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1.
As a means of assessing the relative contributions of watershed (terrestrial) and in-lake processes to overall lake/watershed alkalinity budgets, alkalinity production rates for watersheds and low alkalinity lakes were compiled from the literature and compared. Based on net alkalinity production data, derived using wet or bulk deposition data, mean and median alkalinity production for 20 watersheds in North America and Europe were 89 and 69 meq m?2 yr?1 (range 20 to 235 meq m?2 yr?1). For a subset of 10 watersheds with dry deposition data, terrestrial alkalinity production neutralized an additional 35 meq m?2 yr?1 of acidic deposition. For 11 lakes, mean and median in-lake alkalinity generation were 99 and 88 meq m?2 yr?1 (range 22 to 240 meq m?2 yr?1). Analysis of data indicates that for the low alkalinity systems described here, areal alkalinity production rates for watersheds and lakes are approximately equal. This relationship suggests that watershed area to lake area ratio can be used as a convenient estimator of the relative importance of watershed and in-lake sources of alkalinity for drainage lake systems. For precipitation-dominated seepage lakes and other systems where hydrology limits soil-water contact, hydrologic flow paths and residence times can be of overriding importance in determining alkalinity sources. For regions dominated by drainage lakes with high watershed area to lake area ratios (such as the Northeastern U.S.), however, alkalinity budgets are dominated by watershed processes. Omission of in-lake alkalinity consideration for most lakes in such regions would have little impact on computed alkalinity budgets or on predicted response to changes in acidic deposition loadings.  相似文献   

2.
The generation of alkalinity by SO4 reduction and net storage of reduced S in lake sediments has been estimated from an analysis of sediment cores from 16 lakes in ME, VT, NY, MI, MN, and WY. The cores have been dated by 210Pb. The rate of pre-1850 (background) storage of S in lake sediments suggests that alkalinity contribution to lake water from this process ranged from 0.2 to 9.3 geq L?1, with an average of 4 geq L?1, Background values are similar for all lakes and remain low in the WY lakes up to the present. Maximum alkalinity contributions recorded in sediment, from upper mid-west and eastern lakes, dated between 1850 and 1985 are between 0.4 and 33 geq L?1, with a lake mean maximum of 9.9 geq L?1, Significant increases in recent S storage only occur in eastern lakes. Average values for net S accumulation in the sediment of most lakes for post-1850 sediment are typically less than half of maximum values.  相似文献   

3.
The Influence of acid deposition on stream and lake water chemistry was studied in a forested watershed of Hyogo prefecture, Japan. Monthly sampling of four streams, one artificial lake, and precipitation was carried out from 1995 to 2000. The pH of the monthly bulk precipitation and rainwater were ranged from 4.06 to 7.10. No trends were evident during the monitoring periods. The pH and alkalinity in the four streams, which flow into the artificial lake, ranged from 6.37 to 8.72 and 0.077 meqL?1 to 0.485 meqL?1, respectively. The differences in the water quality of the four streams were related to the geology of each watershed. Lower pH and alkalinity were observed during high- discharge periods. On the other hand, the pH and alkalinity of the outflow from the lake ranged from 6.47 to 7.36 and 0.195 meqL?1 to 0.339 meqL?1, respectively. No acidification of the aquatic environment was observed during the investigated periods. The results suggest that this forested ecosystem has the capacity to neutralize incoming acid deposition.  相似文献   

4.
From data on 30 headwater lakes in north-central Ontario we found that, during the spring snow melt of 1981, all lakes underwent serious declines in alkalinity. Generally, SO4 2?, alkalinity, Ca+ and Mg2+ concentrations were reduced by runoff and rain then recovered to intermediate levels after the major inputs declined. As expected, a range in responses was evident with lower alkalinity systems showing the greatest changes. The observed changes, however, were consistent with acid loading having depleted alkalinity. In calculating an input-output budget for each lake, we found that changes in Cl?, Na+, and K+ were consistent with atmospheric inputs being the major source as the difference between the expected input and the actual contribution from rain and snow had a mean near zero. There appears to be a significant, ? 45%, watershed source of sulphate that we hypothesize is from dry deposition occurring prior to snowfall and is eluted with the melting process. With refinements to a mass balance approach explaining the watershed source of SO4 2? and Al, we feel it is possible to predict springtime lake changes given a few chemical and simple morphometric variables.  相似文献   

5.
A large data base on inland lakes in the Upper Great Lakes Region (UGLR) was used to evaluate assumptions and relationships of empirical acidification models. Improved methods to calculate background alkalinity and background SO4 2? are reported; SO4 2? enrichment factors indicate that terrestrial SO4 2? sources and watershed or lake sinks must be considered for site-specific background SO4 2? estimates. Significant relationships were found between lake acidification estimated as change in SO4 2? and precipitation acidity but not between changes in lake alkalinity and precipitation acidity in this lightly impacted region.  相似文献   

6.
Interstitial water profiles in epilimnetic sediments of lakes with varying water column alkalinities were collected to assess the origin and importance of sedimentary alkalinity in freshwater lakes. Release of Ca2+ and NH4 +, and consumption of SO4 ? are the most important contributors to alkalinity production m sediments of non-acidic lakes. In acidic lakes, Fe2+ and Mn2+ replace Ca2+ as the dominant cation contributors to alkalinity production. The sedimentary alkalinity flux is an important component of the acid neutralizing capacity of freshwater lakes. However, the presence of large alkalinity gradients in sediment porewaters does not necessarily indicate a large source of alkalinity for the lake, as a significant portion of the alkalinity iu associated with the formation of Fe2+, Mn2+ and NH4 + Oxidation of Fe2+ and Mn2+ at the anoxic-oxic interface and biological removal of NH4 + in the overlying water column results in consumption of the co-diffusing alkalinity.  相似文献   

7.
Alkalinity production in terrestrial and aquatic ecosystems of Canada, the U.S.A., Norway and Sweden is calculated from either strong acid titrations or budgets for base cations and strong acid anions, using mass-balance budgets. Where alkalinity budgets for lakes and their catchments are calculated in acid-vulnerable geological settings, in-lake processes often contribute more to lake alkalinity than yield from terrestrial catchments. Nitrate and sulfate removal, and Ca exchange with sediments are the predominant alkalinity generating mechanisms in lakes. Nitrate and sulfte removal rates increase as the concentrations of NO? 3 and SO4 2? in lake water increase, so that in-lake acid neutralizing capacity increases as acid deposition increases. Both processes occur in sediments overlain by oxic waters, at rates which seem to be controlled primarily by diffusion.  相似文献   

8.
This work treats data from 75 small, mainly oligotrophic Swedish forest lakes. The aim is to study and evaluate the temporal variation of different Hg-dose and lake sensitivity parameters vs. Hg in 1-kg pike and small perch (<10 g). The lakes were treated with different remedies (such as lake liming) during 1987 in order to reduce Hg-levels in fish. Lake water chemistry has a large seasonal variation but the yearly means is clearly affected by the treatments (mean alkalinity is increased from 0.05 to 0.19 mcq*L−1). There is a marked change of Hg in perch 2 yr after treatment; the median decrease is 33%, a further time delay of about 2 yr is suggested for Hg in pike. Among the dose parameters, Hg in material from sediment traps and in water the fraction RIHg seem to be affected by the remedies with an accentuated decrease during 1988, while a slight increase of total-Hg (THg) in water can be observed. A regression model where the Hg content in perch (Hg-pe) is predicted by Hg-dose, pH and lake water retention time is presented (r2=0.71, n=22) as an example of the importance of using time compatible data with respect to the effect parameter (Hg-pe).  相似文献   

9.
Ion mass budgets were measured for 2 water yr (June–May, 1981–83) for a high and a ).ow elevation lake and their associated catchments. The lakes are located in the Turkey Lakes Watershed (TLW) in central Ontario, Canada, which is an undeveloped basin located on the Canadian Shield, 50 km north of Sault Ste. Marie. The ionic budgets of the lakes show that atmospheric deposition directly to the lakes' surfaces is the principal input pathway for H+ and NH4, whereas basic cations, SO4, NO3, and probably alkalinity are supplied primarily by inflow from the surrounding terrestrial basin and/or upstream lake. The lakes strongly retain H+ (i.e. output ? input), weakly retain the N species, and are in balance (i.e. output = input) for other ions except Ca and alkalinity which show an excess output compared to measured + estimated inputs. We hypothesize that an input of groundwater and/or seepage accounts for most of the Ca and alkalinity imbalance although the existence of within-lake alkalinity generation is probable also.  相似文献   

10.
Acid sensitive headwater lakes (n=163) throughout Finland have been monitored during autumn overturn between 1987–1998. Statistically significant decline in sulphate concentration is detected in 60 to 80 percent of the lakes, depending on the region. Median slope estimates are from ?1.1 µeq L?1 in North Finland to ?3.3 µeq L?1 in South Finland. The base cation (BC) concentrations are still declining especially in southern Finland (slope ?2.5 µeq L?1), where every second lake exhibits a significant downward trend. The BC slope is steeper for lakes with less peatlands, more exposed bedrock, longer retention time and southerly location, but these factors are inter correlated. Gran alkalinity slope medians for the three regions range from 1.4 to 1.8 µeq L?1 yr?1. No significant negative alkalinity trends were detected. The similarity in the slopes of SO4, BC and alkalinity in this data compared to seasonal sampling data from Nordic Countries can be regarded as indirect evidence that autumnal sampling is representative for long term monitoring for these ions. There are no indications of increased organic carbon in lakes, as found in some recent trend analyses of similar regional data sets. Although the processes behind the positive development in these lakes have to be revealed with site- specific intensive studies, this data suggests, that the initial recovery from lake acidification in Finland is a regional phenomenon.  相似文献   

11.
Studies were conducted at the deepest location of the meromictic Piaseczno pit lake, southern Poland, which was created in abandoned sulphur opencast. Pearson correlation and PCA were used to established the relationship between the elements and physico-chemical parameters of the water, whereas discriminant test to study vertical and time differentiation of Cd, Pb, Sr, Cu, Zn, Mn, and Fe concentrations. The results indicated both vertical (except Cu and Zn) and time differentiations of studied elements in the lake water. The highest concentrations of Cd, Pb, and Sr were found in the monimolimnion, that of Mn and Fe in the anoxic water. Depth profiles of Cu and Zn did not show any pronounced trend. Pb and Sr distributions in the water were related to alkalinity, Cl? and COD, Cd to alkalinity and Cl?, Mn and Fe to the redox conditions, Mn to water pH, and Fe to the alkalinity. The upper (0–15 cm) layer of the sediment consisted mainly of S (24.2 Atom%), Fe (21.62%), Ca (18.4%), Si (14.3%), and (Al 6.3%) and reflected mainly processes proceeded in the anoxic water-sediment interface. Calculated accumulation coefficients (K d) of the elements in the sediment are discussed.  相似文献   

12.
It has been hypothesized that human mercury (Hg) exposure via fish consumption will increase with increasing acidic deposition. Specifically, acidic deposition leads to reduced lake pH and alkalinity, and increased sulphate ion concentration ([SO4 2?]), which in turn should cause increased Hg levels in fish, ultimately resulting in increased human Hg exposure via fish consumption. Our empirical test of this hypothesis found it to be false. We specifically examined Hg levels in the hair of Ontario Amerindians, who are known consumers of fish from lakes across the province, and observed a weak negative association with increasing sulphate deposition. An examination of Hg levels in lake trout, northern pike and walleye, three freshwater fish species commonly consumed by Ontario Amerindians, found a similar weak negative association with increasing sulphate deposition. Further analysis of these fish data found that fish [Hg] was most significantly (positively) associated with lake water concentrations of dissolved organic carbon (DOC), not pH, alkalinity or [SO4 2?]. Lake DOC levels are lower in regions of greater acidic deposition. We propose an alternate hypothesis whereby human Hg exposure declines with increasing acidic deposition. In particular, we propose that increasing sulphate deposition leads to reduced lake DOC levels, which in turn leads to lower Hg in fish, ultimately reducing human Hg exposure via fish consumption.  相似文献   

13.
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   

14.
It has been observed that the alkalinity concentrations in the hypolimnia of many thermally stratified lakes increase over the duration of the summer. We have quantified the processes, both redox and exchange, that contributed to the alkalinity increases measured in two lakes that are situated on the Precambrian Shield of Ontario, Canada by measuring hypolimnetic mass balances for all substances involved in alkalinity-generating or -consuming reactions. These include nitrate, ammonium base cations, iron, manganese, sulphate, organic anions, as well as alkalinity itself. In one lake, iron reduction was the dominant source of alkalinity; since this process is probably reversed at fall overturn when hypolimnetic waters mix with oxygenated surface waters, the alkalinity generated by this mechanism is likely temporary in nature. In the second lake, iron reduction and sulphate reduction were both important the latter should provide more permanent alkalinity.  相似文献   

15.
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16.
Thirty three lakes were surveyed in 1983 in the North Cascades area of Washington State and 27 additional lakes were surveyed in 1984 to characterize lake chemistry in the area. Lakewater ANC was less than 100 ueq 1?1 for 37% of the lakes and less than 200 ueq 1?1 for 68% of the lakes. The North Cascades are very similar to unimpacted sensitive areas of North America and Northern Europe in mean alkalinity and (Ca + Mg). Bedrock geology appears to have a significant influence on surface water ANC with lakes on granitic and metamorphic bedrocks having the lowest ANC.  相似文献   

17.
From a level of 1 kg ha?1yr?1 in north central Minnesota, emission-related wet SO4 deposition increases across northern Wisconsin and northern Michigan to about 18 kg ha?1yr?1 in south central Michigan. Samples taken from 82 clearwater (low color) lakes across this region in the summer of 1984 showed a pattern of acidification in proportion to deposition. We found a linear increase in the difference between alkalinity and Ca+Mg and in lake SO4 concentration with increasing deposition. We developed a simple equation to predict the emission-related SO4 deposition levels that will cause the alkalinity of sensitive clear-water lakes to go to zero.  相似文献   

18.
Chemical conditions at lake charr (Salvelinus namaycush) spawning sites were monitored during snowmelt in low alkalinity lakes in Ontario, Canada. Embryos within the interstitial water of the spawning substrate were exposed to abrupt and potentially toxic levels of H+ and inorganic Al as acidic runoff water inundated the shallow nearshore sites. Early runoff events, those that occurred while the lake ice was still snow-covered and under-ice water temperatures were <2°C, appeared to be most threatening, because of deep penetration of the runoff water. These highly site-specific events exhibit wide temporal and spatial variability.  相似文献   

19.
The base neutralizing capacity (BNC), or alkalinity consumption, of acidic lake sediments may influence the amount of neutralizing agent required to neutralize a lake if the sediment BNC is large relative to the BNC of overlying waters. The extent ofin situ sediment BNC in acidic Bowland Lake (pH 5.0) was inferred by (1) measuring the loss of Ca-45 to acidic sediments from labeled lake water neutralized with CaCO3, and (2) measuring exchangeable Ca in sediments collected prior to and following neutralization of Bowland Lake with calcite (CaCO3). The sediment BNC derived from the Ca-45 radiolabeling experiment was 0.01 mg CaCO3 g?1 w wt. The mean losses of Ca-45 from the aqueous phase of neutralized and untreated sediment/water mixtures were not significantly different. The mean pH of both neutralized and untreated mixtures decreased to 4.0 during the incubation, possibly because of oxidation of reduced sediments. Sediment BNC estimates derived from literature data for several lakes may be overestimated because of the inclusion of anoxic sediments containing significant amounts of reduced Fe. There was no significant difference in exchangeable Ca between sediments from untreated Bowland Lake and sediments collected 10 m after whole-lake neutralization indicating that little of the supplied alkalinity had been lost to the sediments. Hence,in situ sediment BNC was probably small in Bowland Lake.  相似文献   

20.
Aluminum was added as aluminum sulfate (alum) to Lake 114, a small, shallow lake of the Experimental Lakes Area, northwestern Ontario, in spring and summer point-source additions. Aluminum and H+ gradients were established during the additions, with high Al and low pH (about 1000 μg L?1 Al, pH 4.7) near the alum sources, and background conditions (< 50 μg L?1 Al, pH 5.7) further from the sources. Approximately 80% of the added Al was lost from the water column in two weeks. Phosphorus concentrations remained unchanged during the additions, whereas lake alkalinity decreased and sulfate increased close to the sources. Dissolved organic carbon (DOC) concentrations decreased slightly (from 540 μM L?1 to about 500 μM L?1) near the alum source during the summer addition.  相似文献   

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