水里溪上游集水區溪流水質的空間變異分析

The purpose of this study was to understand the spatial variability of stream water quality in the upper Shui-Li Creek watershed. Monthly stream discharges were investigated and water samples were collected at 5 monitoring sites in the study area during the period from January 2004 to February 2005. From the samples, 14 stream water quality parameters were analyzed, including conductivity, pH, water temperature, dissolved oxygen, cations (Ca(superscript 2+), Mg(superscript 2+), Na(superscript +), K(superscript +), and NH4(superscript +)) and anions (F(superscript -), Cl(superscript -), SO4(superscript 2-), NO3(superscript -), and HCO3(superscript -)) ionic concentrations. The multivariate statistic methods including factor analysis and cluster analysis were applied to analyze stream water quality characteristics. Results showed that stream water had weak alkalinity. Dominant cations of stream water were Ca(superscript 2+) and Mg(superscript 2+), while dominant anions were HCO3(superscript -) and SO4(superscript 2-). Conductivity, concentrations of Na(superscript +), Ca(superscript 2+), Mg(superscript 2+), and HCO3(superscript -) in stream water decreased with the increase of discharge. However, concentration of NO3(superscript -) increased with the increase of discharge. Higher SO4(superscript -) concentrations at the monitoring sites of WC-4 and WC-5 were primarily due to different geological characteristics. On the basis of factor analysis, stream water quality in the study area was closely related to geologic weathering, runoff pathways, human activities, air temperature change, vegetative functions, and atmospheric deposition. In addition, monitoring sites were classified into 3 groups using cluster analysis.