Using stable nitrogen isotopes to reproduce the process of the impact of human activities on the lakes in the Yunnan Guizhou Plateau in the past 150–200 years.

Nitrogen deposition in lake sediment is an important factor reflecting the evolution of lake environments. Over the past 150–200 years, lakes in China have been affected by natural factors and anthropogenic factors, and nitrogen deposition has increased. As a result, it is critical to reconstruct the spatiotemporal variation trend of nitrogen deposition and analyse the nitrogen source and driving factors. On a regional scale, based on the sediment TN, δ15N and C: N ratio variation trends, this study analysed the buried nitrogen variation trend in Yunnan-Guizhou Plateau lakes over the past 150–200 years. The effects of lake morphology on nitrogen deposition were also analysed by using natural lake parameters. At the watershed scale, the δ15N isotope in the sediment was used to distinguish the sediment sources. On this basis, this study analysed the relationship between nitrogen deposition in nine lakes and the socioeconomic conditions during 1949–2010. The results show that (1) during the last 150–200 years, the TN, δ15N and the C: N ratio in the sediments increased. (2) Lake depth and area are the main natural factors affecting the extent of nitrogen deposition. (3) Before 1950, the nitrogen in the lake sediments in the region was sourced mainly from natural sources such as precipitation, woodland, grassland and aquatic plants. After 1950, man-made sources such as sewage and farmland became the main sources of nitrogen. (4) Human social and economic activities have an increasingly significant influence on the lake water environment in the Yunnan-Guizhou Plateau and are also the main factors leading to the deterioration of the aquatic environment. Unlabelled Image • The nitrogen deposition in YGP lakes have increased significantly over the last 150–200 years. • Lake nitrogen deposition and its increase rate varied significantly among different lakes in the YGP. • The TN changes were affected by recent human activities and environmental policies. • The controls on lake nitrogen deposition varied among different lakes in the YGP. [ABSTRACT FROM AUTHOR]