Abstract:

This study was conducted in the Huoditang natural forest area, which is a part of the forest water supply region for the Middle Line of the South to North Water Transfer Project. The area is located at a medium altitude across the southernslope of the Qinling Mountain range. Stream water samples were collected at the outlets of two small watersheds and two tributaries in the area over an eight year period. Annual changes in stream water chemistry were analyzed and possible causes for these changes were proposed. The results showed that the pH value of the stream water in the Huoditang natural forest area tended to decrease during the sampling period. In contrast, NO^3-, NH⁺⁴, Ca, Mg, Cd and Pb concentrations tended to increase. The changes in the pH value and NO^3-, Ca, Mg, Cd concentrations could mainly be attributed to pollution from local vehicular traffic. The concentration of Pb in stream water increased during this period. We attribute this to an increase in the release of Pb from soil and minerals as the pH value of rainwater declined. The K, PO^3-4, Na, Mn and Zn concentrations in stream water tended to decrease during the observation period. These changes are probably related to the revegetation of the forest. According to the results of this case study, we predict that the stream water pH value in the forest water supply region for the Middle Line of the South to North Water Transfer Project will tend to decrease while the concentration of NO^3-, Ca, and Mg will tend to increase. The changes in these factors will not be large enough to have a significant adverse impact on water quality however. At the same time, K, PO^3-４, Na, Mn and Zn concentrations will tend to decrease. That decrease in PO^3-4 concentrations will help to reduce the probability of water eutrophication in the Danjiangkou Reservoir, the main water storage area for the the Middle Line.The Cd, Pb concentration in stream water will tend to increase, and this problem must be addressed, even if the change is very small.

Key words: the Middle Line of the South to North Water Transfer Project, Huoditang, Qinling Mountain, natural forest, water quality, annual change, trend