Spectral intensity in some Scottish freshwater lochs

Abstract

In the course of investigations on the ecology of submerged aquatic macrophytes a narrow-bandwidth spectroradiometer has been used to measure underwater spectral intensity (390-750 nm) in a series of lochs approaching the extremes in optical and chemical properties of Scottish fresh waters. Cosine response and immersion-effect properties of the collector were determined in the laboratory with a colUmated hght source. Diffuse attenuation coefficients, Fe, ranged from 0-55 in Loch Croispol, a calcareous loch, to 2-9 in Loch Leven, a lowland eutrophic loch. Underwater spectral intensity (1 m) relative to subsurface values show a proportional increase in shortwave radiation in the blue-green water of Loch Croispol, while the converse is true of the peaty brown water of Loch Uanagan. Attenuation coefficients were derived over 25 nm wavebands in Lochs Croispol, Leven and Uanagan. The water in the latter two lochs is optically similar although Leven is rich in phytopiankton and has an extinction peak at 675 nm. Uanagan represents the brown-water type of loch most common in Scotland. Loch Croispol has attenuation coefficients for shorter wavelengths at least ten times lower than the other two lochs and only approaches their values at 750 nm. Croispol resembles Crater Lake, Oregon. The colour range at the maximum colonizable depths by rooted macrophytes of brown (Uanagan 4 m) to blue-green (Croispol 6 m) water is equivalent to 196-0 and 230-6 kJ/Einstein (48-2 and 55-6 kcal/Einstein). Red/far-red ratios even in plankton-rich water (Leven) were at least three times the value for sunlight (1-3) and within the total photic zone reached three-figure proportions. Possible implications for light-sensitive seeds of aquatic species and for morphogenesis and zonation are discussed.

Sensitivity of mayfly nymphs to red light: implications for behavioural ecology

“…Although various fishes are known to have visual pigments that maximize sensitivity to ambient environmental light (Levine & MacNichol, 1979;Munlz & Mouat, 1984;Heinermann & Ali, 1985), little is known of the vision of immature aquatic insects. Although it can be assumed that the vision of aquatic insects is matched to their photic environment, which in organically enriched freshwaters is shifted towards the red (James & Birge, 1938;Schindler, 1971;Spence, Campbell & Chrystal, 1971;Muntz & Mouat, 1984;Howard-Williams & Vincent, 1985;Reimchen, 1989), this idea has not been tested. This is a report on a behavioural study of the sensitivity of mayfly nymphs to red (650 nm) and infra-red (950 nm) light, the results being discussed in terms of experimental methodology and photic adaptation.…”

Seasonal attenuation of quantum irradiance (400–700 NM) in three Nebraska reserviors

“…Prieur (1970) showed a decrease of quantum flux with depth from stations at Villefranche-sur-mer and sud Cap Ferrat, France . Spence et al (1971) calculated the number of quanta per 25 nm waveband from spectral irradiance data collected in two Scottish freshwater lochs . Kirk (1977a) demonstrated the attenuation and reflectance of down-welling quantum irradiance in various inland and coastal waters in south-eastern Australia .…”

Adaptation of visual pigments to the aquatic environment

“…Levels of chlorophyll, DOM and suspended solids vary dramatically within short periods in most inshore waters and plankton blooms and variations in run-off cause unpredictable and extreme variations in spectral transmissions, and hence in the light available for vision. Freshwater is similarly changeable and can vary from extremely clear to green, yellow or brown, although some freshwaters such as Scottish tarns are so heavily stained with DOM that red light penetrates best (Spence et al, 1971) and in the blackwater tributaries of the Amazon far-red or even infra red wavelengths predominate (Muntz, 1978;Muntz and Mouat, 1984). Because of the extreme effect of filtering on the spectrum of light available for vision underwater, and the great variability in this spectral filtering in different waters, the study of the evolution of visual spectral sensitivity of animals living in different waters can be thought of as using the underwater environment as a 'natural laboratory' (Levine, 1982).…”