Runoff concentration and load of nitrogen and phosphorus from a residential area in an intensive agricultural watershed.

To evaluate the runoff load of nitrogen (N) and phosphorus (P) in a rural residential area with high N deposition and few wastewater treatment systems in East China, we monitored the concentrations of N and P during 21 rainfall events in a typical village catchment in Jiangsu Province, China. The results showed that the average event mean concentrations (EMC, mg L(-1)) were 6.20 for dissolved nitrogen (DN), 4.18 for nitrate nitrogen (NO3(-)), 0.26 for ammonium nitrogen (NH4(+)), 1.76 for dissolved organic nitrogen (DON), 0.40 for dissolved phosphorus (DP) and 0.32 for phosphate (PO4(3-)). In addition, the annual loads (kg ha(-1)year(-1)) were 24.1 for DN, 16.3 for NO3(-), 1.01 for NH4(+), 6.83 for DON, 1.56 for DP, and 1.25 for PO4(3-). Concentrations of DN and DP in runoff water were 2.57 and 4.06 times higher than those in rainfall, indicating that waste produced by anthropogenic activity was the dominant pollution source of receiving water in rural residential areas. The average discharged concentrations of DN and DP exceeded the Class V surface water quality standard promulgated by the Ministry of Environmental Protection of China, suggesting that the surface runoff should be dealt with for controlling N and P during rainfall events. The runoff characteristics differed among pollutant species, as DP, PO4(3-) and NH4(+) showed medium mass first-flush, whereas that of DN, NO3(-) and DON was weak. These differences should be considered when planning mitigation measures and developing water quality models.