The effect of anthropogenic acidification on the hydrofauna of the lakes of the West Tatra Mountains (Slovakia)

Fourteen West Tatra lakes were studied, of which one could be considered to be recently anthropogenically acidified and eight others classified as acidification-endangered. In the anthropogenically acidified lake, the zooplankton assemblage has been substantially altered (three mountain-lake crustacean species have been eliminated). Several littoral macrobenthic species sensitive to acidification have either been eliminated from the acidified and acidification-endangered lakes or occur only sporadically. The effect of acidification has so far not been observed on the benthic fauna of the lakes medial which is probably due to the higher pH below the surface of sediment. In comparison with the High Tatra, acid depositions have had a less pronounced effect on the lakes of the West Tatra.     

Soil acidification reduces the effects of short‐term nutrient enrichment on plant and soil biota and their interactions in grasslands

Soil nitrogen (N) and phosphorus (P) contents, and soil acidification have greatly increased in grassland ecosystems due to increased industrial and agricultural activities. As major environmental and economic concerns worldwide, nutrient enrichment and soil acidification can lead to substantial changes in the diversity and structure of plant and soil communities. Although the separate effects of N and P enrichment on soil food webs have been assessed across different ecosystems, the combined effects of N and P enrichment on multiple trophic levels in soil food webs have not been studied in semiarid grasslands experiencing soil acidification. Here we conducted a short‐term N and P enrichment experiment in non‐acidified and acidified soil in a semiarid grassland on the Mongolian Plateau. We found that net primary productivity was not affected by N or P enrichment alone in either non‐acidified or acidified soil, but was increased by combined N and P enrichment in both non‐acidified and acidified soil. Nutrient enrichment decreased the biomass of most microbial groups in non‐acidified soil (the decrease tended to be greatest with combined N and P enrichment) but not in acidified soil, and did not affect most soil nematode variables in non‐acidified or acidified soil. Nutrient enrichment also changed plant and microbial community structure in non‐acidified but not in acidified soil, and had no effect on nematode community structure in non‐acidified or acidified soil. These results indicate that the responses to short‐term nutrient enrichment were weaker for higher trophic groups (nematodes) than for lower trophic groups (microorganisms) and primary producers (plants). The findings increase our understanding of the effects of nutrient enrichment on multiple trophic levels of soil food webs, and highlight that soil acidification, as an anthropogenic stressor, reduced the responses of plants and soil food webs to nutrient enrichment and weakened plant–soil interactions.     

How many fish populations in Finland are affected by acid precipitation?

Synopsis The number of fish populations affected or lost from small lakes in southern and central Finland due to acid precipitation is estimated. Tolerance limits (pH and labile aluminum) of common fish species were obtained from a fish status survey of 80 lakes. These tolerance values were used to estimate the proportion of affected lakes from the water chemistry data of 783 statistically selected lakes. The proportion of anthropogenically acidified lakes was estimated by calculating pre-acidification pH and aluminum concentrations of the lakes, using a steady-state model based on water chemistry. The number of fish populations for which acidification has affected growth or population structure was estimated at between 2200 and 4400. Out of these, the number of fish populations that have disappeared due to acid precipitation would be about 1000–2000. Almost 60% of the affected or lost populations are roach, Rutilus rutilus, the most sensitive of the common fish species in small lakes in southern and central Finland. Less than 15% of the damaged population is European perch, Perca fluviatilis, the most common species. This is due to the substantially higher tolerance of perch to acidified water in comparison with roach.     

Biodiversity, metabolism and applications of acidophilic sulfur-metabolizing microorganisms

Extremely acidic, sulfur-rich environments can be natural, such as solfatara fields in geothermal and volcanic areas, or anthropogenic, such as acid mine drainage waters. Many species of acidophilic bacteria and archaea are known to be involved in redox transformations of sulfur, using elemental sulfur and inorganic sulfur compounds as electron donors or acceptors in reactions involving between one and eight electrons. This minireview describes the nature and origins of acidic, sulfur-rich environments, the biodiversity of sulfur-metabolizing acidophiles, and how sulfur is metabolized and assimilated by acidophiles under aerobic and anaerobic conditions. Finally, existing and developing technologies that harness the abilities of sulfur-oxidizing and sulfate-reducing acidophiles to extract and capture metals, and to remediate sulfur-polluted waste waters are outlined.     

Tracking Recovery Patterns in Acidified Lakes: A Paleolimnological Perspective

Long-term data are often lacking to effectively assess patterns of lake acidification and recovery. Fortunately, paleolimnological techniques can be used to infer past changes in lakewater acidity and related variables by means of biological indicators, such as diatom valves and chrysophyte scales, preserved in ²¹⁰Pb-dated sediment cores. We summarize paleolimnological data that we have gathered from 36 Sudbury (Ontario) and 20 Adirondack Park (New York) lakes to estimate the magnitude of lake acidification and any subsequent recovery in these lake systems. In both regions, many lakes were shown to have acidified considerably, some over two pH units, since the 1850s. Although some recovery was noted in both lake regions, Sudbury lakes generally showed larger increases in inferred lakewater pH with recent declines in sulfur emissions. Possible explanations of these differences include the greater decrease in sulfate deposition in the Sudbury area, as well as generally longer residence times of lakes in Sudbury, perhaps allowing for more in-lake alkalinity generation. In addition, Sudbury lakes generally had higher pre-industrial pH levels, suggesting that lakes with higher natural buffering capacities are more likely to recover more quickly with declines in deposition, even if they had been acidified to a great extent.     

Longterm assessment of spruce vitality in the Fichtelgebirge (West Germany) under ongoing acid depostion

Historical land-use and especially acid precipitation seem to have altered the natural habitat conditions for Norway spruce (Picea abies (L.) Karst.) in Central Europe.Many forest decline studies of the last ten years evaluate the continual anthropogenic stress situation for Norway spruce. Especially in regions with high acidic deposition, regeneration of spruce stands seems to be impossible without soil melioration. In a first estimate the assumed H⁺-deposition and additionally the propensity of soils to acidification in spruce stands is characterized. After studying several soil parameters, exposition and climatic factors were processed by means of a Geographical Information System in order to draw a balance of human impact on habitat conditions of Norway spruce.Both the spatial distribution of spruce vitality under natural conditions (without human impact) in the research area Fichtelgebirge (northeast Bavaria) and the prospective vitality of spruce under actual human impact is shown. From this comparison it is concluded that without air pollution abatement and without amelioration of the heavily acidified sites spruce regeneration can not be expected even in the long run. The actual forest damage and some restoration programs give evidence of this assumption.     

Subfossil chironomids (Diptera,Chironomidae) in three Tatra Mountain lakes (Slovakia) on an acidification gradient

Three lakes were studied in the High Tatra Mountains at altitudes from 2000 to 2157 m a.s.l., which represent three categories of acidity status recognised in the Tatra lakes in the 1980s: non-acidified, acidified, and strongly acidified. Subfossil chironomid remains from dated sediment cores covering ca. throughout 200 years were analysed. The chironomid thanatocoenoses of all cores layers reflected ultra-oligotrophic non-acidified conditions in L’adové pleso. Nevertheless, the finding of the acid-tolerant species Zalutschia tatrica in littoral samples in 1980s indicates that the littoral zone was more influenced by acidification than deeper areas of the lake. Three stages of lake developmental history can be distinguished in the acidified lake Vy?né Wahlenbergovo pleso based on the chironomid subfossil record: the pre-acidification stage before the 1920s, the anthropogenic acidification stage between the 1920–1980s, and the recovery of the lake from the end of the 1980s. The period of acidification was accompanied by a decline in chironomid numbers, while chironomid fauna composition was unchanged during the whole investigated history of the lake. None of the chironomid taxa present prior to the acidification period disappeared during the peak of acidification. The most apparent change in the sediment record taken from the strongly acidified lake Starolesnianske pleso was recognised in the layers corresponding to the period 1960–1980. It is characterised by the disappearance of the dominant acid-sensitive Tanytarsus lugens group and the dominance of acidtolerant Tanytarsus gregarius group. The most recent chironomid assemblage probably benefits from the amount of food resources as a result of increased lake productivity induced by acidification.     

Bioindication in Norwegian rivers using non-diatomaceous benthic algae: The acidification index periphyton (AIP)

Impacts of acidification on aquatic communities have been obvious in Scandinavia since the end of the 19th century and recent model simulations show that in Norway, acidification of surface waters will continue to be an issue in the coming decades. Here, we present a new index based on non-diatomaceous benthic algae (acidification index periphyton, AIP) that can be used to describe the mean annual acidity of Norwegian rivers. The AIP was applied to 608 samples from unlimed rivers all over Norway and values ranged from 5.35 to 7.28, thus covering a range from acid to neutral conditions. Application of the AIP to both limed sites and sites that formerly were acidified demonstrate that the algal community reacts with a several years delay to both river liming and natural recovery. The AIP is most sensitive between mean annual pH values of approximately 5.5 and 7.0 and can be especially useful in detecting the first signs of an acidification trend or the last steps of a recovery process.     

Antarctica: The final frontier for marine biological invasions

Antarctica is experiencing significant ecological and environmental change, which may facilitate the establishment of non‐native marine species. Non‐native marine species will interact with other anthropogenic stressors affecting Antarctic ecosystems, such as climate change (warming, ocean acidification) and pollution, with irreversible ramifications for biodiversity and ecosystem services. We review current knowledge of non‐native marine species in the Antarctic region, the physical and physiological factors that resist establishment of non‐native marine species, changes to resistance under climate change, the role of legislation in limiting marine introductions, and the effect of increasing human activity on vectors and pathways of introduction. Evidence of non‐native marine species is limited: just four marine non‐native and one cryptogenic species that were likely introduced anthropogenically have been reported freely living in Antarctic or sub‐Antarctic waters, but no established populations have been reported; an additional six species have been observed in pathways to Antarctica that are potentially at risk of becoming invasive. We present estimates of the intensity of ship activity across fishing, tourism and research sectors: there may be approximately 180 vessels and 500+ voyages in Antarctic waters annually. However, these estimates are necessarily speculative because relevant data are scarce. To facilitate well‐informed policy and management, we make recommendations for future research into the likelihood of marine biological invasions in the Antarctic region.     

Intergenerational effects of CO2‐induced stream acidification in the Trinidadian guppy (Poecilia reticulata)

Rising atmospheric carbon dioxide levels are driving decreases in aquatic pH. As a result, there has been a surge in the number of studies examining the impact of acidification on aquatic fauna over the past decade. Thus far, both positive and negative impacts on the growth of fish have been reported, creating a disparity in results. Food availability and single‐generation exposure have been proposed as some of the reasons for these variable results, where unrealistically high food treatments lead to fish overcoming the energetic costs associated with acclimating to decreased pH. Likewise, exposure of fish to lower pH for only one generation may not capture the likely ecological response to acidification that wild populations might experience over two or more generations. Here we compare somatic growth rates of laboratory populations of the Trinidadian guppy (Poecilia reticulata) exposed to pH levels that represent the average and lowest levels observed in streams in its native range. Specifically, we test the role of maternal acclimation and resource availability on the response of freshwater fishes to acidification. Acidification had a negative impact on growth at more natural, low food treatments. With high food availability, fish whose mothers were acclimated to the acidified treatment showed no reduction in growth, compared to controls. Compensatory growth was observed in both control–acidified (maternal–natal environment) and acidified–control groups, where fish that did not experience intergenerational effects achieved the same size in response to acidification as those that did, after an initial period of stunted growth. These results suggest that future studies on the effects of shifting mean of aquatic pH on fishes should take account of intergenerational effects and compensatory growth, as otherwise effects of acidification may be overestimated.     

Land use impacts on stream community composition and concordance along a natural stress gradient

Most ecosystems are subjected to multiple stressors derived from natural and anthropogenic sources and community responses to human disturbance in naturally stressful habitats may differ from those in more benign habitats. We examined the influence of a natural (geology-driven acidity) vs. human-induced stress (land drainage) and their interaction on the composition and concordance of stream diatom, bryophyte and invertebrate communities. To account for differing drainage impacts in circumneutral (sedimentation) and naturally acid (reduced pH and increased metal concentrations) streams we investigated concordance in three groups of streams: reference (circumneutral and naturally acidic reference), circumneutral (reference and drained) and naturally acidic (reference and drained) streams. We expected diatoms to respond more strongly to anthropogenic acidification and more weakly to sedimentation compared to bryophytes and invertebrates. We expected overall strong concordance among the three taxonomic groups, but especially so in reference streams. All three organism groups had distinct species composition in naturally acidic vs. circumneutral streams. Concordance between communities was overall strong, especially so in the reference streams. All groups responded to drainage disturbance in both types of streams. Invertebrates were slightly less responsive to increased acidification in the naturally acidic streams but were more affected by sedimentation in the circumneutral streams than were the other two groups. The natural stressor affected communities more than the anthropogenic stressors. Naturally stressed communities were affected by an anthropogenic stressor as much as those in more benign habitats, although the additional stressor was similar to the initial stress (further reduction of stream pH). Naturally acid streams may need special concern in bioassessment because models based on circumneutral reference sites will likely produce biased predictions for these streams.     

Alteration of trophic interactions between periphyton and invertebrates in an acidified stream: a stable carbon isotope study

The hypothesis according to which proliferation of periphytic algae under acid conditions results from a release of grazing pressure is tested. Stable carbon isotope analysis is used to investigate the autochthonous/allochthonous balance of invertebrate feeding in streamside artificial channels that were experimentally acidified. We find that the relative contribution of autochthonous food sources (epilithon) to total invertebrate biomass was slightly lower (after 1 mo of acidification) or not altered (after 2 mo) under acidified conditions when compared with a control. Feeding shifts were exhibited by some invertebrate taxa and provided evidence that acidification modifies trophic interactions between attached algae and primary consumers. Cross-treatment calculations showed that reduction of grazing pressure after the first month of acidification was an effect rather than the cause of periphyton proliferation. Our approach using stable carbon isotope analysis and biomass measurements of macroinvertebrates allows the quantification of the trophic base of lotic secondary producer communities under both experimental and natural conditions.     

Heavy Metal Concentration in the Urban Environment of Addis Ababa,Ethiopia

This work assesses the issue of whether the measured concentrations of heavy metals in soil, rocks, surface and ground waters in Addis Ababa can be related to anthropogenic contamination or natural weathering of rocks. Heavy metal analyses of rocks, soils, streams, springs and boreholes have been carried out to identify the presence of potentially harmful solutes. The maximum concentration of total chromium measured is 269 ppm in the northern, industry-free zone of Addis Ababa in the B ₂-horizon of soil profile (cambisol). The Ni/Cr ratio in the rocks is higher than soils, which could indicate the presence of high concentrations of Cr in soils is from weathering processes. A comparative study of different samples collected from various parts of the city indicates that the chemical composition of the hydrothermally affected volcanic rocks plays an important role in increasing heavy metal concentration in the study area. The fresh country rocks contain relatively low concentrations of heavy metals, as shown by background values. The statistical evaluation indicates that the hydrothermally altered rocks contain far higher mean heavy metal concentrations than the fresh acidic rocks (background values). Consequently, soils derived from altered rocks are enriched with respect to heavy metals. From this study it was possible to observe that the rock and soil outcrops of Addis Ababa are anomalously rich in heavy metals derived from hydrothermal activity. Therefore, heavy metal concentrations in the surrounding rocks and soils are related to geogenic sources whereas anthropogenic contribution as a cause of these concentrations is minor.     

The impact of drought and acidification on the chemical exports from a minerotrophic conifer swamp

A seven year chemical budget of a minerotrophic conifer swamp located on the PreCambrian Shield, Ontario, Canada and subjected to anthropogenically acidified deposition is presented. Contrary to other published studies, this swamp retains sulphate during wet years and exports it during dry years. Alkalinity is always retained (acidity is exported) and base cations are almost always exported. It is predicted that if this pattern continues, the cation exchange sites of the swamp will become increasingly saturated with protons and aluminum ions, and the waters passing through the swamp will be increasingly acidified.     

Moderate acidification affects growth but not survival of 6-month-old oysters

Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed abundance and have fewer smaller individuals than unaffected populations, despite having similar recruitment levels to unaffected sites during dry periods. We examined how the timing and duration of exposure to ASS runoff influences the growth and survival of successfully settled oysters. We predicted that among 6-month-old oysters, growth and survival would be (1) lower among individuals continuously exposed to ASS-acidified waters than those that are episodically exposed, and (2) most negatively affected during rainfall events, which enhance transport of ASS runoff to estuaries. Six-month-old Sydney rock oysters, Saccostrea glomerata, were deployed at ASS-affected and unaffected sites within each of two south-east Australian estuaries. After 10 weeks, oysters were transplanted within and across sites in an estuary and maintained in situ for another 10 weeks. Oysters that remained for 20 weeks at ASS-affected sites grew at just over half the rate of oysters at reference sites. Oysters transplanted from acidified to reference sites grew more than oysters transplanted from reference to acidified sites or oysters that remained at reference sites. Unexpectedly, overall oyster mortality was low. Greater rainfall, and hence a lower pH, is likely to have accounted for the greater impact of acidification on growth during the second 10 weeks. Where oysters recruit to a 6-month age cohort, they may be able to tolerate subsequent, moderate, acidification events. Reduced growth during acidification periods may be offset by positive growth during intervening dry periods.     

Surface water chemistry characteristics in the Lake Storgrønningen drainage area, Høylandet, during periods of high and low discharge

The surface water chemistry of Høylandet has beenstudied by performing two synoptic surveys, duringhigh runoff in the autumn of 1986 and during a lowflow period in the summer of 1988. Based on watersamples of up to 38 chemical variables from 75 sites,analyses show considerable variation in the chemicalcomposition. There is a strong altitude gradient, i.e.very dilute poorly buffered waters dominate at higherelevations near the timberline while progressivelyhigher salt content and alkalinities arecharacteristic at lower altitudes more dominated byforests. The influence of mires is less pronounced.The overall water quality is of oligotrophic naturewith low concentrations of strong acid anions andmetals known to be enriched under acidifiedconditions. The natural pH gradients are considerablebut with no indication of anthropogenic acidification.The data provide little support for the hypothesisthat in-catchment production of organically derivedacidity leads to acid runoff, which in thesecatchments appears compensated by increasedweathering. The findings are in general accordancewith other Høylandet catchment studies. It isconcluded that this area may serve as a representativepristine surface runoff analogue for catchmentscurrently affected by atmospheric deposition of strongmineral acids.     

Geographic variation in acid stress tolerance of the moor frog,Rana arvalis. I. Local adaptation

Abstract Spatially varying directional selection together with restricted gene flow among populations is expected to lead to local adaptation. One environmental factor that potentially causes strong directional selection, but is little explored in evolutionary terms, is naturally and anthropogenically induced acidity. We studied local adaptation to acidity in four Swedish populations (two originating from areas that have suffered from severe anthropogenic acidification during the 1900s and two from areas which have remained neutral due to higher buffering capacity) of the moor frog Rana arvalis in a laboratory experiment by investigating whether differences in acid tolerance correspond to population origin. Embryos were raised from fertilization to hatching at three different pH levels (pH 4.0, 4.25 and 7.5), corresponding to levels experienced by these populations in nature, and acid stress tolerance was measured in terms of embryonic survival, hatchling size, and age. Evidence for local adaptation in all of these traits was found, the acid origin embryos having higher survival and less impaired growth performance under acid conditions than the neutral origin embryos. Our estimated rates of divergence (0.007–0.102 haldanes) suggest a rapid adaptation process in response to anthropogenic environmental change, and that the different traits have evolved at relatively similar rates.     

Limnological Features of Different Acidic Drinking Water Reservoirs in the Erzgebirge (Germany)

The biological and chemical investigations of three drinking water reservoirs differing in their acidic and trophic conditions (neutral/meso-eutrophic; circumneutral/oligotrophic; acid/oligomesotrophic) and of some of their tributaries in the Erzgebirge (Germany) are presented. It is shown that the chemistry of acidic waters is very different from circumneutral ones, particularly with respect to hardness, acid neutralizing capacity, pH and aluminium. As acidity in running and stagnant waters increases, the filtrable aluminium concentration also rises. A consequence of the changed chemical and biological conditions and their direct and indirect effects on the organisms is an overall decrease in the number of species (despite the fact that also some species newly appear in the acidified waters). Furthermore, a loss of food web complexity is observed and the trophic structure changes, e.g. fish have disappeared and invertebrate predators have become more numerous. In the acidic reservoir, species well adapted to waters low in pH and hardness (e.g. Synura sphagnicola) are more abundant and commonly benthic animals (e.g. Chydorus sphaericus) are able to extend their habitat to the open waters.     

Studies on zooplankton in two acidified high mountain lakes in the Alps

Being located in remote areas, alpine lakes are good indicators of regional and global pollution, and are particularly sensitive to atmospheric depositions. When situated in areas where acidic rocks dominate, they are sensitive to acidification. In the framework of an international project partially funded by the EU, a two-year study on zooplankton was carried out on two lakes, Lake Paione Inferiore (LPI) and Lake Paione Superiore (LPS), selected because of their susceptibility to acidification. In particular, LPS is permanently acidified, with pH ranging between 5.3 and 6.2, and LPI is acidified during the ice melt, when pH drops to 6.1 units. In addition, LPI is subjected to further anthropogenic interference, since fish (Onchorynchus mykiss) have been repeatedly introduced into the lake during the last thirty years. Literature information is available on the species composition and the seasonal dynamics of the zooplankton communities of the two lakes before these anthropogenic disturbances took place. Previously, the two lakes had a similar species composition and abundant zooplankton. An analysis of the present-day situation reveals significant changes compared to the past. Both acidification and the introduction of fish are responsible for the marked alterations observed. By reconstructing of the past cladocera assemblages and by analysing the literature on lakes with different impacts of the two factors (pH and fish), we can estimate the relative importance of the two different anthropogenic disturbances on species composition and abundance of the zooplankton communities of the two lakes. This revised version was published online in August 2006 with corrections to the Cover Date.