Lake Development and Limnological Response to Prehistoric and Historic Land-Use in Diss, Norfolk, U.K.

Abstract

(1) The history of Diss Mere, Norfolk, U.K. was reconstructed by diatom and pigment analysis of a sediment core, with emphasis on the influence of changing vegetation and land-use on lake history. (2) The lake was mildly nutrient-rich (mesotrophic) early in its history. (3) The lower part of the core shows large variations in diatom concentrations and distinct lithological changes, including broad bands of silt and short sections of laminated sediments, which suggest fluctuating lake levels in the early Holocene. (4) Increased concentrations of the blue-green algal pigment oxcillaxanthin indicate the expansion of Oscillatoria about 6000 years B.P., probably in response to increased stabilization of the water column. (5) The subsequent preservation of over 3 m of laminated sediments in the mid-Holocene and extremely high pigment concentrations indicate a long period of moderate water levels and seasonal hypolimnetic oxygen depletion. (6) Increased pigment concentrations and percentages of diatom taxa characteristic of moderately enriched lakes correlate with pollen evidence of Neolithic and Bronze Age forest disturbance. (7) The termination of the laminated sediments and a transition from a Cyclotella-dominated diatom assemblage to one dominated by Stephanodiscus spp. correlate with pollen evidence of widespread deforestation. Thus rapid and sustained eutrophication of the mere probably resulted from increased nutrient inputs caused by forest clearance. (8) The mere remained eutrophic throughout the remainder of its history, and subsequent shifts in the diatom community indicate limnological responses to agricultural practices associated with Cannabis cultivation and later to the growth of a town around the mere.