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Impacts of Acid Deposition on Water Quality and Aquatic Biota

PI: John Schwartz, Civil and Environmental Engineering;
a Cooperative Agreement between National Park Service and UT

picture of GSMNP
Figure 2. Photos of the Noland Divide Watershed, high-elevation monitoring station in the Great Smoky Mountains National Park. From upper left to lower right, MS student Andrew Veeneman calibrating a water quality sonde at a H-flume, and installing a new pressure transducer at the same site; Dr. John Schwartz at one of the two 3-ft H-flumes, and the instrumentation in the soil lysimeter pit.
picture of GSMNP
Figure 1. High-elevation landscape view within the Great Smoky Mountains National Park

Project Description—For decades, acidic air pollutants from regional and local sources have been transported by prevailing wind currents and deposited onto high-elevation watersheds in the Great Smoky Mountains National Park (GRSM), on the Tennessee/North Carolina border (Figure 1). In order to investigate the potential effects of acid deposition on stream water quality, the GRSM began a Water Quality (WQ) Monitoring Program in 1991 consisting of: 1) detailed hydrologic and biogeochemical monitoring at Noland Divide Watershed (NDW), a high-elevation forested site, and 2) Park-wide stream survey monitoring for spatial mapping and temporal trend analysis of stream acidification. Figure 2 shows photos at the NDW monitoring station. In addition to the routine monitoring, special studies are conducted to investigate questions that remain on the fate, biogeochemical transformation, and transport of acid/base ions and dissolved metals. This past year two special studies are on-going; they are: 1) a sulfate isotope analysis to quantify the mass flux of sulfate generated from the high-elevation Anakeesta pyritic shale formation in comparison to acid deposition inputs; and 2) a throughfall chemistry mapping, which has been over 15 years since the last GRSM effort by Dr. Kathleen Weathers at Cornell University (Fig. 3). We work to gether with Dr. Charles Driscoll at Syracuse University, in which his research team developed and uses the BGC-PnET model for estimating critical loads in the GRSM.

map of GSMNP
Figure 3. Map of the Great Smoky Mountains National Park showing the 23 throughfall monitoring sites, and the watersheds sampled on a bimonthly basis per grab samples and analyzed for acid anions, base cations, and dissolved metals.

One of the most interesting investigations is the observed responses in deposition and stream chemistry due to emission reductions from local and regional coal-fired power plants. Many geochemistry parameters of wet/dry deposition at the monitoring site show strong and direct responses to emissions reductions: measured deposition amounts decreased, precipitation pH and ANC increased, and nitrogen speciation in precipitation samples shifted; all within the same 2008-2009 time frame. Through fall sulfate deposition has declined from above 1,500 eq/ha/yr before 2007 to approximately 500 eq/ha/yr after which. However, the changes in deposition have not yet translated to significant changes in stream sulfate concentrations or annual mass exports. It appears the lack of response in stream sulfate is influenced by the biogeochemistry in associated with the nitrogen cycle dynamics, base cation availability, and carbon-sulfate dynamics.

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Photo of Andrew Veeneman sampling water on Palmer Creek in the Great Smoky Mountains.

Annual Activities 2016-17—Long-term research continues in the Great Smoky Mountains National Park (GRSM) investigating the impacts of acid deposition from atmospheric pollution due to various sources including coal-fired power plants, vehicle exhaust, and agriculture. Various research projects are active with the cooperative agreement. A high-elevation monitoring station at Noland Divide is maintained which includes a deposition collector, full weather station, soil lysimeter pit with vacuum pump collection system for three horizons, soil moisture and air temperature probes, throughfall collectors, flow recorders at two 3-ft H flumes and water quality data sondes. Streamlet water samples are collected biweekly along with water samples collected from the other devices. This research is specifically to enhance our understanding of the biogeochemical processes within high elevation watersheds exposed to acid deposition. Watershed budgets for acid anions and base cations examining mass net export has provided key information on the fate and transport of acid pollutants. At the station, we reported the rapid drop in sulfate deposition immediately following the installation of air pollution equipment at TVA’s Bull Run and Kingston Power Plants. Our team also assists in the routine bimonthly Park-wide stream water collections, in which our Water Quality (WQ) Laboratory at the University of Tennessee conducts the chemical analyses. This effort is part of a broader National Park Service (NPS) Initiative called the Vital Sign Program. This program is a 20-year research effort to ensure water, air, soil, and vegetation surveys are coordinated in space and time nationally. We have two special on-going studies, Masters student Andrew Veeneman is revising the throughfall deposition map, which is over 15 years dated since the last published park-wide characterization of acid deposition in the GRSM.  Doctoral student Adrian Gonzalez is investigating sulfate dynamics in the GRSM, which includes the use of isotopes for source tracking of atmospheric (meteoric)  and pyrite geology contributions of sulfate to streams. This research includes soil biogeochemical processes for retention potential and the environmental factors influencing export from small catchments.  

Our cooperative agreement for water quality analysis is expanding and now includes the Appalachians Highlands Network. The goal for this year is to officially accredit our Water Quality Laboratory and hire a full-time lab manager. The Carolina-Florida Coastal Vital Signs Program plans to use our water quality facilities with specific research goals in 2018. Other NPS programs have expressed interest in our water quality analytical and research capabilities. With our WQ laboratory accreditation and program expansion, research opportunities among UTK faculty are expected to grow. 

Annual Activities 2015-16—During 2015 at the NDW site precipitation volumes collected from the throughfall (TF) and open-site collection (OS) sites were 241 cm and 141 cm, respectively. Mean pH of samples collected at TF and OS sites was 5.18 ± 0.5 and 5.24 ± 0.1, respectively. Total sulfate deposition at TF for 2015 was 394 equivalents per hectare (eq ha-1), or 18.9 kilograms per hectare (kg-SO4 ha-1). Total inorganic nitrogen (T.I.N.; sum of ammonium & nitrate) deposition at TF was 696 eq ha-1, or 32.0 kg-TIN ha-1. Soil water pH at the NDW monitoring station was 4.53 ± 0.16, 4.64 ± 0.02, and 4.63 ± 0.14, in the upper, middle and lower soil horizons, respectively. The NE and SW streamlets during 2015 had an annual average pH of 5.77 ± 0.02 and 5.97 ± 0.02, respectively. These streamlets had a mean acid neutralizing capacity (ANC) of 7.3 ± 0.4 and 14.2 ± 0.8 microequivalents per liter (µeq L-1), respectively. Of the Park-wide stream survey sites monitored in 2015, 35 of the 265 samples had a pH below 6.0 and an ANC below 20 µeq L-1. These were collected from a few sites historically observed with low pH and ANC stream water, including Double Springs Gap Shelter, Cosby-Rock creek watershed, and Porter-Cannon creek watershed. Total dissolved aluminum (Al) in only six samples (collected from only three sites) in 2015 was ≥ 0.08 mg L-1, a toxicological threshold concentration very near the analytical reporting limit of 0.05 mg/L. These sites are also associated with the lowest measured stream water pH and ANC, consistent with dissolution of aluminum from soils and bedrock minerals. The water pH at Vital Signs stream monitoring sites in 2015 was 6.30 (overall mean; N = 265) and ranged between 5.24 and 7.53. A combination of factors in individual GRSM watersheds, i.e., bedrock geology, soil, and vegetation appears to define the how biogeochemical processes influence the fate and transport of acid deposition pollutants migrating through the soils and entering streams.