Phytoplankton succession during acidification with and without increasing aluminum levels

An in situ mesocosm experiment was performed to investigate the role of aluminum in controlling phytoplankton community succession during lake acidification. Large (2000 liter) mesocosms were suspended in mesotrophic East Twin Lake, Ohio, USA. Duplicates were either untreated controls (pH 8.8), acidified to pH 4.5 over 23 days, or acidified and spiked with 200 microg/liter Al in incremental additions. Filamentous blue greens, diatoms and other chrysophytes became extinct in both acid treatments, but declined most rapidly where Al levels were also increased. The large desmid Closterium and the filamentous chlorophyte Mougoetia became dominant in the Acid treatment. In the Acid + Al treatment, these algae also became dominant, but the species with greatest biomass was the dinoflagellate Peridinium inconspicuum. Acidification (with or without added Al) also resulted in a significant shift in the algal size spectrum to larger (> 20 microm) cells.     

Littoral zooplankton responses to acid and aluminum stress during short-term laboratory bioassays

During autumn 1990, littoral zooplankton were collected from three alkaline lakes in Ohio, USA. Toxicity tests were performed, in which animals were placed into treatments of pH 4.5, with or without 500 microg litre(-1) Al added. Percentage survival after 24 h was determined for each test species, and compared to survival in controls (pH roughly 8.0). Three distinct responses were observed: (1) Four cladocerans, Simocephalus serrulatus, Diaphanosoma birgii, Acantholeberis curvirostris and Chydorus sphaericus, were tolerant of both acid and Al, with no significant reductions in survival in the treatments. (2) The cladoceran Eurycercus lamellatus and the capepod Acanthocyclops vernalis were sensitive to both acid and Al, and suffered 100% mortality in both treatments. (3) The cladocerans Camptocercus rectirostris, Alona costata and Pleuroxus denticulatus, and the copopod Mesocyclops edax showed decreased survival in the acid treatment, and a significantly greater decrease in the acid plus Al treatment. For nine of the ten test species, the results were consistent with previous survey and paleolimnological studies. The results indicate that direct toxic effects of H+ and Al ions largely determine the responses of these common littoral species to acidification.     

Artificial acidification of a non-acidic and an acidic headwater stream in Maine, USA

Two headwater streams with low DOC and different pHs (4.5-4.8 and 5-6.5) were acidified with H2SO4 to pH 4.1 and 4.5, respectively, for 24-h periods. Neutralization of the added acid occurred by protonation of ANC (HCO3-dominated in the higher pH stream), desorption of Ca (< 15 microeq litre(-1)) and Mg (<6 microeq litre(-1)), and desorption and dissolution of AL (<250 microg litre(-1)) from the stream bed. The concentrations of dissolved organic carbon (DOC) remained constant within the experimental reaches. The concentrations of Na, K an H4SiO4 also remained constant, indicating no detectable increase in the rate of chemical weathering in the stream bed. After acid addition was stopped, concentrations of Ca, Mg and Al decreased to below background, indicating reversible ion exchange as the principal mechanism for the mobility of Ca and Mg and to a lesser extent for Al. Repeated acidifications indicated that significant regeneration of cations on the exchange surfaces of the stream substrate occurs rapidly.     

Response of phytoplankton communities to acidification and recovery in Killarney Park and the Experimental Lakes Area,Ontario

It has been widely speculated that controls of SO2 emissions would stimulate recovery of acidified freshwater lakes in Canada, the United States and Europe. Phytoplankton communities from 22 lakes near Killarney Park Ontario, covering a pH range from 4.5-7.7, were studied from 1998-2000 and compared to data from experimentally acidified (pH decreased 6.7 to 4.5) and recovered (pH increased to 6.0) Lake 302 South at the Experimental Lakes Area (ELA), northwestern Ontario to assess recovery from acidification. Based on historical data, pH levels have rebounded to above 6.0 in several lakes in the Killarney area that were previously acidified to pH 5.0-5.5. Phytoplankton biomass was not correlated to pH, but there was a highly significant relationship between species richness and pH. Recovery trajectories were observed in a subset of 6 lakes, combining species diversity data from the present study with historical data. Correspondence analysis indicated that several of the lakes that experienced increased pH have shifted towards phytoplankton assemblages typical of circumneutral environments.     

Effects of experimental acidification on mobilisation of metals from sediments of limed and non-limed lakes

In order to study the influence of pH on the mobilisation of metals from lake sediments, intact sediment cores with overlying water were sampled from one lime treated lake and one acidified lake. The overlying water of two cores from each lake was successively acidified to pH 4.2 over a period of 3 months. In the acid treated samples from the limed lake, the initial concentrations of Al, Cd, Mn, Pb and Zn in the overlying water were generally lower and the final concentrations were higher than in the acid treated samples from the acidified lake. The labile inorganic fraction of Al (Al(i)) was increasingly dominating as pH decreased. Redox potential and pH in the sediment indicated that the upper two centimetres were involved in the exchange reactions. The experiment showed that mobilisation of metals from sediments can occur and the results indicated that mobilisation could contribute to increased concentrations of metals in lake water during reacidification of formerly lime treated lakes.     

Chemical and biological effects of acid, aluminium and lime additions to a Welsh Hill-stream

Chemical and biological responses to simultaneous additions of acid, aluminium and lime were investigated in contiguous 250m-reaches of a chronically acidic stream in Wales. Treatments were applied for 24 h, and from the upstream end were as follows: zone A-untreated, pH 5.0, 0.37 mg litre(-1) filterable Al; zone B-acidified to pH 4.5, 0.40 mg Al litre(-1) (47% of Al attributed to release from the stream bed due to acid additions); zone C-acidified to pH 4.5 and Al dosed to 0.67 mg litre(-1); zone D-dosed with limestone slurry, resulting in pH 7.2, 0.13 mg Al litre(-1). In all reaches, the chemistry of the interstitial water at depths of 0.15 and 0.3 m never fell below pH 5.5, with corresponding decreases in Al and increases in base cation concentrations. Brown trout, Salmo trutta, and crayfish, Austropotamobius pallipes, held in the stream showed decreases in plasma [Na(+)] and haemolymph [Na(+)], respectively, in all acidic zones (A, B, C): these responses were mitigated by liming (zone D). Thus both chronic and simulated episodic levels of pH and dissolved Al were sub-lethally toxic to test species of aquatic fauna. This experiment also demonstrates a stream bed source/sink of Al, and the availability of a possible refuge from acidic surface waters within the substratum.     

Acid and aluminum effects on the survival of littoral macro-invertebrates during acute bioassays

Six common macro-invertebrates were exposed to soft water at pH 4.5, with or without 200 microg liter(-1) Al added. Survivals were determined at 6, 12, 24 and 48 h and compared with neutral pH, Al-free controls. The order of acid-sensitivity among the test animals, from greatest to least (with mean 24/48 h survivals in the pH 4.5, low Al treatment in parentheses), was: Caenis sp. (2%) > Hyalella azteca (12%) > Enallagma sp. (20%) > Gyraulus sp. (55%) > Chironomidae (94%) > Hydracarina (99%). Aluminum significantly reduced the survivals of Gyraulus, Hyalella and Chironomidae. The latter group experienced no significant mortality at pH 4.5 except when Al was present. In contrast, the Hydracarina were unaffected by both acid and acid plus Al exposure, and the survivals of Enallagma and Caenis at low pH were enhanced by Al. These differential responses to the treatments indicate that both acid and Al stress may control the structure of the littoral macroinvertebrate community in acid lakes.     

Physiological recovery from episodic acid stress does not mean population recovery of Gammarus fossarum

The physiological responses of the acid-sensitive amphipod Gammarus fossarum exposed in situ to acid stress (pH4.5 and 5.5) and then transferred back to neutral water were investigated. Survival rate and haemolymph [Cl(-)] and [Na(+)] were assessed after 24, 48 and 72h of exposure in acidic streams and after a recovery period of 12, 24, 36, 48 and 60h. After 24h, exposure to slightly acidic (pH5.5) and strongly acidic water (pH4.5) led to a severe and significant depletion in haemolymph [Na(+)] and [Cl(-)] compared to organisms exposed in circumneutral water (pH7.3). However, after only a 12h-period of transfer back in neutral water and whatever the previous exposure time (24, 48 and 72h) in both slightly and strongly acidic water, haemolymph [Na(+)] and [Cl(-)] were equal or superior to the control level without associated mortality. In spite of this fast physiological recovery capacity, populations of G. fossarum living in streams undergoing episodic acid stresses were drastically affected thus, demonstrating the high acid-sensitivity of this species. We discuss the possible reasons of population regression and the absence of population recovery.     

Changes in trace metal concentrations in lake water and biota during experimental acidification of Little Rock Lake, Wisconsin, USA

Little Rock Lake, a small (18 ha), low-alkalinity (25 microeq litre(-1), pH 6.1) seepage lake in northern Wisconsin, was divided into two basins by a flexible, inert barrier and, beginning in spring 1985, the north basin was acidified in three 2-year steps to pH 5.6, 5.1 and 4.7. The annual average pH of the reference basin remained near 6.1. As part of a comprehensive programme to determine the chemical and biological responses to acidification, minor metals (Al, Fe, Mn) and trace metals (Cd, Cu, Pb, Zn) in lake water (0.4 microm pore filtered samples), periphyton, zooplankton, and yellow perch (Perca flavescens) were measured. At pH 5.6, dissolved Mn and Fe increased in the acidified basin. At pH 5.1 and 4.7, dissolved Al, Fe, Mn, Cd and Zn were elevated in the acidified basin. At pH 4.7, dissolved Pb in the acidified basin became elevated over reference basin levels. Dissolved Cu remained similar in both basins down to pH 4.7. Cd burdens in periphyton collected on artificial substrates were lower in the treatment basin at pH 5.1 (1.8 microg g(-1) dry wt.) than in the reference basin at pH 6.1 (7.5 microg g(-1) dry wt.), but Al and Fe burdens in periphyton were similar in both basins. Likewise, Cd levels in muscle tissue of perch from the treatment basin at pH 4.7 were lower (26 ng g(-1) dry wt.) than in the reference basin at pH 6.1 (36 ng g(-1) dry wt.); Al and Fe burdens were similar in perch muscle tissue from both basins. Levels of Cd and Fe in zooplankton from the acidified basin at pH 4.7 were approximately equal to 2x higher than in animals from the reference basin. In both basins of the lake, Al and Cd levels in lake biota decreased with increasing trophic level, demonstrating that food chain biomagnification does not occur for these metals.     

Influence of acidification of CCB (Cu/Cr/B) impregnated wood on fungal copper tolerance

Copper tolerant fungi are known for more than 60 years but the complete mechanisms of copper tolerance by these fungi are still not fully understood. Copper tolerance has previously been linked to oxalic acid excretion by copper tolerant brown rot fungi. The oxalic acid then reacts with copper in the wood to form an insoluble and therefore less toxic copper oxalate. It has been suggested that copper tolerance could be due to lowering of the pH of the medium rather than the low solubility of copper oxalate. In order to elucidate this presumption, copper/chromium/boron (CCB) treated wood specimens were acidified with organic (oxalic, acetic, lactic, formic) and inorganic (sulphuric) acids and exposed to copper tolerant (Antrodia vaillantii, Leucogyrophana pinastri) and copper sensitive (Poria monticola, Gloeophyllum trabeum) brown rot fungal strains according to the mini block procedure. After eight weeks of exposure, the wood specimens were isolated and their mass losses determined. Additionally, electron paramagnetic resonance (EPR) measurements on the exposed specimens were performed. The EPR spectra of the specimens decayed by A. vaillantii were very similar to the EPR spectra of the specimens acidified with oxalic acid. Additionally, acidification of the CCB impregnated specimens made them significantly more susceptible to decay by both the copper tolerant and copper sensitive brown rot fungi.     

Complex biological responses to the experimental acidification of Little Rock Lake, Wisconsin, USA

Acidification can affect aquatic organisms directly through hydrogen ion toxicity, and indirectly through disrupted food web dynamics and altered abiotic conditions. Field populations from selected taxa were studied during the Little Rock Lake whole-basin acidification experiment to illustrate patterns whose timing suggests direct (i.e. immediate) or indirect (i.e. delayed or non-uniform) responses to pH change. As the treatment basin was acidified to pH 5.6, 5.2 and 4.7, immediate changes consistent with a direct pH response were observed for species representing several trophic levels. For other taxa (e.g. littoral invertebrates associated with filamentous algal mats, several species of pelagic zooplankton), indirect mechanisms induced by food web changes were more likely explanations for abundance patterns. The results presented here suggest that the responses of aquatic ecosystems to acidification involve a complex interplay between direct pH effects and subsequent indirect interactions.     

Long-term trends in water chemistry of acid-sensitive Swedish lakes show slow recovery from historic acidification

Long-term (1987–2012) water quality monitoring in 36 acid-sensitive Swedish lakes shows slow recovery from historic acidification. Overall, strong acid anion concentrations declined, primarily as a result of declines in sulfate. Chloride is now the dominant anion in many acid-sensitive lakes. Base cation concentrations have declined less rapidly than strong acid anion concentrations, leading to an increase in charge balance acid neutralizing capacity. In many lakes, modeled organic acidity is now approximately equal to inorganic acidity. The observed trends in water chemistry suggest lakes may not return to reference conditions. Despite declines in acid deposition, many of these lakes are still acidified. Base cation concentrations continue to decline and alkalinity shows only small increases. A changing climate may further delay recovery by increasing dissolved organic carbon concentrations and sea-salt episodes. More intensive forest harvesting may also hamper recovery by reducing the supply of soil base cations.     

Effects of acidification on the availability of toxic metals and calcium to wild birds and mammals

The effects of acidification on wildlife inhabiting aquatic or semi-aquatic environments are reviewed, with particular reference to the possibility for increased dietary exposure to Hg, Cd, Pb and/or Al, and decreased availability of essential dietary minerals such as Ca. It is concluded that: (1) piscivores risk increased exposure to dietary methyl-Hg in acidified habitats, and Hg concentrations in prey may reach levels known to cause reproductive impairment in birds and mammals; (2) piscivores do not risk increased exposure to dietary Cd, Pb or Al because these metals are either not increased in fish due to acidification, or increase are trivial from a toxicological perspective; (3) insectivores and omnivores may, under certain conditions, experience increased exposure to toxic metals in some acidified environments. Exposure levels are likely to be sufficiently low, however, that significant risks to health or reproduction are unlikely. More importantly, these wildlife species may experience a drastic decrease in the availability of dietary Ca due to the pH-related extinction of high-Ca aquatic invertebrate taxa (molluscs, crustaceans). Decreased availability of dietary Ca is known to adversely affect egg laying and eggshell integrity in birds, and the growth of hatchling birds and neonatal mammals. Acidification-related changes in the dietary availability of other essential elements, such as Mg, Se and P, have not been established and require further investigation; (4) herbivores may risk increased exposure to Al and Pb, and perhaps Cd, in acidified environments because certain macrophytes can accumulate high concentrations of these metals under acidic conditions. The relative importance of pH in determining the metal concentrations of major browse species, and the toxicological consequences for herbivores wildlife, is not well established and requires further study. A decreased availability of dietary Ca is also likely for herbivores inhabiting acidified environments.     

Effects of acidic solutions on element dynamics in the monsoon evergreen broad-leaved forest at Dinghushan,China

BACKGROUND: Soil metal dynamics are affected by acid deposition. Little knowledge is available about the process in the lateritic soils under the monsoon forest in south China. METHODS: Samplings of Acmera acuminatissima, Cryptocarya concinna and Schima superba were grown from October, 2000 to July, 2002 in pots with a natural acid lateritic forest soil from Dinghushan. Pots were watered weekly with an acid solution (pH 3.05, 3.52, 4.00 or 4.40) or with tap water. Fe, Mn, Cu and Al were measured in soils, leachates and sapling leaves. RESULTS: Soil extractable Fe and leachate Al and Mn concentrations increased with a decreasing treatment pH. Soil reactive Al exhibited the opposite trend and decreased over time. The Ca/Al and Mg/ (Al+Mn) ratios did not decrease in the leaves of Schima superba, but decreased with a decreasing treatment pH for Cryptocaria concinna. Both ratios only decreased in the pH 3.05 treatment for Acmena CONCLUSIONS: Cu will not be toxic for plants since soil extractable Cu was not high and Fe will not be toxic either given that its root uptake was inhibited by Mn. Acid rains will lead to increased Mn and Al mobility in soil. Cryptocaria concinna will be the most sensible species to these changes (nutrient deficiency and direct Mn toxicity), while Schima superba should retain a good growth.     

Growth responses of three legume species exposed to simulated acid rain

Seedlings of Vicia faba L., Phaseolus multiflorus L. and Pisum sativum L. were raised during exposure to simulated acid rainfall treatments of pHs 5.6, 4.5, 3.5 and 2.5 at a rate of 30 mm per week. All three species were found to be adversely affected by the more acid pH 3.5 and pH 2.5 treatments after 7-8 weeks of exposure. There were total plant dry weight reductions of 40% for V. faba, 31% for P. sativum and 28% for P. multiflorus exposed to the pH 2.5 treatment, as compared to those grown in the control (pH 5.6 treatment). In addition, V. faba was found to be sensitive to the pH 4.5 treatment with an 18% reduction in total plant weights (compared to plants grown in the pH 5.6 treatment). In P. multiflorus, reduction in the dry weights of shoots in response to increasing acidity of rain was not accompanied by reduction in root weights, indicating an interference in the partitioning of assimilates. It is concluded that these three species, and V. faba in particular, may be growing below their potential in much of the UK.     

Short-term physiological responses to a severe acid stress in three macroinvertebrate species: a comparative study

The present study focuses on the sensitivity among freshwater invertebrate species to acidic stress. Three common macroinvertebrate species in the Vosges Mountains (North-Eastern France), Gammarus fossarum (Amphipoda), Hydropsyche pellucidula (Trichoptera) and Dinocras cephalotes (Plecoptera) were exposed for 24, 72 and 120 h to natural acidified water (pH=4.73+/-0.08, [Ca2+]=39.1+/-0.6 micromol l(-1), [Al(tot)]=28.4+/-1 micromol l(-1)). Short-term exposure to acid stress caused significant decreases both in survival rate and haemolymph ions ([Cl-] and [Na+]). The relative sensitivity to a natural acidic stress slightly differed among the species and was in the following order: G. fossarum, as the most sensitive, then H. pellucidula and D. cephalotes. Results of this study confirm the interest of in situ tests to assess the toxicity of short-term acid exposure. Finally, our results reinforce the hypothesis that transient acidification can offset the recovery of sensitive species of macroinvertebrates in streams chemically recovering from acidification either through liming or declining deposition.     

Aluminum binding to ion exchange sites in acid-sensitive versus acid-tolerant cladocerans

Two acid-sensitive cladocerans, Daphnia galeata mendotae and D. retrocurva, and one acid-tolerant one, Bosmina longirostris, were exposed for 24 h to pH 5.0 and 200 microg liter(-1) total Al. The entire procedure was replicated on three dates in summer 1989. Mortality rates were determined, and the extent of Al binding to ion exchange sites determined using hematoxylin staining. Both daphnids consistently experienced near 100% mortalities, while mortalities for B. longirostris were always near zero. The daphnids showed marked Al binding at the maxillary glands, the site of ion exchange, while B. longirostris showed no noticeable Al binding.     

Recovery of crustacean zooplankton communities from acidification in Killarney Park,Ontario, 1971-2000: pH 6 as a recovery goal

Despite reductions in atmospheric SO4(2-) deposition and resultant decreases in surface water acidity, widespread biological recovery from acidification has not yet been documented. Temporal trends in crustacean zooplankton species richness (number of species) and composition were examined between 1971-2000 in 46 Killarney Park lakes, Ontario, Canada, to assess the degree of biological recovery in lakes with significant water quality improvements, i.e. pH now > 6, compared to 2 other groups: i) lakes which never acidified; and ii) lakes which are still acidified (pH < 6). Time trends in species richness could not be distinguished among the 3 groups of lakes, nor did changes in species richness indicate recovery. In contrast, the zooplankton community composition of lakes in which the pH increased to above 6, as measured by a multivariate index of species abundances, changed from a "damaged" state to one typical of neutral lakes. Some recovery in composition was also documented for the acidic lakes. While still acidic, the pH levels of these lakes have risen. The extent and pace of recovery in Killarney Provincial Park bodes well for the future of other acidified regions in North America and Europe.     

Effects of acid rain on growth and nutrient concentrations in Scots pine and Norway spruce seedlings grown in a nutrient-rich soil

The effects of artificially applied acid precipitation on growth and nutrient concentrations of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) seedlings were investigated in a long-term acid irrigation experiment in field conditions. Seedlings of northern and southern origin were planted in boxes containing peat and composted soil rich in nutrients, and sprinkler irrigated with water acidified with nitric and sulphuric acids to pH 3 or pH 4 for periods varying from two to three and a half growing seasons during 1986-1989. Water irrigated (pH 5.4-7.6) and non-irrigated groups of seedlings were also included in the experiment. At the end of the experiment needles, main and lateral shoots and roots were collected from the seedlings for the determination of height growth and biomass partitioning, and for the analysis of S, N, Mg, P, K, Ca, Mn and Fe concentrations. The treatment effects compared to the irrigated control were studied using multivariate analyses of variance and covariance. In the pine seedlings the total dry matter production increased by 25-70% compared with the irrigated controls when the total wet deposition to the seedlings exceeded 67 kg S ha(-1) and 36 kg N ha(-1) (e.g. after two growing seasons' exposure of the pH 3 treatment). The increase was mainly due to an increase in needle dry weight (54-72% greater at pH 3) and root weight (20-65% greater at pH 3), whereas the height growth or shoot weight growth were less affected. The northern provenance pine seedlings responded more clearly to the pH 3 irrigation than the southern ones. The treatments had no consistent effects on any of the growth variables studied in the spruce seedlings, however. The pines had higher root and foliage Ca concentrations as a result of the acid irrigation, whereas in spruce, acid rain decreased the Ca concentration in needles and shoots. Root Mn and Fe concentrations were higher in both species as a result of the pH 3 treatment. A higher soil conductivity and Ca concentration resulted from the prolonged pH 3 treatment. The results strongly support the hypothesis that the long-term growth and nutrient allocation response of conifers to acid precipitation is dependent both on the tree species and on the nutritional status of the soil.     

The ecology of acidification and recovery: changes in herbivore-algal food web linkages across a stream pH gradient

We examined the effects of acidification on herbivore-algal food web linkages in headwater streams. We determined the structure and abundance of consumer and benthic algal assemblages, and gauged herbivory, in 10 streams along a pH gradient (mean annual pH 4.6-6.4). Biofilm taxonomic composition changed with pH but total abundance did not vary systematically across the gradient. Mayflies and chironomids dominated under circumneutral conditions but declined with increasing acidity and their consumption of algae was strongly reduced. Contrary to expectations, several putative shredder species consumed algae, maintaining the herbivore-algal linkage where specialist grazers could not persist. These shifts in functioning could render the communities of acidified streams resistant to reinvasion when acidity ameliorates and water chemistry is restored to a pre-acidification condition. This hypothesis is discussed in the light of recent trends in the chemistry and biology of the UK Acid Waters Monitoring Network sites.