Dynamics and chemistry of dissolved organic carbon in precambrian shield catchments and an impounded wetland

We examined the sources, sinks, and fluxes of dissolved organic carbon (DOC) and its chemical fractions over a 4-year period in upland and wetland catchments in the Experimental Lakes Area, Ontario. In an upland catchment, the major sources of DOC were precipitation, vegetation, and soil organic matter, resulting in a summer (June to October) export of 2.1 g.m(-2). DOC concentrations in peat pore water ranged from 20 to 60 mg.L-1 and were related to hydrologic pathways. DOC export from catchments containing wetlands ranged from 0.8 to 5.7 g.m(-2) and export from the peatland portion of the catchment was estimated to be 28-30 g.m(-2). Flooding to a depth of 1.2 in in the peatland section of one catchment resulted in an increase in pore-water and pond DOC concentrations, attributed to the decomposition of plant tissues and peat. Because only 14% of the catchment was flooded, impoundment did not result in a significant increase in DOC export. Between 85 and 93% of DOC was contained in the acid fractions, with small amounts in the neutral fractions. Flooding increased the proportion of the hydrophilic neutral fraction in peat pore waters for 2 years after flooding.