CLIMATE AND LAND USE: UNRAVELING FORCING FACTORS IN LAKE PRODUCTIVITY FROM A ~2000 YEAR SEDIMENT CORE RECORD IN WESTERN IRELAND

The value of lake sediments for historiography lies in their propensity to produce continuous records of natural and anthropogenic changes. Multi-proxy paleolimnological studies, therefore, can provide detailed insight into various aspects of an area’s environmental history, such as long-term climate patterns, individual climatic events, land use changes, and ecosystem perturbations. In this study, we examine a lake in western Ireland with a catchment composed entirely of Carboniferous limestone. Lough Carra, a polymictic marl lake in Mayo County, Ireland, is large, spanning 14.4km², yet has an average depth of only 1.7m. However, a number of deep basins and sinkholes are present, reaching up to 18m in depth.

An 8m core was collected from the easternmost basin of Lough Carra near the mouth of the River Annies at a depth of 14m. The bottom 6.5m is well laminated. It is composed of a continuous ~2000 year sediment record as determined from preliminary ¹⁴C and ²¹⁰Pb analyses. Large carbon isotope shifts are present in the bulk organic and inorganic phases, from -30 to -33 and from -2 to -5, respectively. The shift occurs right after a ~1854 “marker” bed resulting from a flooding event in the catchment that destroyed drainage works built two years prior. In addition, steady increases towards the modern occur in PO₄ concentrations and Hg within the sediment, indicating anthropogenic input. To further constrain nutrient dynamics in the lake detailed phosphate analysis and C/N ratios coupled with N-isotopes are being employed. Both will be useful in determining the catchment’s environmental history in terms of natural and anthropogenic changes.