Seasonal variations in the washoff and leaching dynamics of throughfall ionic fluxes represent a significant process affecting the biogeochemical cycling of forested ecosystems - particularly for temperate deciduous forests. Most studies on temperate deciduous forests aggregate seasonal throughfall fluxes to the leafed (growing) and leafless (dormant) periods, yet the phenological conditions controlling seasonality demand finer-scale demarcations. In particular, the state of knowledge regarding transitional stages and washoff/leaching variability is weak. To fill these gaps this study examines washoff and leaching dynamics of Na+, Mg2+, K+, Ca2+, Cl-, SO42-, and NO3- throughfall fluxes derived from 16 sequentially sampled rain events across both seasonal and transitional periods. As throughfall washoff and leached solute fluxes are also closely-coupled to rainfall conditions, we further examine the effects of storm characteristics on seasonal washoff (using Na+ and Cl-) and leaching (using K+, Ca2+, & Mg2+) trends through intrastorm event comparison plots and factorial MANOVA. The MANOVA results show highly significant differences in leached and washoff solute fluxes across meteorological conditions (p<0.05) and among the seasonal divisions (p<0.00001). In fact, the greatest differences in leached fluxes were not between the standard leafed and leafless seasons (33-50% greater during the leafed season), but between the transitional periods (10-200 fold greater during senescence than leaf-out). Overall, for all leached ions barring NO3-, leached flux was greatest during senescence, followed by either the leafless or full leafed season, and least during leaf-out. NO3- fluxes were low across seasonal divisions, and uptake was observed during leaf-out. Washoff flux was greatest during full leaf (likely due to enhanced aerodynamic roughness and surface area for precipitation scavenging), followed by senescence, leaf-out, and the leafless season. Event comparisons used to evaluate the effects of meteorological conditions on seasonal washoff and leaching dynamics further indicate that antecedent dry period, precipitation amount, duration and intensity exert apparent influences over the timing and flux of washoff and leached canopy-derived solutes to the forest soil within storm events across seasonal divisions.
Available at: http://works.bepress.com/john_vanstan/26/