The responses of alpine lake ecosystems to combined climate and human impacts are ecologically important to understand. It is necessary to differentiate natural, climate-forced ecosystem changes from those driven by human disturbance with a long-term (i.e. 102–103-yr) perspective. Here a14C, 210Pb and 137Cs-dated sediment core covering approximately 2500 years was analyzed for diatoms, pigments, cladocerans and geochemistry in Lugu lake-catchment in southwest China to examine the response of the lake to climate change and human impacts. Between 1000 and 1300 AD, a warming climate coupled with declining summer monsoon precipitation resulted in the increase of oligotrophic taxa and low catchment runoff. Prior to 1300 AD the lake ecosystem was primarily responding to natural, regional climate-related processes. After 1300 AD, the clear ecological shifts and reorganizations in community structure across multiple trophic levels suggest that major transitions took place in the Lugu ecosystem. An increase in Poaceae (grass) pollen from 1300 AD indicates human settlement in the area, and is followed by rapid decline in Tsuga, most likely a consequence of logging. Use of change point analyses of the multi-proxy data demonstrate that the lake ecosystem has been highly variable since 1300 AD and exhibiting enhanced vulnerability to both natural and anthropogenic disturbance. Our results suggest that agriculture-climate interactions played a major role in the ecological transitions over the last ～700 years. This conclusion provides insight into how the anthropogenic land-use intensity, vegetation cover and surface erosion fluctuated with natural temperature and precipitation change over the past 2000 years.

Qian Wang, N. John Anderson, Xiangdong Yang, Min Xu. 2020. Quaternary Science Reviews. DOI: https://doi.org/10.1016/j.quascirev.2020.106238.