| The southern slope of Qingling Mountain is the main water source for the Middle Route Project in South-to-North Water Diversion. The Huoditang forest area is situated in the center of the middle southern slope of Qingling Mountain, where the conditions of water amount and quality have important effects on society and economy. Therefore, during from 2002 to 2004 we conducted some integrated research on forest hydrological effects in the area. Based on studying the hydrological processes in the Huodigou watershed in the area, we built the models revealing the variations of precipitation and runoff with time, and analyzed the correlativity between precipitation and runoff. Also we analyzed the qualities of different kinds of water and classified them with fuzzy algorithmic integrated evaluation approach. The results show that: (1) According to the annual runoff characteristics in the Huodigou watershed, the hydrological condition in the area can be divided into three periods: lacking-water runoff period (from November to March next year), runoff accounting for 11.2% of annual runoff, mainly underground runoff varying little; snowmelt runoff period (from April to may), runoff accounting for 9.1% of annual runoff, including underground, snowmelt and less rainfall runoff, mainly snowmelt runoff; and flood runoff period (from June to October), runoff accounting for 79.7%, including underground and rainfall runoff, mainly rainfall runoff. The annual variations of runoff in the Huodigou watershed are affected by air temperature and precipitation. And the conserving-water effect of forest greatly regulates the dynamics of runoff in the watershed. (2) The water quality of runoff does not significantly differ among the four forestry watershed. The differences in the water quality between precipitation and runoff in the forestry watershed are significant, reflected from the six indexes: Na, Mg, Ca, K, BOD and pH value, which show that the water quality has been greatly changed after precipitation passes through forest ecosystems. (3) There are not significant differences in the water quality between runoff in the farmlands and precipitation, but significant between they and runoff in the forestry watershed, dependent on the seven indexes: Mg, Ca, K, total N, COD, BOD and pH value. It shows that the effects of forest ecosystems and agricultural ecosystems on water quality are significantly different. (4) Within the Huodigou watershed, the total matter input from precipitation is 191.361kg/hm2'a and the total matter output from runoff is 218.110kg/hm2-a. The total matter input is more than the total matter output. Thus, there are 82.1% Zn, 98.8% Fe, 94.7% Cd, 91.0% Pb, 79.8% ,total N and 70.6% Na are stored. However, for Mg and Ca, the stores decrease because of the more runoff outputs than precipitation inputs. (5) Within the Huodigou watershed the mean concentrations of BOD and COD in runoff are less 6.99 mg/L and 14.66mg/L respectively than those in precipitation, i.e. decreasing 94.8% and 69.0% respectively. The mean concentration of DO in runoff in the watershed is more 1.38 mg/L than that in precipitation, i.e. increasing 19.9%. There exist also the same rules in the other forestry watershed. These show that forest ecosystems can regulate the concentration of oxygen balance index in precipitation, thus improve the water quality of precipitation. (6) Based on the fuzzy algorithmic approach, the six indexes Zn, CODcr, DO, Cd, Pb and NH4+-N were used to make an integrated evaluation to runoff in the forestry watershed, runoff in the croplands and precipitation. The results show that for the runoff in the forestry watershed, the water quality is evaluated as the first class, i.e. the water with excellent quality without being polluted; for the runoff in the farmlands, the water quality the second class, i.e. the water being slightly polluted; and for precipitation, the water quality the third class, i.e. the water being polluted in a certain degree.
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