Spatiotemporal variation and influencing factors of nitrogen and phosphorus in lake sediments in China since 1850

Chinese lakes have been affected by climate change, agricultural intensification and population increases since 1850. However, the spatiotemporal variations in nitrogen and phosphorus in lake sediments and the factors influencing these variations are poorly understood. This research analysed the spatiotemporal variations in the mass accumulation rate (MAR) and total nitrogen (TN) and total phosphorus (TP) concentrations of sediments since 1850 and the responses of these factors to the influence of natural and anthropic factors through the collection of data from 56 lake sediment samples in China. After 2000, the average MAR value (2794 g/m(2)/yr), TN concentration (0.35%) and TP concentration (0.96 & PTSTHOUSND;) of lake sediments were significantly higher than the average values during 1850-1900 (p < 0.05). During the study period, the MAR of the lake sediments in the eastern plain (EP) was the highest in the country, and the increase was also largest in this region. The TN concentrations of lake sediments in the Northeast Plain (NEP) were the highest in the country, and the TN concentrations of lakes in the Yunnan-Guizhou Plateau (YGP) underwent the largest increase. The TP concen-trations in the sediments of the YGP were higher than the national average during the study period, and the lakes in the NEP had the highest increase in TP concentrations. The result showed climate and lake morphology are important factors controlling the indices in lakes' sediment in Qinghai-Tibet Plateau (QTP) since 1900. Climate and lake morphology are major impact factors for lakes' sediment indices in NEP, EP, Mongolia-Xinjiang Plateau (MXP) and YGP in 1900-1950. After 1950, anthropic factors gradually replaced natural factors and became the main factors affecting these four regions and anthropic factors promoted the increase of nutrient concentration in lake sediments. The results of this study show that sustainable agricultural development policies and population policies can help control the quality of nutrients entering lakes, thereby reducing the concentrations of nutrients in lake sediments in the future.