Acidification of a small stream on Kureha Hill caused by nitrate leached from a forested watershed

Nitrate leakage to a stream from a small forested watershed on Kureha Hill in Toyama Prefecture, Japan was investigated in order to assess its acid-ba se chemistry. Kureha Hill, located in Toyama City, receives high nitrogen l oading from the atmosphere. In this area, there are several small streams c haracterized by a high concentration of nitrate and low ANC. Hyakumakidani, one of the most acidic streams on that hill, the average pH and ANC were 5 .2 and -8 mu eq/l, respectively. The weighted average nitrate concentration , which was 125 mu eq/l, increased up to 370 mu eq/1 during high-discharge periods caused by heavy rainfall, while ANC decreased to -24 mu eq/1 at the same time. Our preliminary study using a two-stage tank model simulating t he flow paths in the soil indicated that during high-discharge periods, the increased subsurface flow containing a high concentration of nitrate contr ibuted to the increased nitrate concentration. In this watershed, the annua l nitrogen budget from Aug. 1998 to Aug. 1999 showed that the loss of nitro gen exceeded the bulk nitrogen deposition, indicating that this watershed i s under condition of nitrogen saturation. However, no visible attenuation h as been observed.