2005-2019年洞庭湖平原耕地面源污染迁移轨迹及空间格局

洞庭湖平原因不合理的农业生产活动导致严重的耕地面源污染问题，揭示洞庭湖平原近10余年耕地面源污染迁移轨迹及空间格局，可为洞庭湖平原下一步科学防治耕地面源污染提供参考。该研究以洞庭湖平原湖南省部分的21个区（县、市）为实例，利用清单分析法构建农田化肥、人畜排泄物和农田固废3类污染单元，测算化学需氧量（Chemical Oxygen Demand，COD）、总氮（Total Nitrogen，TN）和总磷（Total Phosphorus，TP）3类污染物排放情况，并运用空间分析、重心模型和冷热点分析研究2005－2019年洞庭湖平原耕地面源污染轨迹迁移变化及空间格局。结果表明：1）从时序上看，2005－2019年间3类污染物排放总量和排放强度总体上均呈现下降趋势；从空间分布上看，COD排放强度等级分布更为集中，洞庭湖平原耕地面源污染程度呈现出“东部>西部>中部”的空间格局；2）从重心模型分析来看，3类污染物排放强度重心在东西方向上的移动更显著，并且重心移动速度呈现阶段变化；3）从冷热点分析来看，3类污染物空间分布格局差异性显著，COD最为明显，TP次之，TN最小，热点区域大多分布于洞庭湖平原东部，冷点区域大多分布于洞庭湖平原中部。研究说明了在生态文明建设过程中，洞庭湖平原耕地面源污染情况有所好转，并且各地区耕地面源污染程度和治理都具有差异性，为今后因地制宜地治理耕地面源污染提供理论依据和思路。

Migration trajectory and spatial pattern of cultivated land non-point source pollution in Dongting Lake Plain from 2005 to 2019

The Dongting Lake Plain is one of the most important food production bases in China. However, the non-point source pollution has posed a great threat to social and economic development in the cultivated land, due to a large number of chemical fertilizers and pesticides that have widely been used unreasonably during agricultural production in recent years. It is also very serious for the pollution of livestock and poultry breeding. Taking 21 county-level administrative units in part of Hunan Province in the Dongting Lake Plain as the research area, the inventory analysis was made to construct three types of pollution units for the farmland fertilizer, human and livestock excrement, as well as farmland solid wastes. Some parameters were calculated, including the total emission and intensity of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The temporal and spatial evolution of non-point source pollution was determined in the cultivated land, further to analyze the movement trajectory of emission intensity barycenter and the degree of spatial agglomeration, using the center of gravity model and the cold/hot spot analysis. The results showed that: 1) There was a great decrease in the total emissions and emission intensity of COD, TN, and TP from the cultivated land non-point source pollution in the study area from 2005 to 2019. It was related to the promotion of ecological farming, soil testing formula technology, as well as the scale control of livestock and poultry breeding. There were also the spatial distribution characteristics of "east>west>central" in the pollution degree for three types of pollutants. 2) Three types of pollutants all moved in the longitude and latitude directions, but there was a more obvious in the east-west direction, where the barycenter of emission intensity presented a tendency to run westward. The adjustment and implementation of pollution prevention policies were attributed to the shift of the barycenter of the emission intensity in the three pollutants. 3) There were significant differences in the spatial patterns of the three pollutants. Specifically, the COD pollution was significantly different, TP was followed, and TN was the smallest in various regions. Hot spots were mostly distributed in the east of the Dongting Lake plain around the basin. The main reason was that these areas were on the edges of the intersection of the Dongting Lake and the Yangtze River, with advantageous location, rapid urbanization and industrialization, and stronger arable land utilization. The cold spots were mostly distributed in Nanxian and the surrounding areas in the middle of the Dongting Lake Plain. The concept of ecological civilization was contributed greatly to the distribution. As a result, much attention needs to pay to the treatment of non-point source pollution in the cultivated land and surrounding counties. Consequently, the non-point source pollution was improved in the cultivated land in the process of ecological civilization construction. There was also a great difference in the degree and control of cultivated land non-point source pollution in various regions. The finding can provide a sound theoretical basis to manage the non-point source pollution of cultivated land.