ASSESSING THE EFFECTS OF NITROGEN DEPOSITION ON MOUNTAIN WATERS: A STUDY OF PHYTOPLANKTON COMMUNITY DYNAMICS

摘要

We assessed the phytoplankton communities and the relevant aquatic chemistry in three large lakes in the Greater Yellowstone Ecosystem. While N limitation of phytoplankton is most common, it appears that a recent regional increase in atmospheric N deposition is causing both P and Si limitation to occur to some degree. N additions in semi-continuous laboratory bioassays of mixed diatom assemblages produced a dramatic increase in biomass in two of the three study lakes. Relative abundances of species were altered relative to control treatments with both added N and Si. Higher levels of N primarily favored the alga Fragilaria crotonensis. This result is consistent with previous laboratory and field observations which suggest that F. crotonensis is not a good competitior for N, and only thrives in N rich environments. We hypothesize that continued increases in N loading will alter natural species assemblages in all the study lakes.