Watershed vs in-lake alkalinity generation: A comparison of rates using input-output studies

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.     

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.     

Alkalinity production in epilimnetic sediments: Acidic and non-acidic lakes

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.     

In-lake alkalinity generation by sulfate reduction: A paleolimnological assessment

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.     

May a fast-flushing dystrophlc headwater lake mitigate acid rain?

Mass budget data for the dystrophic headwater lake Huzenbacher See (Black Forest, Germany) revealed annual in-lake retention rates for sulfate, protons, nitrate and negative alkalinity with values up to 15%, 43%, 60%, and 48%, respectively. These rates are related to the sum of all relevant annual loadings entering the lake from the watershed by eleven gauged lake tributaries, by groundwater inflow into the lake and by open precipitation on the lake and its floating Sphagnum peat mat surfaces. Microbial processes as denitrification, nitrate reduction and sulfate reduction are likely involved in the in-lake retention of imported acidity and the in-lake alkalinity generation. The hypolimnion of the lake and its sediments, the littoral soils and the floating Sphagnum peat mat, which surrounds the central part of the lake, are among the sites where these anaerobic processes can occur. Nitrate uptake by the floating Sphagnum peat mat, by the littoral stands of the macrophyte Nuphar lutea, and by phytoplankton can support this in-lake alkalinity generation, too.     

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.     

Cadmium Aqueous Exposure and Uptake of the Estuarine Isopod Cyathura carinata

We studied the isotopic composition of organic matter in the sediments of eight mountain lakes located in the Tatra Mountains (Western Carpathians, Poland). The sediments of the lakes were fine and course detritus gyttja, mud, and sand. The total organic carbon content varied from 0.5 to 53 %. The C/N ratio indicated that in-lake primary production is the major source of the organic matter in the lakes located above the treeline, whereas terrestrial plant fragments are the major organic compounds in the sediments of dystrophic forest lakes. We also found that a clear trend of isotopic curves toward lower values of δ ¹³C and δ ¹⁵N (both ~3 ‰) began in the 1960s. This trend is a sign of the deposition of greater amounts of NO _x from the combustion of fossil fuels, mainly by vehicle engines. The combustion of fossil fuels in electric plants and other factories had a smaller influence on the isotopic composition. This trend has been weaker since the 1990s. Animal and human wastes from pastures and tourism had a surprisingly minor effect on lake environments. These data are contrary to previous data regarding lake biota and suggest the high sensitivity of living organisms to organic pollution.     

Acidification by nitric acid — Future considerations

HNO₃ is more efficient in acidifying lakes than has been generally believed. This is because as nitrate loading to lakes increases, the efficiency of in-lake nitrate removal decreases markedly. Efficiencies decrease because algal N requirements are exceeded and because denitrification, which becomes an important removal process, is not as efficient as algal removal. Thus, nitrate and the accompanying H⁺ accumulate and HNO₃ becomes an important factor in acidification. Data from an experimentally acidified system suggest that midsummer surface-water nitrate concentrations in excess of only 1 µmol L^?1 indicate that algal requirements have been exceeded. While 1 µmol L^?1 NO₃ ^? is not a significant quantity in terms of affecting the acidity of the water, it is useful as an indicator to identify lakes where algal requirements have been exceeded and where further increases in HNO₃ loading could lead to lake acidification.     

Climate Change as the Primary Cause for pH Shifts in a High Alpine Lake

Chemical and biological sedimentary records of a high alpine lake were used to reconstruct palaeoecological conditions and compared with two centuries of instrumental temperature measurements. Air temperature determined the lake water pH throughout the past 200 yr almost regardless of the level of atmospheric deposition. Our data suggest a strong climate forcing of the acid-base balance in sensitive high-altitude lakes. Their physico-chemical conditions and biota strongly depend on the duration of ice and snow cover which is significantly different between warm and cold periods. Beside changes in weathering rates, in-lake alkalinity generation and water-retention time, delayed freezing in autumn and earlier ice-out dates with a shorter duration of CO₂ over-saturation could be crucial for the tight temperature-pH coupling.     

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).     

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.     

Metals in small Norwegian lakes: Relation to atmospheric deposition of pollutants

Water chemistry data from 165 lakes in Norway are discussed in relation to contribution from long-range transported air pollutants. Concentrations of lead and antimony in terrestrial mosses are used to express the relative contribution from long range transport to each lake. The contents of Al and Zn in lake water and of ‘excess’ SO₄ in low Ca lakes show high correlations with the relative heavy metal deposition values from moss analysis. The ‘excess’ SO₄ in low Ca lakes correlates strongly with Al and too a lesser extent with Mn and Fe. It is suggested that the lake water levels of Al and Mn, and even to some extent Fe, are significantly affected by acidic precipitation enhancing the leaching of these metals from mineral matter in soils and sediments. In the case of Zn, airborne supply to the lakes and their catchments appears to strongly affect the water content.     

Base neutralizing capacity of sediments from an acidic lake

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.     

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.     

Trends in the Chemistry of Acidified Bohemian Lakes from 1984 to 1995: I. Major Solutes

Temporal changes in major solute concentrations in six Czech Republic lakes were monitored during the period 1984–1995. Four chronically-acidic lakes had decreasing concentrations of strong-acid anions (C_SA = SO₄ ^2- + NO^{3 -} + Cl^-), at rates of 3.0 to 9.0 μeq L^-1 yr^-1. Decreases in SO₄ ^2-, NO₃ ^-, and Cl^- (at rates up to 5.1 μeq L^-1 yr^-1, 3.2 μeq L^-1 yr^-1, and 0.6 μeq L^-1 yr^-1, respectively) occurred. The response to the decrease in deposition of S was rapid and annual decline of SO₄ ^2- in lake water was directly proportional to SO₄ ^2- concentrations in the acidified lakes. Changes in NO₃ ^- concentrations were modified by biological consumption within the lakes. The decline in C^SA was accompanied in the four most acidic lakes by decreases in Al_T, increases in pH at rates of 0.011 to 0.016 pH yr^{- 1}, and decreases of Ca²⁺ and Mg²⁺ (but not Na⁺) in three lakes. The acid neutralizing capacity (ANC) increased significantly in all six lakes. Increases in base cation concentrations (CB = Ca²⁺ + Na⁺ + Mg²⁺ + K⁺) were the principal contributing factor to ANC increases in the two lakes with positive ANC, whereas decrease in C_SA was the major factor in ANC increases in the four chronically-acidic lakes. The continued chemical recovery of these lakes depends on the uncertain trends in N deposition, the cycling of N in the lakes and their catchments, and the magnitude of the future decrease in S deposition.     

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.     

The effect of acidification,liming and reacidification on macrophyte development,water quality and sediment characteristics of soft-water lakes

Rapid expansion of Juncus bulbosus L. and the concomitant suppression of isoetid plant species has often been observed in acidifying soft water lakes in Western Europe. Experimental studies have shown that this mass development of J.bulbosus was caused by changes in the carbon and nitrogen budgets in these ecosystems. Acidification leads to temporarily strongly increased carbon dioxide (CO₂) levels in the slightly calcareous sediment and to accumulation of ammonium as a result of a reduced nitrification rate in acidifying waters. Many acidifying Scandinavian soft water lakes, however, have a well developed macrophyte vegetation. It is suggested that this is related with the non-calcareous sediments of these lakes. After liming, however, mass development of J. bulbosus and/or Sphagnum spec. has been observed in Swedish and S.W. Norwegian lakes. From field experiments it has become clear that part of the lime is deposited on the sediments leading to an increase of mineralisation rates, CO₂ production, sediment pore water levels of phosphate and ammonium and to a decrease of the nitrate concentrations in the sediment. These changes have been earlier observed in acidifying West European waters. Rooted species like J.bulbosus can only benefit from the higher nutrient levels in the sediment when the CO₂ level of the water layer is relatively high as this species is adapted to leaf carbon uptake. It is demonstrated that gradual reacidification by the acid water from the catchments and the increased flux of carbonic acid from the limed sediments to the overlying water leads to increased CO₂ levels in the water layer of the limed lakes already a few months after liming.     

Solute fluxes and sulfur cycling in forested catchments in SW Germany as influenced by experimental (NH4)2SO4 treatments

Results are presented from the research project Arinus which investigates biogeochemical cycling in Norway spruce (Picea abies KARST.) ecosystems in the Black Forest (SW Germany) and effects of experimental (NH_{4 2}SO₄ additions. The interaction of the terrestrial and aquatic system is assessed using an integrated approach which combines flux measurements in representative plots on the stand level with input-output budgets of small catchments. The approach, field installations and experimental manipulations are described. Results from element flux measurements in the untreated systems are presented and processes controlling N and S transformations are discussed for two catchments representing contrasting site conditions. Even though the S budget is negative for both systems there is a distinct difference in the relation between organicvs. inorganic S fractions in the soil. Sulfate mineralization and desorption, respectively are discussed as controlling processes. Sulfate retention is not only a function of soil properties, but also of water fluxes and pathways. The uptake of added SO ₄ ^2? was highly controlled by the counter-cation. Microbial N retention in the soil was highly influenced by the site management history. The extent of streamwater acidification was highly dependent on the transformations and mobility of N and S in the soils which in turn controlled cation leaching and alkalinity.     

High Carbon Dioxide Evasion from an Alpine Peatland Lake: The Central Role of Terrestrial Dissolved Organic Carbon Input

We measured carbon dioxide (CO₂) fluxes across air?Cwater interface with floating chambers in Lake Medo (a small, shallow lake in peatland) on the eastern Tibetan Plateau in the warm season of 2009. During the study period, mean CO₂ fluxes was 488.63?±?1,036.17?mg?CO₂?m^?2?h^?1. The flux rate was high compared to those of lakes in other regions, and represented a ??hotspot?? of CO₂ evasion. Temporal variation of CO₂ flux was significant, with the peak value in the beginning and lowest point in the end of warm season. High concentration of dissolved organic carbon (DOC) in lake water (WDOC) was found to highly correlated to CO₂ flux (R?=?0.47, P?<?0.01, n?=?54). Besides, fluorescence index of WDOC showed its terrestrial origin character. In accordance with lakes in northern and boreal regions, terrestrial DOC concentration in water column was the most important regulator of CO₂ flux from this lake. We suggest that large area of peatlands in catchments support high concentration of DOC in this lake, and consequently high CO₂ evasion.