Experimental Acidification of a Sphagnum-Dominated Peatland: First Year Results

Abstract

A poor fen (3.6 ha) in northwestern Ontario was experimentally acidified with HNO3 and H2SO4 to study the effects of acid precipitation on the dominant Sphagnum species and on the chemistry of the surface waters and pore waters. The nitrate concentration in the surface waters of the fen increased from < 0.07 μeq∙L−1[Formula: see text] to between 20–70 μeq∙L−1 during or just after each acidification event. Subsurface [Formula: see text] concentrations remained unchanged and surface [Formula: see text] concentrations returned to background levels within a day. The mire as a whole retained over 99% of the added [Formula: see text], probably due to nitrate assimilation by the Sphagnum. Sulfate concentrations in the surface pools increased from 5 μeq∙L−1 to 130 μeq∙L−1 with acidification and gradually decreased in the following 7 to 14 days. Pore water concentrations of [Formula: see text] decreased and H2S increased indicating sulfate reduction even in the highly acidic environment (pH 4). The decrease in concentration of [Formula: see text] in the surface pools due to SO4 reduction and assimilation was not as rapid as the decrease in [Formula: see text] concentration due to plant assimilation. The dominant Sphagnum species increased in growth with the added [Formula: see text] and [Formula: see text], particularly in the oligotrophic areas of the mire. In the minerotrophic area, only those species isolated from the water table showed increased growth due to acidification. Results here indicate that in the early stages of acidification the mire is capable of taking up the added [Formula: see text] and [Formula: see text], probably in an assimilatory reduction process which generated additional alkalinity in the mire.