Journal of Conference Abstracts

Using GIS to Relate Surveyed Biogeochemical Parameters to Mapped Predictors of Acid Sensitivity

Keith R. Bull¹ (K.Bull@ite.ac.uk), Jackie M. Ullyett¹ (J.Ullyett@ite.ac.uk), Tim E. H. Allott² (tallott@geography.ucl.ac.uk), Jane R. Hall¹ (J.Hall@ite.ac.uk), Ron Harriman³ (harrimanr@marlab.ac.uk) & Tim Sparks¹ (T.Sparks@ite.ac.uk)

¹ ITE Monks Wood Abbots Ripton, Huntingdon, Cambs, PE17 2LS, U.K.

² ECRC, Department of Geography, University College London, 26 Bedford Way,
London WC1H OAP, U.K.

³ SOAFD, Freshwater Fisheries Lab, Faskally, Pitlochry, Perthshire PH16 5LB, U.K.

Survey sampling strategies are important for environmental biogeochemical studies. They not only determine the spatial distribution of any measurements to be made, but can also influence the values measured and the spatial interpretation of the results (e.g., maps). Previous work (Hall et al., 1995) has identified relationships between freshwater critical loads estimates and the sensitivity of surface waters to acidification as predicted by soil characteristics, geology type, and land use. The 1,500 water samples used for this comparison were collected for a national map of freshwater critical loads and the sampling strategy aimed, in general, to collect one sample from each 10 km grid square of Britain (Critical Loads Advisory Group, 1994). In the current study, GIS has been used to explore the spatial patterns of the same critical loads and their associated pH data, and to investigate further their relationships with mapped sensitivity. This has taken into account the regional distribution and patterns of sensitivity as identified on the soil, geology and land cover maps.

In addition, our study considered parts of a more recent survey of lakes in north-west Europe; the data were drawn from the results for Scotland (134 lakes) and Wales (52 lakes). The sampling strategy used for collecting these samples was different from the critical loads mapping study. Lakes sampled were randomly selected from the total populations of lakes in areas of Scotland and Wales. However, populations were stratified on the basis of lake area and the random selection made on each stratum to provide a "representative sample" of the populations. As for the critical loads survey, GIS was used to consider the data in terms of the spatial patterns of acid sensitivity in the region sampled, as well as the sensitivity at the location of the sampling point itself.

The spatial distributions of the samples collected in the two surveys were quite different, but each provided information which could be used to relate predicted sensitivity to measurements. The advantages of each type of survey, and the spatial interpretation of the measured data for mapping purposes are discussed.

References

Hall, JR, Wright, SM, Sparks, TH, Ullyett, JM, Allott, TEH, Hornung, M. Water, Air and Soil Pollution, 85, 2443-2448 (1996).

Critical Loads Advisory Group 1995. Report of the sub-group on freshwaters to the UK Department of the Environment. Institute of Terrestrial Ecology: Edinburgh, ISBN: 1870393 25 2 (1995).