The significance of in-lake production of alkalinity

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.     

Alkalinity regulation in maine headwater lakes: Terrestrial vs. lacustrine contributions in summer

Twenty-seven Maine lakes in felsic terrane were sampled in May and October 1986, bracketing the summer interval of minimum flushing, in order to statistically test a hydrogeochemical process model that separates Gran alkalinity (ANC) production into terrestrial vs lacustrine components. Significant ANC increases over the 5 mo were restricted to relatively shallow lakes with large contiguous watersheds, and/or lakes where contact zones in the local bedrock offered increased potential for summer groundwater inflow. Summer ANC increases depended mainly on terrestrial contributions; in-lake alkalinity generation was 16±5 meq m^?2 over 5 mo, of which ca. 11 meq m^?2 resulted from biological assimilation of directly-deposited nitrate-N. The remaining 5±5 meq m^?2 cannot be assigned with confidence, but is thought to reflect lacustrine sulfate reduction. The over-summer changes in ANC and conductance of Maine headwater lakes in upland granitic terrane approached statistical detection limits resulting from pure analytical and sampling error. This convergence highlights the importance of even small analytical biases when analyzing limnological time series, and confirms the utility (statistical efficiency) of the one-time, comparative sampling design adopted during the U.S. EPA's Eastern Lake Survey (ELS).     

Acidification of Nova Scotia Lakes

Although water chemistry of precipitation and lakes in Nova Scotia is dominated by C1 from sea salt, correction for marine influence reveals that the dominant anion in acidified lakes is SO₄. Atmospheric deposition of non-marine SO₄ (SO₄) and NO₃- for the period 1977–1980 at 4 stations in southwest Nova Scotia averaged 47 meq SO₄ ^* m^?2 yr^?1 and 21 meq NI₃-m^?2 yr^?1 compared with 38 and 13 meq, respectively, for the average of 3 stations in the northeastern third of the province. Precipitation pH increased from 4.5 to 4.8 along the same axis. Almost 50% of the SO₄ deposition occurred when storms came from the southwest, indicating low pressure tracks which pass south of major Canadian sources of S. SO₄ ^* deposition in metropolitan Halifax (1982 bulk data) was 87 meq m^?2 yr^?1, due to local emissions of ca. 28 300 tonne S in the area, as well as LRTAP. Concurrent deposition of NO₃-N was 15 meq m^?2 yr^?1 (2.1 kg ha^?1 yr ^?1). Loadings from SO₄ deposition in the Halifax area amount to 42 kg ha^?1 yr^?1 and clearly exceed the federal guideline (M.O.I., 1983) of 20 kg ha^?1 yr^?1. Water chemistry of southwest, northeast, and Halifax area lakes show the same general SOI trends as observed for atmospheric deposition. In addition we find a positive relationship between SOI concentrations in the urban lakes and proximity to the center of the urban area.     

Polluted precipitation and the geochronology of mercury deposition in lake sediment of northern Minnesota

Elevated Hg levels in game fish from wilderness lakes in northern Minnesota led to the present study of sediment cores from two lakes to ascertain the source and history of Hg deposition. Natural background levels of Hg were found to range from 0.03 to 0.06 μg g^?1, with cultural levels as high as 0.16 μg g^?1. Reconstructed geochronologies reveal a dramatic two-fold increase in Hg flux, from 0.008 to 0.017 μg cm^?2 yr^?1, occuring after the year 1880, suggesting an anthropogenic influence. No industrial or geologic source of Hg is found in the study watersheds. The entire historical increase in Hg flux can be accounted for by atmospheric loading provided that 1/5 of all the Hg presently supplied to the watershed via precipitation is ultimately deposited in lake sediment. Hg levels in fish are not correlated with Hg levels in lake sediment, although there is a link to acid-sensitivity of lake water, amount of acid-neutralizing geologic material exposed in the watershed, and watershed area/lake volume ratio. Thermal stratification of lake water and a complexation-adsorption mechanism are proposed to account for variations in Hg levels observed in sediment collected from different sites.     

Chemistry of soft-water seepage lakes in the upper midwest: Lacustrine alkalinity production in summer

A total of 26 soft-water, seepage lakes in the Northern Highlands (NH) of Wisconsin (N =16) and the Upper Peninsula (UP) of Michigan (N=10) were sampled four times between early May and mid October 1984 as part of the ‘PIRLA’ Project (Paleolimnological Investigations of Recent Lake Acidification). Because of low antecedent recharge of the local water-table, this ‘summer’ interval likely featured minimal groundwater inputs (<2 cm over lake surface) to most of these seepage lakes. Based on this hydrogeologic relationship, and on regional deposition data, I evaluated short-term net epilimnetic (June–August) and whole-lake (May–October) sediment-water exchange of ANC, base cations, acid oxy-anions, Al, DOC and silicic acid in these lakes using a simplified mass balance algorithm. Silica, nitrate and ammonium were all efficiently retained in these seepage lakes. The assimilation of NO₃ ^? (19±4 meq m^?2) slightly exceeded assimilation of NH₄ ⁺ (16±4), resulting in a net internal ANC production of only +3 meq m^?2 over 161 d between early May and mid October 1984. Over this same interval ANC production resulting from lacustrine S retention averaged +35±8 meq m^?2 in the NH, but was too variable to be statistically significant (+21±21 meq m^?2) in the UP. Epilimnetic S retentions in mid summer were more comparable (21±4 in NH; 14±5 meq m^?2 in UP). McNearney Lake (UP) illustrates how high sulfate, linked to low alkalinity, high Al, low P, and low productivity, can become a negative correlate of lacustrine S retention. Temporal changes in base cations in the 26 lakes were generally small and erratic compared with uncertainties in deposition inputs and analytical errors, rendering estimates of related ANC production inconclusive. Even small analytical biases can be critical when designing and interpreting lake monitoring studies.     

The cation denudation rate as a quantitative index of sensitivity of eastern Canadian rivers to acidic atmospheric precipitation

A model has been developed that relates the cation denudation rate (CDR) of a watershed (the rate that cations derived from chemical weathering are carried off by runoff), the atmospheric load of excess SO₄, and the pH of the river. Chemical and discharge data for rivers in Nova Scotia and Newfoundland were used to develop and test the model, which is based upon the common major ion chemistry of soft surface waters, and may be expressed by three statements: (1) CDR (meq m^?2 yr^?1) ? Excess SO₄ ^?? load (meq m^?2 yr^?1) = HCO₃ ^? (meq m^?2 yr^?1), (2) HCO₃ ^? (meq m^?2 yr^?1)/Runoff (m³ m^?2 yr^?1) = HCO₃ ^? (meq m^?3), (3) pH = pK + \(pP_{CO_2 } \) ? pHCO₃ ^?. The model in concentration form applies well to lakes. A detailed analysis of the data for the Isle aux Morts River, Newfoundland, is presented, showing that the CDR varies throughout the year, affected by both discharge and seasonal pattern.     

Relations between lake acidification and sulfate deposition in Northern Minnesota,Wisconsin, and Michigan

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.     

Changes in water quality in the Laflamme Lake Watershed Area,Canada

The Laflamme Lake Watershed Area is located in a sensitive region on the Canadian Shield and is subjected to wet atmospheric loading between 17 and 25 kg ha^?1 yr^?1. From 1981 to 1988, the level and fluctuations of the atmospheric deposition of acidifying substances has led to various responses in the water chemistry of headwater lakes in the area. The general trend in atmospheric inputs is a gradual increase of acidifying substances from 1981 to 1985 followed by a 2 yr decrease then a return to previous values. In the two lakes with almost no alkalinity acidification has occured throughout the 1983 to 1988 period. In the four lakes with slightly higher alkalinity values, a reversal in acidification is seen when atmospheric loading decreased in 1986. Along with the interannual trends, seasonal variability to acidification occurs with sensitivity of surface waters being highest during spring melt. Sensitivity to acidification can also be altered by watershed processes and in the Laflamme Lake Watershed, soil processes are effective in altering the acidity of precipitation before it reached the lake. In this watershed, wet atmospheric inputs of H⁺ and NO₃ ^? are larger than surface water outputs while the reverse occurs for Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^? and SO₄ ^2?.     

Effects of Reduced S Deposition on Large-Scale Transport of Sulphur in Swedish Rivers

Sulphur deposition has diminished by about half during the last decade. For Sweden consistent estimates of total deposition are available for 1991, and 1994–97. Based on these estimates and using GIS the deposition for large drainage areas during one decade are calculated. These values are compared with the measured S transport in rivers covering about 85% of the Swedish territory, thus enabling the construction of a S budget for Sweden. The majority of the drainage areas have a net loss of S, which can be attributed to desorption of S in the soil. During the period of high deposition in the 1980:s (>60 meq m^?2 yr^?1 in southern Sweden) S was adsorbed, and retarded acidification. There still seems to be some S-adsorption in the northern parts of the country, where the deposition is less (now <20 meq m^?2 yr^?1).     

Ozone Sensitivity Differences in Five Tomato Cultivars: Visible Injury and Effects on Biomass and Fruits

A complete record derived from the core from the Daihai Lake in a remote area provides new insights into the changing atmospheric heavy metal deposition associated with historical industrial activities, the Asian monsoon, long-range transport, and the chemical composition of matter derived from weathering of catchment. The fluctuation of lithogenic element concentration in the lake sediments can readily be explained by a particle sorting effect induced by the Asian monsoon. The variation of atmospheric deposition of Cu and Pb shows a similar profile in the lower part of the core sediments, and coincides with environmental change, with high atmospheric deposition coupled with wet, temperate period; while low deposition with dry, cold period, indicating a transport variation of heavy metal pollutants entrained by the Asian summer monsoon. From the beginning of nineteenth century, the atmospheric deposition of Cu and Pb decreased and then slowly increased. This may be associated with the destroyed industry induced by long-term wars in China and the less heavy metal pollutants relative to the weak Asian summer monsoon in this period. Comparison between atmospheric-derived metal and sediment trap metal using Ga as the reference element shows that atmospheric Cu and Pb budgets do not exceed the fluvially-induced Cu and Pb budgets in the indirectly disturbed area. On average, there have been approximately 5.4 mg m^?2 yr^?1 of Cu and 5.1 mg m^?2 yr^?1 of Pb atmospherically deposited in the region.     

Seasonal,annual and long-term variability in the water chemistry of a remote high mountain lake: Acid rain versus natural changes

Seasonal fluctuations as well as long-term trends in water chemistry were studied in Schwarzsee ob Sölden (Tyrol, Austria), an oligotrophic softwater lake situated at 2796 m a.s.l. The catchement is composed of granite, plagioclase and micaschists containing considerable amounts of sulphur, with little soil cover. The lake is ice covered for about nine months, during this time the deepest layers (>16m) become anoxic. During summer overturn, alkalinity (ALK) is lowest (?8 μeq l^?1) in the whole water column, whereas pH reaches its minimum (4.88) at the surface during snowmelt. A decrease of pH from 5.8 to 5.4 during winter is caused by CO₂ oversaturation, but deep water ALK increases to up to 130 μeq l^?1 due to in-lake ALK generation by reductive processes and base cation (BC) release. The seasonal pattern of ALK in SOS is driven by in-lake processes in winter, the snowmelting in spring and watershed processes and precipitation during summer. Since 1989 summer sulfate concentrations in SOS, originating mainly from the catchment, show a tendency to increase presumably caused by enhanced weathering. In contrast, SO₄ ^2? concentrations in other high mountain lakes which are dominated by atmospheric depositions show a decreasing trend. SOS is a good example for the complexity of interactions between catchment and in-lake processes which act at different time scales and depend on climate changes and atmospheric inputs.     

A simple dose-effect model of lake acidity in Québec (Canada)

A simple dose-effect model expressing the relationships between lake acidity, weighted mean annual sulfate concentration in wet deposition, Ca, Mg and true color (as an index of organic anion concentration) is presented. The agreement between observed and estimated pH for more than a 1000 lakes is high according to the Pearson coefficients of correlation (0.81 to 0.90) and the standard error of estimation (0.22 to 0.27 pH unit). Results obtained with this model show that an airborne sulfate target loading of 20 kg ha^?1 yr^?1 would be too high to adequately protect sensitive lake ecosystems. A target loading of 15 kg ha^?1 yr^?1 in wet deposition would be best suited for the protection of the greater portion of sensitive lakes. However, a target loading of 10 kg ha^?1 yr^?1 would be required to protect the most sensitive lake ecosystems.     

Response to a smelter closure in Cascade mountain lakes

A statistically significant decrease in sulfate was observed in high elevation Cascade lakes during 1983 through 1988. The total decrease averaged 2.2 μeq L^?1 in two slow-flush lakes and 4.2 μeq L^?1 in three fast-flush lakes for 1983–1985 vs 1986–1988, respectively. Coincident with these changes in sulfate concentrations were a sharp decrease of SO₂ emissions from the ASARCO smelter (100 km SE of the lakes), from 87 to 70 kt yr^?1 during 1983–1984 to 12 in 1985, the year of its closure, and a gradual change in SO₂ emissions from Mt. St. Helens, from 39 to 27 during 1983–1984 to 5 in 1988. The sharpest decreases occurred in non-marine sulfate in fast-flush lakes from 1984 to 1985 (about 2 μeq L^?1) and in slow-flush lakes from 1985 to 1986 (1 μeq L^?1, which point to the ASARCO closure as the sole cause. However, some of the more gradual decline in non-marine sulfate observed during 1983 through the 1988 sampling periods may have been due to a slow washout of sulfate enriched ash from the 1980 Mt. St. Helens' eruption. Sulfate concentrations in precipitation also declined significantly by about 2 μeq L^?1, but changes in volume-weighted sulfate content were not significant. Lake alkalinity did not show a consistent increase in response to decreased sulfate. This was probably due to either watershed neutralization of acidic deposition or the greater variability in alkalinity measurements caused by small changes in acidic deposition making it difficult to detect changes.     

Influence of atmospheric deposition on lake mass balances in the Turkey Lakes Watershed,Central Ontario

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.     

Primary production in a eutrophic acid lake

Total P concentrations, chlorophyll concentrations, and phytoplankton production were investigated bi-weekly in Tibbs Run Lake, Monongalia County, West Virginia, from March 1977 to March 1978. Mean H⁺ concentration in the lake was 25.1 μeq 1^?1 (pH 4.6). The acidic condition of the lake is attributed to inputs of acid via precipitation (mean H⁺ concentration of the bulk precipitation was 79 μeq 1^?1, pH 4.1), and the low buffering capacity of the watershed (bedrock composition of sandstone). Effect of the watershed is shown by the net retention of imput of P (ca. 26%) and H⁺ (ca. 68%). Total P loading to the lake was 0.495 g P m^?2 yr^?1. The single inflow accounted for 95% of the total loading while bulk precipitation accounted for the remainder. Mean summer chlorophyll concentration was 22.2 mg m^?2. Phytoplankton production expressed volumetrically as aP-vol-x value was 9.78 mg C m^?3 h^?1. Regression analysis indicated that H⁺ do not affect chlorophyll concentrations or phytoplankton production but rather that P limits algal biomass. Trophic status of Tibbs Run Lake based on a P budget model, chlorophyll concentration, and volumetric production all indicate that the lake is meso-eutrophic.     

Headwater lake chemistry during the spring freshet in North-Central Ontario

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.     

Cadmium and lead contamination of soils near plastic stabilizing materials producing plants in Northern Taiwan

Atmospheric mobilization and exchange at the air-water interface are significant features of biogeochemical cycling of Hg at the Earth's surface. Our marine studies of Hg have been extended to terrestrial aquatic systems, where we are investigating the tropospheric cycling, deposition and air-water exchange of Hg in the mid-continental lacustrine environs of northcentral Wisconsin. This program is part of a multidisciplinary examination into the processes regulating the aquatic biogeochemistry of Hg in temperate regions. Trace-metal-free methodologies are employed to determine Hg and alkylated Hg species at the picomolar level in air, water and precipitation. We have found Hg concentrations and atmospheric fluxes in these fresh water systems to be similar to open ocean regions of the Northern Hemisphere. A well constrained mass balance for Hg has been developed for one of the lakes, Little Rock Lake, which is an extensively studied clear water seepage lake that has been divided with a sea curtain into two basins, one of which is untreated (reference pH: 6.1) while the other is being experimentally acidified (current pH: 4.7). This budget shows that the measured total atmospheric Hg deposition (ca. 10 μg m⁻² yr⁻¹) readily accounts for the total mass of Hg in fish, water and accumulating in the sediments of Little Rock Lake. This analysis demonstrates the importance of atmospheric Hg depositional fluxes to the geochemical cycling and bioaccumulation of Hg in temperate lakes. It further suggests that modest increases in atmospheric Hg loading could lead directly to enhanced levels of Hg in biota. Analogous modeling for monomethylmercury (MMHg) is as yet limited. Nevertheless, preliminary data for the atmospheric deposition of MMHg indicate that this flux is insufficient. to account for the amounts of MMHg observed in biota. An in-lake synthesis of MMHg is implicated. The importance of volatile Hg which is principally in the elemental form, and its evasion to the atmosphere is also illustrated. We suggest that the in-lake production of Hg° can reduce the Hg (II) substrate used in the in-lake microbiological synthesis of MMHg.     

Influence of Acid Deposition on Inland Water Chemistry - A Case Study from Hyogo Prefecture, Japan -

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.     

Empirical models for lake acidification in the upper Great Lakes Region

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.     

Response of Reservoir Water Quality to Nutrient Inputs from Streams and In-Lake Fishfarms

This study demonstrates how land-use characteristics influence stream water chemistry in a Korean watershed and how stream conditions and in-lake point sources determine trophic state, algal biomass and phytoplankton composition. Measurements of nutrient loads showed that 68% of total phosphorus (TP) loads was originated from the watershed and the remaining 32% came directly from in-lake fish farms. Based on mass balance models, annual areal phosphorus (L _p) and water loading (q _s) were 1.032 g m^-2 and 25 m³ m^-2 yr^-1, respectively, and the total annual P-input exceeded dangerous loading levels according to Vollenweider's classification (1976). In situ Nutrient Stimulation Bioassays (NSB), Trophic State Index (TSI), and mass N:P ratios showed that phosphorus was the primary element regulating algal chlorophyll in the system, and non-algal turbidity and zooplankton effects on algal growth were minor. A high regressioncoefficient in the empirical relationship between chlorophyll (Chl) and TP supported the evidence of strong P-limitation, and model comparisons suggested that our observed Chl values were largely underestimated in models developed for world-wide lakes. Direct P-input to the trophogenic zone from the in-lake fishfarms and streams with intense human-use resulted in massive bluegreen algal blooms, indicating that the highly available input fraction may explain the deviation. Under the circumstances, reduction in P-loading is an essential measure for long-term eutrophication control in this system.