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By Sarah Mechan, Edward Burgess, and Réamonn Fealy
Situated on the western fringe of Europe and subject to the moderating influence of the Atlantic Ocean, Ireland is fortunate to have a temperate maritime climate that is particularly suited to grassland agriculture. With conditions facilitating a grass growing season that extends almost throughout the entire year, grass-based dairy and beef production constitute the primary agricultural sectors. From a land area of 6.9 million hectares, 4.2 million hectares are used for agriculture. With 80 percent of agricultural area devoted to pasture and hay and grass silage, 10 percent to rough grazing, and the other 10 percent to tillage, it is little wonder that Ireland is known as the "Emerald Isle."
However, as in other countries, issues around maintaining a high-capacity, productive agricultural sector while ensuring a sustainability-based farming approach remain a focus for all stakeholders. In partnership with farmers and other stakeholders, the Irish Agricultural Catchments Programme (ACP) is mandated to support productive agriculture while protecting water quality. It is funded by the Irish Department of Agriculture, Fisheries and Food and run by Teagasc, Ireland's Agriculture and Food Development Authority. ACP advisers provide an intensive advisory and planning service to farmers in small river catchment areas (500 to 2,900 hectares) with support from their colleagues both locally and nationally. They help the farmers improve their profitability and implement the necessary agri-environmental measures contained in the National Action Programme recently introduced under the European Union (EU) Nitrates Directive. This directive aims to protect water quality across Europe by preventing nitrates and phosphorus from agricultural sources from polluting surface and groundwater. ArcGIS software-based applications have played a primary role in facilitating both the establishment and operation of the program.
The selection of catchments was influenced by EU guidelines that indicate monitoring efforts should be concentrated in "areas of intensive crop and livestock production . . . with elevated nitrate concentrations . . . adjacent to existing or projected eutrophication areas . . . with similar land use, soil type, or agricultural practice." Thus, it was necessary to devise a method for selecting small catchments (from 400 to 1,200 hectares) that were farmed intensively, either predominantly grassland or arable, and at risk of high phosphorus or nitrogen losses from land into the rivers that drain them.
Given the spatial and environmental context of the task of candidate catchment selection, the role for a GIS-based methodology was immediately obvious. Given a long association with Esri products and a significant investment by the Spatial Analysis Unit in Teagasc in both ArcGIS Desktop and ArcGIS Server software, Teagasc chose ArcInfo to build a geodatabase to hold and manage the range of datasets required for the task, which were supplied from a diverse group of government departments and agencies. Oracle was chosen as the main database solution for the operational stage of the project.
In beginning the selection process, Spatial Analysis Unit staff first examined a national catchment boundary dataset of approximately 6,000 catchments to generate a list of 1,300 possible small river catchments based on size and stream order. These were further divided into two broad categories—grassland and arable cropping. The data analyzed included land use, forestry, area of peat, livestock density, nonagricultural land use, arable cropland, forage areas, housing density, geology, and soil types. A Multiple Criteria Decision Analysis (MCDA) approach was employed in the analysis using the onboard attribute table tools already available in the ArcInfo processing environment.
After detailed consultation with a broad range of experts from scientific, policy, and farm sector backgrounds, various selection criteria were chosen and given weights, reflecting the suitability of the catchments for monitoring by ACP. The internal attribute tables of each of these input parameters were reclassified into appropriate ranges, and these, too, were ranked according to selection suitability. A weighted summation provided an ordered list of catchments ranked by their suitability. The ArcGIS Spatial Analyst extension was used to model the risk at the catchment level of nitrogen or phosphorus moving from land to water. This model implemented a risk assessment procedure devised at the national level for formal reporting to the European Commission on the Water Framework Directive. ACP had at its disposal the most detailed national-scale datasets, and the risk model developed for the program is the most highly resolved available nationally.
The model is primarily based on soil drainage and subsoil hydrologic characteristics. Generally, more poorly drained soils have a greater risk of phosphorus loss through overland flow or runoff, while the more freely drained soils have a greater risk of nitrogen loss through leaching down through the soil. Of the 1,300 eligible catchments initially identified, a short list of 50 top-ranking arable and grassland catchments was drawn up. ACP staff visited these catchments to assess their physical suitability as study sites. Six catchments were selected for detailed study—four that were predominantly grassland and two with a high proportion of arable farming. The GIS-MCDA approach was shown to be particularly suitable to the selection task, and its implementation in ArcInfo proved highly efficient in handling the large number of input datasets and processing requirements.
Upon selection of the catchments for monitoring purposes, ACP needed to establish baseline soil nutrient levels for each catchment area. To achieve this, ACP undertook a field-based sampling campaign to establish soil nutrient status. To accurately represent the variation in soil nutrients across the catchments, high-resolution soil sampling was employed (the average area per sample was approximately two hectares). This high-resolution soil nutrient data facilitated the preparation of accurate nutrient management plans for catchment farmers. However, there was a risk that farmers would find these plans difficult to interpret given the high level of detail they contained and the large number of land management units (whole fields or subfield areas). To make the interpretation of the plans easier, ACP decided to develop clearly labeled, color-coded maps. Each field and sample area was digitized and allocated a unique code as part of the catchment digitizing process. The sample area codes were then entered into a Laboratory Information Management System, along with the corresponding soil sample code. This enabled the results to be linked back to produce intelligent maps. For each farm within the catchment areas, color-coded maps labeled with unique soil sample numbers can now be produced.
Maps illustrated by different colors, displayed in each sample area, can easily be produced in ArcGIS, which shows the phosphorus, potassium, and lime requirements of the crops to be grown. A set of maps can now be printed for each farm in less time than it would take to print the original soil analysis report. This analysis helps each farm increase its crop yield through targeted application of nutrients to match crop requirements and minimizes the leaching of nutrients (and effective loss of a farm resource) into local watersheds. The most satisfying aspect is the feedback from the farmers. They find the maps very informative and easy to use, leaving the advisers more confident that nutrient management on these farms will be carried out in an accurate and informed manner. This technology can be used to overlay many years of soil analysis results to track temporal changes in soil fertility and nutrient management.
Sarah Mechan is data manager for ACP. Her core role within the project is to develop and maintain an information management system to ensure the most efficient data capture and integration from multiple sources. Edward Burgess is an adviser to the farmers in the Castledockerell and Ballycanew catchments. He provides an advisory service to assist farmers' compliance with National Action Programme measures. Réamonn Fealy was part of the initial working group that proposed ACP, and he designed the catchment selection procedure described here. The authors would like to acknowledge the contribution to this article by David Wall, ACP soil scientist, and Ger Shortle, program manager.
For more information, visit the Agriculture and Food Development Authority Web site at www.teagasc.ie/agcatchments.