Assessing the condition of lake habitats: a test of methods for surveying aquatic macrophyte communities

Abstract

The European Union requires member states to monitor the conservation status of water bodies designated under the Habitats and Species Directive. In the UK, macrophytes were identified as useful indicators of conservation status but it was recognised that sampling methods required assessment before nationwide survey work began. At eight lakes, which varied in size (0.9–2797 ha) and trophic status (oligotrophic–eutrophic), we tested a method which uses a combination of three techniques (boat transects, wader transects and perimeter strandline searches) to characterise repeat sectors (six or fewer). The combination of techniques used at a particular lake depended on the accessibility of each sector, the safety of applying the method, expediency and target flora. Species richness and abundance were recorded. By applying indicator metrics/rules to data produced by the method it was possible to categorise the conservation and trophic status of the lakes. Power analysis revealed that the data were statistically robust and could potentially be used to track significant, lake-specific changes in macrophyte flora through time. This analysis also revealed a decreasing return in statistical certainty with increased sampling effort (number of sectors sampled). Little additional certainty was added when more than 4 sectors were sampled per lake. The wader transects proved the most practical means of collecting quantitative data while perimeter surveys were an efficient means of adding useful supplementary semi-quantitative data. Boat surveys, although useful in some situations, particularly in assessing deeper water vegetation, were more time consuming than wader surveys. The potential applications and limitations of these methods are discussed and further tests suggested.