Relationship between landscape metrics and nitrate concentrations of streamwater in the upper Shui-Li Creek watershed

Healthy watersheds provide a variety of ecosystem goods and services to society, and their ability to regulate discharge and purify fresh water is one of the most tangible and valuable merits. Nevertheless, changes of land use have weakened their ability to perform ecological work. It is widely recognized that degradation of water quality has become a major environmental issue in Taiwan. Deterioration of water quality is closely related to the land use in the surrounding watershed. It is urgent to understand the relationship between land use and in-stream water quality. In this study, the landscape patterns of five watersheds in the upstream watershed of Shui-Li Creek were quantified by the way of landscape metrics. In addition, correlation analysis was performed to identify the relationship between landscape metrics and nitrate concentrations. The results of data analysis indicate that nitrate concentrations increase when the patch edge of built-up becomes longer. When the patch area of grassland is bigger and its connectivity is better, the nitrate concentration is lower. Nitrate concentrations also increase when the patch shape of betel palm plantations become more irregular. This may result from fertilization and washout of surface runoff. When the percentage of farmland is high, there are higher nitrate concentrations in the stream, which may also result from the use of fertilization. Therefore, it could be suggested that landscape metrics are useful in understanding in-stream water quality.