Journal of Conference Abstracts

A Comparison of Statistical and Geographical Sampling Strategies for Determining Critical Loads and Other Chemical Characteristics of Scottish Lochs

R. Harriman¹ (Harrimanr@marlab.ac.uk), J. H. B. Birks² (Birks@no.uib.cc), C. Curtis³ (Ccurtis@geog.ucl.ac.uk) & A. E. G. Christie¹ (Christieaeg@marlab.ac.uk)

¹ Freshwater Fisheries Laboratory, Pitlochry PH16 5LB, Scotland, U.K.

² Botanical Institute, University of Bergen, Allegaten 41, N-5007, Bergen, Norway.

³ Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1H 0AP, U.K.

Environmental sampling programmes are usually designed to answer specific questions but on a national basis, it is rarely possible to comment on chemical trends and biological effects because the total population of lakes and streams has not been quantified.

Many of the recent European critical loads programme have used geographical rather than statistical criterion to produce the standardised exceedance maps used for determining S abatement strategies. In the UK, freshwater critical load and exceedance maps were based on one lake site per 10 km². Such sites were deemed to be the most sensitive in the square, based on existing geological and geochemical data.

By contrast, a recently completed north-European sampling programme used a statistical sub-set of lakes from the total population in each country (Norway, Sweden, Finland, North Russia, Denmark, Scotland and Wales). All lakes > 2 ha were identified and a fixed percentage were sampled by each country within 5 size bands. Here we present a comparison of the data for Scottish lochs, from these two surveys, to determine the effect of the skewed distribution of the lochs towards the north-west. Emphasis is placed on critical load distributions using current steady-state models, however differences in N and P status will be discussed in the context of increased N deposition. Although this work was mainly designed to provide a baseline against which any response to future emission reductions could be quantified, the implications of different sampling strategies for mapping critical loads and exceedances will also be discussed.