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Spatial heterogeneity in a small, temperate lake during archetypal weak forcing conditions

Mackay, Eleanor and Jones, Ian and Thackeray, Stephen and Folkard, Andrew (2011) Spatial heterogeneity in a small, temperate lake during archetypal weak forcing conditions. Fundamental and Applied Limnology, 179 (1). pp. 27-40.

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Abstract

Whilst there is significant knowledge of how intensive, episodic physical forcing governs spatial patterns in large lakes, less is known about how more typical forcing in small lakes affects spatial heterogeneity. This study used repeated field sampling and spatial data analysis to examine the horizontal structuring of physical, chemical and biological variables at a range of spatial scales during typical summertime weather conditions. Sampling took place in the surface mixed layer of Esthwaite Water (UK), a typical, small temperate lake. Physical forcing was low over the morning sampling period, as is usually the case at this site: average wind speed was ≈2 m s-1 and the average morning heat flux was 110 W m- 2. Spatial patchiness at small scales was found for all measured variables, at larger scales, where lake morphometry played a role, temperature variation was significantly dependent upon water depth, and chlorophyll-a was significantly dependent upon fetch. We infer that while shallower waters were, as expected, warmer, the associated differential heating in this temperate lake was not sufficient to impact upon other variables. These results also imply that the fetch-related organisation of chlorophyll was due to downwind advection of buoyant plankton in surface waters, and not due to vertical entrainment. Calculated Wedderburn numbers were indicative of a stable system, suggesting that the lack of a significant fetch related temperature structure was due to near-surface motions only and not to thermocline-tilting phenomena. Whilst previous studies have focused on intense and episodic physical events or large systems, we show that physical mechanisms still have an identifiable effect upon horizontal spatial heterogeneity in a small lake during typical, relatively weak, forcing conditions.

Item Type: Article
Journal or Publication Title: Fundamental and Applied Limnology
Uncontrolled Keywords: spatial organisation ; effective fetch ; water depth ; water temperature ; chlorophyll-a
Subjects:
Departments: Faculty of Science and Technology > Lancaster Environment Centre
ID Code: 50140
Deposited By: ep_importer_pure
Deposited On: 30 Sep 2011 13:38
Refereed?: Yes
Published?: Published
Last Modified: 26 Jul 2012 19:36
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/50140

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