Estimating calcium weathering rates and future lake calcium concentrations in the Muskoka–Haliburton region of Ontario

2008 ◽  
Vol 65 (5) ◽  
pp. 821-833 ◽  
Author(s):  
Shaun A Watmough ◽  
Julian Aherne
Keyword(s):  
Steady State ◽  
Water Chemistry ◽  
Timber Harvesting ◽  
Mineral Weathering ◽  
Drainage Basins ◽  
Weathering Rates ◽  
South Central ◽  
Model Predictions ◽  
State Water ◽  
Hydrochemical Model

Calcium (Ca) concentrations in surface waters on the Precambrian Shield are determined primarily by the Ca weathering rate in soil, which requires extensive soil data that generally do not exist. From a water chemistry database comprising approximately 550 lakes in south-central Ontario, Canada, 130 lakes were selected with low Ca concentrations (Ca < 75 µmol·L–1). Calcium weathering is primarily dominated by silicate minerals such as plagioclase and hornblende, allowing the use of Ca–sodium (Na) ratios in lake water to estimate Ca weathering rates. Soil profile data at seven sites indicated that the Ca–Na ratio from mineral weathering is 0.86; correspondingly, Ca weathering rates in lakes ranged from 0.04 to 0.24 kmol·ha–1·year–1 (median of 0.09 kmol·ha–1·year–1). This compares with a range of 0.06–0.24 kmol·ha–1·year–1 (median of 0.14 kmol·ha–1·year–1) obtained using the steady-state water chemistry model. Using these methods to bound potential weathering rates, Ca concentrations in individual lakes at steady state are predicted to decline by 10%–40% compared with current values. Dynamic soil hydrochemical model predictions indicate that Ca concentrations in lakes will be considerably lower than these steady-state predictions within decades if timber harvesting occurs in the drainage basins.

Critical loads of acidity for surface waters in south-central Ontario, Canada: regional application of the Steady-State Water Chemistry (SSWC) model

2002 ◽  
Vol 59 (8) ◽  
pp. 1287-1295 ◽  
Author(s):  
A Henriksen ◽  
P J Dillon ◽  
J Aherne
Keyword(s):  
Steady State ◽  
Water Chemistry ◽  
Critical Load ◽  
Critical Loads ◽  
Lake Chemistry ◽  
Sulphur Deposition ◽  
South Central ◽  
State Water ◽  
Critical Loads Of Acidity ◽  
Sswc Model

Critical loads of acidity and the amount by which these critical loads are exceeded by atmospheric deposition (termed "exceedances") were estimated for 1469 lakes from five regions in south-central Ontario, Canada, using single lake chemistry measurements and sulphur deposition data for the period 1976–1999. Based on the Steady-State Water Chemistry (SSWC) model, four of the five regions had low critical loads, which is consistent with the underlying geology (silicate bedrock) and the thin glacial soils in these regions. Sulphur deposition in the study area showed a clear downward trend over the time period, with a decrease of approximately 50% to current levels of approximately 44 meq·m–2·year–1. As a result of the declining deposition, the portion of lakes with critical load exceedances has dropped substantially, from 74–82% in the four sensitive regions in 1976 to 11–26% in 1999. The pentile critical load is typically used as a regional target to account for uncertainties, but also to ensure that a sufficient percentage of lakes are protected (95%). This suggests that further reductions in emissions are required to reduce depositions to approximately 34 meq·m–2·year–1 (11 kg S·ha–1·year–1) to prevent critical load exceedance.

scholarly journals Current, steady-state and historical weathering rates of base cations at two forest sites in northern and southern Sweden: a comparison of three methods

2020 ◽  
Vol 17 (2) ◽  
pp. 281-304 ◽  
Author(s):  
Sophie Casetou-Gustafson ◽  
Harald Grip ◽  
Stephen Hillier ◽  
Sune Linder ◽  
Bengt A. Olsson ◽  
...  
Keyword(s):  
Steady State ◽  
Soil Depth ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Soil Horizon ◽  
Soil Horizons ◽  
Weathering Rate ◽  
Weathering Rates ◽  
Forest Sites

Abstract. Reliable and accurate methods for estimating soil mineral weathering rates are required tools in evaluating the sustainability of increased harvesting of forest biomass and assessments of critical loads of acidity. A variety of methods that differ in concept, temporal and spatial scale, and data requirements are available for measuring weathering rates. In this study, causes of discrepancies in weathering rates between methods were analysed and were classified as being either conceptual (inevitable) or random. The release rates of base cations (BCs; Ca, Mg, K, Na) by weathering were estimated in podzolised glacial tills at two experimental forest sites, Asa and Flakaliden, in southern and northern Sweden, respectively. Three different methods were used: (i) historical weathering since deglaciation estimated by the depletion method, using Zr as the assumed inert reference; (ii) steady-state weathering rate estimated with the PROFILE model, based on quantitative analysis of soil mineralogy; and (iii) BC budget at stand scale, using measured deposition, leaching and changes in base cation stocks in biomass and soil over a period of 12 years. In the 0–50 cm soil horizon historical weathering of BCs was 10.6 and 34.1 mmolc m−2 yr−1, at Asa and Flakaliden, respectively. Corresponding values of PROFILE weathering rates were 37.1 and 42.7 mmolc m−2 yr−1. The PROFILE results indicated that steady-state weathering rate increased with soil depth as a function of exposed mineral surface area, reaching a maximum rate at 80 cm (Asa) and 60 cm (Flakaliden). In contrast, the depletion method indicated that the largest postglacial losses were in upper soil horizons, particularly at Flakaliden. With the exception of Mg and Ca in shallow soil horizons, PROFILE produced higher weathering rates than the depletion method, particularly of K and Na in deeper soil horizons. The lower weathering rates of the depletion method were partly explained by natural and anthropogenic variability in Zr gradients. The base cation budget approach produced significantly higher weathering rates of BCs, 134.6 mmolc m−2 yr−1 at Asa and 73.2 mmolc m−2 yr−1 at Flakaliden, due to high rates estimated for the nutrient elements Ca, Mg and K, whereas weathering rates were lower and similar to those for the depletion method (6.6 and 2.2 mmolc m−2 yr−1 at Asa and Flakaliden). The large discrepancy in weathering rates for Ca, Mg and K between the base cation budget approach and the other methods suggests additional sources for tree uptake in the soil not captured by measurements.

A critical review of mass balance methods for calculating critical loads of nitrogen for forested ecosystems

1993 ◽  
Vol 1 (2) ◽  
pp. 145-156 ◽  
Author(s):  
L. H. Pardo ◽  
C. T. Driscoll
Keyword(s):  
Steady State ◽  
Atmospheric Deposition ◽  
Water Chemistry ◽  
Critical Load ◽  
Mass Balance ◽  
Critical Loads ◽  
Balance Method ◽  
Mass Balance Method ◽  
Basic Cation ◽  
State Water

Critical loads are used in the assessment of air pollution and regulation of the causative emissions to prevent or mitigate ecological damage. We critically review four mass balance methods for calculating critical loads for nitrogen deposition: the steady-state water chemistry method, the nitrogen mass balance method, the basic cation mass balance method, and the steady-state mass balance method. The critical loads may be calculated with respect to effects of acidification associated with nitrate leaching or effects of elevated nitrogen such as eutrophication, excess nitrate loss, and nutrient imbalances. The most useful method for calculating the critical load for nitrogen with respect to effects of elevated atmospheric deposition of nitrogen is the nitrogen mass balance method. The steady-state water chemistry method can be readily applied for regional-scale calculations because it requires only water chemistry data from synoptic surveys of surface waters and does not explicitly consider biogeochemical processes. Both of the other approaches are severely limited by lack of quantitative information on rates of mineral weathering. If weathering data were available, the steady-state mass balance method could be more effectively used to assess critical loads with respect to acidification. Similarly, the basic cation mass balance method could be used to calculate critical loads for both acidity and elevated nitrogen effects. Because of the complexity of the nitrogen cycle, it is not possible to obtain a single critical load for the whole ecosystem. Rather, one should analyze and synthesize several values of critical loads that reflect different components of the ecosystem and different ecological effects of elevated nitrogen deposition (e.g., acidification and eutrophication effects).Key words: atmospheric deposition of nitrogen, acidification, critical loads, nitrogen cycling.

scholarly journals Current, steady-state and historical weathering rates of base cations at two forest sites in northern and southern Sweden: A comparison of three methods

2019 ◽  
Author(s):  
Sophie Casetou-Gustafson ◽  
Harald Grip ◽  
Stephen Hillier ◽  
Sune Linder ◽  
Bengt A. Olsson ◽  
...  
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Soil Depth ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Soil Layers ◽  
Weathering Rate ◽  
Weathering Rates ◽  
Forest Sites

Abstract. Reliable and accurate methods for estimating soil mineral weathering rate are required tools in evaluating the sustainability of increased harvesting of forest biomass. A variety of methods that differ in concept, temporal and spatial scale and data requirements are available for measuring weathering rate. In this study, release rates of base cations through weathering were estimated in podsolised glacial tills at two experimental forest sites, Asa and Flakaliden, in southern and northern Sweden, respectively. Three different methods were used: (i) historical weathering since deglaciation estimated with the depletion method, using Zr as assumed inert reference; (ii) steady-state weathering rate estimated with the PROFILE model, based on quantitative analysis of soil mineralogy; and (iii) base cation mass balance at stand scale, using measured deposition, leaching and changes in base cation stocks in biomass and soil over a period of 12 years. In the 0–50 cm soil layer at Asa, historical weathering of Ca, Mg, K and Na estimated by the depletion method was 4.7, 3.1, 0.8 and 2.0 mmolc m−2 yr−1, respectively. Corresponding values at Flakaliden were 7.3, 9.0, 1.7 and 4.4 mmolc m−2 yr−1, respectively. Steady state weathering rate for Ca, Mg, K and Na estimated with PROFILE was 8.9, 3.8, 5.9 and 18.5 mmolc m−2 yr−1, respectively, at Asa and 11.9, 6.7, 6.6 and 17.5 mmolc m−2 yr−1, respectively, at Flakaliden. Thus at both sites, the PROFILE results indicated that steady-state weathering rate increased with soil depth as a function of exposed mineral surface area, reaching a maximum rate at 80 cm (Asa) and 60 cm (Flakaliden). In contrast, the depletion method indicated that the largest postglacial losses were in upper soil layers, particularly at Flakaliden. With the exception of Mg and Ca in shallow soil layers, PROFILE appeared to produce consistently higher weathering rates, particularly of K and Na in deeper soil layers. In contrast, the depletion method appeared to to produce consistently lower rather than higher weathering rates, due to natural and anthropogenic variability in (reference) Zr gradients. The mass balance approach produced significantly higher weathering rates of Ca, Mg, and K (65, 23, 40 mmolc m−2 yr−1 at Asa and 35, 14 and 22 mmolc m−2 yr−1 at Flakaliden), but lower Na weathering rates similar to the depletion method (6.6 and 2.2 mmolc m−2 yr−1 at Asa and Flakaliden). The large discrepancy in weathering rates for Ca, Mg and K between mass balance and the other methods suggest that there were additional sources for tree uptake in the soil besides weathering and measured depletion in exchangeable base cations.

Calcium Budgets for Catchments as Interpreted by Strontium Isotopes

1989 ◽  
Vol 20 (2) ◽  
pp. 85-96 ◽  
Author(s):  
Gunnar Jacks ◽  
Göran Åberg ◽  
P. Joseph Hamilton
Keyword(s):  
Steady State ◽  
Forest Ecosystem ◽  
Coniferous Forest ◽  
Strontium Isotopes ◽  
Runoff Water ◽  
Weathering Rate ◽  
Weathering Rates ◽  
Exchangeable Calcium

Strontium isotopes in precipitation, soil and runoff water can be used to establish a ratio of wet plus dry deposited Sr to Sr released by weathering. This ratio is especially enhanced in areas with old acid Proterozoic rocks (0.6-2.5 Ga) and Archean rocks (&gt;2.5 Ga). Since Sr and Ca behave in an analogous way in the coniferous forest ecosystem the results for Sr can be used for the determination of Ca. If the deposition of calcium can be calculated reasonably accurately the weathering rate can also be estimated. Five catchments have been investigated using this approach. Three of them seem to be close to a steady state, wherein the losses and gains of calcium to the system are equal. In the two southern-most catchments there seems to be an ongoing loss of exchangeable calcium. The loss by runoff occurs with sulphate being the dominant anion. Weathering rates of 1.5 to 4.8 kg Ca/ha year have been estimated.

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