Underwater Spectral Attenuation and Its Effect on the Maximum Depth of Angiosperm Colonization

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Abstract
Data collected from 23 Alberta [Canada] and literature values for 45 other north temperate lakes were used to develop regression models to evaluate the effect of underwater light quality on the maximum depth of angiosperm colonization. Unlike most north temperate lakes, eutrophic Alberta lakes have unusually low levels of dissolved colour and, as a result, transmit blue light particularly well. Comparison of regression equations relating the maximum depth of angiosperm colonization (zc) and Sechhi depth (D) for lakes with low colour (zc0.5 = 0.69 log(D) + 1.76) and with high colour (zc0.5 = 1.22 log (D) + 1.10) showed that for any Secchi depth, aquatic angiosperm colonized to greater depths in lakes lower colour. These results demonstrate that light quality as well as light quantity determine the maximum depth of angiosperm colonization in lakes. Regional differences in the relation between zc and Secchi depth may therefore be due to variations in the underwater light spectrum.