Acidification Stress Research Articles

Long-term changes in forest growth : Potential effects of nitrogen deposition and acidification

In spite of numerous experimental studies, it has, sofar, not been possible to link historic changes inforest growth to acid deposition at regional scales,partly due to difficulties in modeling the ecologicalcomplexity of forests. We analyzed radial incrementdata from increment cores from >31 000 spruce forestplots in southern Norway from 1954–1996. Using acombination of a bio-stratification model to controlconfounding factors, and a catchment model foracidification, we demonstrate for the first time aspatial and temporal co-variation between forestgrowth and both nitrogen deposition and acidification,as indicated by acidity critical loads exceedances.Increases in growth during the 1960–1970s, followed bya subsequent decline in the 1980–1990s, were bestexplained by combined actions of acidification,nitrogen deposition and climatic stress on forestgrowth. While forest conditions varyprimarily with natural growing conditions, the resultssuggest that boreal forests are sensitive to moderatelevels of nitrogen and sulphur deposition whereacidity critical loads are low, and that effects maybe observed over relatively short time scales.

SPATIOTEMPORAL VARIABILITY OF TEMPERATE LAKE MACROINVERTEBRATE COMMUNITIES: DETECTION OF IMPACT

Field assessments of environmental impacts often are confounded by at- tempts to isolate effects of interest (perturbation-induced impacts) from noise introduced by natural spatial and temporal variability. Detection of impact often is constrained by variability of the data, the number of independent samples, the magnitude of impact to be detected, and statistical assumptions. Analysis of the spatial and temporal variability of macroinvertebrate indicator metrics of 16 Swedish lakes, situated in the boreo-nemoral ecoregion, revealed that standardized effect sizes (i.e., effect sizes expressed in standard deviation units) and estimates of statistical power varied markedly among habitats and with choice of indicator metric. In general, indicator metrics relying on measures of the number of taxa (taxon richness, diversity, and ASPT, average score per taxon), and pollution-specific metrics relying on taxon tolerance to pollution (acidification index) had higher standardized effect size and greater statistical power (primarily due to lower variability) than did measures of macroinvertebrate density and biomass. Indicator metrics for macroinvertebrate com- munities of sublittoral habitats often revealed greater standardized effect sizes and statistical power estimates than did metrics for profundal habitats, indicating that sublittoral habitats may provide more robust estimates of acidification stress. The greatest standardized effect occurred for the pollution-specific acidification index of littoral habitats. Selecting indicator metrics for field assessment of impact should be carefully done, and in particular, more focus should be placed on evaluating the robustness of indicator metrics by analyzing indicator metric variance, expected effect size, and statistical power.

Spatiotemporal Variability of Temperate Lake Macroinvertebrate Communities: Detection of Impact

Field assessments of environmental impacts often are confounded by attempts to isolate effects of interest (perturbation-induced impacts) from noise introduced by natural spatial and temporal variability. Detection of impact often is constrained by variability of the data, the number of independent samples, the magnitude of impact to be detected, and statistical assumptions. Analysis of the spatial and temporal variability of macroinvertebrate indicator metrics of 16 Swedish lakes, situated in the boreo-nemoral ecoregion, revealed that standardized effect sizes (i.e., effect sizes expressed in standard deviation units) and estimates of statistical power varied markedly among habitats and with choice of indicator metric. In general, indicator metrics relying on measures of the number of taxa (taxon richness, diversity, and ASPT, average score per taxon), and pollution-specific metrics relying on taxon tolerance to pollution (acidification index) had higher standardized effect size and greater statistical power (primarily due to lower variability) than did measures of macroinvertebrate density and biomass. Indicator metrics for macroinvertebrate communities of sublittoral habitats often revealed greater standardized effect sizes and statistical power estimates than did metrics for profundal habitats, indicating that sublittoral habitats may provide more robust estimates of acidification stress. The greatest standardized effect occurred for the pollution-specific acidification index of littoral habitats. Selecting indicator metrics for field assessment of impact should be carefully done, and in particular, more focus should be placed on evaluating the robustness of indicator metrics by analyzing indicator metric variance, expected effect size, and statistical power.

Developmental stability in perch (Perca fluviatilis) in acidic aluminium-rich lakes

Fluctuating asymmetry is defined as random deviation from perfect bilateral symmetry resulting from environmental or genetic disturbances (termed developmental noise) during early embryonic development. Developmental instability is defined as the inability of an organism to follow the a priori defined growth trajectory that results in perfect bilateral symmetry, owing to insufficient buffering of the disruptive effects of developmental noise during development. Fluctuating asymmetry has been proposed for use as a measure of developmental instability. In this study we tested whether fluctuating asymmetry can be an early indication of acidification stress. Samples were taken from 10 perch (Perca fluviatilis) populations exposed to varying pH levels and aluminium concentrations. We scored 13 bilateral meristic and morphometric characters to assess fluctuating asymmetry. The level of fluctuating asymmetry in the mandibular pores and one index summarizing three of the meristic characters were significantly correlated with the acidification level. When the lakes were split into two groups, "acidified" and "control," each consisting of five lakes, the same pattern emerged. The variance of fluctuating asymmetry estimates was larger in the acidified lakes than in the control lakes. These findings imply that perch in acidic environments experience developmental perturbations during early embryogenesis, resulting in deviating bilateral morphology. The variation in fluctuating asymmetry among lakes was at the same level as previously found among age groups within one acidified lake. Based on these findings, the use of fluctuating asymmetry as a management tool to evaluate the viability of fish populations in acidified waters is of limited value unless a more comprehensive approach is used.

Calculating critical S and N loads and current exceedances for upland forests in southern Ontario, Canada

A steady-state mass-balance model was used to calculate critical loads of S and N deposition for maintaining acceptable long-term acidity levels within upland forests in southern Ontario. Preliminary estimates about critical S and N loads were obtained using existing information about soils, vegetation and atmospheric ion deposition from 12 forest sites, all located within provincial parks or conservation areas. The following were considered: wet atmospheric deposition of all major cations and anions; availability for plant uptake of N, Ca, Mg, and K in the rooting space of each soil; nutrient uptake and storage in the growing woody biomass of the forest stands; estimates of soil weathering; and mean annual air temperature, precipitation, and evapotranspiration. From this, regional isopleth maps were generated to depict the following: (1) current deposition patterns; (2) critical acidification loads and their current exceedances (or nonexceedances) for two acidification effects criteria for soil solutions, namely (i) acceptable Al concentrations ([Al]leach,crit) and (ii) acceptable Al to base cation concentration ratios ([Al]/[BC]leach,crit); (3) critical N-eutrophication loads and their current exceedances for acceptable levels of NO3-N concentrations in soil solutions ([NO3-N]leach,crit). It was found that the northern part of the study area (part of the Canadian Shield) is currently subjected to atmospheric S and N deposition in excess of critical loads, with [Al]leach,crit set at 0.02 mequiv./L or [Al]/[BC]leach,crirt set at 0.15 equiv./equiv. This sensitivity to acid precipitation is, as calculated, primarily due to shallow and weathering-resistant soils and soil parent materials (mostly granitic). The middle portion of the study area is calculated to receive N slightly in excess of the N eutrophication limit, when [NO3-N]leach,crit is set at 0.1 mequiv./L. Considerable co-deposition of base cations (Ca, Mg, K) in the middle and southern part of the study area alleviates some of the atmospheric acidification stress. This stress is further neutralized by the soils and bedrock of this region (predominantly calcareous).

Condition factor and whole-body sodium concentrations in a freshwater fish: Evidence for acidification stress and possible ionoregulatory over-compensation

Condition factor, “K”, was measured for 1202 blacknose dace (Rhinichthys atratulus) from three streams in Shenandoah National Park (USA) of different acid neutralizing capacities (ANCs). “K” is a ratio of weight standardized to length; it is an indication of the health of the individuals in a population. R. atratulus condition factor in the low-ANC stream was found to be significantly lower (11%) than that of dace measured for fish from the intermediate- and high-ANC streams. This difference, according to the results of related investigations, is likely to be biologically significant. Whole-body sodium concentrations were measured as an additional test of sublethal stress in these streams. During summer base flow conditions, mean whole-body sodium concentrations of adult R. atratulus maintained in cages were found to be highest in the low-ANC stream and lowest in the high-ANC stream. The lower condition factor of dace in the low-ANC stream may be related to whole-body sodium concentration and ion regulation. Ion regulation in the low-ANC stream may be more metabolically costly because of chronic sublethal pH stress. R. atratulus may maintain high body Na+ concentrations in low ANC- and ionic strength waters in order to provide a buffer against large episodic pH depressions. The metabolic cost of this ionoregulatory over-compensation may necessitate the diversion of energy from somatic growth and explain the poorer condition of fish from such waters.

Effect of simulated acid rain on the growth of Japanese conifers grown with or without fertilizer

Three-year old cuttings of Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa) and Sawara cypress (Chamaecyparis pisifera) were grown in pots with andosol and were exposed to simulated acid rain (SAR) at pH 2.0, 3.0, and 4.0 for 23 months. Total precipitation was 2460, 3960, or 5450 mm and SAR contained sulfuric, nitric and chloric acid at equivalent ratio of 5∶2∶3. Deionized water of pH 5.6 was a control. Exposure to SAR at pH 2.0 induced visible foliar injuries, but not any visible symptoms at pH 3.0 or higher. Total dry weights of 3 conifer cuttings grown with fertilizer were about two fold of those in plants grown without fertilizer and they reduced significantly by the exposure to SAR at pH 2.0. However, Cryptomeria japonica without fertilizer increased dry weights even though plants developed reddish-brown necrosis in large parts of tops. These 3 coniferous cuttings did not show any significant growth reduction at pH 3.0 and 4.0. Soil pH after receiving 5450 mm of SAR at pH 2.0 was 4.0 and molar ratio of (K+Ca+Mg)/Al in water and 1M ammonium acetate soluble fraction of the soil was about 0.3 and 0.4. respectively. However, dry weight of root in plants grown without fertilizer did not decrease. This suggested that growth reduction in plants fertilized and exposed to pH 2.0 was due to a reduction in photosynthetic organs associated with visible injuries, but not direct linkage with root growth inhibition due to soil acidification stress.

The combined effects of acidification stress and kinetin on chlorophyll content, dry matter accumulation and transpiration coefficient inSorghum bicolor plants

Increasing soil acidity (from pH 6.5 to pH 2.0) decreased chlorophyll (Chl)a andb contents, dry matter accumulation by plants and the transpiration coefficient. Chl stability to heat significantly increased with increased soil acidity. The Chla/b ratio was increased significantly at pH 5 and 4 and decreased at pH 3 and 2. SprayingSorghum shoots with kinetin solutions counteracted the above adverse effects on Chl content and dry matter accumulation. Kinetin-treated plants showed a lower transpiration coefficient than the untreated plants.

Prediction of Lake Trout (Salvelinus namaycush) Presence in Low-Alkalinity Lakes near Sudbury, Ontario

Surveys of 30 low-alkalinity lake trout (Salvelinus namaycush) lakes near Sudbury, Ontario, were conducted to assess factors that affect lake trout presence under acidification stress. At the time of the surveys the lakes varied widely in pH (4.5–6.9), concentrations of toxic metals (Al 12–300 μg∙L−1), and the status of lake trout populations (extinct–abundant). Fish community structure (species richness, species assemblages) reflected and was readily predicted from measured water quality variables. A PCA factor composed of pH, alkalinity, and conductivity was the variable that best predicted lake trout presence (correct discrimination (> 92%). The results of this study provide managers with easily obtainable predictors for monitoring lake trout status under changing levels of acidic deposition.

Interactive effects of exogenous growth regulators and artificial acid rain on cytokinins and gibberellins in maple seedlings

Vegetation experiments were conducted under greenhouse conditions in which long-term effects of simulated acid rain on the shoots, and short-term effects of acidified root medium on the roots of two maple species (Acer pseudoplatanus L. andAcer negundo L.) were studied. Both alternatives of the acidification stress were studied with respect to exogenous applications of auxins and gibberellins. Changes in seedling growth caused by acid rain were not marked, but changes in the levels of endogenous growth regulators were detected, both the long-term exposure ofAcer pseudoplatanus L. seedling shoots to acid rain and the short-term acidification of root environment resulted in enhanced cytokinin activity and in decreased gibberellin activity. But when A.pseudoplatanus L. seedlings were pretreated with gibberellins, their activity was further increased by increased acidity.Acer negundo L. seedlings responded to the acidification of their root environment with enhanced cytokinin activity only when pretreated with exogenous auxins. The differences in the responses ofA. pseudoplatanus L. and A.negundo L. to the acidification can be explained in terms of their distinct physiological properties, including changes recorded in chlorophyll content. The results obtained show that a pretreatment of maple seedlings with exogenous growth regulators can modify the effects of increased acidity in the environment on their physiological status as characterized by the level of endogenous cytokinins and gibberellins.

Acidification stress of root environment as related to endogenous cytokinins and gibberellins in oak seedlings

Activity of endogenous cytokinins and gibberellins was determined in the shoots and roots of oak seedlings following the submersion of roots in water acidified with sulphuric add to pH 3.0, 2.5, 2.0, 1.7 and 5.6 (control) for 6 and 72 h. After 6 h the cytokinins increased in the shoots and in roots at pH 2.5 and 2.0, respectively. None of the tested pH values decreased the cytokinin activity. The acidification of solutions exhibited no remarkable influence on gibberellin activity. Only slight stimulation of the gibberellin activity was exhibited at pH 2.0. After 72 h a slight decrease in the activity of cytokinins was observed in the shoots at pH 2.5, remarkable decrease was revealed at pH 2.0 and 1.7. Nevertheless, in the roots stimulation of cytokinin activity appeared up to pH 2.0 (the highest at pH 2.5), and significant decrease was shown at pH 1.7. The activity of gibberellins in shoots showed similar dependence of changes as the activity of cytokinins in roots. Acidification stress exerted no influence on the gibberellin. activity in roots.

Potential importance of spatial and temporal heterogeneity in pH, Al, and Ca in allowing survival of a fish population: A model demonstration

Discrepancies usually exist between the results of bioassay studies and the status of natural fish populations. One cause of such discrepancies is the spatial and temporal heterogeneity in the stressing factors or contaminant concentrations in natural systems. To provide a means of relating laboratory and field bioassay results to natural populations, we have modified an existing Monte Carlo mathematical model to track the movement and survival of fish in a body of water, represented by a two-dimensional grid, subject to acidification stress. We assumed that the fish (adults or the less mobile and generally more sensitive early life stages) are able to sense realistic gradients of pH, aluminium (Al), and calcium (Ca) (or alkalinity) and to move to reduce the chemical stress. We have also considered the effects of food availability and habitat preference on fish movement. Each fish takes one spatial ‘step’ at a time, the direction being randomly selected but also biased by the above factors. A function for accumulation and repair of damage is implemented within the model to relate mortality to the variable exposure history the fish accumulate by moving in the chemically heterogeneous environment. Using the model, we evaluated the influence of the strength and sensitivity of fish avoidance behavior, the presence or absence of the refuge, and the timing of multiple pulses on fish survival. The results highlight the potential importance of a chemically heterogeneous natural environment in allowing a population to survive under average water-quality conditions that laboratory bioassays suggest should prohibit survival. Laboratory and field behavior experiments, including characterization of water chemistry on a microscale in the field, are suggested to explore this phenomenon further.

Analysis of Planktonic Rotifer Assemblages from Sudbury, Ontario, Area Lakes of Varying Chemical Composition

Planktonic rotifer samples were collected from 47 Sudbury, Ontario, area lakes to determine factors influential to species distributions. The lakes ranged from highly acidic and metal contaminated to circumneutral with low metal concentrations. Median rotifer abundance was substantially higher in non-acid (pH > 5.2) than in acid (pH < 5.2) lakes, although differences in species distributions were evident. Application of detrended correspondence analysis to rotifer species densities revealed broad separation of communities from acid and non-acid lakes. Assemblages from acid lakes were highly similar in species composition and dominance, while those from non-acid lakes were generally much more heterogeneous. It was hypothesized that planktonic rotifer communities converged in species composition as a consequence of the stress of lake acidification, in a pattern similar to that previously described for planktonic crustaceans. Among the best predictors of rotifer community composition were lake pH and the concentrations of manganese and aluminum.

Integrated and individual biochemical responses of rainbow trout ( Salmo gairdneri) to varying durations of acidification stress

1. Rainbow trout displayed a variety of biochemical responses when exposed to pH 4.5 for periods of 6–48 hr. 2. Some adaptive or recovery responses occur in rainbow trout after 12–24hr of continuous exposure to reduced pH, with most biochemical variables returning to near control levels following 48 hr of nonexposure. 3. The integrated biochemical response of trout to acidification stress was determined by incorporating all 10 measured biochemical variables into a discriminant analysis procedure. 4. Measures of electrolyte homeostasis (sodium), carbohydrate metabolism (glucose), lipid metabolism (triglycoride) and amino acid metabolism (serum glutamate oxaloacetate transaminase) provide the best indicators of individual biochemical responses of trout to reduced pH. 5. Determination and interpretation of fish response to reduced pH can differ, depending on whether individual or multiple biochemical variables are being evaluated.