Optimization of management strategies for reducing nitrogen loading in China

Terrestrial Nitrogen (N) loading in the environment has seen a steady increase over the past several decades as a result of more intensive anthropogenic activities. Quantifying N loading for an extended period is important for effective N management. In this study, a statistical model is constructed to describe the relationship between N loading and anthropogenic activities at watershed scale for 211 watersheds covering the entire land area of China. Subsequently, a portfolio optimization model is used to optimize the future management efforts of the long-term N loading. Our results show that N loading in China due to anthropogenic activities has increased significantly over the past 60 years (1949-2010), with the rate of increase at approximately 1 Tg N/year. When designing future N loading management strategies, the next 30 years is divided into three temporal stages and assume that the total amount of expenditure is fixed. The results of portfolio optimization analysis show that the best allocations of management efforts (e.g. capital investments, making new policies, improving technology, or alike) among three temporal stages are 28.55% (2021-2030), 71.45% (2031-2040) and 0 (2041-2050). Furthermore, it is suggested that the future population growth scenario has the largest influence on the results of the portfolio optimization analysis.