Dong, X.; (2010) Using diatoms to understand climate-nutrient interactions in Esthwaite Water, England: evidence from observational and palaeolimnological records. Doctoral thesis , UCL (University College London).

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Abstract

Numerous aquatic systems have experienced eutrophication for several decades and now face the additional pressure of climate change. In order to effectively manage lake systems, a fuller understanding of the impacts of climate and nutrients on lake ecosystems, as well as a knowledge of how current and future climate change interact with nutrient dynamics, is required. This thesis employs contemporary and palaeolimnological records, using diatoms as the key indicator, to understand how climate and nutrients have impacted the lake ecosystem of Esthwaite Water, UK, over a range of timescales from months to several centuries. Firstly, the seasonal variability of planktonic diatom assemblages was examined based on a two-year monitoring dataset. Secondly, the influence of climate and nutrients on the diatom flora of this lake was quantitatively assessed based on statistical analyses (redundancy analysis and generalized additive modelling) of monitoring datasets (a two-year and a 60-year series of physico-chemical lake characteristics and diatoms). Thirdly, historical environmental change, in terms of climatic conditions and lake trophic status, was reconstructed for the last ~1200 years using diatoms, grain size, LOI, pollen, and geochemical analysis combined with 210Pb and 14C dating techniques. The analyses illustrate the complexity of climate-nutrient interactions and the roles of the two drivers on different timescales and at various stages of the lake’s history. Overall, climate impacts were more pronounced when nutrient concentrations were relatively stable. In contrast, during phases of enrichment and particularly in recent decades, the nutrient signal outweighs that of climate. This thesis also highlights the importance of integrating contemporary limnology and palaeolimnology to improve our understanding of environmental change. The combination of these approaches offers an opportunity to test sedimentary diatom representativity and core integrity, and the ecological information derived from contemporary limnology is particularly valuable for refining palaeolimnological inferences.

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