DISSOLVED ORGANIC-CARBON IN NORTHERN HARDWOOD STANDS WITH DIFFERING ACIDIC INPUTS AND TEMPERATURE REGIMES

We monitored concentrations and fluxes of dissolved organic carbon (DO C) in throughfall and forest floor solutions in two northern hardwood stands located at the northern and southern end of a latitudinal acidi c deposition and air temperature gradient in the Great Lakes Region to determine if DOC levels are altered by regional and temporal variatio n in acidic inputs and temperature. Amounts of precipitation received at the two sites were similar, but precipitation pH and air temperatur e, respectively, averaged 4.83 and 13.9 degrees C at the northern grad ient site and 4.29 and 15.1 degrees C at the southern gradient site. V olume weighted DOC concentrations in throughfall were significantly gr eater at the northern (20.5 mg L(-1)) than the southern (15.9 mg L(-1) ) site, but these differences in DOC levels were caused by the differi ng amounts of throughfall passing through the canopy of the two sites rather than levels of precipitation acidity or air temperature. Tempor al variation in the levels of DOC in throughfall was not related to th e variation in either precipitation acidity or air temperature. Like t hroughfall, levels of DOC in forest Boor solutions were not found to b e altered by acidic inputs. However, DOC in these solutions increased with seasonal increases in soil temperature. A regression equation rel ating seasonal variation in soil temperature and forest floor concentr ations of DOC estimated that an observed 2.1 degrees C difference in s oil temperature at the two sites during the growing season could repre sent as much as 3.7 mg L(-1) difference in forest floor solution conce ntrations of DOC.