Using diatoms to understand climate-nutrient interactions inEsthwaite Water, England: evidence from observational andpalaeolimnological records

Numerous aquatic systems have experienced eutrophication for several decades andnow face the additional pressure of climate change. In order to effectively manage lakesystems, a fuller understanding of the impacts of climate and nutrients on lakeecosystems, as well as a knowledge of how current and future climate change interactwith nutrient dynamics, is required.This thesis employs contemporary and palaeolimnological records, using diatoms asthe key indicator, to understand how climate and nutrients have impacted the lakeecosystem of Esthwaite Water, UK, over a range of timescales from months to severalcenturies. Firstly, the seasonal variability of planktonic diatom assemblages wasexamined based on a two-year monitoring dataset. Secondly, the influence of climateand nutrients on the diatom flora of this lake was quantitatively assessed based onstatistical analyses (redundancy analysis and generalized additive modelling) ofmonitoring datasets (a two-year and a 60-year series of physico-chemical lakecharacteristics and diatoms). Thirdly, historical environmental change, in terms ofclimatic conditions and lake trophic status, was reconstructed for the last ~1200 yearsusing diatoms, grain size, LOI, pollen, and geochemical analysis combined with 210Pband 14C dating techniques. The analyses illustrate the complexity of climate-nutrientinteractions and the roles of the two drivers on different timescales and at variousstages of the lake’s history. Overall, climate impacts were more pronounced whennutrient concentrations were relatively stable. In contrast, during phases of enrichmentand particularly in recent decades, the nutrient signal outweighs that of climate.This thesis also highlights the importance of integrating contemporary limnology andpalaeolimnology to improve our understanding of environmental change. Thecombination of these approaches offers an opportunity to test sedimentary diatomrepresentativity and core integrity, and the ecological information derived fromcontemporary limnology is particularly valuable for refining palaeolimnologicalinferences.