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Track: Water Resources
Elaine McAlister
Macaulay Land Use Research Insitute
Craigiebuckler
Aberdeen, SC AB15 8QH
UNITED KINGDOM
Telephone: 011-44-1-224-318611
Fax: 011-44-1-224-311556
E-mail: e.mcalister@mluri.sar.ac.uk
Nelleke Domburg, Richard Aspinal
Environment Mapping and Modeling of a Catchment Using GIS
As farm production has intensified in recent years, nonpoint source pollution of water has become a significant problem. At the Macaulay Land Use Research Institute (MLURI), we are applying GIS technology to help with the management of the River Ythan catchment, Aberdeenshire, Scotland. There has been a 300 percent increase in the amount of nitrogen entering the estuary since the 1960s which is thought to be related to changes in agricultural practice. The estuarine eutrophication has stimulated greater algae growth, which has reduced the amount of food available for wildlife in the National Nature Reserve (the Ythan estuary). This paper discusses how, using spatial analysis techniques and a hydrological model in a GIS framework, we can assess the possible impact of land use scenarios for reducing nitrogen leached to the estuary. Using satellite imagery, we have gained an insight into the distribution of crops and organic and inorganic nitrogen inputs throughout the catchment in an attempt to target
areas of high-risk N loss. With the development of a partially distributed hydrological model in ARC GRID, we can calculate the weekly mean flow at any point on the river network and the daily accumulated flow at the outlet allowing an estimation of nitrate loads entering the estuary. As higher quantities of N potentially are leached from land under certain crop types, we have also investigated the cropping patterns in close proximity to the streams, which may be of importance in deciding future abatement measures. GIS techniques have been particularly useful in enabling us to analyze the effects of agricultural nonpoint source by the following means: the GIS is used to store, coordinate, and manipulate the spatial and satellite data as well as act as a link to databases holding socioeconomic data in tabular form; the network analysis provides a means of interpreting pathways of nutrient loss and connects agricultural land use throughout the catchment with the estuary, allowing for the estimation of
nitrate loads entering the estuary; the output from the GIS is used to communicate the results of analyses in a flexible and visual manner that is immediately understandable.
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