Effects of Acidity and Aluminum on the Physiology and Migratory Behavior of Atlantic Salmon Smolts in Maine, USA

Atlantic salmon, Salmo salar, smolts of hatchery origin were held for 5 to 16 days in ambient (pH 6.35, labile Al = 60 µg L^?1), limed (pH 6.72, labile Al = 58.4 µg L^?1), or acidified (pH 5.47, labile Al=96 µg L^?1) water from the Narraguagus River in Maine, USA. Wild smolts were captured in the same river in rotary traps and held for up to two days in ambient river water. Osmoregulatory ability was assessed by measuring Na⁺/K⁺ ATPase activity, hematocrit, and blood Cl concentration in freshwater, and after 24-hr exposure to seawater. Hatchery smolts exposed to acidic water and wild smolts displayed sub-lethal ionoregulatory stress both in fresh and seawater, with mortalities of wild smolts in seawater. Using ultrasonic telemetry, hatchery-reared ambient and acid-exposed, and wild smolts were tracked as they migrated through freshwater and estuarine sections of the river. The proportion of wild smolts migrating during daylight hours was higher than for hatchery-reared smolts. Wild smolts remained in the freshwater portions of the river longer than either group of hatchery smolts, although survival during migration to seawater was similar for all three treatments. Acid-exposed hatchery-origin and wild Narraguagus River smolts were both under ionoregulatory stress that may have affected their migratory behavior, but not their survival for the time and area in which we tracked them.     

Tolerance to Acid Water Among Strains and Life Stages of Atlantic Salmon (Salmo Salar L.)

Reintroduction of Atlantic salmon (Salmo salar L.) after liming of acidified barren salmon rivers could benefit by choosing acid tolerant strains. Testing different life history stages from fry to smolts of five salmon strains with different acidification history demonstrated strain-specific variation in tolerance to acid aluminum-rich waters for stages from fry to parr. Contrary to expectation, salmon from non-acidified rivers were more tolerant. Differences in sensitivity were found between life history stages. Within a specific life history stage, size-dependent sensitivity was found; small fish being more sensitive to pH while large fish were more sensitive to aluminum. Presmolts showed the same relative tolerance between strains as younger stages. These differences disappeared, however, when the smolt reached full smoltification, probably due to supersensitivity at this stage. Poor water quality during the last period of smoltification and outmigration can thus mask the genetic potential for tolerance to acidic rivers.     

Atlantic salmon resources in the Northeastern United States and the potential effects of acidification from atmospheric deposition

The Atlantic salmon (Salmo salar) was formerly abundant in northeast coastal rivers in the United States from the Canadian border to the Connecticut River, and possibly as far south as the Delaware River. It was eliminated from most of its former range by a combination of overfishing, construction of dams impassable to migrating fish, and municipal and industrial pollution. Reproducing populations are now limited to a few rivers in Maine, but attempts are under way to reintroduce the species to some rivers where populations formerly existed. Most of the native Atlantic salmon rivers are low in acid neutralizing capacity and receive acidic precipitation. The third order streams are not now acidic; however, in some first and second order streams in Maine, pH episodically declines to 4.7 and Al increases to 350 μg g^?1. These conditions could be toxic to sensitive early life history stages of Atlantic salmon. Comparison of chemical conditions in two Maine rivers in 1980–1982 with those in 1969–1970 indicated that the streams have not become more acidic during this interval. Data on the sport catch of Atlantic salmon indicated that populations have generally remained stable or recently increased in the Maine rivers having naturally reproducing populations. The recent increase probably resulted from introductions of hatchery smolts to supplement natural reproduction, and the occurrence of strong year classes in 1978 and 1980. The population in one stream has declined significantly in recent years, but the cause of the decline is probably not related to acidic precipitation. Atlantic salmon resources in the U.S. have apparently not been adversely affected by atmospheric deposition at the present time.     

Responses of atlantic salmon (Salmo salar) alevins to dissolved organic carbon and dissolved aluminum at low pH

Mortality of Atlantic salmon alevins in solutions containing Al and dissolved organic anions (both synthetic and natural) was correlated with Al accumulation in alevin tissues. Both mortality and accumulation could be related to the concentration differences between Al and organic anions. Mortality and body accumulation of Al both increased dramatically as total Al concentrations increasingly exceeded organic anion concentrations. Alevin growth and yolk utilization were both less rapid at inorganic monomeric Al concentrations exceeding 2 μM (50 μg L^-1). The acidic fractions of dissolved organic matter (DOM) are more effective in protecting alevins against Al toxicity than are the neutral and basic fractions. Ambient inorganic monomeric Al is probably not toxic to salmon alevins in acidic Nova Scotian streams, even during snow-melt.     

Water Quality Dependent Recovery from Aluminum Stress in Atlantic Salmon Smolt

In Norway, a variable pH target (pH 6.2–6.4 during most of the year, but 6.4 during the smoltification period) is used to reduce the cost of liming salmon rivers. Here we test the adequacy of this liming strategy. Atlantic salmon presmolts exposed to sublethal acidic water (pH 5.9, <25 µg Ali·L^?1) for more than 3 months showed impaired sewater tolerance, elevated gill-Al concentrations, severe gill tissue changes, elevated blood plasma glucose concentrations, but no effect on blood plasma chloride. It is usually assumed that smolt will recover from prior aluminum (Al) exposure if water quality is restored. Recovery rate is here used as an indirect measure of water quality improvements achieved after treating acid water (pH 5.8, 85 µg Ali·L^?1) with lime to reach pH-target levels of 6.0 – 6.3. Fish were exposed in a channel-tank set-up for >210 hrs in water aged from 1 minute up to 2 hours after treatment (in a flow through system). More Al was eliminated from the gills when the fish were exposed to pH 6.3 than to pH 5.8 or 6.0, and when water was aged after pH increase. Recovery, defined as return of normal gill morphology, blood homeostasis and establishment of seawater tolerance was achieved within 210 hrs in channels treated with lime to pH 6.3, while a similar recovery was not obvious at lower pH values. Liming to pH 6.3 detoxified Al better than pH 6.1.     

Time and Ph-Dependent Detoxification of Aluminum in Mixing Zones between Acid and Non-Acid Rivers

Liming detoxifies aluminum in a time-dependent process following the increase in pH. Transformation of Ali into non-reactive or colloidal forms of Al reduces toxicity. To investigate the effects of pH on the detoxification rate, Atlantic salmon (Salmo salar) parr were exposed in four identical channel-tank setups differing only in mixing ratio (30:70, 16:84 or 6:94) between acid (pH 5.6, total Ali 90 µg Al·L^?1) and non-acid water (pH 6.3, total Ali 3 µg Al·L^?1). Two channels had identical mixing ratio (30:70), but differed with respect to pH (6.0 or >6.4) due to addition of lime. Fish were exposed for 140 hrs. in waters aged from 1 minute and up to 4 hours after mixing. Ali decreased within minutes after mixing at pH 6.4. The detoxification process required hours at pH 6.0. Al accumulation onto fish gills and fish homeostasis was related to Ali. The data suggest that the detoxification process, and therefore the water body affected by ongoing polymerization, was strongly influenced by pH, where a pH target for liming set at pH 6.4 detoxified water faster than a pH target of pH 6.0.     

Differences in acid tolerance during the early life stages of three strains of brook trout,Salvelinus fontinalis

Brook trout, Salvelinus fontinalis, embryos and fry from three sources (an acidic watershed in Kejimkujik Park at pH 4.7 to 5.3, a neutral watershed at pH 7, a hatchery at pH 7) were exposed separately to lethal and sublethal levels of acidity (pH 7.0, 5.2, 4.7, 4.3, 3.9), beginning at fertilization. Significant differences in mortality between the strains at low pH were observed and these suggested a genetic component to acid tolerance. Mortality in the strain from the acidic watershed was the lowest, followed by the second wild strain. Survival in both wild strains at low pH was much better than survival in hatchery embryos. These differences in survival at sublethal acidity (4.7 to 7.0) were principally the result of high mortality shortly after fertilization. After this period, survival stabilized. Only at pH 4.3 did substantial mortality occur at hatching. The early embryonic stage therefore appears to be the most susceptible to sublethal acid stress in brook trout. Hatchery strain embryos were also introduced at the eyed stage at 213 degree-days. Subsequent survival of this group was better at low pH than that of hatchery embryos introduced at fertilization, thereby indicating an early or cumulative deleterious effect. Higher acidity retarded hatch in all cases. The time to 50% hatch was delayed by 1.2 degree-days with each increase of 1 μM H⁺.     

Acid Toxicity Levels in Nova Scotian Rivers Have Not Declined in Synchrony with the Decline in Sulfate Levels

The Atlantic salmon (Salmo salar) resource of eastern Canada is impacted by acid rain in the Southern Upland (Atlantic Coast) area of Nova Scotia. Salmon runs in this area have become extinct in 14 rivers, are severely impacted in 20 rivers, and lightly impacted in 15 rivers. Water chemistry and fish communities in nine Southern Upland salmon rivers were studied from 1982 to 1996 as part of the effort to monitor the effects of the emission controlprograms in Canada and the United States. There hasbeen no statistically significant change in total ioncontent of Southern Upland river water, but there wasa significant decline in sulfate levels that was balanced by an increase in organic anions, and declines in calcium and magnesium that were balanced by increases in sodium and potassium. A geochemical scenario is proposed to account for these chemical changes. River water pH levels showed no overall linear trend, but at borderline toxicity sites the year-to-year variations in pH were correlated withchanges in juvenile salmon population densities. Tenfish species were collected, but none showed anysignificant overall time trend in population density.Fish species diversity was positively correlated with pH.     

Effects of Acidification on Salmonid Spawning Behavior

We studied the effects of acidification on female sexual behavior in brown trout (Salmo trutta) and compared the results with those in hime (land-locked sockeye) salmon (Oncorhynchus nerka) (Kitamura and Ikuta, 2000). The results were similar to those of sockeye salmon. Spawning brown trout were extremely sensitive to the acidity of ambient water, and nest-digging behavior was severely inhibited (p<0.05) by very slight acidification (pH below 6.4). However, there were some differences between the two species. Female trout and salmon showed almost no digging below pH 5.0 and 6.0 (Kitamura and Ikuta, 2000), respectively. When the ambient water was returned to nearly neutral (pH6.6) conditions, digging in hime salmon reappeared in 4 of the 6 fish tested (Kitamura and Ikuta, 2000), whereas digging in brown trout reappeared in all 6 fish tested. The above-mentioned differences in behavioral response between the two species appear to reflect the species difference in terms of vulnerability to acidification (Ikuta et al., 1992). Avoidance of slightly acidic water in selection of spawning site or cessation of spawning behavior in weakly acidic environments may be the most potent cause of the reduction of salmonid populations in the early stages of acidification.     

Possible mechanisms of aluminum toxicity in a dilute,acidic environment to fingerlings and older life stages of salmonids

The respiratory, acid-base, and ionoregulatory responses of juvenile rainbow trout (Salmo gairdneri) were monitored during exposure of the fish in the laboratory to inorganic Al (2.8 μM) over the pH range 4.0 to 6.5. Responses to Al were most severe at pH 6.1 and 4.5, mortality being primarily due to asphyxia at pH 6.1 and to electrolyte loss at pH 4.5. Competition between the H⁺-ion and Al for binding at the gill surface is offered as an explanation for the decreased toxicity of Al at pH 4.0, one which is compatible with the free-ion toxicity model that has been developed for other metals. The physiologically distinct response of S. gairdneri to Al at pH 6.1 is less amenable to unambiguous interpretation. If a mixed ligand hydroxo-Al complex is incorporated in the free-ion model, and if it is assumed that the two Al species, [Al-L-gill] and [HO-Al-L-gill], provoke distinct toxicological responses, then a bimodal toxicological response to Al is indeed predicted. An alternative explanation of the apparent toxic action of Al at pH 6.1, i.e., at pH values close to that of minimum Al solubility, is the precipitation of solid Al(OH)₃ at the gill surface, i.e., a ‘physical’ effect rather than a biochemical one.     

Characteristics of Monomeric Al Concentration in An Acidified River

The Kusurisambetsu River is a tributary of the Noboribetsu River. These rivers flow through Hokkaido Prefecture, Japan. Because the upper reaches of the river are acidified by a caldera lake and basin, the river water contains aluminum in high concentration, together with iron and sulfate. The drainage area at the lower reaches is not acidified. Therefore, the acidified water of the river is neutralized by the alkalinity of water from the drainage area. The water at the mouth is neutral in pH, although about 1 mg/L of aluminum is detected. Heavy rainfall occurred in Autumn 1993, and many adult salmon were killed at the lower reaches of the river. This prompted study of the neutralization process of river water, the Al concentration change, and the influence of rainfall. Determination of Al found total Al concentration to be roughly constant at the mouth of the Noboribetsu River. However, the concentration of monomeric Al varied with pH, which varied according to rainfall and flow volume. Monomeric Al showed a minimum concentration of roughly pH 6.0. At pH of greater than 6.0, the presence of some kinds of polymeric Al is determined by filtration fraction. This suggests that the death of salmon is caused by monomeric Al when conditions are acidic. Liming test of the river water confirmed that the monomeric Al that was toxic under acidic conditions became non-toxic under alkaline conditions.     

The effects of liming on juvenile stocks of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in a Norwegian river

The effects of liming on juvenile stocks of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in the river Vikedalselva in southwestern Norway were assessed. From 1987 to 1989, the river was limed only during the spring snow melt, and pH varied in the range between 5.5 and 7.0. In 1990 to 1993, the river was limed to pH 6.2 from 15 February to 1 June and to pH 5.7 during the rest of the year. Since 1994, the pH during late winter and spring was maintained above 6.5. Prior to liming fish kills were evident during spring snow melt, but these have not occurred since liming. Electrofishing in the autumn between 1981 and 1994 showed no significant change in densities of juvenile salmon and brown trout after liming, mean densities ranged between 19–50 and 9–32 individuals 100 m^–2 respectively. A significant linear correlation between production and biomass of both species was found, indicating that factors directly controlling density affect juvenile production and cause production to remain below carrying capacity. In spite of a clear increase in pH and a reduction in the concentration of labile aluminium after liming, the conditions still do not seem to be optimal for juvenile salmonids. We suggest that a complexity of different factors impose limitations on fish production in the river: inadequate egg deposition, environmental factors such as water temperature and flow, osmoregulatory failure in mixing zones between limed and acidic water and gill damage through deposition of aluminium and iron. However, there are several indications of a reduction in toxic effects after the pH was raised to 6.5 during spring snow melt.     

Modelling pH buffering and aluminium solubility in European forest soils

The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]_aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)₃. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)₃ occurs but is the exception.     

Metal concentration in the gill,gastrointestinal tract,and carcass of white suckers (Catostomus commersoni) in relation to lake acidity

Adult white suckers were collected from four lakes in Maine that ranged in pH from 7.0 to 5.4. The gastrointestinal tract and remainder of the carcass of fishes of similar age and size from each lake, and gills from additional fishes of similar size, were analyzed for Al, Cd, Pb, and Zn. Carcasses were also analyzed for Hg. Concentrations of Al, Cd, and Pb were highest in the gastrointestinal tract and lowest in the carcass; Zn concentration was highest in the gill. For carcass, all metals except Al differed significantly among lakes, for gill tissue Cd and Pb differed, and for gastrointestinal tract, only Cd differed among lakes. Where differences were significant, patterns among lakes were similar in each tissue analyzed. Concentrations of Cd, Hg, and Pb were negatively correlated with lake water pH, acid neutralizing capacity (ANC), Ca, and lake:watershed area, and positively correlated with lake water SO₄, indicating that concentrations were higher in fish from more acidic lakes. Zinc concentrations in gills were unrelated to lake acidity, and carcass concentrations were higher in the less acidic lakes, which is the opposite of the pattern for the other metals studied. Zinc in gastrointestinal tract did not differ among lakes. Although the lakes we studied were located in undisturbed watersheds and did not receive any point source discharges, fish metal concentrations were comparable to or higher than those reported from waters receiving industrial discharges.     

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.     

Water quality requirement of Atlantic salmon (Salmo salar) in water undergoing acidification or liming in Norway

Atlantic salmon are severely affected by acidification in Norway. Water quality criteria for the salmon have to be based on the most sensitive stage, the smolt stage. The sensitivity to acidic water increases enormously during smolting, the seawater tolerance being especially vulnerable. Even moderately acidic water (pH about 6) with low inorganic monomeric aluminium (LA1) concentrations (<20μg. L^?1) and short-term episodes may be harmful. Mixing zones in limed or unlimed rivers may also represent a problem for seaward migrating smolts. In limed salmon rivers, the national liming goal has been increased to pH 6.5 during smolting (1 February to 1 July) and to 6.2 the rest of the year as a result of our experiments. In contrast to what has been found for brown trout, salmon strains originating from watercources undergoing acidification were not more tolerant than those from non-acidic watercourses. At the moment no such “tolerant” strains are available for restocking limed rivers in Norway.     

The case for liming some Nova Scotia salmon rivers

Long range transport of H₂SO₄ has caused many Nova Scotian rivers to decline in pH to the point where their Atlantic salmon (Salmo salar) stocks have been destroyed or much diminished. Chemical records show a declining pH trend in N.S. rivers since the early 1950's. The annual variation in hydrogen ion activity is positively correlated with sulphate and Al and negatively correlated with organic anions. It is technically feasible to restore the acidified salmon habitat by the addition of limestone, and the total cost of mounting a liming program to restore the lost habitat has been calculated. The pre-acidification Atlantic salmon production capacity was estimated from physical habitat surveys and tag return data. The estimated costs of the liming program are much greater than the anticipated economic benefits of the salmon restoration. Present plans are for a small liming program to establish a series of refuges for the preservation of nuclei of native salmon stocks.     

A summary of the impact of acid rain on atlantic salmon (Salmo salar) in Canada

Within the present North American range of Atlantic salmon, severe acid rain effects are limited to the Southern Upland area of Nova Scotia. In the Southern Upland, long range transport of H₂SO₄ has caused many rivers to decline in pH to the point where their Atlantic salmon stocks have been destroyed or much diminished. Chemical records show a declining pH trend in N.S. rivers since the early 1950s. Eighty % of the annual variation in H⁺ concentration can be accounted for by a multiple linear regression model on excess sulphate, total Al and organic anions. It is technically feasible to restore the acidified salmon habitat by the addition of limestone; the total cost of mounting a liming program to restore the lost habitat has been estimated at $4.75 × 10⁶ yr^?1. The pre-acidification Atlantic salmon production capacity of the Southern Upland was estimated from physical habitat surveys and tag return data to be about 45 000 fish yr^?1. Acidification has caused a 50% decline to the current production level of about 23 000 fish yr^?1. The costs of the liming program, when compared to the economic benefits of the anticipated salmon enhancement, are economically unjustifiable. The eradication of salmon from such large regions will hinder future programs to reestablish the species in their former range when pollution of the atmosphere is eventually brought under control. Present plans are for a small liming program to establish a series of refuges for the preservation of nuclei of native salmon stocks.     

The influence of organic acidity on the acid-base chemistry of surface waters in Maine,USA

Results from surveys of low-ANC lakes (high elevation, and seepage lakes), and of surface waters in dystrophic, acidic bogs, indicate that acidic precipitation and organic acidity are each generally necessary, but not solely sufficient, for chronically acidic status in Maine lakes. Acidic, low DOC (ANC < 0; DOC < 5 mg L^-1) lakes of all hydrologic types are acidic due largely to acidic deposition; high DOC (DOC > 30 mg L^-1) acidic seepage lakes are acidic due largely to organic acidity, and high DOC drainage lakes are acidic due to a combination of both factors. No low DOC drainage lakes are known with pH less than about 5.0, suggesting that organic acidity is necessary to depress lake pH values to below 5 in Maine at current deposition loadings,The dominant anion of low DOC, acidic waters is sulfate. Acidic waters with intermediate concentrations of DOC (5 to 30 mg L^-1), may be dominated by S04 and/or organic acidity. Seepage-input lakes were the only group to include both organically-dominated (37% of the acidic lakes) and S0₄-dominated members (63% of the acidic lakes). High DOC systems are typically low pH bogs, and are all organic acid-dominated.     

不同调理剂对酸性土壤降酸效果及大麦幼苗生长的影响

采用土壤培养及盆栽试验研究5种调理剂(生石灰、油菜秸秆、有机肥、钾硅肥、土壤改良剂,用量均为1.8 g/kg)对酸性土壤(pH值3.9)酸度指标和大麦幼苗生长的影响。土壤培养试验结果表明,施用生石灰、有机肥和钾硅肥均能明显提高土壤pH值,降低土壤交换性酸总量、交换性H+和交换性铝含量。其中以生石灰降酸效果最好,到培养第90 d,相比于对照处理提高了0.66个单位,土壤交换性铝含量减少了2.01 cmol/kg;其次是有机肥和钾硅肥处理,pH值较对照处理分别提高了0.14和0.15,土壤交换性铝含量分别降低了0.23和0.19cmol/kg;油菜秸秆和土壤改良剂处理从酸度指标来看,与对照并没有显著差异。大麦幼苗盆栽试验结果表明,与对照相比,生石灰、油菜秸秆、有机肥、钾硅肥和土壤改良剂处理的大麦幼苗地上部生物量分别增加71.5%、24.1%、27.6%、28.2%、24.7%,大麦株高、根长、根系总表面积和根系活力均显著高于对照处理,根系平均直径减少,有利于养分和水分的吸收。综合结果表明,不同类型的调理剂对酸性土壤的降酸效果不尽相同,其中以生石灰效果最好,秸秆处理尽管没有有效降低土壤酸度但仍可明显促进作物生长,因此也可用作酸性土壤的改良物质,在实际生产中应因地制宜应用各种调节物质来促进作物生长。