Factors Controlling Throughfall Characteristics at a High Elevation Sierra Nevada Site, California

Abstract

AbstractThe composition of throughfall (TF) is influenced by wet and dry deposition on foliar surfaces and by chemical and biological interactions between rain and the foliage. The relative importance of these processes was investigated for TF collected in the summer months of 1985, 1986, and 1987 under three subalpine species, chinquapin (Chrysolepis sempervirens Hjelmqvist), western white pine (Pinus monticola Dougl.), and willow (Salix orestera Schneider), in the Emerald Lake Watershed, Sequoia National Park, California. The depth of rain and days since the last storm were used to predict net‐TF deposition in a multiple linear regression model. Dry deposition to needle surfaces had the greatest influence on western white pine TF composition. Net‐TF data for this species were used to estimate mean dry deposition rates for the summer. These data show that NH+4, NO−3, and SO2−4 dry deposition rates exceed median summer wet deposition rates by 1.5, 1.9, and 1.0 times, respectively. Willow foliage had the greatest influence on TF composition and western white pine the least. Estimated foliar release of cations and organic anions by willow during summer rain is a substantial fraction of annual wet deposition of those ions. Weak organic acid anions derived from foliar release are a significant component of net‐TF in all three species, particularly willow, where summer fluxes of organic acids were at least 51% of the total estimated annual wet deposition of organic anions.