Long-Term Annual and Seasonal Patterns of Acidic Deposition and Stream Water Quality in a Great Smoky Mountains High-Elevation Watershed

The recovery potential of stream acidification from years of acidic deposition is dependent on biogeochemical processes and varies among different acid-sensitive regions. Studies that investigate long-term trends and seasonal variability of stream chemistry in the context of atmospheric deposition and watershed setting provide crucial assessments on governing biogeochemical processes. In this study, water chemistries were investigated in Noland Divide watershed (NDW), a high-elevation watershed in the Great Smoky Mountains National Park (GRSM) of the southern Appalachian region. Monitoring data from 1991 to 2007 for deposition and stream water chemistries were statistically analyzed for long-term trends and seasonal patterns by using Seasonal Kendall Tau tests. Precipitation declined over this study period, where throughfall (TF) declined significantly by 5.76?cm?year^?1. Precipitation patterns play a key role in the fate and transport of acid pollutants. On a monthly volume-weighted basis, pH of TF and wet deposition, and stream water did not significantly change over time remaining around 4.3, 4.7, and 5.8, respectively. Per NDW area, TF SO₄ ^2- flux declined 356.16?eq?year^?1 and SO₄ ^2- concentrations did not change significantly over time. Stream SO₄ ^2- remained about 30???eq L^?1 exhibiting no long-term trends or seasonal patterns. SO₄ ^2- retention was generally greater during drier months. TF monthly volume-weighted NH₄ ⁺ and NO₃ ^- concentrations significantly increased by 0.80???eq L^?1?year^?1 and 1.24???eq L^?1?year^?1, respectively. TF NH₄ ⁺ fluxes increased by 95.76?eq?year^?1. Most of NH₄ ⁺ was retained in the watershed, and NO₃ ^- retention was much lower than NH₄ ⁺. Stream monthly volume-weighted NO₃ ^- concentrations and fluxes significantly declined by 0.56???eq L^?1?year^?1 and 139.56?eq?year^?1, respectively. Overall, in NDW, inorganic nitrogen was exported before 1999 and retained since then, presumably from forest regrowth after Frazer fir die-off in the 1970s from balsam wooly adelgid infestation. Stream export of NO₃ ^- was greater during winter than summer months. During the period from 1999 to 2007, stream base cations did not exhibit significant changes, apparently regulated by soil supply. Statistical models predicting stream pH, ANC, SO₄ ^2-, and NO₃ ^- concentrations were largely correlated with stream discharge and number of dry days between precipitation events and SO₄ ^2- deposition. Dependent on precipitation, governing biogeochemical processes in NDW appear to be SO₄ ^2- adsorption, nitrification, and NO₃ ^- forest uptake. This study provided essential information to aid the GRSM management for developing predictive models of the future water quality and potential impacts from climate change.     

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.     

Dose-response relationships for the addition of limestone to lakes and ponds in the Northeastern United States

A titration based model (DeAcid) has been used to predict treatment dose and times for reacidification for CaCO₃-treated lakes in the Living Lakes, Inc. (LLI) aquatic liming program. Water quality constitutents (pH, ANC and Ca) were used to measure the effectiveness of the dosing model and reacidification rates. Data from 22 lakes or ponds in 5 northeast states have been collected since June 1986. With few exceptions, pH and ANC values ranged from 4.5 to 6.5 and ?30 to +65 ueq L^?1, respectively, in untreated sites and 6.5 to 7.8 and 120 to 300 ueq L^?1, respectively, in sites approximately 30 days after treatment. Changes in Ca concentration levels have been used to evaluate the utility of the dose model for treatment of both inland and coastal waters. For coastal, seepage lakes application of a single-box mass transfer model to observed post-liming changes in ANC and Ca adequately simulates lake response.     

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.     

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.     

Response to a smelter closure in Cascade mountain lakes

A statistically significant decrease in sulfate was observed in high elevation Cascade lakes during 1983 through 1988. The total decrease averaged 2.2 μeq L^?1 in two slow-flush lakes and 4.2 μeq L^?1 in three fast-flush lakes for 1983–1985 vs 1986–1988, respectively. Coincident with these changes in sulfate concentrations were a sharp decrease of SO₂ emissions from the ASARCO smelter (100 km SE of the lakes), from 87 to 70 kt yr^?1 during 1983–1984 to 12 in 1985, the year of its closure, and a gradual change in SO₂ emissions from Mt. St. Helens, from 39 to 27 during 1983–1984 to 5 in 1988. The sharpest decreases occurred in non-marine sulfate in fast-flush lakes from 1984 to 1985 (about 2 μeq L^?1) and in slow-flush lakes from 1985 to 1986 (1 μeq L^?1, which point to the ASARCO closure as the sole cause. However, some of the more gradual decline in non-marine sulfate observed during 1983 through the 1988 sampling periods may have been due to a slow washout of sulfate enriched ash from the 1980 Mt. St. Helens' eruption. Sulfate concentrations in precipitation also declined significantly by about 2 μeq L^?1, but changes in volume-weighted sulfate content were not significant. Lake alkalinity did not show a consistent increase in response to decreased sulfate. This was probably due to either watershed neutralization of acidic deposition or the greater variability in alkalinity measurements caused by small changes in acidic deposition making it difficult to detect changes.     

Acid deposition and lake chemistry in southwest China

A water quality survey has been performed on selected lakes and streams in southwest China. The purpose of the study was to measure the concentrations of acidic deposition and surface water chemistry in a region of severe air pollution, forest decline, and relatively sensitive geology to acidic deposition. We show that, although there are some high elevation lakes of low acid neutralizing capacity (ANC<150μeq L^?1, acidification of lakes has not occurred in southwest China due to production of base cations in soil and dry deposition of dust that serves to neutralize acidic deposition. Water chemistry is buffered by high base cation concentrations (Ca²⁺, Mg²⁺, Na⁺, and K⁺ greater than 300μeq L^?1, and pH values are always greater than 6.5.     

Impact of Acid Mine Drainage (AMD) on Water Quality, Stream Sediments and Periphytic Diatom Communities in the Surrounding Streams of Aljustrel Mining Area (Portugal)

Aljustrel mining area is located in the Iberian Pyrite Belt, one of the greatest concentrations of massive sulphide deposits that extends from Lousal (Portugal) to Aznalcóllar (Spain). The surrounding streams, Roxo, Água Azeda and Água Forte, are influenced by the erosion of the tailing deposits and the input of acid mine drainage (AMD) from the abandoned Aljustrel pyrite mines, recently reopened in 2007. The purpose of this study was to understand how these adverse conditions influenced the stream sediments, water quality and periphytic diatom communities and establish the pre-restoration local conditions to judge the success of rehabilitation program now under way. For stream sediments, the highest metal concentration samples were found at sites F, G and H. Arsenic, Cu, Fe, Pb and Sb detected concentrations, generally exceeded the probable effect concentration values reaching level 4: the highest toxicity level. In surficial water samples of AMD affected sites (F, G and H), low pH values (1.5 to 3.5) and high metal concentrations of As (6,837 μg L^?1), Cd (455 μg L^?1), Cu (68,795 μg L^?1), Fe (1,262,000 μg L^?1), Mn (19,451 μg L^?1), Pb (136 μg L^?1), and Zn (264,377 μg L^?1) were found. In these sites, the diversity index (H′) for diatoms was low (0.6 to 2.8) and the dominant taxa were Eunotia exigua (site F, 33.5%) and Pinnularia acoricola (abundances in sites: F, 86.8%; G, 88.5%; and H, 91.1%). In opposition, in less AMD impacted, H′ was high (1.5 to 4.6) and low metal concentrations and high pH were found. Achnanthidium minutissimum was the dominant taxon in (abundances in sites: A, 76.1% and B, 24.39%). Canonical correspondence analysis showed that spatial variation due to mine influence was more important than seasonal variation, which did not show any pattern.     

Finnish lake survey: the role of organic and anthropogenic acidity

A lake survey consisting of 987 randomly selected lakes was conducted in Finland in autumn 1987. The survey covered the whole country, and the water quality of the lakes can be considered as representative of the approximately 56 000 lakes larger than 0.01 km² in Finland. The median TOC concentration is 12 mg L^-1 and the median pH 6.3. The proportion of lakes with TOC concentrations > 5 mg L^-1 in the whole country is 91 %. Organic anion is the main anion in the full data set (median 89 μeq L^-1). The high organic matter concentrations in Finnish lakes are associated with catchment areas containing large proportions of peatlands and acid organic soils under coniferous forest. The survey demonstrated that organic matter strongly affects the acidity of lakes in Finland. The decreasing effect of organic matter on the pH values was demonstrated by both regression analysis and ion balances. At current deposition levels of ^*SO₄ the pH of humic lakes in Finland is determined to a greater extent by high TOC concentrations than by ^*SO₄ in most areas. In lakes with pH values lower than 5.5 the average organic anion contribution is 56 % and non-marine sulfate contribution 39 %. However, in the southern parts of the country, where the acidic deposition is highest, the minerogenic acidity commonly exceeds the catchment derived organic acidity.     

Change in the acid-base status of an appalachian mountain catchment following forest defoliation by the gypsy moth

Infestation by the gypsy moth (Lymantria dispar) can alter biogeochemical conditions in affected catchments. Stream-water concentration data obtained over the period of 1980–1993 for White Oak Run, a stream in Shenandoah National Park, Va., indicate that change in catchment acid-base status is associated with forest defoliation by the moth larva. Stream-water concentration changes following defoliation included increasing concentrations of strong-acid anions, base-cations, and hydrogen ion, as well as decreasing concentrations of acid-neutralization capacity (ANC) and sulfate. The largest change was in the concentration of nitrate; annual discharge-weighted mean concentrations increased from predefoliation levels consistently less than 5 μeq L^?1 to postdefoliation levels greater than 50 μeq L^?1. An intensification of acidification was indicated by record-high hydrogen ion concentrations and record-low ANC concentrations. The long-term biogeochemical implications of the infestation are uncertain due to the nonlinearity of the observed responses and unknown patterns of recovery and recurrence.     

Québec lake survey: II. Origin and extent of acidification

Over 95% of the province of Québec is located on the Canadian Shield where the bedrock offers a very low acid neutralizing capacity. Some areas of Québec are more vulnerable than others because of shallow soils or soils presenting very low carbonated content. Lakes in these areas tend to be more acidic and more sensitive than elsewhere on the Precambrian Shield. There are two major areas showing high sensitivity (ANC≤100 μeq L^?1): the southwestern portion of Québec and the easternmost part of the province. In the former, lake acidity is mainly driven by SO₄ deposition, while in the latter area, organic acidity appears to be the main controlling factor. The origin of acidification can be related to the pattern of SO₄ deposition, the higher loadings being measured in the southwestern portion of Québec. These depositions follow a west to east decreasing gradient as they are mostly related to sources located west and southwest of Québec.     

Recovery Pattern from Acidification of Headwater Lakes in Finland

Acid sensitive headwater lakes (n=163) throughout Finland have been monitored during autumn overturn between 1987–1998. Statistically significant decline in sulphate concentration is detected in 60 to 80 percent of the lakes, depending on the region. Median slope estimates are from ?1.1 µeq L^?1 in North Finland to ?3.3 µeq L^?1 in South Finland. The base cation (BC) concentrations are still declining especially in southern Finland (slope ?2.5 µeq L^?1), where every second lake exhibits a significant downward trend. The BC slope is steeper for lakes with less peatlands, more exposed bedrock, longer retention time and southerly location, but these factors are inter correlated. Gran alkalinity slope medians for the three regions range from 1.4 to 1.8 µeq L^?1 yr^?1. No significant negative alkalinity trends were detected. The similarity in the slopes of SO₄, BC and alkalinity in this data compared to seasonal sampling data from Nordic Countries can be regarded as indirect evidence that autumnal sampling is representative for long term monitoring for these ions. There are no indications of increased organic carbon in lakes, as found in some recent trend analyses of similar regional data sets. Although the processes behind the positive development in these lakes have to be revealed with site- specific intensive studies, this data suggests, that the initial recovery from lake acidification in Finland is a regional phenomenon.     

Low Success Rate in Re-Establishing European Perch in Some Highly Acidified Lakes in Southernmost Norway

In order to test whether major reductions in acid inputs had improved water quality sufficiently for fish populations to recover, we stocked wild European perch (Perca fluviatilis) in three highly acidified lakes that had previously supported this species, and in one limed lake. The fish, which were introduced from a local lake (donor lake), generally ranged from 12 to 16 cm in total length, and were stocked at densities of 117–177 fish ha^?1. The untreated lakes were highly acid, with minimum pH values and maximum inorganic aluminium concentrations (Al_i) during the spring of 4.6–4.7 and 118–151 µg L^?1 respectively. In the limed lake, the corresponding values for pH and Al_i ranged between 5.8 and 6.6 and 5 and 19 µg L^?1 respectively. Gill-netting in two subsequent years after the introduction yielded only a few recruits (0+) and one adult in one of the three acidified lakes in one year only. However, stocked perch reproduced successfully in both years in the limed lake. There was a significant linear relationship between the catches (CPUE) of juvenile perch (age 0+) in the different lakes in the autumn and the water quality in May (time of hatching), both in terms of Al_i (r ²=0.934, P<0.05) and pH (r ²=0.939, P<0.05). Our data suggest unsuccessful recruitment in waters of pH <5.1 and Al_i>60 µg L^?1.     

Mortality and physiological stress of year-classes of landlocked and migratory Atlantic salmon,brown trout and brook trout in acidic aluminium-rich soft water

Physiological stress, measured as changes in plasma chloride, and mortality were measured on different year-classes of landlocked and migratory Atlantic salmon, two strains of brown trout, and brook trout, in a flow-through system with acidic Al-rich soft water. The oldest year-classes of salmon were smolts. Water from Lake Byglandsfjord (pH = 5.9), was enriched 1 th inorganic Al (as AlCl₃) and H₂SO₄ to pH = 5.1, total Al = 225 ug L^?1 , and labile Al = 135 ug L^?1 . As a reference, lake water was limed by means of a shellsanj filter to pH = 6.2, increasing Ca-concentration from 1.0 to 1.5 mg L^?1. During the 83 hr experiment, neither mortality nor physiological stress occurred in any species or year-class in the limed water. In the acid water, no mortality occurred on any stage of brown trout or brook trout. Among the migratory and landlocked salmon, however, 5% of the alevins died after 49 and 70 hr, respectively. All smolts of both the landlocked and the migratory salmon died after 83 and 35 hr, respectively, the co responding loss rate of plasma chloride was ?0.76 and ?1.26 meq Cl hr^?1. Brook trout, however, increased plasma ion concentration during the experimental period, and hence showed no stress.     

Contrasting the geochemistry of aluminum among peatlands

Aluminum concentrations were measured in surface waters, pore waters and surface peats of 15 wetlands in south-central Ontario. Wetlands were grouped floristically and chemically as mineralpoor, moderately-poor or mineral-rich fen. Mineral-poor fens were dominated bySphagnum, were low in alkalinity (0.31μeq L^?1) and pH (4.5–6.3). Moderately-poor fens had a mixture of vegetation (Sphagnum, sedges and grasses), mid-alkalinity (23–91μeq L^?1) and pH (5.8–6.4). Mineral-rich fens were dominated by sedges and grasses, had high alkalinity (104–181μeq L^?1) and circumneutral pH (6.2–6.3). Surface water Al concentrations were less in mineral-poor versus moderately-poor and mineral-rich fens (F=32.0; P<0.05). Pore water Al concentrations were lower in 4 of 5 mineral versus the mineral-rich fens (F=92.15; P<0.05). In all but two cases pore water Al (all species <0.2μm) were greater within the fen peats versus the overlying surface waters suggesting that peats could act as a source of Al to the overlying waters. In all wetlands, 70 and 30% of peat Al was recovered by a hydroxylamine hydrochloride/acetic extract (primarily inroganic) and an ammonium hydroxide extract (primarily organic), respectively. Differences in “extractable” Al recovered by the two reagents (i.e., inorganic+organic Al) among the 15 wetlands were independent of wetland type. Distribution coefficients, k _d , were different among the 3 types of wetlands (F=25.0; P<0.05) with theSphagnum dominated mineral-poor fens containing higher values versus the sedge and grass dominated mineral-rich fens. Lower surface and pore water concentrations of Al in mineralpoor versus mineral-rich fens may in part be a result of differences in the degree of minerotrophic influences between the two types of peatlands. As well, the greater binding capacity ofSphagnum peat as indicated by higher k _d 's in the mineral-poor fens, may have contributed to the observed lower pore water and surface water Al concentrations in mineral-poor versus mineral-rich fens. It has been postulated that anthropogenic acidification of peatlands will accelerate the transformation of a mineral-rich fen to that of a mineral-poor fen and ultimately to bog. Changes in Al geochemistry that may ensue as this transition occurs include decreases in pore and surface water Al concentrations with concurrent increases in peat bound Al.     

Chemistry differences in two streams entering an acidic lake in the Adirondack Mountains,New York (U.S.A.)

Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H⁺, sulfate-S, and Al and smaller concentrations of base cations and silica than the west inlet (70, 116, 25, 90, 64 and 4, 99, 8, 228, 148 μeq L^?1 of H⁺ and sulfate-S, μmol L^?1 Al, μeq L^?1 total base cations and μmol L^?1 silica in east and west inlets, respectively). Concentrations of base cations in C horizon soil solutions (157 μeq L^?1 total base cations) were smaller and greater than west and east inlets, respectively. This suggests that water flowing into the west inlet contacted deeper mineral layers, whereas water reaching the east inlet did not. Lake and lake outlet concentrations were also intermediate between the two inlets, and the lake was acidic (pH 4.9 to 5.1) with relatively high total monomeric Al concentrations (8 to 9 μmol Al L^?1). The east inlet also had greater DOC concentrations than the west (0.38 and 0.24 μmol C L^?1, respectively), again indicating that soil solutions entering the east inlet passed through the forest floor but had more limited contact with deeper mineral layers in comparison with the west inlet. Differences between the streams are hypothesized to be related to contact of percolating solutions with mineral soil horizons and underlying glacial till, which provides neutralization of acidic solutions and releases base cations. This work indicates that processes controlling surface water acidification can be spatially quite variable over a small watershed.     

Studies of Soils, Soil Water and Stream Water at a Small Catchment near Guiyang, China

Acid deposition is considered to be a major environmental problem in China, but information about effects on soils and waters is scarce. To contribute to increased knowledge about the problem a small catchment (about 7 ha) in the outskirts of Guiyang, the provincial capital of Guizhou in south-western China, was instrumented for collection of precipitation, throughfall, soil water and stream water. In addition soil samples have been collected and analyzed for key properties. Median pH in the precipitation is 4.40 (quartiles: 4.19 and 4.77) and the median sulfate concentration 228 µeq/L (quartiles: 147 and 334 µeq/L). The dry deposition of both SO₂ and alkaline dust is considerable. The sum of wet deposition of sulfate and dry deposition of SO₂ has been estimated to about 8.5 gSm^-2yr^-1. The total S-deposition may be somewhat higher due to dry deposition of sulfate and occult deposition. In soil water, SO₄ ^2- is the major anion, generally ranging from 300 to 2500 µeq/L in the different plots. Calcium is an important cation, but there is also a considerable contribution of aluminum from the soil. In some of the plots the concentrations of inorganic monomeric aluminum (Ali) are typically between 200 and 400 µm. Potential harmful levels of aluminum and/or high Ali/(Ca²⁺ + Mg²⁺) molar ratios occur in the catchment, but damages to vegetation have not yet been reported. In most cases exchangeable aluminum accounts for between 75 and 95% of the total effective cation exchange capacity (CEC_E) in the mineral soils. The aluminum chemistry cannot easily be explained by conventional models as the Gaines-Thomas ion-exchange equation or equilibrium with an Al(OH)₃ mineral phase. The stream water is generally less acidic and has considerably lower concentrations of aluminum than the soil water, even though quite acid events have been observed (pH < 4.4). The median pH values are 4.9 and 5.0 in the two first order streams and 6.3 in the dam at the lower boarder of the catchment.     

On the prediction of acid precipitation events and their effects on fishes

It is possible to predict acid rain events and melts of acid snow some 12 to 24 hr in advance, including estimation of the magnitude and duration of such events. This is sufficient notice to permit monitoring of stream chemistry and fish plasma and muscle ions before acid stress, and to continue this monitoring throughout and after specific events. Such a program has been in place for 2 yr in waters tributary to the Milford Bay Trout Hatchery, Ontario. During one snow melt in February 1984 surface waters showed a decline to pH 4 and associated negative ANC. Rainbow trout held in such water lost plasma Na and Cl rapidly and died within 28 hr. The hatchery water supply, consisting of a mixture of spring and surface water, showed a decline in alkalinity from 300 to 30 μeq.L^?1, and a pH change from 6.6 to 5.4, during snow melt. Total A1 concentration increased from 42 to 222 μg.L^?1 during snow melt with the “reactive” component increasing from 17 to 112 μg.L^?1. Rainbow trout held in this water did not show physiological stress. More rapid run-off of melt water could be expected to exhaust all of the alkalinity in the hatchery water supply permitting the pH to decline and A1 concentration to rise to levels lethal to the hatchery stock of rainbow trout.