Lower Lough Erne - United Kingdom

Lough Erne is the collective name given to Upper Lough Erne (34.5 km2) and Lower Lough Erne (109.5 km2), which are connected by the River Erne in County Fermanagh, Northern Ireland. The Upper Lough and the shallower regions of Lower Lough Erne present an example of a flooded drumlin landscape which has created an intricate mosaic of land and water. As a consequence of differences in depth and area, the water retention time of the Upper Lough is less than one month while that of the Lower Lough is four months. Passing from the shallow Upper Lough (mean depth 2.3m) and through Lower Lough Erne (mean depth 11.9m), phytoplankton abundance is reduced and algal composition alters, as do nutrient and temperature cycles. Phosphorus concentrations (100 mg P l-1) in the Upper Lough create eutrophic conditions, with high summer chlorophyll a concentrations, but phytoplankton abundance in the deep open water of the Lower Lough is more typical of a mesotrophic water body despite comparatively high phosphorus concentrations (60 mg P l-1). The paucity of phytoplankton in this region is attributed to a high back-ground light attenuation from the peat-stained water and the greater depth of the mixed water zone (>35m).