Mapping of Freshwater Lake Wetlands Using Object-Relations and Rule-based Inference

Inland freshwater lake wetlands play an important role in regional ecological balance. Hongze Lake is the fourth biggest freshwater lake in China. In the past three decades, there has been significant loss of freshwater wet- lands within the lake and at the mouths of neighboring rivers, due to disturbance, primarily from human activities. The main purpose of this paper was to explore a practical technology for differentiating wetlands effectively from upland types in close proximity to them. In the paper, an integrated method, which combined per-pixel and per-field classifi- cation, was used for mapping wetlands of Hongze Lake and their neighboring upland types. Firstly, Landsat ETM＋ imagery was segmented and classified by using spectral and textural features. Secondly, ETM＋ spectral bands, textural features derived from ETM＋ Pan imagery, relative relations between neighboring classes, shape fea^xes, and elevation were used in a decision tree classification. Thirdly, per-pixel classification results from the decision tree classifier were improved by using classification results from object-oriented classification as a context. The results show that the technology has not only overcome the salt-and-pepper effect commonly observed in the past studies, but also has im- proved the accuracy of identification by nearly 5%.

Present Situation and Control Ideas of Outbreak of Blue-green Algae in Freshwater Lakes in China

Based on the experience and lessons from previous control of lakes, as well as the present situation of water eutrophication and outbreak of blue-green algae in lakes, general ideas of controlling outbreak of blue-green algae in large and middle lakes were proposed. Firstly, it is needed to control serious outbreak of blue-green algae and then build health aquatic ecosystems and corresponding control goals finally. Secondly, quantity of blue-green algae in lakes and lake eutrophication should be reduced at the same time. Thirdly, quantity of reduced blue-green algae must exceed the natural increase of them in quantity persistently, so that outbreak of blue-green algae will reduce and even be eliminated. Fourthly, engineering measures and corresponding safeguard measures to control outbreak of blue-green algae in lakes should be combined.

Distribution of bacterial communities across plateau freshwater lake and upslope soils

Microorganisms are involved in a variety of biogeochemical processes in natural environments.The differences between bacterial communities in freshwaters and upslope soils remain unclear. The present study investigated the bacterial distribution in a plateau freshwater lake,Erhai Lake（southwestern China）, and its upslope soils. Illumina MiS eq sequencing illustrated high bacterial diversity in lake sediments and soils. Sediment and soil bacterial communities were mainly composed of Proteobacteria, Acidobacteria, Actinobacteria,Bacteroidetes, Chloroflexi and Planctomycetes. However, a distinctive difference in bacterial community structure was found between soil and sediment ecosystems. Water content, nitrogen and p H affected the distribution of the bacterial community across Erhai Lake and its upslope soils. Moreover, the soil bacterial community might also be shaped by plant types. This work could provide some new insights into plateau aquatic and terrestrial microbial ecology.

Fauna and standing crop of freshwater mussels in Poyang Lake, China

Freshwater mussels are a major component of the zoobenthos and they therefore play an important role in freshwater ecosystems. The community composition and the standing crop of freshwater mussels in Poyang Lake, the largest freshwater lake in China and one of two lakes connected to the Changjiang （Yangtze） River, were investigated from February 2008 to May 2009. Mussels were sampled in hydrologically and geographically distinct sampling areas. A total of 42 species and 13 genera were identified, of which 32 species were endemic to China. Two species, Unio douglasiae and Lamprotula caveata, dominated all sampling areas. The number of genera and species, and the number of species within each genus, differed significantly among sampling areas. Freshwater mussels were very abundant, with an overall density of 0.28±0.22 ind./m-＇ and biomass of 4.08±3.96 g/m^2. Significant variation observed among sampling areas and among genera was probably due to the variety of habitats among the areas sampled and to the adaptability of different freshwater mussels to environments. This study suggests that Poyang Lake and other freshwater lakes in the region are important sites of freshwater mussel biodiversity and conservation.

Occurrence and risk assessment of triclosan in freshwater lakes in the middle Yangtze River basin (Wuhan, Central China)

Triclosan(TCS)is an endocrine disrupting chemical which is commonly used as a disinfectant in pharmaceuticals and personal care products(PPCP's).Since early 2020,the worldwide outbreak of COVID-19 has increased the use of PPCP's,so the occurrence and impact of TCS on freshwater lakes should be considered.However,little attention has been given to the effect of TCS on freshwater lakes in China.This study is the first attempt at a risk assessment focusing on the temporal and spatial occurrence of TCS in freshwater lakes in the middle Yangtze River basin.The surface water and sediments of Donghu Lake and Liangzi Lake(Wuhan,Central China)were collected from October 2020 to August 2021.The maximum concentrations of TCS were 466 ng/L and 239 ng/L in surface water,71 ng/g and 25 ng/g(dry weight)in sediments of Donghu Lake and Liangzi Lake,respectively.Significant temporal and spatial differences of TCS were observed within and between the lakes,with the highest concentrations measured in winter.Furthermore,higher concentrations of TCS were observed in areas that are more impacted by human activities.There was a significant positive correlation between TCS and nitrogen in the surface water.A risk assessment using the risk quotient(RQ)method showed that a potentially high risk(RQ>1)was found only in surface waters from Donghu Lake,and that the sediments posed a lower risk than the surface waters.These results provide timely data on the temporal and spatial occurrence of TCS in freshwater lakes in China following the outbreak of COVID-19 and demonstrate a possible high risk of exposure to TCS for aquatic biota.

Characterizing Constituents of Sediment Phosphorus Fractionation in a Freshwater Shallow Lake System

This study aimed to characterize constituents of phosphorus （P） fractionation as wel as reciprocities among factors in sediments of a freshwater shal ow lake. [Method] Surface sediment was discretely sampled at 24 sites through Van Veen grabs. Based on a modified sequential extraction scheme, P fractionation was determined as Fe/Al bound P （Fe/Al-P）, Ca bound P （Ca-P）, solute and re-ductive P （S/R-P） and organic P （OP）. Curve estimation and Pearson product-mo-ment correlation were employed for statistical analysis. [Result] Total P （TP） content ranged from 443 to 774 mg/kg. Inorganic P （IP） was the major component of TP, of which Ca-P was dominated with an average of 51%±9.7%. Average contents of P fractionation were in the fol owing order： Ca-P（51%） 〉 OP（29%） 〉 S/R-P（8%） 〉Fe/Al-P（7%）. The molar ratio of Fe to P was 11 - 20, close to the threshold value of P leaching. [Conclusion] In freshwater shal ow lakes, IP and Ca-P were prone to be relatively high, whereas Fe/Al-P was low compared with deep lakes. Occurrence of spatial y monotonic gradient indicated the primary causation of anthropogenic sources. Imminent sediment P liberation was also expected. Close associations a-mong TP, Fe/Al-P and Ca-P, implying that anthropogenic P was mainly bound to metals in particulates. Significant correlations of TOC and P fractionation highlighted endogenous mechanism and authigenic origin in sediments.

Composition and Evolution of Hydrogen Isotopes of n-Akanes Generated from Anhydrous Pyrolysis of Sediments from Lake Gahai,Gannan,China

To understand the thermal evolution of lacustrine sedimentary n-alkane hydrogen isotopic composition(δD),especially bacterially derived n-alkanes,anhydrous thermal simulation experiments were performed with sediments from Lake Gahai(Gannan,China).We analyzed the original and pyrolysis-generated n-alkanes and theirδD values.The results showed that thermal maturity and n-alkane origins significantly affected the distribution of pyrolysis-generated n-alkanes.In immature to post-mature sediments,the bacterial-derived medium-chain n-alkanes generally had depletedδD values.The maximum difference in averageδD values between the bacterial-and herbaceous plant-derived medium-chain n-alkanes was 32‰,and the maximum difference in δD values among individual n-alkanes was 59‰.We found that the averageδD value of pyrolysis-generated n-alkanes from different latitude was significantly different in immature to highly mature sediments,but similar in post-mature ssediments.The hydrogen isotopes of sedimentary n-alkanes can be used as indicators for paleoclimate/paleo-environment conditions only when sediments are immature to highly mature.During thermal evolution,the δD value of generated individual n-alkanes and the averageδD value increased with thermal maturity,indicating that hydrogen isotopes of sedimentary n-alkanes can be used as an index of organic matter maturity.We established mathematical models of average δD values of generated n-alkanes from immature to post-mature sediments using n C_(21)^(-)/nC_(21)^(+)and average chain lengths.These results improve our understanding of the distribution andδD value of sedimentary n-alkanes derived from herbaceous plants in mid-latitude plateau cold regions.

Assessing the utility of dissolved organic matter photoreactivity as a predictor of in situ methylmercury concentration

Methylmercury（MeHg） bioaccumulation is a growing concern in ecosystems worldwide. The absorption of solar radiation by dissolved organic matter（DOM） and other photoreactive ligands can convert MeHg into less toxic forms of mercury through photodemethylation. In this study, spectral changes and photoreactivity of DOM were measured to assess the potential to control photoreactions and predict in situ MeHg concentration. Water samples collected from a series of lakes in southwestern Nova Scotia in June, August, and September were exposed to controlled ultraviolet-A（UV-A） radiation for up to 24 hr. Dissolved organic matter photoreactivity, measured as the loss of absorbance at 350 nm at constant UV-A irradiation, was positively dependent on the initial DOM concentration in lake waters（r^2=0.94）. This relationship was consistent over time with both DOM concentration and photoreactivity increasing from summer into fall across lakes. Lake in situ MeHg concentration was positively correlated with DOM concentration and likely catchment transport in June（r = 0.77） but not the other sampling months. Despite a consistent seasonal variation in both DOM and Fe, and their respective correlations with MeHg, no discernable seasonal trend in MeHg was observed. However, a 3-year dataset from the 6 study lakes revealed a positive correlation between DOM concentration and both Fe（r = 0.91） and MeHg concentrations（r = 0.51） suggesting a more dominant landscape mobility control on MeHg.The DOM-MeHg relationships observed in these lakes highlights the need to examine DOM photoreactivity controls on MeHg transport and availability in natural waters particularly given future climate perturbations.