The Marl Lakes of the British Isles

Abstract

Abstract Over 100 marl lakes from the British Isles are described and compared. About 75 % of the lakes are extant with the remainder dating from the Late Glacial or Holocene and now completely filled with sediment. Most of the lakes are, or were, Chara-dominated and of glacial origin and the majority are shallow and less than 4 m deep. These lakes contain important plant and animal communities and their sediments provide a valuable fossil and geochemical record of changes since the last glaciation. Most are associated with Carboniferous Limestone, Chalk and Old Red Sandstone formations, and they are widely distributed. Their waters contain a mean dissolved calcium content of 2.79 meq L-1 (140 mg L-1 CaCO3), typical of temperate limestone groundwaters. Marl formation is closely associated with the growth of Chara but these plants are sensitive to disturbance and water pollution. Being shallow, the lakes possess rich emergent and submersed macrophyte floras, providing shelter for diverse invertebrate fauna...