Morphometric analysis of UK lake systems as a compliance tool for the European Water Framework Directive

The European Water Framework Directive 2000 (WFD) stipulates that surface water bodies, such as lakes, should achieve good ecological and chemical status (pollutant levels) by 2015. However, the extant environmental monitoring programmes of most member states have major deficiencies in terms of the baseline data required, thus potentially jeopardising the compliance schedules of the WFD. Great Britain has over 40 000 lakes >1 ha, but bathymetric data are available for less than 2%. This paper presents a collation of available bathymetric data (622 sites) and demonstrates the utility of morphometric analysis to bridge the gap between surveyed and un-surveyed systems. Type-specific relations between mean (D_mv) and maximum (D_max) water depths were developed for natural lakes (r² values ranging from 0.87 to 0.99), as well as modified systems and impoundments (r² values ranging from 0.74 to 0.99). Stepwise regression was also undertaken to predict D_mv and D_max using only map-derived information (such as lake area, catchment area and shoreline length). The results varied markedly between “geological types”, with “medium alkalinity” (MA) lakes giving the highest coefficients of determination (R² of 0.79 and 0.82, respectively). Predicting D_mv is important because it permits calculation of parameters such as the volume (V) (and hence residence time) and dynamic ratio (DR) which provides a measure of the likely extent of sediment re-suspension. This preliminary analysis has demonstrated the potential of the morphometric approach to generate valuable parameters from limited field investment and will provide a valuable stop-gap until the results of the WFD’s comprehensive monitoring programmes are realized.