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Limnology and macrophytic vegetation of Loch Obisary, a deep brackish lake in the Outer Hebrides*

Published online by Cambridge University Press:  05 December 2011

D. H. N. Spence ,
A. M. Barclay  and
P. C. Bodkin
D. H. N. Spence
Affiliation:
Department of Botany, University of St Andrews
A. M. Barclay
Affiliation:
Department of Botany, University of St Andrews
P. C. Bodkin
Affiliation:
Department of Botany, University of St Andrews
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Synopsis

Loch Obisary has a narrow sea inlet to a north basin which is 45 m deep, stratified in summer and winter and joined by shallow channels to an unstratifled south basin.

Mean conductivity (25°C) and sodium measurements indicate that in summer and winter the north basin epilimnion and the south basin comprises about 50%, and the north basin hypolimnion about 80%, sea water. It is calculated that 56% of high tides enter the loch.

Vertical diffuse attenuation coefficients for blue, green and red light are the same in epilimnion and south basin, the blue coefficient being slightly higher than the red in July and much higher in January. In July the blue coefficient in the hypolimnion is lower that the red, as in clear coastal water.

Six out of 24 macrophytes, and eight epiphytes, are confined within 200 m of the sea inlet. Distribution and depth limits of those and other species are discussed in relation to substrate, water chemistry and light. The presence of a halocline in the north basin and its absence from the south basin allow a comparison to be drawn between depth limits set by water chemistry (north basin), and those predicted on the basis of light (south basin) for Potamogeton pectinatus and Nitella opaca.

Type
Research Article
Information
Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences , Volume 78 , Issue 1-2 , 1979 , pp. 123 - 138
Copyright
Copyright © Royal Society of Edinburgh 1979

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Footnotes

*

This paper was assisted in publication by a grant from the Carnegie Trust for the Universities of Scotland.

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