A preliminary review of weathering rates in relation to their method of calculation for acid sensitive soil parent materials

The release of base cations from chemical weathering is the fundamental process by which base cations lost through leaching or biological uptake are replenished. Soils with a high content of easily weatherable minerals will, in general, be readily able to neutralise incoming acidity and satisfy biological requirements through this supply of base cations from weathering. Conversely those soils with a low content of such minerals will be unable to buffer acid inputs or meet biological demands and will be vulnerable to acidification. It is evident therefore that an accurate estimate of the rate of chemical weathering is a prerequisite for any assessment of ecosystem sensitivity to acidification. The principal methods by which these calculations are made can be grouped into those based on element depletion in soil horizons calculated against a conservative element reference, catchment fluxes, laboratory studies and the use of mathematical models which utilise data from each of these sources. A review of the published data has been undertaken to determine if a systematic variation in weathering rates can be observed for a range of parent materials and/or methods used. Variations of 0.03–0.8 keq ha^?1yr^?1 for K⁺, 0.0–1.0 keq ha^?1yr^?1 for Na⁺, 0.01–1.39 keq ha^?1yr^?1 for Mg²⁺ and 0.0–5.8 keq ha^?1yr^?1 for Ca²⁺ were found. In general individual cation weathering rates determined from catchment fluxes, and also the model MAGIC, are dominated by Ca²⁺, with Mg²⁺ being the next most significant release rate. However it has not been possible to determine any other systematic variations due to the limited number of sites where weathering rate has been determined by more than one method.     

Estimation of the Maximum Critical Load for Sulfur in South Korea

The maximum critical load of sulfur and its exceedance by the sulfur deposition of 1994–1997 were mapped for South Korea with a spatial resolution of 11 × 14 km using the steady-state mass balance method. The Korean soil and geological maps were used as basis for the estimations of the critical alkalinity leaching and the weathering rate of base cations. The normalized difference vegetation index data obtained from the Advanced Very High Resolution Radiometer (AVHRR) together with the observed primary productivity of plants were used for the estimation of the critical uptake of base cations. Wet deposition of the non-sea-salt base cations was derived from measured base cation concentrations in precipitation, precipitation rate and air concentration of total suspended particulate while dry deposition of base cations was estimated using the inferential technique using scavenging ratios. The predominant ranges of base cation weathering, uptake and deposition were estimated to be of 200 – 600 eq ha^?1 yr^?1, 200 – 400 eq ha^?1 yr^?1 and 400 – 600 eq ha^?1 yr^?1, respectively. Critical alkalinity leaching was mainly in the range of 1000 – 2000 eq ha^?1 yr^?1 due to relatively high value of precipitation runoff. Exceedance of sulfur critical load was found at 40 % of the ecosystems considered mainly in the southeastern part of Korea, and about 60 % of Korea ecosystems were sustainable against sulfur acidity loadings.     

Deposition Patterns of SO4 2−, NO3 − and H+ in the Brazilian Territory

SO₄ ^2?, NO₃ ^? and H⁺ depositions are estimated in the Brazilian territory based on the existing rainfall chemical data and on annual rainfall distribution over the whole territory. Local and regional depositions are estimated. Rainfall chemical data over the Braziliian territory shows that the average pH values are usually low (between 4.0 and 5.5). These values are observed in the tropical Amazon forest as well as in urban areas. However, the rainwater acidity in the tropical forests are due to organic acids naturally produced by the vegetation while in urban areas the acidity is mainly due to acidic anion deposition (NO₃ ^? and SO₄ ^2?). In some Amazonian areas, the average input values through rainfall for NO₃ ^? is about 0.06 keq.ha.yr^?1 and for SO₄ ^2? is between 0.23 and 0.54 keq.ha^?1.yr^?1. On the other hand, in some urban centers, such as São Paulo, values of .072 keq.ha^?1.yr^?1 for NO₃ ^? and 1.16 keq.ha^?1.yr^?1 of SO₄ ^2? are found and in sites where sulfate sources (coal mining) are present, as for the area of Florianópolis, values as high as 5.59 keq.ha^?1.yr^?1 for SO₄ ^2? are found.     

Nature and Magnitude of Atmospheric Fluxes of Total Inorganic Nitrogen and Other Inorganic Species to the Tampa Bay Watershed, FL, USA

We estimated the total inorganic fluxes of nitrogen (N), sulfur (S), chloride (Cl^?, sodium (Na⁺, calcium (Ca²⁺, magnesium (Mg²⁺, potassium (K⁺ and hydronium (H⁺. The resistance deposition algorithm that is programmed as part of the CALMET/CALPUFF modeling system was used to generate spatially-distributed deposition velocities, which were then combined with measurements of urban and rural concentrations of gas and particle species to obtain dry deposition rates. Wet deposition rates for each species were determined from rainfall concentrations and amounts available from the National Acid Deposition Program (NADP) monitoring network databases. The estimated total inorganic nitrogen deposition to the Tampa Bay watershed (excluding Tampa Bay) was 17 kg-N ha^?1 yr^?1 or 9,700 metric tons yr^?1, and the ratio of dry to wet deposition rates was ～2.3 for inorganic nitrogen. The largest contributors to the total N flux were ammonia (NH₃ and nitrogen oxides (NO _x at 4.6 kg-N ha^?1 yr^?1 and 5.1 kg-N ha^?1 yr^?1, respectively. Averaged wet deposition rates were 2.3 and 2.7 kg-N ha^?1 yr^?1 for NH₄ ⁺ and NO₃ ^?, respectively.     

Calculating critical loads of acid deposition with PROFILE — A steady-state soil chemistry model

A steady state soil chemistry model was used to calculate the critical load of acidity for forest soils and surface waters at Lake GÄrdsjön in S.W. Sweden. The critical load of all acid precursors (potential acidity) for the forest soil is 1.64 kmol_c ha^?1 yr^?1, and 1.225 kmol_c ha^?1 yr^?1 for surface waters. For the most sensitive receptor, the critical load is exceeded by 1.0 kmol_c ha^?1 yr^?1, and a 80% reduction in S deposition is required, if N deposition remains unchanged. The critical load is largely affected by the present immobilization of N in the terrestrial ecosystem which is higher than the base cation uptake. The model, PROFILE, is based on mass balance calculations for the different soil layers. From measurable soil properties, PROFILE reproduces the present stream water composition as well as present soil solution chemistry. The model calculates the weathering rate from independent geophysical properties such as soil texture and mineral composition.     

Biogeochemistry of a forested watershed in the central Adirondack Mountains: Temporal changes and mass balances

Information on atmospheric inputs, water chemistry and hydrology were combined to evaluate elemental mass balances and assess temporal changes in elemental transport from 1983 through 1992 for the Arbutus Lake watershed. This watershed is located within a northern hardwood ecosystem at the Huntington Forest within the central Adirondack Mountains of New York (USA). Changes in water chemistry, including increasing NO₃ ^? concentrations (1.1 μmol _c , L^?1 yr-1), have been detected during this study period. Starting in 1991 hydrological flow has been measured from Arbutus Lake and these measurements were compared with predicted flow using the BROOK2 hydrological simulation model. The model adequately (r²=0.79) simulated flow from this catchment and was used to estimate drainage for earlier periods when direct hydrological measurements were not available. Modeled drainage water losses coupled with estimates of wet and dry atmospheric deposition were used to calculate solute budgets. Export of SO₄ ^2? (831 mol _c ha^?1 yr^?1) from the greater Arbutus Lake watershed exceeded estimates of atmospheric deposition in an adjacent hardwood stand suggesting an additional source of S. These large drainage losses of SO₄ ^2? also contributed to the drainage fluxes of basic cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺). Most of the atmospheric inputs of inorganic N were retained (average of 74% of wet precipitation and 85% total deposition) in the watershed. There were differences among years (56 to 228 mol ha^?1 yr^?1) in drainage water losses of N with greatest losses occurring during a warm, wet period (1989–1991).     

Acid deposition and ion leaching from a podzolic soil under hardwood forest

The contribution of atmospheric acids to cation leaching from a podzolic soil under mature maple-birch forest in central Ontario was examined during 1983. The movement of base cations was associated largely with NO₃ ^?, SO₄ ^2? and organic acid anions in surface soil horizons, with SO₄ ^2? and NO₃ ^? below the effective rooting zone, and SO₄ ^2? and HCO₃ ^? in streamflow. Mineral soil horizons could adsorb little additional SO₄ ^2? or associated cations at current soil solution SO₄ ^2? concentrations. Therefore it is concluded that the soil in situ lacks a strong affinity for SO₄ ^2?. Current annual inputs to the forest of SO₄ ^2? and NO₃ ^? in bulk precipitation (26.4 and 18.2 kg ha^?1, equivalent to 8.8 kg S and 4.1 kg N ha^?1 , respectively) contributed significantly to cation leaching from the soil. In order to maintain exchangeable cations in soil at current levels, a rate of weathering yielding 29.6, 5.0, 4.4 and 2.2 kg ha^?1 yr^?1 of Ca²⁺, Na⁺, Mg²⁺ and K⁺, respectively, would be required.     

Mapping of Base Cation Deposition in South Korea

Deposition of non-seasalt base cations (Ca²⁺ + Mg²⁺+ K⁺) in South Korea was mapped for 1994 to 1997 on a 11 × 14 km grid using the so-called inferential modeling technique. It is found that the annual mean wet deposition of non-seasalt base cations is about 290 eq ha^-1 yr^-1 with a maximum of 470 eq ha^-1 yr^-1 and a minimum of 120 eq ha^-1 yr^-1 while the annual mean dry deposition is about 130 eq ha^-1 yr^-1 with a maximum of 240 eq ha^-1 yr^-1 and a minimum 70 eq ha^-1 yr^-1. Theannual mean total deposition of non-seasalt Ca²⁺ + Mg²⁺ + K⁺ is found to be about 420 eq ha^-1 yr^-1 with the predominant range of 400 eq ha^-1 yr^-1 to 550 eq ha^-1 yr^-1 thatoccupies more than 45% of total deposition of non-seasalt base cations and dry deposition constitutes on average30% of the total base cation deposition. About 30% of the annualtotal deposition of sulfur is found counteracted by depositionof non-seasalt base cations over South Korea.     

Proton Budget for a Japanese Cedar Forest Ecosystem

The proton budget for a Japanese cedar (Cryptomeria japonica) forest in Gunma Prefecture, Japan, was studied by estimating biogeochemical fluxes. The proton budgets were estimated for three individual compartments of the ecosystem: vegetation canopy, and the upper (O horizon + 0–10 cm) and lower (10–100 cm) soil layers. The dominant proton sources in the compartments were atmospheric deposition (1.2 kmol ha^?1 yr^?1), nitrification (5.1 kmol, ha^?1 yr^?1) and base-cation uptake by vegetation (8.0 kmol, ha^?1 yr^?1) respectively. These proton sources were neutralized almost completely within the individual compartments mainly by base-cation release from the canopy or the soil. The sum of internal proton sources was five times as large as that of external ones. Nitrogen input from the atmosphere was 2.2 kmol ha^?1 yr^?1, whereas its output from the lower soil layer was 3.9 kmol ha^?1 yr^?1, indicating that a net loss of nitrogen occurred in the ecosystem. However, this did not cause the acidification of soil leachates because of a sufficient release rate of base cations from the soil.     

Simulation of the long-term soil response to acid deposition in various buffer ranges

A soil acidification model has been developed to estimate long-term chemical changes in soil and soil water in response to changes in atmospheric deposition. Its major outputs include base saturation, pH and the molar Al/BC ratio, where BC stands for divalent base cations. Apart from net uptake and net immobilization of N, the processes accounted for are restricted to geochemical interactions, including weathering of carbonates, silicates and Al oxides and hydroxides, cation exchange and CO₂ equilibriums. First, the model's behavior in the different buffer ranges between pH 7 and pH 3 is evaluated by analyzing the response of an initially calcareous soil of 50 cm depth to a constant high acid load (5000 mol_c ha^?1 yr^?1) over a period of 500 yr. In calcareous soils weathering is fast and the pH remains high (near 7) until the carbonates are exhausted. Results indicate a time lag of about 100 yr for each percent CaCO₃ before the pH starts to drop. In non-calcareous soils the response in the range between pH 7 and 4 mainly depends on the initial amount of exchangeable base cations. A decrease in base saturation by H/BC exchange and Al/BC exchange following dissolution of Al³⁺ leads to a strong increase in the Al/BC ratio near pH 4. A further decrease in pH to values near 3.0 does occur when the A1 oxides and/or hydroxides are exhausted. The analyses show that this could occur in acid soils within several decades. The buffer mechanisms in the various pH ranges are discussed in relation to Ulrich's concept of buffer ranges. Secondly, the impact of various deposition scenarios on non-calcareous soils is analyzed for a time period of 100 yr. The results indicate that the time lag between reductions in deposition and a decrease in the Al/BC ratio is short. However, substantial reductions up to a final deposition level of 1000 mol_c ha^?1 yr^?1 are needed to get Al/BC ratios below a critical value of 1.0.     

Critical deposition levels for nitrogen and sulphur on dutch forest ecosystems

Critical loads for N and S on Dutch forest ecosystems have been derived in relation to effects induced by eutrophication and acidification, such as changes in forest vegetation, nutrient imbalances, increased susceptibility to diseases, nitrate leaching, and Al toxicity. The criteria that have been used are N contents in needles, nitrate concentrations in groundwater (drinking water), and NH₄/K ratios, Ca/Al ratios, and Al concentrations in the soil solution. Assuming an equal contribution of N and S, all effects seem to be prevented at a total deposition level below 600 mol_c ha^?1 yr^?1 due to N uptake by stemwood and acid neutralization by base cation weathering. The most serious effects will probably be prevented at total deposition levels between 1500 and 2000 mol_c ha^?1 yr^?1. The current average deposition in the Netherlands is 4900 mol_c ha^?1 yr^?1.     

Assessment of Critical Loads in Tropical Sal (Shorea robusta Gaertn. F.) Forests of Doon Valley Himalayas, India

The present study was conducted in tropical Sal forest ecosystem of the Doon valley in the Indian Himalayas to assess the critical load of sulfur and nitrogen and their exceedances. The observed pattern of throughfall ionic composition in the study are Ca²⁺>K⁺>Mg²⁺>Cl^?>?HCO3^?>?Na⁺>NO ₃ ^? >?SO ₃ ^2? ???NH ₄ ⁺ >F^?. The sum of cation studied is 412.29 ??eq l^?1 and that of anions is 196.98 ??eq l^?1, showing cation excess of 215.31 ??eq l^?1. The cations, namely Ca²⁺, Mg²⁺, K⁺, Na⁺, and NH ₄ ⁺ , made a contribution of about 67% of the total ion strength, where as anion comprising of SO ₄ ^2? , Cl^?, NO ₃ ^? , and HCO ₃ ^? contributed 33%. The chief acidic components were Cl^?C (12%) and HCO ₃ ^? (8%), while the presence of SO ₄ ^2? (5%) and NO ₃ ^? (6%), respectively. Percentage contribution of bole to total aboveground biomass was ??72.38% in comparison to 2.24?C2.93% of leaf biomass, 10.34?C10.96% of branch biomass and 13.21?C17.07% of bark biomass. There was high and significant variation (P?<?0.001) in the total aboveground biomass produced at different sites. The aboveground net primary productivity (ANPP) in these sites ranged between 2.09 and 9.22 t ha^?1 year^?1. The base cations and nitrogen immobilization was found to be maximum in bole. The net annual uptake of the base cations varied from 306.85 to 1,311.46 eq ha^?1 year^?1 and of nitrogen from 68.27 to 263.51 eq ha^?1 year^?1. The critical appraisal of soil showed that cation exchange capacity lied between 18.37 and 10.30 Cmol (p+) kg^?1. The base saturation percentage of soil was as high as 82.43% in Senkot, whereas in Kalusidh it was just 44.28%. The local temperature corrected base cation weathering rates based on soil mineralogy, parent material class, and texture class varied from 484.15 to 627.25 eq ha^?1 year^?1, showing a weak potentiality of the system to buffer any incoming acidity and thus providing restricted acid neutralizing capacity to keep the ecosystem stable under increased future deposition scenarios in near future. The appreciable BS of the soil indicates the presence of intense nutrient phytorecycling forces within this climate and atmospheric deposition in replenishing base cations in the soil, which includes intrinsic soil-forming processes, i.e., weathering. The highest value of critical load for acidity was 2,896.50 eq ha^?1 year^?1 and the lowest was 2,792.45 eq ha^?1 year^?1. The calculated value of the minimum critical loads for nitrogen varied from 69.77 to 265.01 eq ha^?1 year^?1, whereas the maximum nitrogen critical load ranged between 2,992.63 and 4,394.45 eq ha^?1 year^?1. The minimum and the maximum critical loads of sulfur ranged between 2,130.49 and 3,261.64 eq ha^?1 year^?1 and 2,250.58 and 3,381.73 eq ha^?1 year^?1, respectively. The values of exceedance of sulfur and nitrogen were negative, implying that in the current scenario Sal forests of the Doon valley are well protected from acidification.     

The effect of five years acid treatment on leaching,soil chemistry and weathering of a humo-ferric podzol

This paper describes the effect of treating a nutrient-poor forest soil in monolith lysimeters with H₂SO ₄, pH 3.0, for 4.75 yr. The lysimeters were instrumented with porous cup probes to distinguish processes occurring in each soil horizon. In the A horizon base cation exchange and sulphate absorption were the principal proton- consuming processes whereas lower down the profile Al³⁺ dissolution from hydrous oxides dominated. Acid treatment thus reduced the amount of amorphous Al in the lower horizons, but exchangeable Al was unaffected. Sulphate absorbtion was positively correlated with the distribution of Al hydrous oxides. High rates of nitrification reduced the differences between acid and control monoliths, but acid treatment significantly reduced soil pH down to 75 cm and reduced the levels of exchangeable base cations in the litter and A horizons. Acid treatment increased the leaching rates of base cations and Al. Consideration of the total base cation content shows that acid treatment increased the rate of weathering by 0.7–1.4 k eq ha^?1 yr^?1. The results should be useful in modelling more realistic rates of acid input to similar soils.     

Sulfur Acidity Loading in South Korean Ecosystems

The applicability of critical load (CL) methodology for thedetermination of natural terrestrial ecosystem sensitivity to sulfur acidity loading in South Korea was investigated.The sulfur critical load values, CL_maxS, were calculated for the terrestrial ecosystems of South Korea using the steady-state mass balance approach. The corresponding mapping of CL_maxS was carried out on the scale of 11 × 14 km grid cells. The estimated CL_maxS values depend on the low rate of soil chemical base cation weathering (mainly, 200–400 eq ha^-1 yr^-1), relativelylow base cation depositions (mainly less than 450 eq ha^-1 yr^-1) and base cation uptake (predominantly 300–400 eq ha^-1 yr^-1), and in significant degree on high valuesof acid neutralizing capacity. The latter in turn is connectedwith relatively high values of surface runoff (maximum 9000 m³ ha^-1 yr^-1). It has been shown that about 75%of CL_maxS values are in the range of 1000–2000 eq ha^-1 yr^-1 and about 15% are relatively low values(<1000 eq ha^-1 yr^-1). About 10% of ecosystems haveCL values more than 2000 eq ha^-1 yr^-1. The sensitiveand very sensitive ecosystems occur in the southeastern part of the country whereas the sustainable ecosystems are wide spread in the northeastern part. In accordance with sulfur critical load and sulfur deposition patterns, in 1994–1997 the CL_maxS values were found to be exceeded in about 40% of total number of Korean ecosystems, mainly in the southeastern part of the country. The average yearly valuesof exceedances varied from 176 to 3100 eq ha^-1 yr^-1.     

Influence of acid deposition on element cycling in mature sugar maple forest,Algoma, Canada

Forestry studies were undertaken within the Turkey Lakes Watershed to determine the impact of long-range transport of air pollutants on biogeochemical processes in old-growth sugar maple forest on shallow Precambrian-derived till soils in the Algoma District of Ontario, Canada. Distributions of organic matter and macroelements were determined in the tree- and field-layer vegetation, the forest floor and the mineral soil of the study site. Annual tree growth was largely offset by mortality, resulting in a relatively stable standing stock of ca. 245 t ha^?1. Annual aboveground litter production averaged 3.7 t ha^?1 yr^?1, chiefly in the form of deciduous leaf fall. The average pH of the precipitation (4.3) was reduced considerably by contact with the forest canopy. Throughfall was enriched with other elements, principally K and, to a lesser extent, Ca and Mg. The cationic composition of the forest-floor percolates, on the other hand, was dominated primarily by Ca and only to a lesser extent by Mg and K. The stand receives moderate acid deposition, mainly from average inputs of 33–36 kg ha^?1 yr^?1 of SO₄ ^2? and 24–29 kg ha^?1 yr^?1 of NO₃ ^? distributed throughout the year. Atmospheric inputs add to substantial natural NO₃ ^? production, notably within the forest floor and upper mineral soil, and contribute to leaching of bases, principally Ca and Mg, from the rooting zone. Active recycling of elements together with weathering of primary minerals should assist in preserving the base status of the site.     

Lysimeter study with a cambic arenosol exposed to artificial acid rain: II. Input-output budgets and soil chemical properties

The effects of artificial precipitation with different pH levels on soil chemical properties and element flux were studied in a lysimeter experiment. Cambic Arenosol (Typic Udipsamment) in monolith lysimeters was treated for 6 1/2 yr with 125 mm yr^?1 artificial rain in addition to natural precipitation. Artificial acid rain was produced from groundwater with H₂SO₄ added. pH levels of 6.1, 4 and 3 were used. ‘Rain’ acidity was buffered, mainly due to cation exchange with Ca²⁺ and Mg²⁺, which were increasingly leached due to the acid input. The H⁺ retention was not accompanied by a similar increase in the output of Al ions, but a slight increase in the leaching of Al ions was observed in the most acidic treatment. The net flux of SO₄ ^2? from the lysimeters increased with increasing input of H₂SO₄, but in the most acidified lysimeters significant sorption of SO₄ ^2? was observed. The sorption was, however, most likely a concentration effect. The ‘long-term’ acidification effects on soil were mainly seen in the upper O and Ah-horizons, where an impoverishment of exchangeable Ca²⁺ and Mg²⁺ was observed. An increased proportion of Al ions on exchange sites in the organic layer was observed in the pH 3-treated soil. By means of budget calculations the annual release of base cations due to weathering was estimated to be between 33 and 77 mmol_c m^?2.     

Significance of DOM in the translocation of cations and acidity in acid forest soils

We estimated the contribution of dissolved organic matter (DOM) to cation leaching and the translocation of acidity in three acid forest soils. The analysis was based on monitored (2 years) concentrations of dissolved organic carbon (DOC) in the field, measured total acidities of DOM, and measured as well as predicted weighted mean dissociation constants of the organic acids. Although the forest floor solutions were strongly acidic (pH 3.47–4.10), a considerable proportion of the organic acids was dissociated and organic anions represented 22–40% of the total anions in the mineral soil input. The flux of DOM-associated exchangeable protons from the forest floor to the mineral soil ranged from 0.35 (Wülfersreuth) to 3.72 (Hohe Matzen) kmol ha^?1 yr^?1. In the subsoil, this organic acidity may be neutralized by microbial decomposition of the organic acids, but a part of the hydrogen ions may dissociate and contribute to acidification of the soil solution and to weathering processes. Due to the pronounced retention of DOM in the mineral subsoil horizons, the contribution of DOM to the output of cations and acidity from the soil is much lower than in the surface horizons but still significant.?     

Calculation and Mapping of Sulfur Critical Loads for Terrestrial Ecosystems of Thailand

The essential parameters needed for the calculation of critical load of sulfur, CL(S), are base cation weathering rate, base cation uptake, acid neutralizing capacity leaching and base cation deposition. These parameters are estimated and mapped for the most area of terrestrial ecosystems of Thailand using data of national data soil survey. The values of CL(S) range from <200 to 2,225 eq.ha^?1yr^?1 and about 70% of terrestrial ecosystems are characterized by low values (<200 eq.ha^?yr^?1). These CL values reflect the sensitivity of Thai ecosystems to sulfur deposition.     

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.     

Average critical loads for nitrogen and sulfur and its use in acidification abatement policy in the Netherlands

Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO₃ pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol _c ha^?1 yr^?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol _c ha^?1 yr^?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha^?1 yr^?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol _c ha^?1 yr^?1 has been set in the Netherlands from which the N input should be less than 1000 mol _c ha^?1 yr^?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO₂, NO _x and NH₃ in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.