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Quantifying the relative influences of anthropogenic activities and climate change on soil erosion and deposition during the Holocene, when both forces have been interacting is a complex problem. Analysis of long-term patterns in soil erosion and lake deposition in a basin can provide the basis for untangling the complexities of climate and anthropogenic forcings. In this paper, sedimentary sequences from Xingyun Lake are compared with simulated soil erosion rates in the basin to explore the relationship between river basin soil erosion and lake deposition during the Holocene in Yunnan, China. Modern soil erosion rates are calculated using RUSLE, while Holocene soil erosion rates are estimated using modern rates with reconstructed precipitation and vegetation cover sequences. Through this investigation, we found the following results. First, Holocene vegetation in the lake basin was mainly affected by climate change, and the vegetation experienced the same pattern of changes as the climate. Soil erosion and lake deposition rates, along with changes to vegetation cover, were synchronous with precipitation trends during the Holocene. Second, soil erosion and lake deposition have been exacerbated by human activities, such as deforestation and land reclamation in the Xingyun Lake basin. Finally, this study provides new insights into the effects by anthropogenic impacts and climate forcing on the processes of soil erosion and lake deposition on the millennium scale. [ABSTRACT FROM AUTHOR]

• Striking ecological degradation occurred as a result of abrupt drought event. • Reservoirs respond sensitively to agricultural N and P addition in karst region. • We for the first time present a long-term evidence for the fragility of KEE. • It highlights the extreme importance of eco-environment protection in karst region. Southwest China is the largest continuous karst area in the world, which has suffered from serious ecological degradation. Many researchers have discussed the fragility of karst ecosystem and environment (KEE). However, these studies focused mainly on the particular karst geologic setting and short-term (annual) eco-environmental changes. At longer timescales, knowledge of how KEE responds to external disturbances such as climate changes and human activities is very limited. Based on geochemical analysis of lake sediments in the karst region of Southwest China (KRSC), this paper probes into the evolutionary characteristics of KEE at decadal-centurial timescales. Organic C/N ratios, Sr/Rb ratios and pollen assemblage in Baixian Lake indicate that striking eco-environmental deterioration occurred as a result of the drought event between 3.6 ka B.P. and 2.2 ka B.P. The regional vegetation degraded with dwindling herbs, increasing ferns and decreasing terrestrial productivity. Furthermore, the karst ecosystem had not restored to the earlier level even after a long time. Once degradation happens, the karst ecosystem would be unlikely to recover in the short term. Poor water-soil conservation capacity and weak drought resistance of karst soil should be the inherent mechanism of the fragility of terrestrial KEE. Hongfeng Lake has suffered from rapid eutrophication in the last three decades. Reservoirs respond more sensitively to agricultural N and P addition because of abundant dissolved inorganic carbon (DIC) supply from the carbonate catchment in karst region than in non-karst region. A positive feedback loop may develop among elevated primary productivity, higher deposition fluxes of organic matter, anoxia in hypolimnion and enhanced internal P release in aquatic ecosystem. This positive feedback, together with the DIC fertilization effect and sensitivity to agricultural N and P addition, may explain the fragility of aquatic KEE. This paper for the first time presents a long-term evidence for the fragility of both terrestrial and aquatic ecosystem in the KRSC, and provides new insights into the sensitivity and resilience of KEE to climate change and agricultural activities, highlighting the extreme importance of eco-environment protection in karst region. [ABSTRACT FROM AUTHOR]

We used a 55-cm sediment core from shallow Chaiwopu Lake in the central Tianshan Mountains of Xinjiang, northwest China, to investigate climate and environmental changes in this arid region over the past ~150 years. The core was dated using Cs. We compared temporal changes in several sediment variables with recent meteorological and tree-ring records. Organic matter had a positive correlation with the Palmer Drought Severity Index in the central Tianshan Mountains, and the δC of organic matter had a positive correlation with regional temperature. We applied constrained incremental sum-of-squares cluster analysis to element concentrations in the core and identified three distinct zones: (1) 55-46 cm, ~1860-1910, (2) 46-26 cm, ~1910-1952, and (3) 26-0 cm, 1952-present. Between 1880 and 1910 AD, following the Little Ice Age (LIA), the sediment environment was relatively stable, climate was cold and dry, and the lake water displayed high salinity, in contrast to conditions during the LIA. During the LIA, westerlies carried more water vapor into Central Asia when the North Atlantic Oscillation was in a negative phase, and encountered the enhanced Siberia High, which probably led to increased precipitation. In the period 1910-1950 AD, the lake was shallow and the regional climate was unstable, with high temperatures and humidity. In the last ~15-20 years, human activities caused an increase in sediment magnetic susceptibility, and heavy metal and total phosphorus concentrations in the sediment were substantially enriched. Mean annual temperature displays a warming trend over the past 50 years, and the lowest temperature was observed in the 1950s. There has been an increase in annual total precipitation since the 1990s. The combined influences of climate and human activity on the lake environment during this period were faithfully recorded in sediments of Chaiwopu Lake. This study provides a scientific basis for environmental management and protection. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.