Temporal-spatial Patterns Of Nitrogen Concentrations In Pond And Reservoir Water And Their Dominant Factors In A Small Watershed In Subtropical Hilly Regions,China

The problem of agricultural non-point source pollution has become the focus of attention of all walks of life.Effective prevention and control of agricultural non-point source pollution was a problem that we need to solve urgently.Most of the current researches mainly deal with agricultural non-point source pollution by using ecological ditches,gully ponds and constructed wetland systems,and few researches on "still"ponds and reservoirs.In the natural state,ponds and reservoirs can intercept pollutants such as solid particles and nutrients caused by rainfall-surface runoff,relieve agricultural non-point source pollution and improve surface water quality.Based on the analysis of the Arc-GIS software and its location,the field sampling and the water quality measurement and analysis,the paper carried out the research about pond and reservoir system based on the observation of the Ammonia Nitrogen,Nitrate Nitrogen,Total Nitrogen and Particulate Nitrogen under the domination of different sources of pollution.Based on the factors of water environment and land use types data that were related to the ponds and reservoirs system in the study area,and to explore the temporal-spatial patterns concentrations of nitrogen in pond and reservoir water during the observation period,and the dominant factors were analyzed and confirmed their ability to explain the contribution rate by RDA analysis.Eventually,it would provide the basic data support for the contribution of nitrogen consumption insubtropical hilly regions and clarify the nitrogen biochemical processes in the watershed.The main conclusions are as follows:(1)During the observation period,the time variation of nitrogen concentration in pond and reservoir water was significantly different.The concentrations of ammonia nitrogen,nitrate nitrogen,total nitrogen and particulate nitrogen both reached the maximum in June and then decreased.The changes from July to October were more significant smooth,and then to a slight increase in November,and then the concentration continued to decrease.Corresponding to the spatial distribution pattern of nitrogen concentration in pond and reservoir water,the concentration of nitrogen from the upstream of the river and its tributaries to the downstream of pond and reservoirwas gradually increased.(2)During the observation period,the sources of pollutants(land use type),the area ratio of ponds and reservoir,and the population of ponds and reservoir were the main internal influencing factors of nitrogen concentration in ponds.Affected by the source of the pollutants,the nitrogen concentrations in different types of ponds from small to large were sorted into the forest ponds<the farmland ponds<the fish ponds<the tea garden ponds.The area ratio of ponds and reservoir in small watershed has an important effect on the nitrogen output concentration of small watershed.The larger the area ratio,the lower the nitrogen output.The more the population of ponds and reservoir catchment,the greater the nitrogen concentration in the ponds and reservoir watershed.(3)The water environment factor was the main external influence factor of nitrogen concentration in pond water.Phytoplankton and naturally growing plants were affected by DO and water temperature.The higher the DO,the higher the nitrogen concentration in ponds water.The growth of cultured animals and phytoplankton in pond and reservoirwater could be controlled by controlling the water temperature.(4)During the observation period,the order of explanatory power of each factor on the variation of nitrogen concentration in pond and reservoir water was as follows:land use>population>pond area ratio,indicating that the type of land use has a great influence on the nitrogen concentration in pond and reservoir water.It was an effective measure to control the agricultural non-point source pollution by controlling the areaproportion of ponds and reservoirs,and adjusting the nitrogen emission in residential areas and rationally planning the landscape pattern of ponds and reservoir in the basin.It showed that the natural pond system was an important natural ecosystem for alleviating agricultural non-point source pollution.