Effects of Collection Interval on Quality of Throughfall Samples in Two Northern Hardwood Stands

Abstract

AbstractThe chemical stability of weekly and biweekly throughfall collection intervals were compared at two northern hardwood stands in the Great Lakes region. Throughfall concentrations of Cl−, NO−3, SO2−4, Ca2+, Mg2+, and K+ were not significantly (p ≤ 0.05) affected by the increased collection time, where as throughfall concentrations of NH+4 and H+ collected biweekly were significantly different (p ≤ 0.05) than concentrations of these ions in weekly samples. The 1‐wk increase in collection interval at one stand decreased concentrations of NH+4 and increased concentrations of H+ 88 and 131%, respectively. The chemical instability of these ions appeared to be related to biological assimilation and/or nitrification of NH+4. Stability of these ions decreased with increasing concentrations of inorganic N in the throughfall. These changes in concentrations of NH+4 and H+ may introduce sampling bias when estimating throughfall fluxes or concentrations of these ions from biweekly collections. The decreased stability of these ions with increased concentrations of inorganic N should be an important consideration when selecting sampling intervals for stands that receive differing deposition levels of atmospheric N or have different canopy retention rates of N.