Boreal Mixedwood Watershed Riparian Zone Cation Cycling During Two Contrasting Climatic Years.

Riparian zones are key transfer points of water, alkalinity, and cations from terrestrial to aquatic ecosystems. Base cation cycling in, and fluxes from, forested and alder swamp riparian zones were investigated for one climatically 'normal' and one dry season. The soil extractable base cation pools and pH were higher in the alder riparian type.  Combined measurements of litter, forest floor, mineral soil, and soil solution indicates that base cation uptake in both riparian types occures from the mineral soil. It is not known, however, if uptake is from the upper or deeper mineral soil. Litter N, P. Ca, and Mg indicate the forested ripairan type is more sensitive to base cation depletion than the alder type. Soil solution base cation concentration in the forested ripairan type were attributed to Si-mineral weathering and organic matter mineralization.  In contrast carbonate, probably calcite weathering was more common in the alder riparian zone. Base cation stoichiometry was similar between years and riparian types, but the proportion of anions shifted to dominance by SO42- and organic acids during fall of the drier year, which resulted in a higher flux of those anions. The anion shifts, however, were not reflected in the cation fluxes. Uncertainties in shifts in litter quality, mineralization, and hydrological flux in response to temperature and moisture change require further documentation to adequately deduce the role of such changes, along with rainfall amounts, on base cation cycling in riparian zones