Application of magnetic proxies to reconstruct historical environmental change in catchments of shallow lakes from the Yangtze River Basin, Eastern China

Magnetic proxies have been employed to reconstruct environmental evolution in lake catchments. However, the knowledge about the linkage between magnetic properties of lake sediments and catchment disturbances remains insufficient, which limits the use of magnetic proxies in paleoenvironmental reconstruction. Here, sediment cores from two shallow lakes (Changdang and Xiliang) in the Yangtze River Basin were subjected to detailed magnetic analyses to evaluate whether magnetic signatures of sediment archives can reliably reflect historical changes of human activity intensities and types in their catchments. The results demonstrated that magnetic minerals in sediments of the two lakes were dominated by detrital magnetite, coupled with a minor contribution of high-coercivity minerals. The conventional parameters indicative of magnetic material concentration (χ_lf, χ_ARM, and SIRM) and grain size (χ_fd (%), SIRM/χ_lf) indicated a notable intensification of agricultural activities and the presence of industrial activities in catchments of the two lakes since the 1960s. However, the relationship between these proxies and human activities was complex, with a given proxy exhibiting totally opposite trends forced by different types of human activities, thus limiting the use of these proxies in paleoenvironmental construction. Interestingly, the isothermal remanent magnetization ratio (S₋₃₀₀), a magnetic parameter indicating the relative proportion of high- to low-coercivity magnetic minerals, markedly increased in post–1960s sediments of both lakes, and its values were linearly correlated with catchment GDP and population data. Further, the analysis of previous references suggested this correlation was also present in other lakes. These results together revealed the reliability of using this proxy in indicating anthropogenic disturbance in lake catchments.