Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Spatial heterogeneity in a small, temperate lake during archetypal weak forcing conditions
AU - Mackay, Eleanor
AU - Jones, Ian
AU - Thackeray, Stephen
AU - Folkard, Andrew
PY - 2011/1/4
Y1 - 2011/1/4
N2 - 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.
AB - 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.
KW - spatial organisation
KW - effective fetch
KW - water depth
KW - water temperature
KW - chlorophyll-a
U2 - 10.1127/1863-9135/2011/0179-0027
DO - 10.1127/1863-9135/2011/0179-0027
M3 - Journal article
VL - 179
SP - 27
EP - 40
JO - Fundamental and Applied Limnology
JF - Fundamental and Applied Limnology
SN - 2363-7110
IS - 1
ER -