Tracking recent human impacts on a nutrient sensitive Irish lake: integrating landscape to water linkages

Abstract

High-resolution palaeolimnological analysis was implemented on a sediment core from Lough Muckno, a historically polluted inter-drumlin lake located in northeast Ireland. Focusing on chironomid and fossil pollen analyses, catchment conditions and human impacts on the lake environment during the last c. 200 years are identified and characterized. Chironomid community response to historical land-use change, reconstructed through a combination of pollen analysis and documentary evidence is evaluated in detail. The results provide insights into lake ecological conditions from a meso-eutrophic state in a nineteenth century agricultural setting to a highly eutrophic system in a landscape under modern pastoral management. Increasing livestock numbers and concomitant land fertilization are considered to be the main drivers affecting chironomid assemblages. Redundancy analysis indicates that grassland-based agriculture, inferred from Poaceae (grasses), the dominant component of palynological pastoral indicators, was the main variable controlling chironomid community composition. Lake resilience to nutrient abatement is reflected in a limited chironomid response to declining agricultural activity during the Great Irish Famine (c. 1846) and attempts at point and non-point pollution controls. Integrated interpretation of chironomid, pollen and non-pollen palynomorphs is shown to be a powerful tool for assessing the impacts of modern land-use change on lake ecology through time.