical analysis and denaturing gradient gel electrophoresis (DGGE) were conducted. DGGE fingerprint analysis showed that Microcystis (7/35 bands) and Synechococcus (12/35 bands) were the two most dominant genera present during the study period at all five sites. Cyanobium (3/35 bands) was the third most common genus which has seldom been previously reported in Lake Taihu. Redundancy analysis (RDA) indicated that the cyanobacterial community structure was significantly correlated with NO3 (-)-N, CODMn, and NH4 (+)-N in the winter and spring, whereas it was correlated with water temperature in the summer and autumn. Limiting the nutrient input (especially of N and C loading) in Lake Taihu would be a key factor in controlling the growth of different genera of cyanobacteria.

Modeling the effects of external nutrient reductions on algal blooms in hyper-eutrophic Lake Taihu, China

Harmful algal blooms in Lake Taihu, China, are getting plagued due to excess nutrients loads. Despite several recent strict nutrient management strategies, especially to reduce the external nutrient loads, Lake Taihu still receives large amounts of nutrients from its tributaries. As a result, frequency and intensity of algal blooms have not abated as expected. In this study, a three-dimensional eutrophication model was used to identify the limiting factors for algal growth and the effect of external nutrient loads reduction on water quality. The modeling results showed that the limiting factor for the dominant algae (cyanobacteria) depended on seasonality and location. Water temperature affected algal growth in winter, while light was important for deeper water columns in all seasons. Phosphorus (P) and Nitrogen (N) impacted algal growth from spring to autumn. Results showed that Chlorophyll a (Chl-a) concentrations only decreased about 38%, 26% and 24% in Meiliang Bay, Zhushan Bay and Northwest Zone, respectively when implementing high nutrient reduction scenario (external N and P inputs reduced up to 80% and 50%). External nutrient reduction for both N and P is a prudent and likely most practical solution for reducing bloom potentials and overall trophic state of this currently hypereutrophic system. However, achieving observable algal control is not likely in the short term and other ecological restoration tools will be required to battle with the legacy of several decades of nutrient over-enrichment.

Effects of sediment and turbulence on alkaline phosphatase activity and photosynthetic activity of phytoplankton in the shallow hyper-eutrophic Lake Taihu, China.

Sediments play important roles, as nutrient reservoir, especially in shallow lake ecosystem. The water column of large shallow lakes is often stable but also disturbed by turbulence causing resuspension of sediments. While considerable research has been carried out to investigate the influence of sediment resuspension on nutrient release, fewer studies have been done to understand the contribution of alkaline phosphatase activity (APA) in water as a response to the two conditions (turbulence and stability). Also, effects of the two lake conditions on photosynthetic efficiency of phytoplankton are still poorly understood. This study will evaluate the effect of these two conditions on photosynthetic efficiency and APA. Sediments used in the indoor experiments were collected from Zhushan Bay in Lake Taihu. Turbulence was generated by rotors to simulate the strong wind-induced disturbance in Lake Taihu. Results of the experiments showed that TN and TP in the stable and episodically turbulent conditions were not significantly different, with TN ranging from 1.34 to 1.90mg/L and TP from 0.08 to 0.18mg/L. Whereas, the soluble reactive phosphorus in the episodically turbulent condition was significantly higher than in the stable condition. Episodic turbulence could enhance P cycling by resuspending sediment-associated P, which alleviated algal P limitation. In stable conditions, P deficiency induced the production of high APA, which enhanced the availability of P. Although episodic turbulence could also cause increased algal biomass, photosynthetic efficiency of the algae was also affected not only by the nutrients but also by many other factors, especially light availability. Our results suggest that episodic turbulence is an important driver of biogeochemical cycling in large shallow hypertrophic lake ecosystem.

Spatial and seasonal changes of arsenic species in Lake Taihu in relation to eutrophication

Spatial and seasonal variations of arsenic species in Lake Taihu (including Zhushan Bay, Meiliang Bay, Gonghu Bay, and Southern Taihu) were investigated. Relatively high levels of total arsenic (TAs) and arsenate (As(V)) were observed in hyper-eutrophic regions during summer and autumn, which is attributed to exogenous contamination and seasonal endogenous release from sediments. The distributions of TAs and As(V) were significantly affected by total phosphorus, iron, manganese, and dissolved organic carbon. Arsenite (As(III)) and methylarsenicals (the sum of monomethylarsenic acid (MMA(V)) and dimethylarsenic acid (DMA(V))), mainly from biotransformation of As(V), were affected by temperature-controlled microalgae activities and local water quality parameters, exhibiting significantly higher concentrations and proportions in hyper-eutrophic and middle eutrophic regions during summer compared to mesotrophic region. The eutrophic environment, which induces changes in the main water quality parameters such as phosphorus, chlorophyll-a, iron, manganese, and dissolved organic carbon, can favor the biogeochemical cycling of arsenic in the aquatic systems.

Relative contribution of iron reduction to sediments organic matter mineralization in contrasting habitats of a shallow eutrophic freshwater lake

Iron reduction is one of the important organic matter (OM) mineralization pathway in sediments. Here we investigated the rates and the relative contribution of iron reduction to OM mineralization in Zhushan bay (ZSB, cyanobacterial bloom biomass (CBB)-dominated habitats) and East Taihu Lake (ETL, submerged macrophypes (SM)-dominated habitats) of Lake Taihu, China. Anaerobic microcosm incubation revealed that the rate of iron reduction at ZSB (4.42 μmol cm−3 d−1) in summer was almost 1.5 times higher than at ETL (3.13 μmol cm−3 d−1). Iron reduction accounted for 66.5% (ZSB) and 31.8% (ETL) of total anaerobic carbon mineralization, respectively. No detectable methanogenesis was found at ZSB, while methanogenesis was responsible for 16.7% of total anaerobic respiration in sediments of ETL. Geochemical analysis of solid phase constituents indicated that ZSB surface sediments experienced highly oxidizing conditions with much higher amorphous Fe(III) (71 mmol m−2) than ETL (11 mmol m−2). Conversely, AVS inventories at ETL (38 mmol m−2) were up to 30 times higher than at ZSB (1.27 mmol m−2), indicating significant sulfate reduction in sediments of ETL. Overall results suggested that varying carbon sources and distinct geochemical characterizations of the sediments in contrasting habitats significantly influenced the rate of iron reduction and the pathway of C mineralization in a large freshwater lake.

The Vertical Distribution of Sediment Archaeal Community in the "Black Bloom" Disturbing Zhushan Bay of Lake Taihu.

Using the Illumina sequencing technology, we investigated the vertical distribution of archaeal community in the sediment of Zhushan Bay of Lake Taihu, where the black bloom frequently occurred in summer. Overall, the Miscellaneous Crenarchaeotal Group (MCG), Deep Sea Hydrothermal Vent Group 6 (DHVEG-6), and Methanobacterium dominated the archaeal community. However, we observed significant difference in composition of archaeal community among different depths of the sediment. DHVEG-6 dominated in the surface layer (0–3 cm) sediment. Methanobacterium was the dominating archaeal taxa in the L2 (3–6 cm) and L3 (6–10) sediment. MCG was most abundant in the L4 (10–15 cm) and L5 (15–20 cm) sediment. Besides, DHVEG-6 was significantly affected by the concentration of total phosphorus (TP). And loss on ignition (LOI) was an important environmental factor for Methanobacterium. As the typical archaeal taxa in the surface layer sediment, DHVEG-6 and Methanobacterium might be more adapted to abundant substrate supply from cyanobacterial blooms and take active part in the biomass transformation. We propose that DHVEG-6 and Methanobacterium could be the key archaeal taxa correlated with the “black bloom” formation in Zhushan Bay.

Identifying Watershed Regions Sensitive to Soil Erosion and Contributing to Lake Eutrophication--A Case Study in the Taihu Lake Basin (China).

Taihu Lake in China is suffering from severe eutrophication partly due to non-point pollution from the watershed. There is an increasing need to identify the regions within the watershed that most contribute to lake water degradation. The selection of appropriate temporal scales and lake indicators is important to identify sensitive watershed regions. This study selected three eutrophic lake areas, including Meiliang Bay (ML), Zhushan Bay (ZS), and the Western Coastal region (WC), as well as multiple buffer zones next to the lake boundary as the study sites. Soil erosion intensity was designated as a watershed indicator, and the lake algae area was designated as a lake quality indicator. The sensitive watershed region was identified based on the relationship between these two indicators among different lake divisions for a temporal sequence from 2000 to 2012. The results show that the relationship between soil erosion modulus and lake quality varied among different lake areas. Soil erosion from the two bay areas was more closely correlated with water quality than soil erosion from the WC region. This was most apparent at distances of 5 km to 10 km from the lake, where the r2 was as high as 0.764. Results indicate that soil erosion could be used as an indicator for identifying key watershed protection areas. Different lake areas need to be considered separately due to differences in geographical features, land use, and the corresponding effects on lake water quality.