Ecological assessment of morphological shore degradation at whole lake level aided by aerial photo analysis

Abstract

Hydromorphological alterations of lake shores constitute an important pressure on Central European lakes. The local ecological effects of such alterations can be assessed by multimetric assessment methods based on eulittoral macroinvertebrate communities. However, such tools so far only enable a local assessment even if the European Union Water Framework (EU WFD) requires an assessment at whole-lake level. Since due to time and financial constraints it is not feasible to perform small-scale macroinvertebrate assessments over the whole length of the lake shore, the site-specific ecological assessment result needs to be extrapolated. In this study, we analyse the use of a physical habitat survey method including both ground surveys and aerial photo analysis (HML = HydroMorphology of Lakes survey protocol) to enable an extrapolation from local to whole lake ecological assessment. For that purpose, we correlated individual macroinvertebrate metrics as well as results of a multimetric macroinvertebrate-based index (I) with the areal cover of surrounding natural shore elements, (II) with the hydromorphological impact within an encircling rectangle around the macroinvertebrate sampling site, and (III) with the hydromorphological impact in the adjacent epi-, eu- and sublittoral subsegments. Building up on this, an ecological whole lake assessment was achieved by averaging multimetric index scores calculated for each subsegement based on a regression equation between the multimetric index and the hydromorphological impacts in the three subsegments. This whole lake assessment approach can most likely be applied to geographical regions outside Central Europe and lake types not analysed here (fluvial lowland lakes, prealpine/alpine lakes), but more studies are necessary to verify this. Eventually, the extrapolation presented here may complement existing lake assessments under the EU WFD solely focusing on water quality so far.