Seasonal changes in the underwater light climate of two Canadian shield lakes

Abstract

This study examines the seasonal variation in the underwater spectral distribution of light in a mesotrophic (Lake Cromwell) and an oligo-mesotrophic (Lake Croche) temperate lake. Gilvin is primarily responsible for the strong selective attenuation of blue light in both lakes. As a result of differing gilvin concentrations light transmission maxima of downwelling and upwelling spectra are near 615 nm in Lake Cromwell and 599nm in Lake Croche. With increases in depth both upwelling and downwelling radiance fluxes decrease, are shifted to longer wavelengths and become more monochromatic. The greatest penetration of light occurs in the summer and spring after which a gradual decrease occurs through fall to a minimum value in winter. Under the winter cover the AP,, of downwelling light shifts 10 to 20 nm towards shorter wavelengths. Seasonal changes in downwelling irradiance are related to solar altitude, concentration of suspended particles, phytoplankton populations, amount of gdvin, mixing and winter cover. The brownish colouration of these lakes is explained by reflectance of spectrally impure orangish-red light.

Environmental colour impact on the life of lower aquatic vertebrates: development, growth, physiological and biochemical processes

“…Absorption is also different for rays with different wavelengths. When the light passes 1 m of water, 25% of the red rays and only 3% of the violet are absorbed (McFarland & Munz 1976;Heinermann & Ali 1988;Pegau et al 1997). Rays with a wavelength of 1200 nm do not penetrate into water.…”

Experimental warming and browning influence autumnal pelagic and benthic invertebrate biomass and community structure

“…The increased ice‐free duration can prolong consumer‐resource interactions by extending the growing season, potentially increasing consumer growth, and decreasing the intensity of winter starvation in consumers (Prowse et al, 2011). However, solar radiation also decreases during autumn, especially at more northern latitudes (Heinermann & Ali, 1988), which, combined with browning, can negatively affect primary production (Isles et al, 2021) and therefore reduce food availability in autumn for consumers. Warmer water temperatures further cause increased metabolic costs for consumers, thereby increasing resource demands and decreasing autumn invertebrate biomass (O'Connor et al, 2009) as a response to reduced light‐limited resource production (Hamdan et al, 2021; Karlsson et al, 2009).…”