Low cost limestone treatment of acid sensitive trout streams in the appalachian mountains of Virginia

The method of single point, single application liming has been studied as a means of mitigating anthropogenic acid in trout streams in Virginia. Three critically acid sensitive streams were dosed with a total of five applications of limestone sand and monitored before, during and after the treatments to assess changes in water chemistry and biota. Limestone treatments of 8 to 50 tons (particle sizes 150–1000 μm), with the amounts based on sulfate deposition loading and existent stream water chemistry, were used to restore ‘lost’ acid neutralizing capacity (ANC). Contact time between the limestone bed in the stream bottom and the water was the limiting factor affecting the degree of treatment with bed length primarily controlled by the gradient of the stream at the dosing site. A single site application was able to restore approximately 2/3 of the ANC. Exponential fits of limestone consumption data were used to predict that treaments of similar streams would last from two five years before reliming was necessary. Both total and monomeric aluminum levels were reduced up to 50%, and aquatic biota increased below the treatment sites. Post-liming average values for the three streams were pH 6.66, 82.7 μeq L^?1 ANC and 2.63 mg L^?1 Ca. The average ANC improvement suggests that some 88% of the native trout streams in Virginia, which average 29 μeq L^?1 ANC reduction from acid deposition, could be temporarily restored using single application liming.     

EVIDENCE OF RECOVERY FROM ACIDIFICATION IN MASSACHUSETTS STREAMS

A ten year survey of water quality in 330 Massachusetts streams was conducted to examine the rate and pattern of recovery from acidification. Meta-analysis was used to combine the results of the 330 non-parametric trend tests into an overall test for trend in a variety of water quality variables including pH, acid neutralizing capacity (ANC), and major inorganic ions. Analysis of trends in the raw data indicates both pH and ANC are increasing. After detrending for variations in stream runoff, we estimate the streams are recovering from acidification at a rate of +0.021 pH units/year and +2.4 μeq/L/year, for pH and ANC respectively. These trends appear to be related to declines in sulfate (–1.8 μeq/L/year), while base cation trends were mixed. Meta-analysis reveals the trends are not always homogeneous between seasons or between sites. While it is commonly assumed that the low ANC systems are most ‘sensitive’ to changes in acid or base inputs, we found the greatest rates of change in ANC were associated with the high ANC systems. The greatest increases in pH were seen in the low ANC streams as expected. The results also suggest streams respond quickly to changes in precipitation inputs and stream monitoring networks may be valuable as an early detection technique for changes in environmental quality.     

Characterizing Episodic Stream Acidity During Stormflows in the Great Smoky Mountains National Park

Episodic acidification of surface waters has been observed in the Great Smoky Mountains National Park, similar to other forested watersheds with base-poor bedrock in the eastern US receiving acids from atmospheric deposition. Three remote, forested, high-elevation streams were selected in the Little Pigeon River watershed for study; two of which brook trout have extirpated, and believed to have resulted from severe acidity during stormflows. This research characterized stream chemistry during episodes in order to better understand potential factors that contribute to rapid drops in pH and acid neutralizing capacity (ANC) during stormflows. Autosamplers initialized by sondes, collected samples during storm events for analysis of pH, ANC, cations, and anions over a 15-month period. ANC and pH depressions, and increased concentrations in sulfate, nitrate, and organic acids were observed for all storms at each study site. ANC contribution analysis indicated sulfate was the strongest contributor to ANC depressions, but nitrate, cation dilution, and organic acids were also significant in some cases. Acidic deposition appears to be the primary source of episodic acidification, supported also by the finding that larger stormflows preceded by long, dry periods resulted in significantly larger pH depressions. It appears stream acidification episodes may be driven by acid deposition. However, this study documents the variability of several ion contributors to observed stormflow ANC depressions illustrating the spatial and temporal complexity of watershed processes that influence this phenomenon.     

Acidification and Prognosis for Future Recovery of Acid-Sensitive Streams in the Southern Blue Ridge Province

This study applied the Model of Acidification of Groundwater in Catchments (MAGIC) to estimate the sensitivity of 66 watersheds in the Southern Blue Ridge Province of the Southern Appalachian Mountains, United States, to changes in atmospheric sulfur (S) deposition. MAGIC predicted that stream acid neutralizing capacity (ANC) values were above 20???eq/L in all modeled watersheds in 1860. Hindcast simulations suggested that the median historical acidification of the modeled streams was a loss of about 25???eq/L of ANC between 1860 and 2005. Although the model projected substantial changes in soil and stream chemistry since pre-industrial times, simulated future changes in response to emission controls were small. Results suggested that modeled watersheds would not change to a large degree with respect to stream ANC or soil % base saturation over the next century in response to a rather large decrease in atmospheric S deposition. Nevertheless, the magnitude of the relatively small simulated future changes in stream and soil chemistry depended on the extent to which S emissions are reduced. This projection of minimal recovery in response to large future S emissions reductions is important for designing appropriate management strategies for acid-impacted water and soil resources. Exploratory analyses were conducted to put some of the major modeling uncertainties into perspective.     

Chemical characteristics and temporal trends in eight streams of the Catskill Mountains,New York

Discharge to concentration relationships for eight streams studied by the U.S. Geological Survey (USGS) as part of the U.S. Environmental Protection Agency's (U.S. EPA) Long-Term Monitoring Project (1983–89) indicate acidification of some streams by H₂SO₄ and HNO₃ in atmospheric deposition and by organic acids in soils. Concentrations of major ions in precipitation were similar to those reported at other sites in the northeastern United States. Average concentrations of SO₄ ^2? and NO₃ ^? were similar among streams, but base cation concentrations differed widely, and these differences paralleled the differences in acid neutralizing capacity (ANC). Baseflow ANC is not a reliable predictor of stream acidity at high flow; some streams with high baseflow ANC (>150 Μeq L^?1) declined to near zero ANC at high flow, and one stream with low baseflow ANC (<50 Μeq L^?1) did not approach zero ANC as flow increased. Episodic decreases in ANC and pH during peak flows were associated with increased concentrations of NO₃ ^? and dissolved organic carbon (DOC). Aluminum concentrations exceeding 300 Μg L^?1 were observed during peak flows in headwater streams of the Neversink River and Rondout Creek. Seasonal Kendall Tau tests for temporal trends indicate that SO₄ ^2? concentrations in streamwater generally decreased and NO₃ ^? concentrations increased during the period 1983–1989. Combined acid anion concentrations (SO₄ ^2? + NO₃ ^?) were generally unchanged throughout the period of record, indicating both that the status of these streams with respect to acidic deposition is unchanged, and that NO₃ ^? is gradually replacing SO₄ ^2? as the dominant acid anion in the Catskill streams.     

Climate confounds detection of chemical trends related to acid deposition in upper Midwest lakes in the USA

Between 1983–94, as acid deposition rates declined, SO₄ ^2? concentrations decreased in 18 of 28 lakes monitored by the upper Midwest LTM program. The expected recovery of ANC and pH was less common, however. Differences in climate may account for divergent trend patterns across the region. Only in Minnesota, where climatic shifts were less pronounced, did we observe a general pattern of increasing lake ANC and pH accompanying declines in SO₄ ^2?. In contrast, the widespread negative trends in lake SO₄ ^2? in the upper Michigan lakes were generally not associated with recovery of ANC and pH, but with decreases in Ca+Mg. These cation decreases may be linked to decreased groundwater inputs during the drier climatic conditions characterizing the study period and decreases in Ca+Mg in atmospheric deposition. In many of the Wisconsin lakes, an overall decline in SO₄ ^2? was precluded by SO₄ ^2? increases during a 4-year drought midway through the study period. During the drought, declining lake water level and volume caused evaporative concentration of solutes, and may have decreased the areal extent of sulfate reduction. Despite controls on sulfur emissions across the region, recovery of pH and ANC has been hindered by climatic shifts and concurrent decreases in atmospheric deposition of cations.     

Reduced Acid Deposition Leads to a New Start for Brown Trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in an Acidified Lake in Southern Norway

Acid deposition has led to acidification and loss of fish populations in thousands of lakes and streams in Norway. Since the peak in the late 1970s, acid deposition has been greatly reduced and acidified surface waters have shown chemical recovery. Biological recovery, in particular fish populations, however, has lagged behind. Long-term monitoring of water chemistry and fish populations in Lake Langtjern, south-eastern Norway, shows that around 2008, chemical recovery had progressed to the point at which natural reproduction of brown trout (Salmo trutta) reoccurred. The stocked brown trout reproduced in the period 2008–2014, probably for the first time since the 1960s, but reproduction and/or early life stage survival was very low. The results indicate that chemical thresholds for reproduction in this lake are approximately pH?=?5.1, Al_i?=?26 μg l^?1, ANC?=?47 μeq l^?1, and ANC_oaa?=?10 μeq l^?1 as annual mean values. These thresholds agree largely with the few other cases of documented recovery of brown trout in sites in Norway, Sweden, and the UK. Occurrence and duration of acidic episodes have decreased considerably since the 1980s but still occur and probably limit reproduction success.     

Spatial Distribution of Acid-sensitive and Acid-impacted Streams in Relation to Watershed Features in the Southern Appalachian Mountains

A geologic classification scheme was combined with elevation to test hypotheses regarding watershed sensitivity to acidic deposition using available regional spatial data and to delimit a high-interest area for streamwater acidification sensitivity within the Southern Appalachian Mountains region. It covered only 28% of the region, and yet included almost all known streams that have low acid neutralizing capacity (ANC ≤20 μeq l^?1) or that are acidic (ANC ≤0). The five-class geologic classification scheme was developed based on recent lithologic maps and streamwater chemistry data for 909 sites. The vast majority of the sampled streams that had ANC ≤20 μeq l^?1 and that were totally underlainby a single geologic sensitivity class occurred in the siliceous class, which is represented by such lithologies as sandstone and quartzite. Streamwater acid-base chemistry throughout the region was also found to be associated with a number of watershed features that were mapped for the entire region, in addition to lithology and elevation, including ecoregion, physiographic province, soils type, forest type and watershed area. Logistic regression was used to model the presence/absence of acid-sensitive streams throughout the region.     

Sulphur deposition and changes in Swedish lake chemistry 1988–1993

Acidification of surface waters in northern Europe due to anthropogenic sulphur (S) deposition has led to new emission restrictions based on Critical Loads (CL). There is likely to be considerable interest in documenting the effect resulting S deposition changes have on surface water quality. This paper will focus on how the chemistry of 134 reference lakes in Sweden has changed between 1988 and 1993 in response to a decline in S deposition. Only 10% of the reference lakes had significant declines in sulphate during the 5 year study period. A similar number of lakes had an increase in the acid neutralizing capacity (ANC), but few of those with an increase in ANC were also lakes with significant sulphate decreases. Since there is good evidence that S deposition decreases will eventually result in ANC increases, a five year period is probably too short for evaluating the S protocol in terms of changes in lake chemistry. It takes a number of years to equilibriate to new deposition levels, and weather patterns may also obscure longer term trends.     

Acidification of a Small Stream on Kureha Hill Caused by Nitrate Leached from a Forested Watershed

Nitrate leakage to a stream from a small forested watershed on Kureha Hill in Toyama Prefecture, Japan was investigated in order to assess its acid-base chemistry. Kureha Hill, located in Toyama City, receives high nitrogen loading from the atmosphere. In this area, there are several small streams characterized by a high concentration of nitrate and low ANC. Hyakumakidani, one of the most acidic streams on that hill, the average pH and ANC were 5.2 and ?8 µeq/l, respectively. The weighted average nitrate concentration, which was 125 µeq/l, increased up to 370 µeq/l during high-discharge periods caused by heavy rainfall, while ANC decreased to ?24 µeq/l at the same time. Our preliminary study using a two-stage tank model simulating the flow paths in the soil indicated that during high-discharge periods, the increased subsurface flow containing a high concentration of nitrate contributed to the increased nitrate concentration. In this watershed, the annual nitrogen budget from Aug. 1998 to Aug. 1999 showed that the loss of nitrogen exceeded the bulk nitrogen deposition, indicating that this watershed is under condition of nitrogen saturation. However, no visible attenuation has been observed.     

Acid-base chemistry of high-elevation streams in the great smoky mountains

Longitudinal and temporal variations in water chemistry were measured in several low-order, high-elevation streams in the Great Smoky Mountains to evaluate the processes responsible for the acid-base chemistry. The streams ranged in average base flow ANC from ?30 to 28 μeq L^?1 and in pH from 4.54 to 6.40. Low-ANC streams had lower base cation concentrations and higher acid anion concentrations than did the high-ANC streams. NO₃ ^? and SO₄ ^2? were the dominant acid anions. NO₃ ^? was derived from a combination of high leaching of nitrogen from old-growth forests and from high rates of atmospheric deposition. Streamwater SO₄ ^2? was attributed to atmospheric deposition and an internal bedrock source of sulfur (pyrite). Although dissolved Al concentrations increased with decreasing pH in the study streams, the concentrations of inorganic monomeric Al did not follow the pattern expected from equilibrium with aluminum trihydroxide or aluminum silicate phases. During storm events, pH and ANC declined by as much as 0.5 units and 15 μeq L^?1, respectively, at the downstream sites. The causes of the episodic acidification were increases in SO₄ ^2? and DOC.     

Assessing the Suitability of Acid Neutralising Capacity as a Measure of Long-Term Trends in Acidic Waters Based on Two Parallel Datasets

Acid Neutralising Capacity (ANC), calculated as the difference between base cations and acid anions, is widely used as a measure of freshwater acid status, and an indicator of biological conditions. Unlike pH and alkalinity, ANC is conservative with respect to CO₂ degassing and reactions with aluminium or organic species. However, since ANC is calculated as the residual of a large number of individual ion determinations, it is potentially sensitive even to relatively small analytical errors. For the Round Loch of Glenhead, SW Scotland, consistency of ANC estimation has been assessed based on a duplicate set of major ion analyses undertaken at different laboratories over an 11 year period. Results indicate that, while the two sets of individual ion determinations correspond well, correlation between calculated ANC values is poor. Consequently, estimated ANC trends exhibit severe discrepancies between datasets; one indicates substantial recovery, the other no apparent trend. These problems with ANC estimation are believed to be general to acidic waters and are of particular concern for long-term monitoring, where ANC changes may be small and difficult to detect (although nonetheless potentially biologically significant). In these situations, it is possible that a more stable measurement of ANC may be obtainable based on titration alkalinity, DOC and aluminium concentrations. Using this method, a small but highly consistent increase in ANC is observed over the study period, although much of this can be attributed to a shift from mineral to organic acidity, rather than an overall reduction in acidity.     

Survival of brook trout (Salvelinus fontinalis) embryos and fry in streams of different acid sensitivity in Shenandoah National Park,USA

Shenandoah National Park receives more atmospheric sulfate loading than any other USA national park. pH has been gradually declining in low-ANC streams for more than 10 years. We have completed four 1-to-3 month-long field bioassays in three streams differing in acid neutralizing capacity (ANC), using a total of 18,000 hatchery brook trout eyed-eggs through fry. In three of the four bioassays, embryos/fry showed poorer survivorship in the low-ANC stream, compared to the high-ANC stream. Substantial mortalities occurred under different hydrological conditions, including steady rain plus significant rain events (fall 1992), low rainfall followed by a significant rain event (spring 1993), and steady light rain and snowmelt with no large rain events (spring 1994). In a fourth bioassay (fall 1993), poor survivorship occurred in all three streams due to drought conditions. Trout placed in the intermediate-ANC stream showed variable survivorship, in two bioassays as high as in the high-ANC stream, and in one bioassay as poor as in the low-ANC stream. Baseflow ANC in the intermediate-ANC stream is 40–100 ueq/L, and pH never falls below 6.0. However, during episodes, pH in this stream sometimes fluctuates rapidly in the range of 6.0 to 7.0, and this fluctuation itself may be a source of physiological stress.     

The decline of fauna in small streams in the Swedish mountain range

Investigations in the southern part of the Scandinavian mountain range have shown a direct correlation between snowpack pH and the lowest pH in small streams. In streams with catchments <100>² a snowpack pH below 4.8 resulted in a stream pH below 5.5. As the snowpack pH in the southern mountain range is 4.0–4.6, lower values to the south and at high altitudes, large areas are affected by acid deposition. The acidity of the snowpack is released almost directly into the streams during thaw, due to the large snowpack, rapid thaw, steep terrain and thin soils. The acidification of the snow has lead to an extensive fauna depletion, especially in smaller streams without upstream lakes. The abundance of benthos in acidified streams in the municipality of Härjedalen (11.000 km²) is today only one tenth of the abundance before acidification. Fish populations have declined to the same extent, and several acid-sensitive species have been lost. It is concluded that mountain streams and fauna are extremely sensitive to acidification, and that even large reductions of emissions will be insufficient.     

Assessing the contribution of individual dissolved ions to depressions in acid neutralising capacity of streams in the adirondack and Catskill Mountains,New York

Methods for quantifying the influence of different ions on depressions in ANC, based on those used by Molot et al. (1989), have been employed on streams in the Adirondack and Catskill Mountains of New York. Streams were intensively monitored during the Episodic Response Project of the US EPA Baseflow values were determined for each variable, and for each low-ANC sample the proportion of ANC depression (relative to baseflow) contributed by each ion was calculated, In the Catskill streams Ca²⁺ dilution and NO₃ ^– increases were major causes of ANC depression; SO₄ ^2– dilution and Al mobilisation increased ANC. In the Adirondack streams Ca²⁺ and Na⁺ dilution, and NO₃ ^– and SO₄ ^2– increases, all contributed to ANC depressions. Inter-stream differences in results were linked to differences in stream acidity; in both regions Ca²⁺ dilution dominated ANC depressions in circumneutral streams, whereas NO₃ ^– increases were dominant in acidic streams. Organic anions contributed more to ANC depressions in acidic streams. Al buffering, was negligible in circumneutral streams, but more than halved ANC depressions in the most acidic stream. Individual base cation behaviour differed widely, suggesting that caution should be used when treating them as a uniform group.     

Episodic acidification of three streams in Shenandoah National Park,Virginia, USA

Short-term acidification of surface waters in the eastern United States accompanying rainfall and snowmelt events represents an important aspect of the regional acidification problem. The objectives of this field study were to (1) examine the changes in acid-base chemistry during stormflow conditions, (2) understand the hydrological flowpaths that control streamwater acid neutralizing capacity (ANC), and (3) evaluate the contribution of individual ions to the overall changes in streamwater ANC. Three forested mountain streams in Shenandoah National Park (Paine Run, Piney River, and Staunton River) were chosen based on their similar catchment size (11–13 km²) but different bedrock geology and baseflow ANC. Throughout the three-year study, samples were collected at eight-hour intervals (primarily to establish antecedent baseflow conditions), and at two-hour intervals during events until the flow receded. All samples were analyzed for pH, ANC, and all major cations and anions. During storm events, pH and ANC decreases were observed in all streams, with ANC becoming negative several times in Paine Run. Base cation concentrations typically increased in Paine Run and Staunton River, but usually decreased in Piney River. Sulfate and nitrate concentrations generally increased in all streams. Antecedent baseflow ANC was found to be the best predictor of the minimum ANC. The data from more than 40 episodes on these streams (initiated by 25 different storm events) are interpreted to evaluate the relative importance of natural and anthropogenic sources of acidity to these acid-sensitive natural waters.     

Evaluation of some systems for classifying soil sensitivity to acid deposition in the South African highveld

Abstract. The Skokloster and Stockholm Environmental Institute (SEI) approaches were applied to the assessment of 145 soils of the South African highveld region in terms of sensitivity to acid deposition. The critical load class calculated by variants of these methods was compared with the acid neutralizing capacity (ANC) determined by pH measurement of soil suspended in a dilute acetate buffer solution. This rapid index of ANC correlates well both with ANC determined by an established but more laborious method which involves titration and equilibration of soil with HCl, and with a number of soil properties related to base status. The correlation between Skokloster or SEI critical load classes and ANC was weak. It was concluded that ANC determination would be a preferable basis for classifying these soils in terms of their sensitivity to acid deposition, since the method is direct and integrates the contribution of various soil properties to acid sensitivity instead of requiring the relative contribution to be calculated according to somewhat arbitrary weightings given to broadly defined classes of soil properties.     

Groundwater acidification at Birkenes,southern Norway: Comparing trends of chemical composition of precipitation,throughfall, soilwater and groundwater

Chemical time trends for precipitation, throughfall, and soilwater (1986–1992), and groundwater (1980–1993) at Birkenes, southern Norway, are compared to gain insights into possible causes for the recent increase in groundwater acidification there. Precipitation and throughfall trends do not show evidence for an increase in anthropogenic acids (e.g. sulphate), but seasalt deposition (e.g. chloride) has been marginally greater in 1990–1992 than in most previous years on record. Soilwater composition partly indicates increasing acidification in recent years (pH, Al and ANC), but hardness and sulphate content are decreasing. Soilwater ANC became negative in 1989, revealing a lasting deficit in its potential to buffer acidity. Groundwater shows clear signs of intensifying acidification (pH, Al, ANC, hardness and sulphate), and this may result partly from climatic conditions (mild winters, seasalt episodes) and partly from the deterioration of an acid buffering system within the soil cover. Acidification via sulphate deposition certainly is not a direct cause. The declining hardness of soilwater suggests that the ion-exchange buffer in the soil may have ceased to function properly. The necessity for obtaining long-term time-series of water chemistry is underscored by this study.     

Long-term changes in episodic acidification of streams in Shenandoah National Park,Virginia (U.S.A.)

Episodic acidification-the short-term loss of acid neutralizing capacity (ANC) in surface waters during periods associated with rainfall and snowmelt runoff-has been shown in previous field studies to be a ubiquitous process that can have long-term adverse effects on fish populations. A systematic field study of episodic acidification in five gaged Shenandoah National Park (SNP) streams was initiated in 1991, while a long-term study of changes in acid-base chemistry in four gaged SNP streams has been in operation since 1979. Statistical analysis of the long-term record of mean daily discharge and weekly streamwater chemical composition was performed to identify the dominant processes that control episodic acidification of SNP streams; an objective hydrological separation technique was used to determine whether each weekly sample was taken during antecedent baseflow or stormflow conditions. Using this technique, more than 100 stormflow/baseflow pairs were identified in the long-term (1980–1992) record for White Oak Run from which episodic chemical changes were estimated. Statistical analysis of the resultant data suggested that mean episodic depressions in ANC have increased by nearly a factor of two in White Oak Run since the first outbreak of forest defoliation by the gypsy moth caterpillar during the summer of 1990.     

Predicting Recovery from Acidic Deposition: Applying a Modified TAF (Tracking and Analysis Framework) Model to Maine (USA) High Elevation Lakes

We adapted a reduced-form model, built to predict the aquatic effects of alternative nitrogen and sulfur emissions scenarios on Adirondack lakes, New York, for use on high elevation lakes of Maine (HELM), USA. The Tracking and Analysis Framework (TAF) model was originally designed to evaluate the biotic, economic, and health effects of acid deposition. The TAF model developed in our study was used to assess the biotic effects of different levels of sulfate deposition resulting from alternative emissions scenarios. The aquatic portion of the model is based on a lumped-parameter watershed chemistry model, MAGIC (Model of Acidification of Groundwater in Catchments). The original TAF model was built by calibrating MAGIC to 33 lakes in the Adirondack Mountains. We calibrated MAGIC to 78 HELM lakes, and built reduced-form models from these MAGIC predictions. We evaluated TAF predictions of acid neutralizing capacity (ANC), a fish acid stress index (ASI), and the probability of fish presence in 2030 for four different SO₂ emissions-reduction scenarios. The most dramatic emissions reduction scenario produced only modest increases in mean ANC (16.8 μeq/L ± 7.9 μeq/L) and slight increases in mean predicted probability of presence of acid-sensitive fish (0.07± 0.09) across all lakes. However, a small number of lakes were predicted to have more substantial increases in ANC and improvements in other conditions for acid-sensitive fish. Our results reflect the reality that many of the high elevation lakes of Maine historically had low ANC and that some were even acidic in pre-industrial times. Thus, ’recovery’ for most of the high elevation lakes of Maine will be modest under any scenario of reduced acidic deposition.