The Coupling Features Between Soil Erosion And Climate Changes, And Its Impacts On The Human-environment Interactions In The Longzhong Loess Plateau

Soil erosion, to a large extent, is closely linked with pedosphere, hydrosphere, atmosphere and biosphere. It destroys the initial conditions, as well as breaks the balance among the above living environment, leading to unbalanced terrestrial ecosystem, deteriorative living environment, and many potential crises. Due to the regional differences of natural environment on the earth, soil erosion is diverse in terms of occurrence, development, and manifestation. Soil erosion researches also have geographical features because of uneven science and technology development levels among countries, and different hazard extents of soil erosion. In view of the increasingly serious threats on human living and survival environment, soil erosion has already been taken as a global major issue and gotten highly attentions among governments and academia. Since the latter 20 th century, international scholars conducted massive quantitative simulations, predictions, and risk assessments using various models in soil erosion field; quite a lot quantitative researches also employed using radioisotope tracers. The mentioned achievements, on the other hand, make us realize how serious the soil erosion is.Global climate changes will alter the structure, function, and even the pattern of global terrestrial ecosystem. As an increasingly prominent problem all over the world, the intensity variability of soil erosion under different climate conditions becomes a focus point. For examples, the environment effect of soil erosion is crucial research goal and content in all the major four international scientific plans（WCRP, IGBP, IHDP, and DIVERSITAS）. Currently, as to the coupling relation between soil erosion and climate changes, foreign researchers mainly adopt various models to simulate and predict the soil erosion trend under different climate situations. However, the response of soil erosion to future climate changes is uncertain due to the unsynchronized global climate changes aroused by natural environment differences among countries. In China, researches of response of soil erosion intensity to future climate changes are also conducted using model simulation and prediction, and the results, therefore, have uncertainties. On the other hand, the studies on relationship between soil erosion intensity and climate changes at the geological history scale are limited and controversial. Therefore, a geological indicator is needed to simultaneously reflect both the climate changes and soil erosion evolution in geological history times, to clearly understand the causes and driving forces of soil erosion, and to provide references to the issue of how soil erosion would be affected by future climate.The Loess Plateau, as a region with the most severe soil erosion, as well as a monsoon marginal zone which is sensitive to climate changes, is ideal for the coupling research between soil erosion intensity and climate variability. As a result, identifying the response of soil erosion intensity to climate changes on the Loess Plateau in geological times, is valuable for the ecological protection and conservation in the future. Lake Chaonaqiu is located southwest Liupan Mountain; it is a good spot for ecological environment research because of high latitude and weak human activity disturbance.In this paper, Lake Chaonaqiu was selected to study the relationship between soil erosion intensity and wet/dry climate in small alpine lake catchments in western Loess Plateau. Firstly, the dating method of 137 Cs was used to establish high resolution chronology; then, multiple proxy indicators including particle grain size, TOC, C/N, δ¹³C_org were analyzed to reconstruct precipitation history of Chaonaqiu catchment in the last 300 years; thirdly, series of soil erosion intensity was developed according to grain size variability, and correspondence between soil erosion intensity and climate changes in Chaonaqiu catchment was studied by multiple climatic records comparison; finally, soil erosion pattern that driven by climate changes in Longzhong Loess Plateau was discussed based on comparison studies, and corresponding influences on human activities were proposed to provide example references on how past and future climate changes affect soil erosion.Main achievements are list as the following:（1） we employed sedimentary grain size, δ¹³C_org, TOC, C/N ratio and other proxy indices to reconstruct a precipitation time-series spanning the last ³00 years. The results correlate well with the records of tree rings and historical documents in neighboring regions.（2） We showed that the lake oscillated between two states, i.e., higher vegetation coverage prevailed during wetter periods, which promoted weaker catchment soil erosion. In contrast, during periods of drier climate, lower vegetation coverage promoting higher soil erosion and more terrestrial materials input into the lake, resulting in coarser sedimentary grain size.（3） Several intensive soil erosion events were identified in the sediment cores, such as ¹770AD, ¹835AD, ¹950AD, and ¹970AD. Most of these events occurred during decadal/multi-decadal dry periods, and corresponded with flood events documented in the historical literatures, indicating that erosion of catchment soil by flood events is particularly intense during dry spells, possibly related to the sparse vegetation cover during dry condition.（4） The well correlation between the precipitation and soil erosion of the last ³00 years in Lake Chaonaqiu and the Drought/Flood variations of Longzhong Loess Plateau may reflect the response pattern of soil erosion to climate change over the Longzhong Loess Plateau.