Groundtruthing and Potential for Predicting Acid Deposition Impacts in Headwater Streams Using Bedrock Geology, GIS, Angling, and Stream Chemistry
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Author's personal copy SCIENCE OF THE TOTAL ENVIRONMENT 393 (2008) 249– 261 available at www.sciencedirect.com www.elsevier.com/locate/scitotenv Groundtruthing and potential for predicting acid deposition impacts in headwater streams using bedrock geology, GIS, angling, and stream chemistry C.S. Kirby⁎, B. McInerney, M.D. Turner Department of Geology, Bucknell University, Lewisburg PA 17837, United States ARTICLE INFO ABSTRACT Article history: Atmospheric acid deposition is of environmental concern worldwide, and the determination Received 10 July 2007 of impacts in remote areas can be problematic. Rainwater in central Pennsylvania, USA, has a Received in revised form mean pH of ≈4.4. Bedrock varies dramatically in its ability to neutralize acidity. A GIS 13 December 2007 database simplified reconnaissance of non-carbonate bedrock streams in the Valley and Accepted 17 December 2007 Ridge Province and identified potentially chronically impacted headwater streams, which Available online 6 February 2008 were sampled for chemistry and brook trout. Stream sites (n=26) that originate in and flow through the Tuscarora had a median pH of 5.0 Keywords: that was significantly different from other formations. Shawangunk streams (n=6) and non- Brook trout Tuscarora streams (n=20) had a median pH of 6.0 and 6.3, respectively. Mean alkalinity for Sandstone geology non-Tuscarora streams (2.6 mg/L CaCO3) was higher than the mean for Tuscarora streams Stream impairment (0.5 mg/L). Lower pH and alkalinity suggest that the buffering capability of the Tuscarora is Geographic information systems inferior to that of adjacent sandstones. Dissolved aluminum concentrations were much Pennsylvania higher for Tuscarora streams (0.2 mg/L; approximately the lethal limit for brook trout) than Acid impacted for non-Tuscarora streams (0.03 mg/L) or Shawangunk streams (0.02 mg/L). Hook-and-line methods determined the presence/absence of brook trout in 47 stream reaches with suitable habitat. Brook trout were observed in 21 of 22 non-Tuscarora streams, all 6 Shawangunk streams, and only 9 of 28 Tuscarora stream sites. Carefully-designed hook-and-line sampling can determine the presence or absence of brook trout and help confirm biological impacts of acid deposition. 15% of 334 km of Tuscarora stream lengths are listed as “impaired” due to atmospheric deposition by the Pennsylvania Department of Environmental Protection. 65% of the 101 km of Tuscarora stream lengths examined in this study were impaired. © 2007 Elsevier B.V. All rights reserved. 1. Introduction that central Pennsylvania had average rainfall pH of 4.4, which has slowly increased in recent years (NADP, 2006). In 1.1. Background the northeastern and eastern regions of the USA, sulfate deposition is declining and precipitation pH is increasing Atmospheric acid deposition is a considerable environmen- (NADP, 2006; Driscoll et al., 2003). However, the pH, sulfate and tal problem in many regions worldwide (Rodhe et al., 2002; acid-neutralizing capacity (ANC) responses of streams and Larssen et al., 2006) that are downwind of coal-fired power lakes have not followed the precipitation changes equally in plants and other combustion sources. Data from 2004 showed all regions (e.g., Webb et al., 2004; Kahl et al., 2004; Palmer ⁎ Corresponding author. Tel.: +570 577 1385; fax: +570 577 3031. E-mail address: [email protected] (C.S. Kirby). 0048-9697/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2007.12.026 Author's personal copy 250 SCIENCE OF THE TOTAL ENVIRONMENT 393 (2008) 249– 261 et al., 2004); these pH and ANC increases in streams lag behind take decades after acid deposition is reduced (e.g., Driscoll decreases in atmospheric sulfate deposition due to complex et al., 2003). Ecosystem recovery can experience lag times of soil/groundwater interactions. several decades following chemical recovery (NAPAP, 2005). Some aquatic ecosystems are protected by soils or bed- Similar conclusions are drawn for northern European ecosys- rock geology that provide long-term buffering capability (Lang- tems (Forsius et al., 2003; McCartney et al., 2003; Clair and muir, 1997); the most typical example given is the essentially Hindar, 2005). Because of the dynamic nature of ecosystem inexhaustible buffering capability of carbonate bedrock. Silici- changes relating to acid deposition, we need methods for tar- clastic sedimentary, igneous, and metamorphic rocks com- geting potentially impaired streams in remote areas and for monly have much lower ANC and release alkalinity more slowly rapidly and cheaply assessing chemistry and biology. than carbonates. A Virginia, USA study showed that ANC is highest in crystalline bedrock and lowest in siliciclastic bed- 1.2. Impairment assessments: Simple may not be better, rock (Cosby et al., 1991). A German study concluded that in but it may be more realistic non-carbonate systems, rock acid-neutralizing capacities, ANCs, from which streams derive ANCaq, increased in order Acid precipitation impacts on watersheds and biota are in- from quartzite, shale and greywacke, granite to gneiss (Frei triguing in their complexity, yet startlingly simple in effect: et al., 1998). Schindler et al. (1986) concluded that in some fish have been extirpated and ecosystems dramatically altered. Canadian lakes within-lake biological process provided more Many impacted streams and lakes are often in remote (therefore ANC than geological sources. Welsh and Perry (1997) concluded infrequently-sampled) headwater areas with beautiful habitat that West Virginia streams in two formations commonly had and clear water, thus many impaired streams are not identified pHb5.5 due to inability to neutralize acid precipitation. Sharpe as such, and acid deposition has been referred to as a “silent et al. (1987) found that sandstone formations in the Alleghany killer” for this reason. Plateau of Pennsylvania differed in their ability to provide ANC Governmental departments of environmental protection to streams. or environmental quality are charged with determining the In geological formations with ANCs that experience acid extent of negative impacts on watersheds. In many cases, precipitation, depressed pH values correlate with elevated these agencies have nearly impossible tasks because of the aluminum concentrations, but the relationship is not gov- time and money required to carefully examine a large number erned by a single simple mineral solubility. Dissolved organic of streams, many of which are remote and/or on private land carbon (DOC), hydroxyl, fluoride, sulfate, and silica commonly that is not easily accessed. For example, in Pennsylvania, 17% can complex aluminum in acid streams (e.g., Nordstrom and of the 1.3×105 km of streams had not been officially assessed May 1996; Lindsay and Walthall 1996; Driscoll and Postek for “impairment” of any nature (PA DEP, 2004; PSIE, 2004)as 1996; Doucet et al., 2001), and the presence of such ligands of 2004. The Pennsylvania Department of Environmental Pro- causes the total dissolved aluminum concentration to increase. tection (PA DEP) cannot continuously regularly reassess all Aluminum solution chemistry is further complicated by the of these streams, or even those already deemed impaired. In existence of polynuclear aluminum species (Bertsch and Parker addition, some streams were assessed as “naturally acidic” 1996). when they were likely impaired due to atmospheric deposition Aquatic macroinvertebrates and fish populations suffer (R. Ryder, pers comm, PA DEP, 2007). or are eliminated in aquatic ecosystems where bedrock geol- When agencies do assess, they commonly rely on fewer ogy has little ability to neutralize the excess acid. The exact data than many acid precipitation specialists would consider causes of fish disease, reproductive difficulties, and mortality adequate (PA DEP 2007, PADEP undated). Extensive chemical are complex, as are the effects of aluminum speciation on analyses are the exception rather than the rule (R. Ryder PA toxicity (e.g., Parkhurst et al., 1990; Wood 1989; Wood et al., DEP pers comm). Total or total dissolved aluminum may be 1990; Ingersoll et al., 1990; Maitat et al., 2000). Increasing the only aluminum data collected. Fluoride, DOC, and silica − inorganic monomeric Al (Al3+ and its OH complexes) con- are not likely to be measured, and no aluminum speciation centrations due to decreased pH are primary factors in fish is determined by experiment or by geochemical computer population declines. The presence of dissolved organic carbon programs. Alkalinity by fixed-pH endpoint titration may be the (DOC), fluoride, and silica tend to decrease aluminum tox- only approximation of ANC. icity given the same total concentrations of aluminum (e.g., Parkhurst et al., 1990; Baldigo and Murdoch 1997; Exley et al., 1.3. This study 1997; Exley et al., 2002; McCartney et al., 2003). Measured or calculated acid-neutralizing capacity (ANC) is another value We investigated the relationship between bedrock sand- that is critical to understanding acid precipitation impacts. stone geology and acid neutralization in central and eastern Various methods are used to determine ANC, including Gran Pennsylvania, USA. Pennsylvania receives some of the lowest titration and calculation of ANC from dissolved ions, but there pH rainfall in the USA (NADP, 2006). The headwater streams of is no complete agreement on which measurement or calcula- the Valley and Ridge Geologic Province flow primarily through tion is best (McCartney