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Pollen and charcoal records of a 150 cm long lake sediment core from Taibai Lake in the middle reach of the Yangtze River reveal seven major changes in regional vegetation over the last 1500 years. During the period c. ad 480–710, evergreen broadleaved forest dominated by Castanopsis/Lithocarpus and evergreen oaks occurred in the Taibai Lake catchment. From c. ad 710 to 1050, the vegetation shifted to a mixed conifer and broadleaved forest, with Pinus expanding at the expense of Castanopsis/Lithocarpus. Between c. ad 1050 and 1320, evergreen broadleaved forest reoccupied the studied area. From c. ad 1320 to 1650, the area of primary forest decreased markedly with synchronous reduction in broadleaved trees and Pinus. Between c. ad 1650 and 1740, the biomass declined rapidly, while secondary Pinus forest began to expand. During c. ad 1740–1950, forest extent increased slightly compared with the previous stage, but the landscape was still secondary forest with the minimum proportion of broadleaved trees. After c. ad 1950, the biomass in the surrounding area was very low, with vegetation types similar to that at present (secondary Pinus forest and mixed conifer and broadleaved forest). A detrended correspondence analysis (DCA) with 125 samples and 34 main pollen types is used to separate human and climatic impacts on vegetation. Then, the pollen assemblage, DCA, charcoal record, and magnetic susceptibility are combined to discuss the key factors inducing these vegetation changes. The vegetation changes were mainly controlled by the climatic changes, with the weak impacts of human activities before c. ad 1320. Since then, the intensity of human influences on vegetation increased gradually, entering a transitional period of main controlling factors of vegetation changes from nature to human activities. After c. ad 1740, the vegetation changes were chiefly controlled by human activities, and the climatic signal was weak. [ABSTRACT FROM AUTHOR]

Metals in lacustrine sediment have both anthropogenic and natural sources. Because of intensified human activities, the anthropogenic input of metal elements has exceeded the natural variability. How to distinguish the anthropogenic sources in lake sediments is one of the tasks in environmental management. The authors present a case study, which combined the geochemical and statistical methods to distinguish the anthropogenic sources from the natural background. A 56 cm core (core DJ-5) was collected from Dongjiu Lake, Taihu Lake catchment, China. The concentration distributions of Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Sr, Ti, V and Zn in core DJ-5 indicated that Dongjiu Lake had serious Cd pollution, and the concentrations of Cr, Cu, Pb, Mn and Zn had also exceeded the Chinese State Standards of Soil Environmental Quality in the upper layer of the core. Using Al as a reference element, the other metals were normalized and compared with their baselines to calculate the enrichment factors (EFs). The principal component analysis (PCA) of metal concentrations was performed using ViSta6.4. The results of EFs and PCA indicated that the concentration variations of Cd, Cu, Pb, Mn and Zn were mainly caused by the anthropogenic sources, and the concentration variations of Cr and Ni were influenced by both the anthropogenic and natural factors, while the other metals were mainly derived from the natural sources. Intensified human activities within the lake catchment area resulted in the increase of heavy metal inputs directly and the acceleration of erosion which caused other metal elements to deposit in the aquatic environment. The results of this work will be useful in probing changes forced by humans in the lake environment and in adjusting human activity in restoring the lake environment. [ABSTRACT FROM AUTHOR]

The evidence of human activities around Erhai Lake catchment was revealed by pollen records from a sediment core in the lake, northwest Yunnan Province. The chronologic sequence based on AMS 14C data made it possible for pollen results to compare with archaeological records and historical documents. The preliminary deforestation started from the selective clearance at about 5500 14C a BP, marked by the loss of vertically distributed montane forest and the expansion of second pine woodland across the catchment. The deforestation resulted in the increase of surface runoff and the enhanced erosion in the catchment. The increased herbs of pasture and crop suggested the primitive agriculture and stockbreedlng in study region. With the limited human activity, as well as the suitable climatic condition, second pine forest expanded quickly, resulting in the weakened soil erosion around the basin. The strong forest clearance inferred from pollen occurred since 2160 14C a BP, paralleling to the first dense immigration of population, when Yeyu County was first set up around west coast of Erhai Lake, documented in historic record. The development of agriculture led to the steady enhancement of soil erosion from farming land, increasing the input of fine materials and nutrients to the lake. Moreover, the serious deforestation by human activity stressed the vulnerability in ecosystem of the landscape. The time of primary anthropologic impact recorded from pollen is earlier than that of the oldest archaeological record by 1500 a (14C year). [ABSTRACT FROM AUTHOR]

Based on the function relationship between the shell length of Limnocythere inopinata and the salinity of its living water in Tibetan Plateau lakes, the paleosalinty of Qinghai Lake in the past 900 years was reconstructed through the measurement of the adult body length of Limnocythere inopinata. Meanwhile, the paleosalinity sequence of Qinghai Lake during the same period was rebuilt by the Sr/Ca ratio of the shell of Eucypris inflata combined with the Sr/Ca ratio of living ostracod valves from the species of genus Eucypris inflata and the host water. The paleosalinity results obtained by two different methods were compared and assessed in this paper. To check the result, it was also contrasted with other historical climatic sequences of this area including tree ring and ice core. It was shown that the paleosalinity sequence rebuilt by adult ostracod body length had high reliability, and the paleosalinity reconstruction method by trace elements of ostracod shells was not suitable for Qinghai Lake. From the reconstructed paleosalinty sequence of Qinghai Lake, it can be found that low salinity during 1160-1290 AD showed the humid climate condition on the Mediaeval Warm Period in this area, while the high salinity during 1410-1540 AD, 1610-1670 AD and 17701850 AD which was corresponding to the three cold pulses of the Little Ice Age with a dry climate condition. And the high salinity in the latest several decades was consistent with recent warm and dry trends of the climate in this area. The good consistency of the reconstructed palaeosalinity sequence and the precipitation sequence in this area rebuilt by tree ring proves the reconstruction of past lake salinity is reliable. [ABSTRACT FROM AUTHOR]

Wetland is the conjunction of lake and terrene where human activities are concentrated. From the viewpoints of material transport and cycling in the terrene-lake system, wetland is the buffer where sand and mud, heavy metals, pollutants and nutrients are tarried. In this paper, we provide a case study based on the temporal and spatial distribution of elements in the Wangling River catchment, a small sub-catchment of Longgan like in the middle reaches of the Yangtze River. We have found that wetland can buffer major heavy metals such as Cr, Cu, etc. significantly, but has a little buffer function to some active elements such as Fe and Mn, which are always transported as solutions. Human activities not only influence the distribution of elements, but also weaken the buffer function of wetland. Intensive human activities in the Longgan like area in the past 70 years have been recorded in stream, wetland and lake sediments, especially the human activity events such as deforesting and reclaiming on a large scale in 1958 and the 1980's. Human activities caused the increase of sedimentation rates since the 1950's, as well as the increase of elements' concentrations. The extensive use of fertilizers and pesticides since the 1960's have led to the increase of total P concentrations. Increasing SO; emission accelerate the process of cation exchange in soil, and enhance the leaching of Mn out of soils. Permanent storing of water causes the soil gleyification that also intensifies the leaching of Mn. These are two major reasons for the obvious increase of manganese concentrations in recent 20 years in Longgan Lake. Intensive human activities since the 1950s' have intensified the population in this region and thus destroyed the buffer function of wetland. [ABSTRACT FROM AUTHOR]

Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment, organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Chenghai, a closed, eutropic lake in southern China, provide information on lake historical eutrophication. During the last 660 years, great changes have taken place in productivity and eutrophication of Lake Chenghai in response to human activities. In 1690, the productivity of the lake began to increase as Lake Chenghai became closed from agriculture in the lake's watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an increase in organic carbon, nitrogen, CaCO[sub3], pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, intensive human activities induced modern lacustrine productivity and eutrophic level. Human-induced trophic changes during the past few decades have affected the Lake Chenghai ecosystem to such an extent that it has never experienced before in the last 660 years. [ABSTRACT FROM AUTHOR]

Discusses the paleoclimate and paleoenvironment of Qinghai Lake, China as indicated by a 16,000-year old pollen record. Coldness and dryness before 15,200 years; Varied climate during the late Glacial period; Cold events corresponding to the Oldest Dryas, Older Dryas and Younger Dryas events; Warm period corresponding to the Bolling and Allerod periods.

Presents information on the environmental evolution and southwest monsoon changes recorded by lake sediments from Erhai Lake, Yunnan Province, China. Methodology; Environmental condition in Erhai Lake; Characteristics of lakes in Qinghai-Tibetan Plateau.

Focuses on a study which examined the environmental change and paleoclimatic changes in the Gucheng Lake, Gaochun County, Jiangsu Province, China. Examination of the age of transgression; Details on the features of gammacerance in the core of the lake; Analysis of the diatoms in the core.

The biological pump plays a critical role in the occurrence and fate of hydrophobic organic contaminants (HOCs) mostly in temperate and frigid oligotrophic waters. However, the factors for the long-term occurrence and fate of HOCs in subtropical eutrophic waters remain largely unknown. This study provides novel insights into biogeochemical and physical factors on the annual occurrence, bioaccumulation, and biomagnification of 16 polycyclic aromatic hydrocarbons (PAHs) in the plankton food webs of four Chinese subtropical eutrophic lakes by one-year simultaneous field observations for five compartments. The annual mean ΣPAH 16 in the water columns ranged from 359.69 ± 31.52 ng L −1 to 682.69 ± 65.41 ng L −1 , and increased with the annual mean trophic state index, and phytoplankton biomass of these lakes, but was independent on the proximity of the lakes to urban areas. Biodilution effect played an important role in the occurrence of the PAHs in both phytoplankton and zooplankton. In contrast to previous studies in oligotrophic waters, not only the biological pump but also the equilibrium partitioning and the indirect influence of eutrophication (high pH induced by phytoplankton, and phytoplankton life cycling) modulated the annual occurrence of the PAHs in the water columns of these eutrophic lakes. Biphasic correlations were found between the bioaccumulation factors of the PAHs by plankton and the temperature (n = 97–136, R 2  = 0.06–0.24, p  ≤ .008), and were related to plankton phenology. Bioaccumulation factors by plankton were dependent on the hydrophobicity of the PAHs (n = 16, R 2  = 0.27–0.31, p  ≤ .023), and decreased with plankton biomass (n = 94–103, R 2  = 0.09–0.27, p  ≤ .010). Trophic transfer of the PAHs from phytoplankton to zooplankton increased with phytoplankton biomass (n = 26, R 2  = 0.27, p  = .004), and the temperature (n = 102–135, R 2  = 0.06–0.13, p  ≤ .004), but decreased with lake trophic state index. Biomagnification only occurred during phytoplankton bloom periods. [ABSTRACT FROM AUTHOR]

Climatic and environmental changes in the northeastern Tibetan Plateau are controlled by the Asian summer monsoon (ASM) and the westerlies, two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern Asia. During the past few decades, a series of Holocene palaeoclimatic records have been obtained from sediment cores from Lake Qinghai and from various other geological archives in the surrounding area of the northeastern Tibetan Plateau. However, because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used, the nature of Holocene climatic changes in the region remains unclear and even controversial. Here we review all major classes of the published data from drilled cores from Lake Qinghai, as well as other evidence from lakes and aeolian deposits from surrounding areas, in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the Holocene. Combining the results of moisture and precipitation proxies such as vegetation history, pollen-based precipitation reconstruction, aeolian activity, lake water depth/lake level changes, salinity and sediment redness, we conclude that moisture and precipitation began to increase in the early Holocene, reached their maximum during the middle Holocene, and decreased during the late Holocene - similar to the pattern of the East Asian summer monsoon (EASM) in northern China. It is clear that the region experienced a relatively dry climate and weak EASM during the early Holocene, as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations; generally low lake levels of Lake Qinghai and the adjacent Lake Hurleg and Lake Toson in the Qaidam Basin; and widely distributed aeolian sand deposition in the Lake Qinghai Basin and the nearby Gonghe Basin to the south, and in the eastern Qaidam Basin to the west. We argue that the ostracod δ 18 O record, which is widely used as a proxy of effective moisture and summer monsoon intensity in lake sediments, at least in Lake Qinghai, and which exhibits light values in the early Holocene and heavier values thereafter, cannot be used to reflect the strength of the EASM or the intensity of monsoon precipitation - as is also the case for leaf wax δ 2 H records. Rather, we argue that as is the case of the Chinese speleothem δ 18 O record, which also is often interpreted as an EASM proxy, it reflects variation in the δ 18 O of precipitation. Overall, we suggest that the EASM significantly affected precipitation in the northeastern Tibetan Plateau during the Holocene; and that it increased in strength during the early Holocene, reached a maximum during the middle Holocene and decreased during the late Holocene. [ABSTRACT FROM AUTHOR]