Biogeochemical Influence of Vegetation and Soils in the ILWAS Watersheds

Abstract

The ILWAS catchments (Panther, Sagamore, and Woods) contain closely related variants of the northern hardwood-spruce-fir complex of the Adirondack Region. Dominant species in these watersheds are: American beech, sugar maple, red spruce, red maple, and yellow birch. On an areal basis, the watersheds contain 57 to 88% hardwood cover type and range in percent coniferous cover from 28% in Sagamore watershed to 5% in Woods catchment. Mean live basal area values range from 22 to 30 m² ha^-1 between catchments, while mean live stem densities range from 1400 to 1700 stems ha^-1. Weighted average leaf area indices for the watersheds range from a low of 5.2 in Woods to a high of 7.2 in Sagamore. The higher leaf area in Sagamore watershed may enhance the collection of dry deposition and may explain the higher SO₄ ^2- concentrations in surface waters within that system.

Soils in the ILWAS watersheds are predominantly Becket series Haplorthods, Fragiorthods, and Haplaquods. Soil chemical properties are almost identical in the acid lake catchment (Woods) and the circumneutral lake catchment (Panther). The soils are characterized by a low percent base saturation (generally < 8% B.S.), exhibit pH values ranging from 2.9 in the forest floor to 4.7 in the BC horizon, and contain relatively low concentrations of soluble and adsorbed SO₄ ^2-.

SO₄ ^2- is the dominant solution anion in upper soil layers within all three watersheds and in the lake waters of Woods and Sagamore basins. However, nitrate concentrations are also unusually high in soil solutions, suggesting that the systems may be N-saturated with respect to atmospheric inputs. Levels of organic acidity are elevated in surface horizon solutions and decline significantly with soil depth. In general, soil water chemistries in the Woods and Panther catchments are almost indistinguishable. Thus, the differences in lake pH and alkalinity cannot be explained on the basis of inter-watershed contrasts in soil chemistry and soil solution chemistry. Much of the explanation can be related to inter-watershed differences in hydrologic flow paths, coupled with distinct differences in solution chemistry between separate soil horizons and till strata.