Phytoplankton nutrient deficiency as related to atmospheric nitrogen deposition in northern Minnesota acid-sensitive lakes

Four acid-sensitive lakes were studied. N enrichment generally caused a greater biomass response than P, although N + P almost always yielded the greatest effect and co-limitation was likely in two of the lakes. Predictions based on DlN:TP ratios generally agreed with the growth bioassays; TN:TP and DlN:SRP were not useful and could be misleading. Atmospheric deposition could satisfy most of the daily algal N demand and increase the fertility of these lakes. Results suggest that although water quality protection based solely on P may not protect against this non-point source of nutrients, without these control strategies, P inputs would be expected to have a disproportionately greater stimulation of phytoplankton growth. -from Authors