Evaluation of the role of sea salt inputs in the long-term acidification of coastal New England lakes (original) (raw)
Related papers
Water Resources Research, 1992
Major episodic acidifications were observed on several occasions in first-order brooks at Acadia National Park, Mount Desert Island, Maine. Short-term declines of up to 2 pH units and 130/•eq L -1 acid-neutralizing capacity were caused by HC1 from soil solutions, rather than by H2SO4 or HNO3 from precipitation, because (I) SO½ concentrations were constant or decreased during the p H depression, (2) CI concentrations were greatest at the time of lowest pH, and (3) Na:C1 ratios decreased from values much greater than those in precipitation (a result of chemical weathering), to values equal to or less than those in precipitation. Dilution, increases in NO 3 concentrations, or increased export of organic acidity from soils were insufficient to cause the observed decreases in pH. These data represent surface water acidifications due primarily to an ion exchange "salt effect" of Na + for H + in soil solution, and secondarily to dilution, neither of which is a consequence of acidic deposition. The requisite conditions for a major episodic salt effect acidification include acidic soils, and either an especially salt-laden wet precipitation event, or a period of accumulation of marine salts from dry deposition, followed by wet inputs.
Extreme acidification in small catchments in southwestern Norway associated with a sea salt episode
Water, Air, & Soil Pollution, 1995
During heavy storm events in January 1993 in the coastal areas of south-western Norway, a sea salt episode created extreme acidification in the afforested Svela catchment. Streatn-water chloride increased sharp~ to eight times the normal concentration and the non-marine Na concentration was calculated to -208 bteq L . Negative values indicate that Na was retained in the soil profile..By ion-exchange processes lifts was largely compensated by aa increase in strean~_ concentrations of ,43 and H . Concentrations of inorganic monomeric AI increased from about 20 to 200 ~teq L and pH decreased from 4.90 to 4.45. Due to the low pH and the dramatic increase in inorganic monomeric A1 the water toxicity for aquatic organisms increased. Acidification associated with the storm was also observed in a forested and a non-forested catchment, but never reached the levels of the afforested catchment. The extra vulnerability of afforested catchments may be due to their ability to intercept larger amounts of sea salts than areas less dominated by dense lree stands. Although both pH and AI went back to normal levels for the area after 3-4 months the Na/Cl-relationship in cumulated transport values indicated a longlasting effect (> 2 years) on the soil profile. Reloading the soil profile with Al and H + back to prestorm values will affect the catchments ability to mobilize these ions during future sea salt episodes. More frequent episodes will probably result in less acid and Al-rich stream-water during the episodes than documented here due to incomplete reacidifieafion of the soils.
Water, Air, & Soil Pollution: Focus, 2000
The paired catchment study at the forested Bear Brook Watershed in Maine (BBWM) U.S.A. documents interactions among short-to long-term processes of acidification. In 1987-1989, runoff from the two catchments was nearly identical in quality and quantity. Ammonium sulfate has been added bi-monthly since 1989 to the West Bear catchment at 1800 eq ha −1 a −1 ; the East Bear reference catchment is responding to ambient conditions. Initially, the two catchments had nearly identical chemistry (e.g., Ca 2+ , Mg 2+ , SO 2− 4 , and alkalinity ≈82, 32, 100, and 5 µeq L −1 , respectively). The manipulated catchment responded initially with increased export of base cations, lower pH and alkalinity, and increased dissolved Al, NO − 3 and SO 2− 4 . Dissolved organic carbon and Si have remained relatively constant. After 7 yr of treatment, the chemical response of runoff switched to declining base cations, with the other analytes continuing their trends; the exports of dissolved and particulate Al, Fe, and P increased substantially as base cations declined. The reference catchment has slowly acidified under ambient conditions, caused by the base cation supply decreasing faster than the decrease of SO 2 4 , as pollution abates. Export of Al, Fe and, P is mimicking that of the manipulated watershed, but is lower in magnitude and lags in time. Probable increasing SO 2− 4 adsorption caused by acidification has moderated the longer-term trends of acidification of both watersheds. The trends of decreasing base cations were interrupted by the effects of several short-term events, including severe ice storm damage to the canopy, unusual snow pack conditions, snow melt and rain storms, and episodic input of marine aerosols. These episodic events alter alkalinity by 5 to 15 µeq L −1 and make it more difficult to determine recovery from pollution abatement.
‘Acidic episodes’ in surface waters in Europe
Journal of Hydrology, 1992
Pronounced and short-term changes in freshwater chemistry ('acidic episodes') can have a significant biological impact. More attention has been paid to chronic acidification, and there has been no previous attempt to produce a regional summary of occurrence of episodes in Europe, to describe their chemical characteristics, or to synthesise what is known of their controlling processes. These are the objectives of this review. The basic characteristics of episodes are explained, along with the problems of establishing an adequate description. Because of the relative paucity of other information on water composition, the review is based largely on measurements of short-term pH depressions, although other data are considered where available. Most of the studies reported here were conducted in Norway, Sweden, Scotland and Wales. The differing physical characteristics of the various study catchments are assessed; these influence the hydrochemical responses to hydrological events (snowmelt or rainfall). Antecedent conditions are also important. Nevertheless, it is possible to arrive at some generalising conclusions about episodes. Snowmelt appears to instigate the most pronounced episodes, particularly in lakes. However, rainfall-induced episodes are generally much more frequent. Direct links between the chemistry of the snowmelt or rainfall which induced the episode and surface water chemistry are relatively rare, except in the case of a large input of sea-salt. Sulphate is the strong acid anion most strongly related to pH depression during episodes, although nitrate is important in some locations at snowmelt. Organic acids can play an important role in some peaty catchments. Dilution of base cations during episodes was also observed in most of the studies reviewed. Some depression of pH in surface waters seems ubiquitous during hydrological events, but in areas which have experienced large depositions of pollution, long-term acidification has conditioned catchments for the episodic release of acid. Changing flowpaths through hydrological events are of overwhelming importance in controlling the chemical character of episodes.
Applied Geochemistry, 1999
A simple, unifying approach to classifying quantitatively the susceptibility of catchment soils and surface waters to acidi®cation is suggested. In areas subject to a strong maritime in¯uence, such as the UK and substantial parts of NW Europe, wherever soil mineral weathering rates are low and soils are unfertilised, atmospherically derived base cations of maritime origins have a greater eect than those derived from biogeochemical weathering on the exchangeable soil base cations. This is directly re¯ected in the relative base cation concentrations of the associated drainage waters, which become increasingly Na-dominated. Using 10 sub-catchments of the River Dee in northeastern Scotland, it is shown here that the extent of Na dominance, the ratio of Na + to SNa + +Ca 2+ +Mg 2+ , at any point in a river provides a quantitative index of the upstream weathering rate and thus of the susceptibility of the river concerned to acidi®cation under diverse¯ow conditions. Data from a further 58 sub-catchments from the same river system, and from 4 other catchments from around Scotland, were used to validate this theory. #
Reversal of acidification in upland waters of the English Lake District
Environmental Pollution, 1998
Water chemistry data are reported for ®ve high-altitude standing waters in the English Lake District, with current average pH values in the range 5±7. The waters show long-term increases in pH, ranging from 0.3 to 0.8 pH units, between 1974 and 1997. The pH of Devoke Water, which was acidi®ed only mildly, has returned to values estimated for the pre-industrial period (1850 and earlier). Alkalinity in Devoke Water increased from ca 20 meq litre À1 in the early 1980s to ca 70 meq litre À1 in the 1990s, and alkalinities in three of the other waters have increased by ca 20 meq litre À1 since the 1970s. For the two intensively monitored sites (Devoke Water and Levers Water), signi®cant decreases in the concentration of non-marine sulphate are demonstrated, which have taken place concurrently with decreases in the atmospheric deposition of pollutant sulphur. Approximate calculations suggest that the catchment of Levers Water was a sink for sulphur in the 1970s, and that the catchment of Devoke Water may currently be a source of sulphate. For neither Devoke Water nor Levers Water is there evidence of a long-term decrease in the concentration of non-marine base cations. #