Nitrogen Deposition Effects on Diatom Communities in Lakes from Three National Parks in Washington State.
Bottom Line: However, N deposition at the remaining nine lakes does not seem to exceed a critical load at this time.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(-1) year(-1) for wet deposition for this lake.
Affiliation: US Geological Survey, Tacoma, WA 98402 USA.
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(-1) year(-1) and 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 of Asterionella formosa and Fragilaria tenera beginning 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(-1) year(-1) for wet deposition for this lake.
No MeSH data available.
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Mentions: A total of 12 lakes were selected for this study from Mt. Rainier (MORA), North Cascades (NOCA), and Olympic (OLYM) National Parks in Washington State (Fig. 1). Sites were selected to maximize observation of potential impacts from N deposition. We targeted lakes above the tree line (above ∼1,200 m) at each park to reduce the data variability associated with N fixation and geochemical processing by subalpine plant species, namely the red alder (Alnus sp.) (Rojas et al. 2001). Lakes with significant fish populations were avoided to reduce bioturbation of the sediment and to minimize changes in lake N cycling caused by the presence of fish in order to better isolate N deposition as a cause for diatom changes. We focused on lakes that were less than 25 ha with a maximum depth of 10 m or greater to balance the logistics of water sampling, sediment sampling and reduce disturbances from wildlife while still targeting “typical” lake characteristics within each park. As the main goal of this study was to assess impacts from atmospheric N deposition, lakes that currently and historically were low in nutrients (oligotrophic) were preferred. A summary of site characteristics for each lake is provided in Table 1.Fig. 1
No MeSH data available.