Critical pollution areas within a watershed: A GIS and indexing strategy

Agricultural non-point source pollution has become the major source of poll utants contributing to the degradation of water quality in most of the worl d's water bodies. Nitrogen (N) and phosphorus (P) are major contributors to the eutrophication of surface water bodies, and nitrogen can also cause hi gh nitrate nitrogen (NO3-N) levels in groundwater. High levels of nutrients cause excessive alga growth, depleting dissolved oxygen in the water as th e algae decomposes, and reducing the amount of habitat for animals. Loss of N is also an economic for the farmers besides it's negative environmental impacts. Monitoring nutrient loss from the landscape with diverse soils, ge ology, topography, land use, and management scenarios is very laborious and expensive. Therefore, an alternate assessment technique is necessary to pr ovide an estimate of the critical areas of pollution within a given watersh ed. Evaluation of the critical areas of pollution within a watershed makes the determination of proper remediation means for the pollution infected ar eas possible. This study describes the usage of geographic information system (GIS) and a ppropriate indexing procedures for evaluating the critical areas of polluti on in two selected watersheds; one in northern Maryland, USA and the other in southern Sweden. The watershed in Maryland has an area of about 346 ha a nd soils are predominantly Penn silt loam series. The watershed in southern Sweden is about 1,460 ha with sand being the dominating soil. The assessme nt parameters used in determining proper pollution indexes vary from one lo cation to the next. However, they are principally similar. Parameters consi dered in Maryland include soils, geology, topography, distance from stream, land cover/land use, nutrient management practices. Such data and appropri ate indexing equations were used to develop runoff potential, erosion poten tial and leaching potential for each watershed segment, thus enabling the c omputation of overall watershed pollution index. The indexing strategy for determining nitrogen leaching in southern Sweden included factors such as c rop type, tillage, manure application, and fertilizer overdose. These facto rs were used as multipliers to adjust the "normal leaching rates" for the t ype of soil in southern Sweden. Results obtained from these two studies wil l be presented and usage of the indexing technique as a management tool wil l be discussed. Practical aspects of using such strategy for pollution iden tification and possible remediation will be presented.