Annual wet and dry deposition of sulfur and nitrogen in the snowy range, Wyoming

The collocation of three national networked programs NADP, EPA's CASTNET, a nd the Forest Service's IMPROVE Module A, within a few hundred meters of ea ch other in the pristine Medicine Bow forest of Wyoming has made it possibl e to assess the total amount of sulfur and nitrogen deposition, both wet an d dry for this alpine/subalpine ecosystem. Additional sites within a few ki lometers add spatial depth to this study. Wet deposition assessed using NAD P data accounts for 1 to a little over 3 kg ha(-1) yr(-1) for both nitrogen and sulfur; however, annual trends for the two species differ. Dry deposit ion assessed using both CASTNET (a.k.a. NDDN) and IMPROVE (for sulfur) indi cates 1-2 kg ha(-1) yr(-1) for nitrogen but less than 1 kg ha(-1) yr(-1) fo r sulfur. The overall trend of wet plus dry for nitrogen has been downward from 5 kg ha(-1) yr(-1) in 1989 to 3.6 kg ha(-1) yr(-1) in 1994, while vary ing between 2 and under 4 kg ha(-1) yr(-1) for sulfur. This paper introduce s the sites and presents the three programs and the analysis approach. Spat ial comparisons between sites are investigated. Weekly data are analyzed fr om three NADP sites, separated horizontally 6.8 and 2.4 km and vertically 4 30 and 98 m from the highest elevation site. The site comparisons demonstra te that winter season data requires careful analysis due to the Vagaries of inefficient precipitation collection during high winds and snow fall. (C) 2000 Elsevier Science Ltd. All rights reserved.