[Temporal and spatial variation of nitrogen and phosphorus and eutrophication assessment in downstream river network areas of North Canal River Watershed].

Based on the water quality survey for one year in the downstream river network areas of North Canal River Watershed, variation features of inorganic nitrogen (N) and phosphorus (P) were analyzed, and water eutrophication degree of river network areas was also assessed. The results showed that the average concentration of TN was 12.50 mg x L(-1) (NH4(+)-N, 67.41%); TP was 1.45 mg x L(-1) (SRP, 80.81%). The temporal and spatial variations of N and P in the river network areas were obvious. Various forms of TN and NO3(-)-N concentrations almost had a similar change by month; NH4(+)-N was a little different; TP and SRP also had a similar change. The concentrations of N and P all decreased gradually from water coming region to water leaving region, TN, NH4(+)-N and NO3(-)-N decreased from 19.30, 13.22 and 2.19 mg x L(-1) to 7.98, 4.45 and 1.50 mg x L(-1) on average, respectively; TP and SRP were from 1.95 and 1.59 mg x L(-1) to 1.11 and 0.91 mg x L(-1). Water eutrophication degrees of river network areas were all the highest level at both temporal and spatial scale.