title: Nitrogen Deposition Effects on Diatom Communities in Lakes from Three National Parks in Washington State.
abstract: The goal of this study was to document if lakes in National Parks in Washington have exceeded critical levels of nitrogen (N) deposition, as observed in other Western States. We measured atmospheric N deposition, lake water quality, and sediment diatoms at our study lakes. Water chemistry showed that our study lakes were ultra-oligotrophic with ammonia and nitrate concentrations often at or below detection limits with low specific conductance (<100 μS/cm), and acid neutralizing capacities (<400 μeq/L). Rates of summer bulk inorganic N deposition at all our sites ranged from 0.6 to 2.4 kg N ha-1year-1and were variable both within and across the parks. Diatom assemblages in a single sediment core from Hoh Lake (Olympic National Park) displayed a shift to increased relative abundances ofAsterionella formosaandFragilaria tenerabeginning in the 1969-1975 timeframe, whereas these species were not found at the remaining (nine) sites. These diatom species are known to be indicative of N enrichment and were used to determine an empirical critical load of N deposition, or threshold level, where changes in diatom communities were observed at Hoh Lake. However, N deposition at the remaining nine lakes does not seem to exceed a critical load at this time. At Milk Lake, also in Olympic National Park, there was some evidence that climate change might be altering diatom communities, but more research is needed to confirm this. We used modeled precipitation for Hoh Lake and annual inorganic N concentrations from a nearby National Atmospheric Deposition Program station, to calculate elevation-corrected N deposition for 1980-2009 at Hoh Lake. An exponential fit to this data was hindcasted to the 1969-1975 time period, and we estimate a critical load of 1.0 to 1.2 kg N ha-1year-1for wet deposition for this lake.
authors.affiliation: US Geological Survey, Tacoma, WA 98402 USA.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Sheibley
authors.affiliation: Academy of Natural Sciences, Philadelphia at Drexel University, Philadelphia, PA 19103 USA ; NJ Department of Environmental Protection, Trenton, NJ 08625 USA.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Enache
authors.affiliation: US Geological Survey, Santa Cruz, CA USA.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Swarzenski
authors.affiliation: US Geological Survey, Tacoma, WA 98402 USA.
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Moran
authors.affiliation: US Geological Survey, Tacoma, WA 98402 USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Foreman
keywords: Critical loads; DIN/TP; Diatoms; Lake chemistry; N deposition; National Parks