Effect of the forest ecosystem on water quality in the water supply catchment for the middle line of South-to-North Water Transfer Project: A case study of the Huoditang forest,part of the medium altitude,southern slope of the Qinling mountain range

The objective of this research is to determine the effect of the forest ecosystem on water quality in the Huoditang Forest, part of the water supply catchment for the South-to-North Water Transfer Project.The effect of the forest on water quality was determined by measuring the water quality of rainfall and stream water collected from tributaries within the watershed and at the watershed outlet.The water flow rate in the streams was also taken into account.From July to October, rainfall was slightly acidic.The pH of the stream water was higher than that of the rainfall and was not affected by flow rate.The concentration of NO₃^-,NH₄⁺, and PO₄^3- in the stream water were lower than in the rainwater, indicating that the forest ecosystem was effective for reducing the level of these nutrients in water.This should reduce the probability of water eutrophication in the Danjiangkou Reservoir, the main water storage area for the South-to-North Project.The forest ecosystem also fixed the heavy metals Cd, Pb and Mn.This is helpful for improving water quality.The concentration of K, Na, Ca, Mg and Fe in the water increased as it passed through the region.The increases in Ca and Mg were especially large.The increases in K, Na, Ca and Mg have no effect on water quality, but the increase of Fe in the stream water improves drinking water quality.The forest ecosystem has the important function for reducing Zn in the water as it passes through the catchment area.There is no relationship between water quality and flow rate.Generally, there is no large change in water quality as flow rate varied.The results from this study show that the water quality is stabilized as it passes through the forest ecosystem.