基于流域单元的海湾农业非点源污染负荷估算——以莱州湾为例

Estimation of agricultural non-point source pollution based on watershed unit: a case study of Laizhou Bay

生产力较高、生物多样性丰富、人类利用较早的区域之一,也是全球生态系统中最有价值和最受人类关注的区域之一。同时,海湾也是全球变化反映最敏感、陆海相互作用过程最激烈的地带,是人类活动最频繁的地域。开展海湾入海污染物总量控制研究对保护海洋环境和维护生态健康,协调和促进沿海经济发展与海洋的合理开发利用,实现海洋经济的可持续发展具有重要意义。入海污染物总量是开展海湾环境保护的重要指标,因进入海湾的河流往往较多,河流入海污染物的估算受监测频率、流量的季节变化等因素影响,存在很多困难。农业非点源污染是我国海湾入海污染负荷的重要来源。基于DEM(SRTM Data,90 m分辨率),借助美国ESRI公司的ARC/INFO软件中的ArcHydro模块,进行莱州湾主要入海河流水文分析,利用GIS提取河网,划定流域边界,并划分汇水区和子流域,为流域农业非点源污染入海总量的估算提供基础数据平台。在此基础上,与该流域土地利用专题图叠加,计算各个子流域内不同土地利用类型的面积,利用主要污染物排放系数和入河系数,估算农业污染入海总量。结果表明:COD、NH3-N、TN和TP的每年入海排污总量分别约为236933、23956、53684 t和15922 t。COD、NH3-N、TN和TP的排放量占总排放量的比例分别为71.69%、7.25%、16.24%和4.82%,这说明莱州湾入海主要污染物为COD。在陆海统筹理念指导下,以入海河口为源头,采取溯源追踪的思路,确定影响海湾入海污染负荷的流域单元,提供一种海岸带地区农业非点源负荷估算方法,可为莱州湾入海污染物总量调控提供科学依据,也可作为海岸带综合管理过程中确定陆地范围的参考。

The control of total amounts of pollutants has become an important measure for controlling water pollution in China and is also an important basis for objective management of water resources. Estuary is one of the regions where the productivity and biodiversity are higher and is utilized by human earlier. Estuary is one of the most valuable ecosystems in the world that has attracted human＇s increasing attention. Furthermore, estuary is the most sensitive zone to respond to global changes and a place where the most vigorous interactions between land and sea take place. Estuary is the region where human activities take place more frequently. In particularly, estuaries are the places where a number of rivers enter into seas and receive a large amount of pollutants from lands and human＇s life activities. Thus, estuary and coasts are vigorously disturbed by human activities. Conducting research on controlling total amounts of pollutants that enter estuaries from lands is of great significance for protecting marine environment, maintaining ecological health, promoting coastal economicdevelopment, rationally utilizing marine resources, and for achieving sustainable development of marine economy. Total amount of pollutants that enter seas is an important index for protecting estuary environment. Because numerous rivers flow into estuaries, estimation of total pollutants brought by rivers into sea is influenced by such factors as monitoring frequency and seasonal changes in flow rates. The agricultural non-point source pollution is an important source of pollution load that enter the estuaries in China. Based on DEM （SRTM Data with 90m resolution） and with the help of Arc Hydro module in ARC/INFO software developed by ESRI company, we conducted hydrological analysis on major rivers that enter Laizhou Bay by using GIS to extract river network, define watershed boundaries and divide the catchments and sub-watered, aiming to provide the basic data platform for estimation of total amounts of pollutants from agricultural non-point pollution. On this basis, we calculated the areas of different types of land use in various sub-basins by overlaying them with land-use thematic map, and estimated total amounts of agricultural pollutants entering into sea by using emission factors and river load ratio of major pollutants. Our results revealed that the annual amounts of COD, NH3-N, TN and TP that entered into Laizhou Bay was about 666994, 94398, 114614 and 19574 tons, respectively, accounting for 74.48%, 10.54%, 12.80% and 2.18% of total amounts of released pollutants, indicating COD is the major pollutant that enters Laizhou Bay. This studied was planned and conducted under the guidance of the principle of cooperation between land and sea, by taking the estuary as the source and with the idea of tracing sources, to determine watershed unit that influence marine pollution load. This study could provide an estimation method of agricultural non-point source load and the a scientific basis for controlling total amounts of pollutants that flow into Laizhou Bay, and can also serve as a reference for defining the land range during the process of comprehensive management along the coastal zone.