Jc. Marks et Rl. Lowe, INTERACTIVE EFFECTS OF NUTRIENT AVAILABILITY AND LIGHT LEVELS ON THE PERIPHYTON COMPOSITION OF A LARGE OLIGOTROPHIC LAKE, Canadian journal of fisheries and aquatic sciences, 50(6), 1993, pp. 1270-1278
We investigated the effects of nitrogen, phosphorus, and light on peri
phyton in a clear oligotrophic lake. Experimental treatments consisted
of three levels each of nitrogen, phosphorus, and light in a three-wa
y factorial design. Nitrogen and phosphorus concentrations were manipu
lated using nutrient-diffusing clay substrates; light levels were mani
pulated with shade cloth. Periphyton biovolume and cell densities incr
eased significantly with both nitrogen and phosphorus enrichment but w
ere not affected by shading. Phosphorus enrichment increased periphyto
n accumulation only when nitrogen levels were high, indicating a signi
ficant interactive effect between nitrogen and phosphorus. Differences
in species composition among treatments were mostly due to changes in
the diatoms Nitzschia palea and Rhopalodia gibba. Ambient and phospho
rus-enriched substrates were dominated by R. gibba, which contains a n
itrogen-fixing endosymbiont, and blue-green algae. Nitrogen enrichment
and nitrogen and phosphorus in combination resulted in an assemblage
dominated by N. palea. Unshaded and highly shaded substrates were domi
nated by N. palea and Achnanthes minutissima, but the medium-shade sub
strates were dominated by R. gibba.