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1.
Netting surveys of lakes varying in pH (4.4–7.1) showed that lake trout (Salvelinus namaycush) populations fail to recruit at pH <5.5 and are lost from lakes with pH<5.2. Brook trout (S. fontinalis) were extirpated in lakes with pH <5.0. In regional chemical surveys of Ontario lakes, it was found that 2% of sampled brook trout lakes and 2.5% of lake trout lakes were acidified (alkalinity <0 uEq L?1). Threshold pH levels determined from fisheries assessments were used to estimate that 1% of lake trout and brook trout populations have been lost due to acidification.  相似文献   

2.
Surveys of fish populations were conducted on 74 lakes of the Outaouais hydrographic region during the summers of 1985 and 1986 to assess the potential impact of acidity on ichtyologic fauna. Results show that species diversity declined with the increasing acidity. The color of water does not seem to mitigate the adverse effects of acidity. On the contrary, the number of species decreased similarly in both brown lakess (>30 Hazen) and clear lakes (≤30 Hazen) with the increase of acidity. The species tolerance threshold levels to acidity show that 72% of fish species are no longer captured when pH reaches 5.0, compared to 32% at pH ≤5.5. The pH range 5.0 to 5.5 can possibly be regarded as the break point for the occurrence of most fish species in this area. Analysis of the size frequency distributions show that recruitment failures have occurred in acidic waters for walleye and lake trout. We have estimated that anthropogenic acidification is responsible for the loss of more than 10000 fish populations in the Outaouais area.  相似文献   

3.
Lake Annie, a clear-water seepage lake in south-central Florida remote from significant pollution sources, was sampled by the USGS from 1966 until 1978, and by Battoe and others from 1978 until present. Since 1966, pH and bicarbonate alkalinity have decreased (pH from above 6.0 to about 5.1; bicarbonate from 5.0 to less than 0.5 mg L?1), while specific conductivity and sulfate concentration have increased (cond. from 30 to 55 μS; sulfate from 3.0 to 8.0 mg L?1). The chemical changes are apparently due to acidification from atmospheric deposition. There are no proximate sources of acidity and the stability of lake level indicates there has been no significant concentration or dilution of solutes. It is suggested that Lake Annie's acidification was a threshold phenomenon wherein, following depletion of the watershed's buffering capacity, acidification of the lake was rapid.  相似文献   

4.
The analysis of diatom assemblages in lake sediments is being increasingly used to reconstruct past trends in the pH of acid lakes. This paper briefly reviews the data that are now available for Europe and North America and concludes that the evidence is consistent with the acid deposition hypothesis for recent lake acidification.  相似文献   

5.
Indicator taxa are identified, based on both synoptic surveys and whole lake acidification experiments, for lake acidification in the pH 6.0 to 5.0 range. Acidobiontic diatoms (e.g Asterionella ralfsii, Fragillaria acidobiontica, etc.), periphyton (Mougeotia and related species), macroinvertebrates (e.g. Hyalella azteca, Orconectes sp., etc.), leeches, and cyprinid fishes (e.g. Pimephales promelas, Notropis cornutus, etc.) are identified as target organisms during early phases of lake acidification.  相似文献   

6.
Lake Örvattnet has been monitored extensively for both chemical and biological variables since 1967. The lake acidified during the 1960's and pH was mostly below 5 throughout the 1970's. Due to the acidification, peat moss (Sphagnum spp.) expanded over the lake bottom and the only surviving fish species was perch (Perca fluviatilis), but it experienced reproduction problems. In the mid 1980's, the Sphagnum cover collapsed, and by 1989 it had almost disappeared. There has been a clear recovery of the perch population. Recovery of the lake is also recorded by diatom assemblages in the lake sediment. Diatom-inferred pH increased from 4.7 to 4.9. The development of measured lake-water pH is unclear, but acid episodes in spring have become less severe. By 1993, atmospheric sulphate deposition had decreased by 30–40% in this area of Sweden compared to the late 1960's. Lake-water sulphate concentrations have decreased by ～30% since the 1960's. Nitrogen deposition has increased over the last decades, but is not yet contributing to lake acidification. No major land-use changes have occurred and changes in hydrology cannot explain the observed changes in chemistry and biology. We ascribe the recent recovery in the lake to reduced deposition of sulphate. In conclusion, Lake Örvattnet has begun to recover from acidification.  相似文献   

7.
Empirical field evidence for changing chemical processes in soils caused by atmospheric deposition of pollutants consists of: (1) Long-term water quality data including total dissolved solids, concentrations of specific metals (e.g. Ca), and conductivity; (2) Cation exchange capacity and base saturation values for soils located on precipitation pH gradients; (3) Lysimeter studies; and (4) Chemical analysis of organic soils on precipitation pH and metal gradients. For well-drained organic soils, as precipitation pH decreases, metals are differentially leached at an accelerated rate (Mn>Ca>Mg≥Zn>Cd and Na>Al). Experimental field and laboratory lysimeter studies on soil columns yield similar results, with increases in leaching rates for soil solutions with pH=3 up to 100 × values for soil solutions with pH=5. Nearly 100% of the Pb from precipitation is accumulating in the organic soil layer or sediments. Zn is accumulating in soils and sediments where the pH's of precipitation, soil solutions, and surface waters are generally above 5 to 5.5. At lower pH values Zn and other chemically similar elements are desorbed/leached (net) at an accelerated rate. Chemical analyses of dated sediment cores from high and low altitude lakes, with drainage basins relatively undisturbed for the last 200+ yr, reveal that increased deposition of metals on a regional scale started in the northeastern United States as early as 1880, consistent with increased fossil fuel consumption. This suggests acidified precipitation as early as 1880. Cores from historically acidified lakes (pH<≈5.3 to 5.5) indicate that, as acidification of surface waters occurs (caused by acidic deposition), concentrations of Zn, Mn, and Ca decrease in the sediment. Apparently the metals are leached from the detritus prior to sedimentation. This conclusion results from data from experimental acidification of sediment cores and the general observation that precipitation pH is generally ≥0.5 pH units lower than lake water pH. Accelerated leaching of soil in New England dates to earlier than 1900.  相似文献   

8.
Nutrient concentrations and cycling processes were studied in Little Rock Lake, Wisconsin, U.S.A., during experimental acidification from pH 6.1 to target pH values of 5.6, 5.1 and 4.7 and during the first four years of recovery. Surface waterconcentrations of ammonium, nitrate, soluble reactive phosphate,and total phosphate were not affected, but total nitrogen was lower from year 2 at pH 5.6 until the end of recovery year 3 (pH 5.3). The decrease was attributed to lower dissolved organicN. Annual maximum concentrations of N and P forms at 9 m depth in the hypolimnion increased with decreasing pH, but most of theincrease resulted from a drought-induced decline in lake levelduring acidification that brought the 9 m sampling location closer to the sediment. In contrast to findings elsewhere, acidification of Little Rock Lake had no effect on rates of nitrification during winter ice-cover. Dissolved silica concentrations increased slightly at pH 4.7, probably because of a pH-induced decrease in the diatom population, but hydrologicfactors were more important in controlling silica levels than waspH. Most of the predictive hypotheses made about the effects ofacidification on nutrient forms and processes or their recoveryin the lake were qualitatively correct.  相似文献   

9.
A three year study (1981 to 1983) was conducted to determine possible influences of wetland acidification on the reproduction and growth of the Eastern Kingbird (Tyrannus tyrannus). This species uses emergent aquatic insect prey to feed its nestlings. Egg characteristics and nestling growth were monitored for birds nesting in 26 lakes in the Killarney region near Sudbury, Ontario (pH range 4.27 to 6.26). The major percentage of variation in kingbird reproductive factors including clutch initiation, egg weight loss and torso-metatarsus bone growth was explained by differences between siblings and among nests on a single lake. A smaller percentage of the variance in reproductive parameters was explained by the variation in water chemistry among lakes. Canonical correlation showed that sulfate, nitrate/nitrite, alkalinity, pH, and several metals (Fe, Mn, Al) accounted for a minor but significant variance in growth characteristics. These water chemistry parameters are influenced by lake acidification. The relationship observed between lake acidity and kingbird reproduction is therefore measurable but minor compared to the influence of genetic and inter-nest variables. The study showed no food limitation for the kingbird attributed to lake acidity.  相似文献   

10.
Whole wheat bread is an important source of minerals but also contains considerable amounts of phytic acid, which is known to impair their absorption. An in vitro trial was performed to assess the effect of a moderate drop of the dough pH (around 5.5) by way of sourdough fermentation or by exogenous organic acid addition on phytate hydrolysis. It was shown that a slight acidification of the dough (pH 5.5) with either sourdough or lactic acid addition allowed a significant phytate breakdown (70% of the initial flour content compared to 40% without any leavening agent or acidification). This result highlights the predominance of wheat phytase activity over sourdough microflora phytase activity during moderate sourdough fermentation and shows that a slight drop of the pH (pH value around 5.5) is sufficient to reduce significantly the phytate content of a wholemeal flour. Mg "bioaccessibility"of whole wheat dough was improved by direct solubilization of the cation and by phytate hydrolysis.  相似文献   

11.
The retention properties of acidic and non-acidic lake sediments were determined in order to assess the effects of lake acidification on the immobilization of P from solution by sediments. The adsorption of P by solids was described by the Langmuir model which was used to determine the sorption parameters, e.g. sorption maxima and equilibrium constant of adsorption. The pH of solution and the chemical and mineralogical characteristics of sediments affect mainly the magnitude of adsorption maxima. The binding strength of the adsorbed complex is similar for all the investigated sediments (Δ=?25.3 to ?28.5 kJ mol?1) and it is affected little by variation in pH or by chemical and mineralogical composition of sediments. The results indicate that the magnitude of P removal is determined more by sediment chemistry and mineralogy (amorphous Al/Fe oxy-hydroxides, carbonate content) than by pH of the water.  相似文献   

12.
The regeneratable forms of pollutant metals in lake sediments were estimated using different chemical extractants and the effects of lake acidification on the mobilization of such metal fractions studied in laboratory microcosm. The release of each metal was found to increase exponentially below a threshold pH value, which was about 4.0 for Cu, Ni, Zn, Cd and Fe. The data suggest that a large percentage of pollutant metals are mobile as determined by chemical extraction techniques and long-term release experiments.  相似文献   

13.
Little Rock Lake was experimentally acidified in 1984–1990 during which sulfuric acid was added to one basin, decreasing pH from 6.1 to 5.6, 5.1 and 4.7. The lake has been allowed to recover without manipulation since autumn 1990. By the third year of recovery, ～40% of the change necessary to return to pre-acidification values of pH, acid neutralizing capacity (ANC), sulfate (SO4 2?) and calcium (Ca2+) had occurred. During recovery years 1–2, ANC was closely predicted by models based on acidification phase observations, but recovery during years 3–4 was slower than predicted. A possible explanation for the slowed recovery is acidification of the upper 0–5 cm of sediment, which acts as a sink for the ANC generated via SO4 2? reduction, the primary recovery mechanism. Trends for Zooplankton did not follow pH recovery very closely. Species diminished by acidification (e.g. Keralella cochlearis, Daphnia dubia) have not recovered, but species that dominated the community at pH 4.7 (e.g. K. taurocephala, D. catawba) have not maintained high populations. The time required for the Zooplankton community to recover to pre-manipulation conditions is uncertain. Delays also have been observed for the mayfly species Caenis, which had disappeared at pH 4.7. In contrast, reproductive success of largemouth bass (Micropterus salmonides) mirrored that observed during acidification; egg hatch and survival of young-of-the-year to autumn recurred when pH exceeded response levels documented during acidification. Overall, recovery has not closely followed the pattern predicted by acidification responses.  相似文献   

14.
Concentrations of monomethylmercury [CH3Hg] were measured in the water and seston of five nearly pristine Wisconsin lakes, which span a range of pH from about 4.6 to 7.2. Previous studies had established a clear inverse relationship between [CH3Hg] in fish and the pH of lakes in this region. Here, we examined the pH dependency of [CH3Hg] in lake water and explored the partitioning of CH3Hg between water, seston, and fish as a function of pH. Results indicate that [CH3Hg] in lake water tends to increase as pH decreases, but that seasonal and spatial variability of [CH3Hg] in individual lakes confounds a simple analysis of the relationship. The partitioning of CH3Hg was related only weakly, if at all, to pH. Average partitioning coefficients (log kd=log (Cp/Cw)) were higher for yearling yellow perch (6.0 to 6.5) than for seston (5.5 to 6.0) but did not vary significantly between lakes. This suggests that acidification has a stronger effect on the supply of CH3Hg to the ecosystem than on specific rates of uptake by the biota.  相似文献   

15.
Sinha  R.  Small  M. J.  Ryan  P. F.  Sullivan  T. J.  Cosby  B. J. 《Water, air, and soil pollution》1998,105(3-4):617-642
A reduced-from modelling approach is used to predict soil and lake acidification as part of an integrated assessment of acid deposition effects and control strategies. The reduced-form model is based upon the mechanistic, lumped parameter watershed chemistry model, MAGIC (Model of Acidification of Groundwater in Catchments). Recent improvements to MAGIC are described, and its reduced-form representation in the Tracking and Analysis Framework (TAF), an integrated assessment model for decision and uncertainty analysis, is presented. Reduced-form models are developed for lake acid neutralising capacity (ANC), calcium, pH, and aluminium; and for soil base saturation. The model for lake ANC incorporates long-term depletion of the watershed acid neutralisation fraction, as is predicted to occur with MAGIC. In test calibrations for 33 representative watersheds in the Adirondacks, the resulting reduced-form model provides a close approximation to MAGIC, with average root mean square errors of 0.79 μeq l-1 for ANC, 1.09 μeq l-1 for calcium, 0.16 for pH, 2.52 μeq l-1 for aluminium, and 0.09% for soil base saturation. In addition, improved fish viability models are incorporated in the integrated assessment model, and predictions are demonstrated for a future deposition reduction scenario for the Adirondack region.  相似文献   

16.
A total of nine sediment cores were collected from the five deep basins of Kejimkujik Lake, located in southwestern Nova Scotia, Canada, in order to track changes related to surface-water acidification and to test reproducibility of results between sediment cores from different basins in a large lake. Present-day and pre-industrial (c. 1850) samples were analyzed from all cores and detailed diatom profiles were undertaken on three cores to determine the timing of acidification. All three detailed diatom profiles show declines in inferred pH starting in the early 1930–1940s. Since the 1940s, diatom-inferred lakewater pH has declined from a background pH of ～5.8 (± 0.4) to a current diatom-inferred pH of ～4.9 (± 0.1). This corresponds to the current (2001–2002) range of measured lakewater pH?=?4.7–5.2 with a mean pH?=?4.9. Species diversity of diatoms also declines markedly in all cores with the Hill’s N2 index decreasing from ～5 to near 1. The pre-impact diatom assemblages were dominated by Aulacoseira spp. and have since changed to dominance by Asterionella ralfsii var. americana (>45 μm). All nine sediment cores showed similar changes in diatom assemblages, diatom-inferred pH, and timing of the onset of acidification. Thus, paleolimnological inferences from deepwater sediment cores were highly reproducible in this large, morphometrically complex lake system.  相似文献   

17.
Investigations in the southern part of the Scandinavian mountain range have shown a direct correlation between snowpack pH and the lowest pH in small streams. In streams with catchments <100>2 a snowpack pH below 4.8 resulted in a stream pH below 5.5. As the snowpack pH in the southern mountain range is 4.0–4.6, lower values to the south and at high altitudes, large areas are affected by acid deposition. The acidity of the snowpack is released almost directly into the streams during thaw, due to the large snowpack, rapid thaw, steep terrain and thin soils. The acidification of the snow has lead to an extensive fauna depletion, especially in smaller streams without upstream lakes. The abundance of benthos in acidified streams in the municipality of Härjedalen (11.000 km2) is today only one tenth of the abundance before acidification. Fish populations have declined to the same extent, and several acid-sensitive species have been lost. It is concluded that mountain streams and fauna are extremely sensitive to acidification, and that even large reductions of emissions will be insufficient.  相似文献   

18.
Fifteen Finnish Lapland lakes have been investigated to study pollution levels and possible acidification effects on nickel (Ni), copper (Cu), cobalt (Co), zinc (Zn), cadmium (Cd), lead (Pb), manganese (Mn), iron (Fe), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and aluminium (Al) concentrations in sediments. Four lakes have average water pH lower than 6.0 and alkalinity lower than 0.050 meq/1. Contamination factor (Cf, ratio of metal concentrations in the uppermost to the deepest layers for a given lake sediment core) of Pb is high, particularly for acidic and acidifying lakes (Cf=5.2–10.4). Ni, Cu, Co, Zn and Cd concentrations increase insignificantly towards sediment surface of some lakes (with a neutral pH) with the rare exception. The influence of passible lake acidification consists of decreasing Cu, Cd, Al, Zn concentrations and organic material contents (loss on ignition) towards the sediment surface. The buffer capacity index (BCI), determined as the ratio of the sum of alkaline and alkaline-earth metals (K, Na, Ca, Mg) to Al, is lower for acidic lakes (from 0.12 to 0.36), whereas for the other lakes the BCI values are higher (from 0.42 to 1.34). Thus, BCI-values, decreased contents of Al, Cd, Zn and Cu, as well as organic matter contents (OMC in the upper lake sediment suggest acidification of freshwater environments.  相似文献   

19.
A detailed review of the zooplankton literature found strong evidence that lake acidification consistently causes declines in crustacean and rotifer species richness, the relative abundance of cyclopoids and daphnids, and the relative abundance of 16 particular zooplankton species. Five species were found to consistently increase as lake pH declines. Inconsistent effects were observed on crustacean biomass and mean organism size. Biomonitoring response variables recommended to detect incipient community changes include the relative abundance of pH sensitive species, overall crustacean and rotifer community composition plotted in abundance ordination space, crustacean and rotifer species richness, and the relative abundance of acid tolerant species. If acidification effects have been detected using the above response variables, then more detailed monitoring to understand the functional characteristics of affected systems (e.g. crustacean biomass, rotifer biomass and/or overall community size spectra) is appropriate. A lake selection procedure is recommended to maximize the number of systems containing sensitive species, and ensure a set of reference systems whose acidity is unlikely to change significantly.  相似文献   

20.
Phosphorus cycling processes were studied in an acidic lake to test the oligotrophication hypothesis. P storages and inputs were measured; in situ and laboratory experiments measured pH effects on planktonic uptake and release, macrophyte release, and sediment-water exchange of SRP. Planktonic rates showed little response to pH; release from macrophytes initially was slowest at highest pH (5.5), but after 225 days was not affected over the pH range 3.7 to 5.5. Maximum SRP sorption by sediments occurred at pH 4.0 to 5.5; decreasing sorption above pH 5.5 provides some support for the oligtrophication hypothesis.  相似文献   

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