[Uncertainty analysis of water environmental capacity in the nonpoint source polluted river]

Based on the one-dimension model for river water environmental capacity (WEC) and the statistical analysis of the measured hydrological and water quality variables, a uncertainty analysis method for the WEC in nonpoint source polluted river was developed, which included the sensitivity analysis for input parameters of the model and the probability distributions analysis for the WEC using Monte Carlo simulation approach. The method, which described the uncertainty derived from the adopted information of the river system and the randomicity from the occurrence of nonpoint source pollution, could provide different WEC combined with reliabilities for different hydrological seasons. As a case study, the total nitrogen (TN) WEC in the Changle River located in southeast China was calculated using the method. Results indicated that the TN WEC with 90% of reliability were 487.9, 949.8 and 1392.8 kg x d(-1) in dry season, average season and flood season, respectively, and the dilution effect of river water flow accounted for the main content of WEC. In order to satisfy water quality target of the river, about 1258.3-3591.2 kg x d(-1) of current TN quantity that entered into the river should be reduced in watershed, and the largest reducing quantity of TN was occurred during flood season. The uncertainty method, which reflected hydrology and water quality variations in the nonpoint source polluted river, provided a more reliable and efficient method for the WEC calculation.