Effect of non-point source pollution on water quality of the Weihe River

Non-point source pollution is an important factor that affects the water quality of the Weihe River. To study the effect of the pollution on the water quality of the Weihe River, five flood events and three normal discharge events during non-flood period were monitored from July to December in 2006, at the Lin-tong section. In order to identify how sediment influenced the water quality of the river, raw and supernatant samples taken from the monitored events were analyzed. Supernatant samples were siphoned from 5 cm below the water surface of the raw samples at the lab afterwards the raw samples were shaken up and laid for 30 minutes in the beakers. The results indicated that: 1) The concentrations of SS, COD, TP and TN in the raw samples from flood events were higher than those from normal discharge events. The higher values of the COD, TP and TN in the raw samples resulted from natural humic matters in surface soil. 2) The load transport rate of analyzed water quality indexes increased gradually to its maximum and then drop down, matching that in the discharge hydrograph. The concentrations of SS, NH3-N, NO2-N, NO3-N, COD, and TP in the raw samples increased initially and then decreased, while the concentration of dissolved orthophosphate and TN in the raw samples decreased gradually and then increased. The peak time of concentration and load transport rate of SS as well as COD, TP and TN in the raw samples were close to or lagged behind the time of peak flow. Generally, the peak time of concentration and load transport rate of dissolved orthophosphate, dissolved total-phosphate, NH3-N, NO2-N, and NO3-N occurred prior to the time of peak flow. 3) The mean concentration method was used to calculate the NPS pollution load at Lin-tong section, and the results are credible. In 2006, the proportions of the NPS pollution load to the total load for COD, TP, TN and inorganic nitrogen were more than 30%.