Land-Use,Stream Order And Stream Water Quality

With the development of agriculture and industry, the pollution of river ecolsysem becomes more and more serious. The low order stream is the main water source of rivers, and holds the most extensive area in the drainage basin, is the main reason that arose the non-point source pollution of river ecolsystem. Identification of the key causes of low order stream pollution could offer theory basis for the water pollution control. Stream water was sampled along the Ash River continuum from 1st order to 5th order in Shangzhi City, Heilongjiang Province, China for three times in spring, summer and autumn respectively. The concentrations of NH₄⁺-N, NO₃^--N, total dissolved inorganic nitrogen (TDIN-N, including NO₃^--N, NH₄⁺-N), PO₄³--P and total phosphorus (inorganic and organic phosphorous, TP), pH value, DO, turbidity, temperature were analyzed. The related environmental settings and stream order were recorded for each sampling location. Comparisons of stream water quality under different land use and of different stream orders were made, and analyzed the seasonal change of stream water quality. The results showed:The difference of stream water quality under different land use was found. The water quality of the forested stream was better than that of the cropland and town area stream, the NO₃^--N, TDIN concentration, pH value, turbidity and temperature in the forest stream was relatively low. But the concentration of PO₄³--Pn TP were relatively high, even significant high in the summer, and DO was relatively low. Comparison between water quality indexes of cropland streams vs. town area streams showed that the difference was small, thereinto, the concentration of NH₄⁺-N,PO₄³--P, TP were slightly higher than, the concentration of NO₃^--N, TDIN, pH value, DO were lower than those of the town area streams. There was difference between streams of different stream order. The water quality of 1st, 2nd order stream was better, pH value, DO, turbidity, temperature were lower than those of other order streams, other indexes were in the middle of those of other order streams. The water quality of 3rd order stream was maily impacted by the stocking, the concentration of PO₄³--P, TP and temperature were significantly higher than those of other order streams (p<0.05). The water quality in 4th order stream was influenced by the fertilization, thereinto the concentration of NO₃^--N, TDIN were significantly greater than those of the lower order (1st through 3rd) that in summer (p<0.05). pH value, DO, turbidity, temperature in the 5th order stream were significantly higher than those in the low order stream (p<0.05), no consistentvariety rule was found in other indexes, but they were higher than those in low order stream in the while.With the change of seasons, in the while, the stream water quality displayed certain change trend. The concentration of NH/-N first decreased then increased, while N03"-N^ TDIh^ PO43'-P> TP^ pH value increased all the while, TDIN, N/P, and DO decreased, turbidity and temperature first rised then fall. The range of change in water quality indexes was different under different land use and different stream order.