THE INFLUENCE OF HYDROLOGIC CONDITIONS AND PEAT OXIA ON THE PHOSPHORUS AND NITROGEN DYNAMICS OF A CONIFER SWAMP

A mass balance approach was used to determine the factors influencing phosphorus and nitrogen dynamics in wetlands common to headwater catch ments of the Precambrian Shield. The relationships of runoff, water le vel, water temperature, and anoxia to the annual and seasonal total ph osphorus (TP) and total nitrogen (TN) retentions of a headwater Sphagn um-conifer swamp during 1987-1988 were examined. Annual retentions of TP (4%) and TN (10%) were low in the swamp. On an annual basis, inputs exceeded outputs of total reactive P, NO3-N, and NH4-N and outputs ex ceeded inputs of total unreactive P and total organic N. Seasonal tren ds in P and N retention were inversely correlated with runoff. Positiv e monthly retention coincided with low runoff and increased biotic ass imilation during the growing season. Water table drawdown during the s ummer was associated with peat aeration and increased levels of P and N in surface and pore water. High levels of P and N in the swamp surfa ce water during the fall and winter were coupled with increased runoff , saturated overland flow, and potentially low biotic assimilation res ulting in a net release of TP and TN. Large flow through of waterborne inputs and flushing of regenerated P and N occurred during peak snowm elt runoff resulting in low annual retention.