Historical changes in the major and trace elements in the sedimentary records of Lake Qinghai, Qinghai-Tibet Plateau: implications for anthropogenic activities.

Sediment sequences in Lake Qinghai spanning the past 100 years were explored to assess the effects of changes in local land desertification, dust input and agriculture on sediment deposition in different parts of Lake Qinghai. Three short sediment cores (QH01, QH02, QH07) were collected from the main lake and one sediment core (Z04) from a sublake (Lake Gahai) of Lake Qinghai, China, during 2012 and 2013. The concentrations of Fe, Mn, Al, Rb, Ti, Ca, and Sr were analysed to determine the effects of historical and regional anthropogenic activities in the Lake Qinghai catchment from 1910 to 2010. The elemental concentrations in the sediment cores ranged from 1.85 to 2.79% for Fe, 397 to 608 µg/g for Mn, 3.04 to 5.64% for Al, 13.5 to 19.7 µg/g for Rb, 0.171 to 0.268% for Ti, 9.43 to 13.9% for Ca, 652 to 1020 µg/g for Sr, and 0.049 to 0.075% for P. Good correlations were found between the concentrations of Fe, Mn, Al, and Rb, and the Ti/Al ratios in the sediments suggest that these elements share a similar source. The enrichment factors (EFs) of Ti [EF(Ti)] and P [EF(P)] in each core were utilized to reflect variations in anthropogenic activities from 1950 to 2010. EF(Ti) ranged from 1 to 1.17 in QH01 and QH02, reflecting the variation of land desertification areas in the Buha River catchment from 1950 to 2010. The EF(Ti) showed positive linear correlations with the variation in cropland area in Gangcha County, suggesting that agricultural activity in the Quanji River and Shaliu River catchments was enhanced from 1950 to 2010. The sediment records showed similar biogeochemical changes in most lakes and bays in China, indicating that the intensity of changes in anthropogenic activities was caused by national policy enforcement from the 1950s to 2010. EF(Ti) can serve as a tracer for anthropogenic activities in Lake Qinghai, with the anthropogenic activities in different parts of the Lake Qinghai catchment represented in the homologous sediments from parts of Lake Qinghai over the past 100 years. The variation of EF(P) increased from 1 to 1.55 from deep layer to upper layer in all sediment cores, reflecting the increased fertilizer input and tourism activity from 1980 to 2010, a period during which the lake was evolved into a eutrophic lake.

Regional environmental change and human activity over the past hundred years recorded in the sedimentary record of Lake Qinghai, China.

Environmental change and human activity can be recorded in sediment cores in aquatic systems such as lakes. Information from such records may be useful for environmental governance in the future. Six sediment cores were collected from Lake Qinghai, China and its sublakes during 2012 and 2013. Measurements of sediment grain-size fractions indicate that sedimentation in the north and southwest of Lake Qinghai is dominated by river input, whereas that in Lake Gahai and Lake Erhai is dominated by dunes. The sedimentation rates in Lake Qinghai were calculated to be 0.101-0.159 cm/y, similar to the rates in other lakes on the Qinghai-Tibetan Plateau. Using these data and sedimentation rates from the literature, we compiled the spatial distribution of sedimentation rates. Higher values were obtained in the three main areas of Lake Qinghai: two in river estuaries and one close to sand dunes. Lower values were measured in the center and south of the lake. Measurements of total organic carbon (TOC), total nitrogen (TN), phosphorus concentrations, and TOC/TN ratios in three cores (QH01, QH02, and Z04) revealed four horizons corresponding to times of increased human activity. These anthropogenic events were (1) the development of large areas of cropland in the Lake Qinghai watershed in 1960, (2) the beginning of nationwide fertilizer use and increases in cropland area in the lake watershed after 1970, (3) the implementation of the national program "Grain to Green," and (4) the rapid increase in the tourism industry from 2000. Profiles of Rb, Sr concentrations, the Rb/Sr ratio, and grain-size fraction in core Z04 indicate that the climate has become drier over the past 100 years. Therefore, we suggest that lake sediments such as those in Lake Qinghai are useful media for high-resolution studies of regional environmental change and human activity.