A direct comparison of throughfall plus stemflow to estimates of dry and total deposition for sulfur and nitrogen

Abstract

At a mid-elevation hardwood forest located near Ithaca, NY, bulk net throughfall (NTF) plus stemflow (SF) for sulfur and nitrogen were compared with dry deposition estimates of sulfur and nitrogen, using the inferential techniques adopted by the 50-station National Dry Deposition Network (NDDN). Total deposition (wet plus dry) of sulfur and nitrogen are also compared. Annual dry (NDDN) and total deposition estimates for sulfur were 4.5 and 13.4 kg S ha −1, respectively during 1992. Annual NTF plus SF deposition was 6.0 kg S ha −1 and throughfall (TF) plus SF was 14.9 kg S ha −1. For total (wet + dry) sulfur deposition the two approaches differed by 10%. Annual dry (NDDN) and total nitrogen deposition estimates were 3.6 and 11.4 kg N ha −1, respectively, during 1992. Annual NTF + SF deposition and total deposition, measured as NO 3 − + NH 4 + were 3.2 and 11.0 kg N ha −1, respectively. If organic nitrogen is included NTF + SF is 4.6 kg N ha −1, and total TF + SF deposition is 12.4 kg N ha −1. Stemflow was a significant component of total deposition at our site, representing 16% of the sulfur and 12–13% of the nitrogen deposition. Our results, as well as those from the Integrated Forest Study, and others, support the hypothesis that NTF + SF and TF + SF represent reasonable estimates of dry and total sulfur deposition respectively. NTF + SF and TF + SF have the potential to estimate dry and total nitrogen deposition also. However, using TF + SF techniques for estimating total or dry deposition of nitrogen may be appropriate only on a time scale of several weeks or longer.