Pre- and Post-Clearcutting Effects on Mass Loading and Leaching of Phosphorus and Carbon from Litterfall to Boreal Headwater Lakes

Abstract

Shoreline trees (predominantly black spruce, jack pine and white cedar) surrounding four boreal lakes located in northwestern Ontario, Canada were found to contribute an average of 0.3 + 0.1 (SD) kg ha^-1 lake surface yr^-1 total dissolved phosphorus (TDP) and 1.8  + 0.7 (SD) kg ha^-1 lake surface yr^-1 dissolved organic carbon (DOC). These values are estimated to represent from 19 to 56% of the total allochthonous TDP inputs and less than five percent of the total allochthonous DOC inputs to the study lakes. Inputs of airborne and laterally transported litterfall were reduced 77% around two lakes following riparian and catchment clearcutting. About half of this decline in litterfall was attributable, however, to non-treatment, inter-annual climatic effects. No differences were found in the mass losses, and therefore inferred nutrient leaching rates, of either leaf or wood litter in lakes following clearcutting. Despite major decreases in mass element loadings from litterfall, no substantial differences have been observed in the aqueous concentrations of TDP and DOC in lakes whose shoreline forests and catchments have been clearcut. One possible explanation for this result could be that decreased nutrient inputs from reduced litterfall were balanced out by elevated nutrient inputs to lakes from increased erosion following timber harvesting.