The use of remote sensing and GIS in watershed level analyses of non-point source pollution problems Prakash Basnyat * , L.D. Teeter, B.G. Lockaby, K.M. Flynn School of Forestry, Auburn University, 207 M.W. Smith Hall, Auburn University, Auburn, AL 36849, USA Accepted 24 September 1999 Abstract Basin characteristics such as land use/land cover, slope, and soil attributes affect water quality by regulating sediment and chemical concentration. Among these characteristics, land use/land cover can be manipulated to gain improvements in water quality. These land use/land cover types can serve as nutrient detention media or as nutrient transformers as dissolved or suspended nutrients move towards the stream. This study examines a methodology to determine nitrate pollution `contributing zones' within a given basin based on basin characteristics. In this process, land use/land cover types were classi®ed and basins and `contributing zones' were delineated using geographic information system (GIS) and remote sensing (RS) analysis tools. A `land use/land cover-nutrient-linkage-model' was developed which suggests that forests act as a sink, and as the proportion of forest inside a contributing zone increases (or agricultural land decreases), nitrate levels downstream will decrease. In the model, the residential/urban/built-up areas have been identi®ed as strong contributors of nitrate. Other contributors were orchards; and row crops and other agricultural activities. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Water quality; GIS; Nitrate; Forested buffers 1. Introduction Because of the fact that some correlation exists between pollution loading and land use (Perry and Vanderklein, 1996), there is a potential for improving water quality with proper land use management prac- tices. From a land use perspective, agricultural activ- ities have been identi®ed as major sources of non- point source (NPS) pollutants (sediments, animal wastes, plant nutrients, crop residues, inorganic salts and minerals, pesticides) (Viessman and Hammer, 1993) and are known to impact water quality. Resi- dential/urban/built-up areas are another dominant fac- tor in generating large amounts of non-point source (NPS) pollution from storm-water discharge. The imperviousness of many urban areas increases their storm-water discharge, and even small rains are cap- able of washing accumulated pollutants into surface waters. Changes in water quality can indicate a change in some aspect of terrestrial, riparian, or in-channel ecosystem. From a pollution perspective, among the many water quality elements related to ecologically healthy systems, nitrogen is one of the most proble- matic nutrients (Perry and Vanderklein, 1996). Nitrogen concentration downstream is a function of multiple controlling factors, and different streams have differ- ent responses to the set of controlling factors. One of Forest Ecology and Management 128 (2000) 65±73 * Corresponding author. 0378-1127/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII:S0378-1127(99)00273-X