A Strategy For Nitrogen Pollution Control In Shixi Creek Watershed Using In-situ Monitoring And QUAL2K Model

Water is an important natural resource for human survival and is at the core of sustainable development.However,Climate change and human activities have caused serious water shortages and water pollution problems.A great number research focuses on large and medium watersheds and lakes and reservoirs in China.Few case strategy for nitroen pollution control of creek watershed using in-situ monitoring and model.So,evaluation spatio-temporal variability in water quality and identifying key impact factors and controlling source of pollution,would provide a technical basis for N pollution control of creek watersheds,and set an example for others to follow.Shixi watershed in the upstream of Jinjiang River was selected for in-situ monitoring,multivariate statistical analysis,geographic information technology,water quality model,and scenario analysis will be used for planning N pollution control approach for Shixi creek watershed.The major results are as follows:Both riverine nitrogen forms and concentrations showed significant spatiotemporal variations.Based on water quality monitoring analysis conducted 27 times from March 2017 to March 2019,nitrogens in the Shixi creek watershed as NO3--N and NH4+-N,The component that contaributed the most to the nitrogen pollution was NO3--N in both upstream and downstream,and was NH4+-N in midstream.The concentrations of nitrogen were found in following order:midstream>downstream>upstream.The nitrogen concentrations found in tributary was higher than that found in mainstream.The nitrogen concentrations found in left bank was higher than that found in right bank.The average concentrations of TN and NH4+-N were highest in the winter,and were lowest in the summer.The average concentrations of NO3--N and NO2--N were highest in the spring,and were lowest in the fall.The Interannual variations showed that the concentration of NH4+-N decreased slightly,the concentration of NO3--N decreased sharply,and the concentration of NO2--N increased significantly.The results of water quality impact analysis reveled that Built-up and Agriculture areas were relevantly positive related to water quality.Forest had a positive effect on water quality.In flood season,Argriculture activities caused nitrogen pollution in flood season.In non-flood season,Forest coverage positively affected the levels TN;Land use for Argriculture and Orchards coverage negatively affected the levels NH4+-N;Built-up,Argriculture and Orchards coverages negatively affected the levels NO3--N.The streamflow was significantly negatively correlated with the concentrations of nitrogen pollution indicators.QUAL2K model was integrated with scenarios analysis to simulate the water quality and to develop its controlling measures for watershed governance.Based on the characteristics of Shixi creek watersheddivided six simulated sections,and the tributaries were generalized as point source inputs.The domestic sewage,livestock wastewater and agricultural wastewater were generalized as non-point source inputs.Using the monitoring data collected from the spring,summer,fall and winter of 2017,the model parameters nitrification rate and denitrification rate were corrected.The monitoring data collected from the spring,summer,fall and winter of 2018 were used to validate.The results demonstrated that the QUAL2K model is useful in the Shixi creek watershed.The results of scenarios analysis showed that the Shixi creek watershed achieved a 34%reduction of pollution sources,a reduction of 65%of domestic sewage,a reduction of 98%of livestock wastewater,A more than 25%reduction of domestic sewage,and a more than 55%livestock wastewater,the water quality of the outlet can be upgraded to the level Class ?.It is believed that the TN concentration can reduce by 3.2-45.5%,NH4+-N concentration can reduce by 4.6?50.4%,and the water quality can be upgraded to the level Class ? by application of some controls(small water ditch,construction of sewage treatment plant,and setting up rural decentralized sewage treatment facilities).In addition,the water quality of Shixi creek watershed can also be improved by shutting down the livestock,reduce the domestic sewage,and implemente ecological restoration measures.