Nitrogen budget and surface water nitrogen load in Changshu: a case study in the Taihu Lake region of China

The Taihu Lake region in China is highly developed, but surface water pollution has become a serious environmental problem in recent years, with nitrogen (N) a major pollutant. To assess the impact of human activity on N cycle and to evaluate the sources of N in surface water in the region, a N-budget for Changshu, a representative county in the Taihu Lake region, was established by using N-related human activities data from an intensive household survey conducted in 2007, measurement data on N fluxes and literature data on other necessary parameters. Chemical fertilizer was the largest N input, accounting for 56.3%. Nearly 30% of the N ended up in surface water. Untreated human and animal waste was the major source of N transported to water. The huge amount of N load to surface water would result in N concentrations of >6.0 mg N L⁻¹ even after denitrification removal in wetlands.