Abstract
Nitrogen outflow and its variance after rainfall events were investigated at the small watershed with pig farms. The unlined storage ponds are used to store animal waste in this area. The area of watershed is 15.3 ha and the number of pigs is about 800. Pig stocking density is 52 head/ha. Water sampling and measuring of discharge was conducted for 70 days by parshall measuring flume and automatic water sampler. Nitrate nitrogen concentrations were very high during ordinary time unaffected by rain, and the average was 44.8 mg/L. After rainfall, the discharge increased rapidly, and decreased gradually almost within a few days. During the period affected by rain, nitrate nitrogen concentration decreased by dilution, and the average value in this period was 34.5 mg/L. Nitrate nitrogen load increased during this period, because the load was washed out by rain. The average concentration of total flow was 42.5 mg/L, which correspond to 95% of the value of ordinary flow. This shows that the concentration at the ordinary time may be used for presumption of the total amount of outflow load at this watershed.
