Vertical distribution of algae and pigments in relation to underwater light climate in Lake Superior

Session: Great Lakes Primary Production: Methods, Results, and Management Implications (2)

Andrew Bramburger, Natural Resources Research Institute, University of Minnesota Duluth, [email protected]
Christopher Filstrup, University of Minnesota Duluth, [email protected]
Euan Reavie, University of Minnesota Duluth, [email protected]

Abstract

Algae contain a variety of auxiliary photosynthetic pigments aside from chlorophyll a. These pigments give the major divisions of algae their characteristic colorations and are reflected in their common names (i.e. green or blue-green algae). We examined relationships between the vertical distribution of  pigments and wavelength-specific light intensity through the water column at several locations along the south shore of Lake Superior during stratified conditions. Stations represented a variety of tributary plumes, as well as offshore areas and a nearshore cyanobacterial bloom. We used particulate absorbance measurements from discrete depths to coarsely estimate relative abundance of algal pigments in the water column and compared these results to hyperspectral radiance profiles. We also collected algal samples in order to taxonomically characterize the algal community at different depths. Preliminary results show that the underwater light climate differs widely among tributary-influenced stations, and the vertical distribution of algal pigments varies with light climate, and particulate chlorophyll profiles are not consistent with in situ fluorescence-inferred chlorophyll. Further, available irradiance at the deep chlorophyl maximum is not within the exitation spectrum of chlorophyll a. These results suggest that the DCL contributes little to water culumn-integrated primary production.