水里溪上游集水區土地利用與溪流水中硝酸鹽濃度關係之探討

The purpose of this paper was to study the relationship between land use and nitrate concentration of streamwater in the upper Shiu-Li creek watershed. The results showed there was a positive relationship between the nitrate concentration of streamwater and stream discharge. The nitrate concentration increased with the increased discharge. The most dominant land use type in the study area was forestland, and the other following types were betel nut plantation, built site, and grassland, respectively. These land use types were closely related to the historic change of local agricultural development. In addition, based on Pearson correlation analysis, there was a positive relationship between the nitrate concentration of streamwater and proportion of agricultural land use areas. Especially, for riparian buffers with a width of 25 m and 50 m, the proportion of betel nut plantations and nitrate concentration of streamwater had a very significant positive correlation. Because most betel nut plantations were near the streamside we suggest establishing a forest protection strip with a width of 50 m around streams to reduce nutrients flowing into stream from upland brought by runoff and sediments. The forest protection strip can intercept sediments and filter water quality. Besides, we should pay attention to location selection of agricultural sites and practice methods of fertilization and cultivation. Therefore, sustainable development of watershed management could be carried out in the future.