Atmospheric deposition is acknowledged to be an important process in the biogeochemical cycling of forests, yet no single study is known that has examined both throughfall and stemflow chemistry in relation to atmospheric deposition across time scales, from within discrete events to season. This research partitions stemflow and throughfall solute fluxes (K+, Na+, Mg2+, Ca2+, Cl-, NO3-, SO42-) from two tree species with disparate canopy structures into their leaching and dry deposition washoff components to examine differences within and among individual rain events. Seasonal-scale leaching and washoff dynamics are investigated utilizing event-based chemical enrichment and depletion ratios. Intrastorm leaching percentages generally increase as throughfall pathways are initiated and expand for base cations, yet decrease for dominant anions across species. All intrastorm Fagus grandifolia Ehrh. (American beech) stemflow solute fluxes started with high dry deposition percentages then shifted toward increased leachate contributions. Liriodendron tulipifera L. (yellow poplar) was much more inconsistent, with dry deposition percentages of anions generally increasing, Na+ and Mg2+ dry deposition proportions decreasing (with the exception of the last two samples attributed to the initiation of new flowpaths), and K+ and Ca2+ leaching remaining more or less stable throughout an event. Generally, the stemflow washoff component from smooth-barked F. grandifolia was greater than the rough-barked, more plagiophile L. tulipifera at the interstorm scale, whereas L. tulipifera generated larger stemflow leached percentages. These findings: (1) underscore the essential role of new flowpath initiation, expansion, and maturation on a tree’s surface to solute enrichment and transport to the forest floor as a canopy wets-up and reaches saturation; and (2) indicate that the temporal scale of analysis of canopy-derived fluxes can improve our understanding of the effect of variable time scales on biogeochemical cycling in forests.
Delphis F. Levia, Newark, Delaware, USA, 19716-2541
Levia, D.F., J.T. Van Stan, C.M. Siegert, S.P. Inamdar, M.J. Mitchell, S.M. Mage, P. McHale. (2010): Atmospheric Deposition and Corresponding Variability of Throughfall and Stemflow Chemistry Across Temporal Scales in a Mid-Atlantic Broadleaved Deciduous Forest . Abstract H53F-1106. AGU Fall Meeting, San Francisco, CA, December 13-17..