Nitrogen Deposition Effects on Diatom Communities in Lakes from Three National Parks in Washington State.

Richard W Sheibley,Peter W Swarzenski,Patrick W Moran,Mihaela Enache,James R Foreman

doi:10.1007/s11270-013-1857-x

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−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.

Highlights

Human alteration of global biogeochemical cycles has been well documented and observed changes have been dramatic over the last century (Galloway et al 1995; Schlesinger 1997; Vitousek et al 1997)
Park-averaged N and S summer bulk deposition was greatest at North Cascades (NOCA), with OLYM having the lowest values, and Mount Rainier National Park (MORA) lying in between (Table 2)
Estimates of N deposition across 12 lakes in three National Parks were variable within and across Parks based on summer bulk deposition samples

Summary

Introduction

Human alteration of global biogeochemical cycles has been well documented and observed changes have been dramatic over the last century (Galloway et al 1995; Schlesinger 1997; Vitousek et al 1997). Atmospheric deposition of N is of particular concern because effects are usually greatest near the sources of pollution (Fenn et al 2003a), impacts of N enrichment from deposition can be seen in areas located far from pollution sources (Saros et al 2003; Elser et al 2009; Greaver et al 2012) making increased N deposition a local, regional, and national issue. There has been a significant increase in studies pertaining to the effects and impacts of increased N deposition on terrestrial and aquatic ecosystems in the USA in the last 15 years (Fenn et al 2003b; Sickman et al 2003; Elser et al 2009; Pardo et al 2011; Greaver et al 2012)

Objectives

Discussion

Conclusion