An approach to modelling the impact of prehistoric farming on Holocene landscape phosphorus dynamics

The lake sediment phosphorus (P) record at Hatch Mere (Cheshire, UK) is investigated to assess the role of human activity in modifying Holocene landscape P export dynamics, and to develop an approach to incorporating this effect into a pre-existing long-term, large-scale landscape model of natural P export. Analysis of the lake sediment record shows that the catchment P yield is low and constant prior to ca. 6000 BP, but then increases up to the present day. This increase occurs in steps that coincide with the Neolithic, Bronze Age and Medieval periods, and the first half of the 20th century, consistent with an anthropogenic cause. Such an interpretation is supported by close correlation of the P export flux with the estimated regional population density. We demonstrate that the effect of human activity on landscape P dynamics can be incorporated into the existing P export model by scaling the soil secondary P leakage rate coefficient to population density. The findings of this study suggest that lake sediment P accumulation rate data may provide a novel method for estimating prehistoric local population density. Additionally, we show that the pre-Neolithic landscape P export was low, and we reject the widely held view that Hatch Mere is naturally eutrophic.