Time scales of physical change in the lake environment

Wilson, Harriet (2022) Time scales of physical change in the lake environment. Doctoral thesis, Dundalk Institute of Technology.

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Abstract

Thermal stratification underpins most of the biogeochemical and ecological processes in lakes. The maximum depth of the surface layer in a lake (“epilimnion depth” or “mixed layer depth”), in particular, affects the vertical distribution of energy, organisms and organic materials in lakes. A full understanding of the epilimnion depth is essential for lake studies, especially given the potential sensitivity of this parameter to global climate change. There is, however, a lack of consistency in the definition of this metric in existing literature. There is also an absence of studies exploiting high-frequency data to examine the variability in epilimnion depth over time and across lakes. To address these gaps, a comprehensive comparison of methods was undertaken to estimate epilimnion depth using data from two European lakes. This showed that estimated epilimnion depth estimates varied substantially depending on the method and threshold used. There was also a high level of sensitivity to the critical threshold value used in calculations. A method defined as the shallowest depth where the density was 0.1 kg m-3 more than the surface density gave the most consistent results. Using the recommendations from the previous chapter, multi-lake comparison of mixed layer depth dynamics was conducted for 19 lakes, using data from a total of 100 summers. This study revealed large differences in the day-to-day variability of the summer epilimnion depth and emphasised the role of lake area in determining variability in this metric. Given that the epilimnion depth is a widespread and ecologically meaningful metric in limnology, these findings have far-reaching applications especially when predicting the impacts of extreme in-lake changes. A systematic literature review found that most studies that addressed the effects of climate extremes on in-lake changes based their metric of extremeness on local weather data. A comparison of weather-related extreme events and in-lake mixing events was undertaken for two sites over 30 years and found that that extreme weather-related and in-lake mixing events often did not co-occur. These results highlighted the importance of using in-lake based extreme event metrics for lake-focused science. Collectively, the research presented in this dissertation contributes towards rethinking existing and future methods in lake science for the protection of lake ecosystems.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	Lake studies.
Subjects:	Science
Research Centres:	UNSPECIFIED
Depositing User:	Sean McGreal
Date Deposited:	14 May 2024 15:06
Last Modified:	14 May 2024 15:06
License:	Creative Commons: Attribution-Noncommercial-Share Alike 4.0
URI:	https://eprints.dkit.ie/id/eprint/884

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