Comparisons of Phytoplankton and Epilithic Algae of Selby Lake – Gates of the Arctic National Park and Preserve, Alaska

Abstract

ABSTRACT Selby Lake in Gates of the Arctic National Park and Preserve was assessed as oligotrophic due to measurements of low nutrient concentrations and resultant low planktonic biomass as total chlorophyll. An orthograde oxygen profile in early summer also indicated an oligotrophic condition. Total nitrogen averaged about 0.4 μg·L−1 and total phosphorus about 4 μg·L−1, resulting in a TN:TP ratio of about 100, which indicated the planktonic algae were probably limited by phosphorus. Nutrient stimulation bioassays confirmed this. Nitrogen alone was not stimulating to plankton algal growth, but nitrogen and phosphorus added together in the bioassays stimulated growth more than just phosphorus, as is often found in oligotrophic lakes. Aerial observation of Selby Lake and similar nearby lakes had indicated that epilithic benthic algal biomass was probably relatively high because the extensive shallows were visibly green. When recent growth in the ice-scour zone (< 2 m) was sampled in early July, the whole lake average standing crop of epilithic algae was estimated as approximately equal to the whole lake standing crop of phytoplankton. Biomass was greater near inlets than away from inlets. Epilithic algal biomass varied inversely with the temperature of inlets and directly with the inlets' total nitrogen concentration. Root zone fixation of atmospheric nitrogen by alders may be the source of N in the enriched inlets, and cold inlets probably plunge to the lake bottom, bathing the epilithicalgae with nutrients. The importance of benthicalgae in clear-oligotrophic lakes with extensive shallows need to be recognized.