基于GIS的福建农田氮磷地表径流流失与污染风险评估

GIS-based pollution risk assessment of nitrogen and phosphorus loss in surface runoff in farmlands in Fujian Province

为了掌握福建省农田氮磷地表径流流失特征,以福建省的9个地级市为研究边界,通过对其辖区1985—2016年间农田氮、磷化肥施用量的调查,计算农田化肥氮磷的地表径流流失量,并在耦合农田化肥地表径流流失量、降雨和河网密度3个因素的基础上,分析福建省各地级行政区域农田化肥氮磷的污染风险等级,应用地理信息系统(GIS)分析其氮、磷污染的空间分布。结果表明:32年间福建省化肥施用量由4.911×105 t增加到1.239×106t,年均增长3.03%;漳州市氮肥和磷肥的施用强度最大,分别达880.40 kg×hm^(-2)和429.21 kg×hm^(-2);氮磷地表流失量较高的区域主要集中在漳州市,其氮、磷地表流失强度分别达8.71kg×hm^(-2)和1.99kg×hm^(-2)。从氮、磷污染风险等级看,南平市氮、磷肥的流失风险值均最高,分别达63.19%和63.37%,属于高氮磷污染风险区域;厦门市氮、磷肥的流失风险值均最低,分别为0.53%和0.53%,属于低污染风险区域;其他市处于两者之间。可见,漳州市农业发展中应注重氮、磷肥的减量化;南平市则注重对农田氮、磷地表径流流失的风险防范;全省应加大力度发展生态农业,以助力福建省生态文明先行示范区、生态文明试验区的建设。

Nitrogen and phosphorus loss in surface runoff from farmlands has been the main cause of water eutrophication.Fujian Province is one of the regions with the highest intensity of fertilizer application per unit area of land in China.The subtropical monsoon climate zone and hilly region with heavy summer and autumn rains on steep hill-slope farmlands in Fujian increase the risk potential for pollution.Thus to analyze current conditions and characteristics of nitrogen and phosphorus loss in surface runoff from farmland in Fujian Province,we selected nine prefectural level cities in Fujian Province as the study areas to estimate the loss of nitrogen and phosphorus in surface runoff in farmlands based on investigated data of fertilizer use in the cities for the period from 1985 to 2016.By integrating the three factors of pollution risk(fertilizer loss,rainfall and drainage intensity),we evaluated nitrogen and phosphorus pollution risk from farmland fertilizer to determine critical areas of primary concern.We used the ArcGIS platform to make thematic maps for visualizing the spatial distribution of contaminated areas by nitrogen and phosphorus.The results showed that fertilizer application in Fujian Province increased during the 30-year period from 4.911×10^5 t to 1.239×10^6 t,with an annual average rate of increase of 3.03%.The amount of fertilizer use in Fujian Province was highest(1.243×106 t)in 1999,accounting for 3.01%of total fertilizer use in China.The intensities of nitrogenous and phosphate fertilizer use in Zhangzhou City were largest,with respective values of 880.40 kg·hm-2 and 429.21 kg·hm-2.The high nitrogen and phosphorus surface runoff were concentrated in Zhangzhou City,which were respectively 1.571×10^6 t and 3.590×10^5 t,with nitrogen and phosphorus loss intensities of 8.71 kg·hm-2 and 1.99 kg·hm-2.However,pollution risk values of nitrogen and phosphate fertilizer were highest in Nanping City,reaching respectively 63.19%and 63.37%-a high risk of nitrogen and phosphorus pollution.Xiamen City had the lowest risk values,respectively 0.53%and 0.53%.The others were in between and in the following decreasing order:Ningde City(57.22%and 54.48%)>Sanming City(53.34%and 53.34%)>Longyan City(51.38%and 51.20%)>Zhangzhou City(46.73%and 46.73%)>Quanzhou City(45.49%and 40.25%)>Fuzhou City(34.35%and 33.80%)>Putian City(18.59%and 16.93%).By using cluster analysis,these nine cities were divided into three groups-heavy to moderate pollution risk(Sanming City,Longyan City,Ningde City and Nanping City),moderate to light pollution risk(Quanzhou City,Zhangzhou City and Fuzhou City)and low pollution risk(Xiamen City and Putian City).We concluded that Zhangzhou City needed to emphasize on reducing nitrogen and phosphorus fertilizer use in agriculture.Nanping City needed to hammer at risk control of nitrogen and phosphorus loss in farmlands.The others cities needed to strengthen the development of ecological agriculture to facilitate the construction of Fujian Experimented Region of Ecological Civilization and the promotion and optimization of control measures of nitrogen and phosphorus loss in surface runoff.