Yanmin Cao

One century sedimentary record of lead and zinc pollution in Yangzong Lake, a highland lake in southwestern China

Reconstruction of trace metal pollution histories and sources may help us to regulate current pollutant discharge. This is especially important for the highland lakes in southwestern China, which are facing trace metals pollution. We present sedimentary records of 11 metals accumulated in Yangzong Lake since the 1870s, a highland lake in southwestern China. Pollution of lead and zinc (Pb and Zn) was differentiated based on principal component analysis, geochemical normalization, and lead isotope ratios. Nearly all the metals as well as grain size composition show generally constant values before the mid-1980s, denoting stable detrital input in the catchment. Fluctuations in the concentrations of the metals as well as grain size composition since the mid-1980s indicate an increase in soil erosion with strengthened human disturbance in the catchment. After geochemical normalization, Pb and Zn showed constant values before 1990 AD and then a gradual increase in parallel with the variations in 208Pb/206Pb and 207Pb/206Pb ratios, indicating that Pb and Zn pollution occurred. Combining the data of 208pb/206Pb and 207Pb/6Pb ratios in the sediments of Yangzong Lake, leaded gasoline, Pb-Zn ore and coal, and consumption or production historical trends, we deduced that the enhanced Pb and Zn pollution in Yangzong Lake is caused primarily by ore mining and refining.

Chironomid-inferred environmental change over the past 1400 years in the shallow, eutrophic Taibai Lake (south-east China): Separating impacts of climate and human activity

A sediment core from Taibai Lake, a shallow and eutrophic lake (SE China), was analysed for chironomids to track environmental changes in the lake. Nutrient dynamics over the past 1400 years were traced based on subfossil records and a regional chironomid-inferred total phosphorus (CI-TP) transfer function. Between ad 600 and 1370, the coexistence of several macrophyte-related taxa such as Dicrotendipes, Paratanytarsus and Endochironomus reflected a clear-water state with flourishing plants, and total phosphorus (TP) reconstructions ranged from 40 to 60 µg/L. For the time span from ad 1370 to 1650, the prevalence of Paratanytarsus penicillatus-type indicated a slight decline of TP to lower than 50 µg/L, but CI-TP increased to previous levels between ad 1650 and 1940. Since the 1950s, Chironomus plumosus-type dominated the chironomid community, which illustrated that the lake suffered from high nutrient loadings and CI-TP increased from 80 to 140 µg/L. The results suggest that 50–60 µg/L of TP concentration is the reference condition for Taibai Lake, and ~80–110 µg/L might be considered as the nutrient threshold range between the plant-dominated and algal-dominated status. Variance partitioning analysis (VPA) was used to determine the relative influence of climate and human factors on the lake ecosystem. The analyses revealed that long-term climate change appeared to be the main determinant regulating the chironomid assemblages; however, the impact of human activities on the aquatic ecosystem prevailed over that of climate factors since the 1950s. This study improves our understanding of complex trajectories of aquatic ecosystem development at centennial to millennial timescales, which are influenced by both anthropogenic and climatic factors in a densely populated region. The main finding also provides reference for sustainable management in this lake and other analogous floodplain lakes.

Use of siliceous algae as biological monitors of heavy metal pollution in three lakes in a mining city, southeast China

In order to assess the ecological status of three lakes in a historical mining city (SE China), water metal concentrations and surface sedimentary diatoms and chrysophyte cysts were analyzed in 20 sampling sites. The significant correlations between the algal indices and the cumulative criterion unit (CCU) scores confirmed the importance of heavy metals in shaping algae communities. In the metal-polluted sites, diatom assemblages were dominated by metal-tolerant species, such as Nitzschia palea and Nitzschia perminuta. In the unpolluted samples, diatom assemblages were characterized by Cyclostephanos dubius, Discostella pseudostelligera and Aulacoseira species (mainly A. alpigena, A. granulata and A. ambigua). These dominant taxa in the unpolluted samples might be sensitive to metal contamination but tolerant of eutrophication. In addition, nonspherical cysts were much more abundant in the polluted sites, indicating that their presence should be indicative of metal contamination in this region. This study provides some clues for future metal pollution assessment through the use of siliceous algae in metal polluted lakes.

Spatially different nutrient histories recorded by multiple cores and implications for management in Taihu Lake, eastern China

The Taihu Lake, a large shallow lake in the floodplain of the Changjiang (Yangtze) River in the eastern China, is faced with challenging ecological problems resulting from eutrophication, which has affected the regional freshwater supply of a large population. Although efforts have been made to assess the nutrient evolution histories in the northern bays, little is known regarding nutrient histories in different parts across the entire lake basin. In this paper, we present nutrient histories for different parts of the lake based on chironomid transfer functions applied to four short cores obtained from the northern, western and eastern regions of the lake. The chironomid-inferred total phosphorus (CI-TP) concentrations were compared with the phosphorus concentrations obtained by using instrumental and sedimentary data. The results suggest that trophic evolution histories were asynchronous throughout the lake during the past decades in response to different ecological regimes controlled by the nutrient input, wind direction and shoreline topography. The restoration of aquatic plants may be an effective option for the management of lake rehabilitation to ‘natural’ conditions. Given the multiple factors controlling the biotic communities in such a large and complex lake, combined analyses among the multi-proxies encountered in the sediments are necessary for comprehensive insight into paleolimnological studies. The spatial heterogeneity in the ecological trajectories within this complicated ecosystem suggests that different management practices should be undertaken for specific lake zones in the Taihu Lake.

Combined effects of nutrients and trace metals on chironomid composition and morphology in a heavily polluted lake in central China since the early 20th century

Eutrophication and trace metal pollution seriously threaten the health of lake ecosystems; however, little is known about the response of zoobenthos to their combined impacts. In order to detect their effects on the biotic community of a lake, subfossil chironomids were analyzed in a sediment core from Sanliqi Lake, a hypereutrophic and severely metal-polluted lake located in the middle reaches of the Yangtze River in central China. The sediment core provides a record of environmental changes since the 1930s. Increases in pollutant concentrations began before the 1990s, and increases in total P and Pb began from the 1950s. Significant increases in nutrient and metal concentrations in the 1990s document the acceleration of eutrophication and metals pollution. As a consequence, macrophyte-related chironomid taxa (e.g., Cricotopus sylvestris-type and Dicrotendipes sp.) which dominated the subfossil assemblages prior to the 1990s were replaced by pollution-tolerant species (i.e., Tanypus chinensis-type and Procladiuschoreus-type) thereafter. Chironomid diversity gradually decreased from the 1950s with an abrupt change occurring in 1995. Multivariate statistical analyses reveal that subfossil chironomid assemblages are significantly correlated with total N, Pb, and Cd, highlighting the combined impact of nutrients and trace metals on the chironomid communities. In addition, the relative abundance of Procladiuschoreus-type with mouthpart deformities increased over time and is significantly positively correlated with trace metals and nutrients. Nevertheless, further laboratory studies to assess the linkage between sediment contamination and mouthpart deformities are needed in order to enhance the utility of the latter as an indicator of environmental health.

C, N STABLE ISOTOPE RECORDS OF ENVIRONMENTAL CHANGES IN BOSTEN LAKE DURING THE PAST 200 YEARS: C, N STABLE ISOTOPE RECORDS OF ENVIRONMENTAL CHANGES IN BOSTEN LAKE DURING THE PAST 200 YEARS

Two sediment cores were recovered from the Bosten Lake in order to investigate the changes in both the lake system and source of organic materials during the last 200 years.Based on 210Pb/137Cs chronology,stable isotopes of organic carbon and nitrogen as well as Loss on Ignition(LOI),grain size and magnetic susceptibility(MS) were analyzed.The results indicate that the agricultural activities in the catchment of the Bosten Lake have much earlier influence in the lake center rather than in the river mouth.Due to the general increase in regional humidity during 1810—1883 AD,δ13Corg declined rapidly in the core BST16,while abrupt increases in δ15N were found as more terrestrial material could reach the lake center.After the establishment of Xinjiang Province in 1884 AD,intensified agricultural activities have led to marked decrease in the medium grain size,and relatively higher δ13Corg and lower δ15N in the core BST16.Since 1950 AD,large scale agricultural activities have led to the rapid decrease in δ13Corg and increase in δ15N,indicating a general increase in the trophic level.Further decrease in δ15N together with the increasing δ13Corg after the 1990s indicates that nitrogen fixation by algae began to dominate the lake primary productivities.