The taxonomical composition of an algal community under nitrogen (N) and phosphorus (P) enrichment in two Swedish lakes.

Abstract

It is still a matter of discussion if changes in C:N:P (carbon:nitrogen:phosphorus) ratios of an algal community are due to a change in species composition or due to a change in storage products in an unaltered algal community. Therefore, I studied the taxonomical response of an algal community growing on nutrient diffusing clay pots (control, N enrichment, P enrichment, N+P enrichment) in two Swedish lakes. Pilot studies had shown N limitation of both lakes and C:N:P ratios that decreased under nutrient enrichment. I found a change in community structure in both lakes under N addition and under P addition in Lake Annsjon. The algal community on the control pots of both lakes was dominated by taxa adapted to N limiting conditions. In Lake Erken, the dominating taxa were diatoms, Oedogonium, Mougeotia, N fixing bluegreen algae and Aphanothece. The Lake Annsjon community consisted of diatoms, Oedogonium and N fixing bluegreen algae. Epithemiaceae dominated the diatom community in both lakes. Nutrient addition induced a change in community structure. The dominant algae were indicators of high nutrient concentrations. N addition in Lake Erken lead to a community dominated by Stigeoclonium and Phormidium. Cocconeis pediculus and Gomphonema parvulum replaced Epithemiaceae. P treatments in Lake Annsjon had a higher abundance of Tolypothrix. N enrichment in Lake Addsjon led to a loss of Oedogonium and an increase in Phormidium. Achnanthidium minutissima and Gomphonema parvulum replaced the Epithemiaceae.