No abstract

National parks in the United States are protected areas wherein the natural habitat is to be conserved for future generations. Deposition of anthropogenic nitrogen (N) transported from areas of human activity (fuel combustion, agriculture) may affect these natural habitats if it exceeds an ecosystem-dependent critical load (CL). We quantify and interpret the deposition to Class I US national parks for present-day and future (2050) conditions using the GEOS-Chem global chemical transport model with 1/2° × 2/3° horizontal resolution over North America. We estimate CL values in the range 2.5–5 kg N ha⁻¹ yr⁻¹ for the different parks to protect the most sensitive ecosystem receptors. For present-day conditions, we find 24 out of 45 parks to be in CL exceedance and 14 more to be marginally so. Many of these are in remote areas of the West. Most (40–85%) of the deposition originates from NO_x emissions (fuel combustion). We project future changes in N deposition using representative concentration pathway (RCP) anthropogenic emission scenarios for 2050. These feature 52–73% declines in US NO_x emissions relative to present but 19–50% increases in US ammonia (NH₃) emissions. Nitrogen deposition at US national parks then becomes dominated by domestic NH₃ emissions. While deposition decreases in the East relative to present, there is little progress in the West and increases in some regions. We find that 17–25 US national parks will have CL exceedances in 2050 based on the RCP8.5 and RCP2.6 scenarios. Even in total absence of anthropogenic NO_x emissions, 14–18 parks would still have a CL exceedance. Returning all parks to N deposition below CL by 2050 would require at least a 50% decrease in US anthropogenic NH₃ emissions relative to RCP-projected 2050 levels

The core parks included three west coast (OLYM, MORA, and SEKI), three Alaska parks (NOAT, GAAR, DENA), and two parks in the Rocky Mountains (ROMO and GLAC). We selected two sampling sites (i.e. lakes) in each park, with the exception of NOAT and GAAR, where we sampled one site in each, for a total of 14 sites. Lakes were selected to have no glaciers in their watersheds, relatively simple bathymetry, minimal inlets and outlets and an established salmonid spp.population that we were permitted to sample. B.) Sample matrices and the rationale for their selection:The WACAP study was designed as a screening study to assess contaminant concentrations across large-scale spatial gradients and temporal scales relevant to western national parks. The seven ecosystem components selected for analysis were: air, snow, water, lake sediments, lichens, conifer needles, and fish. These components were chosen for the reasons described below.End-of-season snowpack samples contain an integrated record of wet and dry contaminant deposition occurring during the snow-accumulation season. A significant proportion of the contaminant load in snowpack may be delivered to the ecosystem during snowmelt (with specific fates varying by contaminant). We used snowpack samples, collected from the vertical face of snow pits dug from the snow surface to the ground, to calculate contaminant flux delivered via snow (3).We used passive air sampling devices (PASD) to: (a) obtain a measure of SOCs in ambient air by means of a simple, standardized technology to compare loadings among parks and across geographic and elevational gradients, (b) compare PASD and vegetation

Concentrations of polybrominated diphenyl ethers (PBDEs), pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons were measured in 136 fish from 14 remote lakes in 8 western U.S. National Parks/Preserves between 2003 and 2005 and compared to human and wildlife contaminant health thresholds. A sensitive (median detection limit--18 pg/g wet weight), efficient (61% recovery at 8 ng/g), reproducible (4.1% relative standard deviation (RSD)), and accurate (7% deviation from standard reference material (SRM)) analytical method was developed and validated for these analyses. Concentrations of PCBs, hexachlorobenzene, hexachlorocyclohexanes, DDTs, and chlordanes in western U.S. fish were comparable to or lower than mountain fish recently collected from Europe, Canada, and Asia. Dieldrin and PBDE concentrations were higher than recent measurements in mountain fish and Pacific Ocean salmon. Concentrations of most contaminants in western U.S. fish were 1-6 orders of magnitude below calculated recreational fishing contaminant health thresholds. However, lake average contaminant concentrations in fish exceeded subsistence fishing cancer thresholds in 8 of 14 lakes and wildlife contaminant health thresholds for piscivorous birds in 1 of 14 lakes. These results indicate that atmospherically deposited organic contaminants can accumulate in high elevation fish, reaching concentrations relevant to human and wildlife health.