Changes in land-leaching nitrogen and its linkages to lake algal blooms in China

Abstract Over the past 50 years, nutrient discharge into freshwater ecosystems has significantly increased due to intensive fertilizer application in China. This has led to frequent environmental issues associated with nutrient enrichment, such as algal blooms, in a number of individual lakes. However, the linkages between terrestrial nutrient sources and algal bloom occurrence (BO) at large scales remains under-explored. Here, we simulated the long-term changes in nitrogen (N) leaching from terrestrial ecosystems using a dynamic vegetation model Lund–Potsdam–Jena general ecosystem simulator at the national scale from 1979 to 2018, and examined its connection to satellite-derived BO in 56 large lakes across China. Our findings reveal that N leaching exhibited significantly increasing trends in 74.5% of the national landmass, with an overall rate of 0.40 kg N ha −1 yr −2 for the past four decades. Using a 95% quantile regression model, we analyzed the linkage between N leaching and BO from 2003 to 2018. The results indicated significantly positive correlations in the lakes of the Yangtze Plain during autumn and the lakes of northern China and the Yunnan–Guizhou Plateau during both summer and autumn. These findings suggest that terrestrial N discharge critically contributes to algal bloom variations in warmer seasons. Our study provides a comprehensive understanding of escalating N discharge from terrestrial ecosystems and highlights the potential benefits of fertilization management in mitigating and controlling inland water eutrophication in China.