Plateau lake ecological response to environmental change during the last 60 years: a case study from freshwater Lake Yangzong, SW China

Abstract

The effects of anthropogenic activity and climate change on lake ecosystems for nine large plateau lakes in Yunnan Province have recently received much attention; however, most studies have focused on the deepest lake sediments and ignored the lake sediments adjacent to the populated area. To evaluate the sedimentation rates and ecological changes, four 210Pb- and 137Cs-dated sediment cores were collected along the long axis of Yangzong Lake, a fault-controlled north-south strike lake located in Yunnan Plateau in July 2006 and July 2016, respectively. We combined a biological indicator (diatom assemblage) with geochemical indicators (total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP)) for core S0 in the southern part of the lake to examine the ecological changes in response to anthropogenic disturbances within the lake over the last 60 years. The results showed that the sedimentation rate in the southern part of the lake (S1) was significantly higher than that in the central (S2) and northern (S3) parts of the lake. Redundancy analysis (RDA) and Pearson correlation analysis identified significant correlations between TP and Aulacoseira granulata, Cyclotella ocellata, and Cyclotella rohomboideo-elliptica (correlation coefficients: − 0.66, − 0.63, and 0.81, respectively, p < 0.01). There was a clear shift in the diatom community from oligotrophic to eutrophic species becoming dominant after the 1990s, coinciding with the intensifying human activities around the lake. Furthermore, there were two periods of diatom absence in core S0, which was associated with two periods of rapid depositional events. These are likely associated with the intensification of industry, mining, road construction, and agriculture within the lake catchment. These findings highlight the sensitivity of freshwater ecosystems in the shallow-water area of a lake to human activities, with implications for future water quality in fault-controlled lakes.