Base cation mineral weathering and total release rates from soils in three calibrated forest watersheds on the Canadian Boreal Shield

2005 ◽  
Vol 85 (2) ◽  
pp. 245-260 ◽  
Author(s):  
Rock Ouimet ◽  
Louis Duchesne
Keyword(s):  
Forest Soil ◽  
Monitoring Network ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Extensive Literature ◽  
Release Rates ◽  
Ecosystem Research ◽  
Forest Watersheds ◽  
Boreal Shield

Total release rates of base cations (Ca, Mg, K, and Na) from soils and from watersheds were evaluated using three methods. Three methods, one of which is new, were also used to evaluate mineral weathering rates of soils for three calibrated forest watersheds in the forest ministry’s monitoring network (Réseau d’étude et de surveillance des eco ystems forestiers: Quebec Forest Ecosystem Research and Monitoring Network; RESEF) on the Canadian Boreal Shield. We also compiled an extensive literature review of forest soil base cation release rates, focussed on northeastern North American forest soils of granitic lithology. With the exception of the total release and mineral weathering of Ca from soils at the Lake Laflamme Watershed site, and the total release of K from the three watersheds, soils and watershed release rates for the three watersheds were within the confidence interval of release rates compiled for forest ecosystems with similar granitic environment (compiled data for solum [mmol (+) m-2 yr-1 ± 95% CI], Ca: 33.8 ± 16.3, Mg: 16.8 ± 4.2, K: 13.0 ± 5.6, Na: 11.1 ± 3.0, and sum of base cations (BC): 61.2 ± 11.0; compiled data from watersheds, Ca: 82.8 ± 24.6, Mg: 50.8 ± 17.0, K: 7.8 ± 2.2, Na: 44.7 ± 12.8, and BC: 186.0 ± 49.9). Given the uncertainties associated with the calculations, there was little overall difference between total release rates and weathering release rates from soils for two of the three watersheds. Key words: Weathering rate, forest soil, granitic environment, watershed, PMB method, compositional trends

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.

scholarly journals Modelling of base cation emissions, concentrations and deposition in the UK

2010 ◽  
Vol 10 (9) ◽  
pp. 21989-22018 ◽  
Author(s):  
M. Werner ◽  
M. Kryza ◽  
A. J. Dore ◽  
M. Błaś ◽  
S. Hallsworth ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Wet Deposition ◽  
Fine Particles ◽  
Sea Water ◽  
Monitoring Network ◽  
Base Cations ◽  
Base Cation ◽  
Sea Surface ◽  
Time Step ◽  
The Uk

Abstract. Base cations exerts a large impact on various geochemical and geophysical processes both in the atmosphere and at the Earth surface. One of the essential roles of these compounds is impact on surface pH causing an increase in alkalinity and neutralizing the effects of acidity generated by sulphur and nitrogen deposition. During recent years anthropogenic emissions of base cations in the UK have decreased substantially, by about 70% for Na+, 78% for Mg2+, 75% for Ca2+ and about 48% for K+ for the period 1990–2006. For the island regions, such as the is UK, the main source of base cation particles is the aerosol produced from the sea surface. Here, the sea salt aerosol (SSA) emissions are calculated with parameterisations proposed by Maårtensson et al. (2003); ultra fine particles, Monahan et al. (1986); fine particles and Smith and Harisson (1998); coarse particles continuously with a 0.1 μ m size step using WRF-modelled wind speed data at a 5 km × 5 km grid square resolution with a 3 h time step for two selected years 2003 and 2006. SSA production has been converted into base cation emissions, with the assumption that the chemical composition of the particle emitted from the sea surface is equal to the chemical composition of sea water, and used as input data in the Fine Resolution Atmospheric Multi-pollutant Exchange Model (FRAME). FRAME model results, yearly mean concentrations and total wet deposition at a 5 km × 5 km grid resolution, are compared with concentrations in air and wet deposition from the National Monitoring Network and measurements based estimates of UK deposition budget. The correlation coefficient for wet deposition achieves high values for Na+ and Mg2+, and for Ca2+ there is significant scattering. Base cation concentration is also represented well, with some overestimations on the west coast and underestimations in the centre of the land.

scholarly journals Base cations in the soil bank: non-exchangeable pools may sustain centuries of net loss to forestry and leaching

SOIL ◽  
2019 ◽  
Vol 5 (2) ◽  
pp. 351-366 ◽  
Author(s):  
Nicholas P. Rosenstock ◽  
Johan Stendahl ◽  
Gregory van der Heijden ◽  
Lars Lundin ◽  
Eric McGivney ◽  
...  
Keyword(s):  
Microbial Biomass ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Major Constituent ◽  
Chemical Extraction ◽  
Spectroscopic Techniques ◽  
Nutrient Return ◽  
Nutrient Pools ◽  
Clay Interlayer

Abstract. Accurately quantifying soil base cation pool sizes is essential to interpreting the sustainability of forest harvests from element mass-balance studies. The soil-exchangeable pool is classically viewed as the bank of “available” base cations in the soil, withdrawn upon by plant uptake and leaching and refilled by litter decomposition, atmospheric deposition and mineral weathering. The operational definition of this soil bank as the exchangeable (salt-extractable) pools ignores the potential role of “other” soil nutrient pools, including microbial biomass, clay interlayer absorbed elements, and calcium oxalate. These pools can be large relative to “exchangeable” pools. Thus neglecting these other pools in studies examining the sustainability of biomass extractions, or need for nutrient return, limits our ability to gauge the threat or risk of unsustainable biomass removals. We examine a set of chemical extraction data from a mature Norway spruce forest in central Sweden and compare this dataset to ecosystem flux data gathered from the site in previous research. The 0.2 M HCl extraction released large pools of Ca, K, Mg, and Na, considerably larger than the exchangeable pools. Where net losses of base cations are predicted from biomass harvest, exchangeable pools may not be sufficient to support more than a single 65-year forest rotation, but acid-extractable pools are sufficient to support many rotations of net-ecosystem losses. We examine elemental ratios, soil clay and carbon contents, and pool depth trends to identify the likely origin of the HCl-extractable pool. No single candidate compound class emerges, as very strongly supported by the data, as being the major constituent of the HCl-extractable fraction. A combination of microbial biomass, fine grain, potentially shielded, easily weatherable minerals, and non-structural clay interlayer bound potassium may explain the size and distribution of the acid-extractable base cation pool. Sequential extraction techniques and isotope-exchange measurements should be further developed and, if possible, complemented with spectroscopic techniques to illuminate the identity of and flux rates through these important, and commonly overlooked, nutrient pools.

scholarly journals Soil weathering rates in 21 catchments of the Canadian Shield

2012 ◽  
Vol 16 (3) ◽  
pp. 685-697 ◽  
Author(s):  
D. Houle ◽  
P. Lamoureux ◽  
N. Bélanger ◽  
M. Bouchard ◽  
C. Gagnon ◽  
...  
Keyword(s):  
Base Cations ◽  
Base Cation ◽  
High Reactivity ◽  
Mineral Weathering ◽  
Forest Growth ◽  
Canadian Shield ◽  
Geochemical Model ◽  
Soil Weathering ◽  
Weathering Rates ◽  
Profile Model

Abstract. Soil mineral weathering represents an essential source of nutrient base cation (Ca, Mg and K) for forest growth in addition to provide a buffering power against precipitation acidity for soils and surface waters. Weathering rates of base cations were obtained for 21 catchments located within the temperate and the boreal forest of the Canadian Shield with the geochemical model PROFILE. Weathering rates ranged from 0.58 to 4.46 kmolc ha−1 yr−1 and their spatial variation within the studied area was mostly in agreement with spatial variations in soil mineralogy. Weathering rates of Ca and Mg were significantly correlated (r = 0.80 and 0.64) with their respective lake concentrations. Weathering rates of K and Na did not correlate with lake concentrations of K and Na. The modeled weathering rates for each catchment were also compared with estimations of net catchment exportations. The result show that modeled weathering rates of Ca were not significantly different than the net catchment exportations while modeled weathering rates of Mg were higher by 51%. Larger differences were observed for K and Na weathering rates that were significantly different than net catchment exportations being 6.9 and 2.2 times higher than net exportations, respectively. The results for K were expected given its high reactivity with biotic compartments and suggest that most of the K produced by weathering reactions was retained within soil catchments and/or above ground biomass. This explanation does not apply to Na, however, which is a conservative element in forest ecosystems because of the insignificant needs of Na for soil microorganisms and above ground vegetations. It raises concern about the liability of the PROFILE model to provide reliable values of Na weathering rates. Overall, we concluded that the PROFILE model is powerful enough to reproduce spatial geographical gradients in weathering rates for relatively large areas as well as adequately predict absolute weathering rates values for the sum of base cations, Ca and Mg.

scholarly journals Modelling of marine base cation emissions, concentrations and deposition in the UK

2011 ◽  
Vol 11 (3) ◽  
pp. 1023-1037 ◽  
Author(s):  
M. Werner ◽  
M. Kryza ◽  
A. J. Dore ◽  
M. Blaś ◽  
S. Hallsworth ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Wet Deposition ◽  
Fine Particles ◽  
Sea Water ◽  
Monitoring Network ◽  
Base Cations ◽  
Base Cation ◽  
Sea Surface ◽  
Time Step ◽  
The Uk

Abstract. Base cations exert a large impact on various geochemical and geophysical processes both in the atmosphere and at the Earth surface. One of the essential roles of these compounds is impact on surface pH causing an increase in alkalinity and neutralizing the effects of acidity generated by sulphur and nitrogen deposition. During recent years anthropogenic emissions of base cations in the UK have decreased substantially, by about 70%, 78%, 75% and 48% for Na+, Mg2+, Ca2+ and K+, respectively, over the period 1990–2006. For the island regions, such as the UK, the main source of base cation particles is the aerosol produced from the sea surface. Here, the sea salt aerosol (SSA) emissions are calculated with parameterisations proposed by Mårtensson et al. (2003) for ultra fine particles, Monahan et al. (1986) for fine particles and Smith and Harisson (1998) for coarse particles continuously with a 0.1 μm size step using WRF-modelled wind speed data at a 5 km × 5 km grid square resolution with a 3 h time step for two selected years 2003 and 2006. SSA production has been converted into base cation emissions, with the assumption that the chemical composition of the particle emitted from the sea surface is equal to the chemical composition of sea water, and used as input data in the Fine Resolution Atmospheric Multi-pollutant Exchange Model (FRAME). FRAME model annual mean concentrations and total wet deposition at a 5 km × 5 km grid resolution, are compared with concentrations in air and wet deposition from the National Monitoring Network and measurements based estimates of UK deposition budget. The correlation coefficient for wet deposition achieves high values (R = 0.8) for Na+ and Mg2+, whereas for Ca2+ the correlation is poor (R < 0.3). Base cation concentrations are also represented well, with some overestimations on the west coast and underestimations in the centre of the land.

scholarly journals Soil weathering rates in 21 catchments of the Canadian Shield

2011 ◽  
Vol 8 (3) ◽  
pp. 5743-5768 ◽  
Author(s):  
D. Houle ◽  
P. Lamoureux ◽  
N. Bélanger ◽  
M. Bouchard ◽  
C. Gagnon ◽  
...  
Keyword(s):  
Base Cations ◽  
Base Cation ◽  
High Reactivity ◽  
Mineral Weathering ◽  
Forest Growth ◽  
Canadian Shield ◽  
Geochemical Model ◽  
Soil Weathering ◽  
Weathering Rates ◽  
Profile Model

Abstract. Soil mineral weathering represents an essential source of nutrient base cation (Ca, Mg and K) for forest growth in addition to provide a buffering power against precipitation acidity for soils and surface waters. Weathering rates of base cations were obtained for 21 catchments located within the temperate and the boreal forest of the Canadian Shield with the geochemical model PROFILE. Weathering rates ranged from 0.58 to 4.46 kmolc ha−1 yr−1 and their spatial variation within the studied area was mostly in agreement with spatial variations in soil mineralogy. Weathering rates of Ca and Mg were significantly correlated (r = 0.80 and 0.64) with their respective lake concentrations. Weathering rates of K and Na did not correlate with lake concentrations of K and Na. The modeled weathering rates for each catchment were also compared with estimations of net catchment exportations. The result show that modeled weathering rates of Ca were not significantly different than the net catchment exportations while modeled weathering rates of Mg were higher by 51 %. Larger differences were observed for K and Na weathering rates that were significantly different than net catchment exportations being 6.9 and 2.2 times higher than net exportations, respectively. The results for K were expected given its high reactivity with biotic compartments and suggest that most of the K produced by weathering reactions was retained within soil catchments and/or above ground biomass. This explanation does not apply to Na, however, which is a conservative element in forest ecosystems because of the insignificant needs of Na for soil microorganisms and above ground vegetations. It raises concern about the liability of the PROFILE model to provide reliable values of Na weathering rates. Overall, we concluded that the PROFILE model is powerful enough to reproduce spatial geographical gradients in weathering rates for relatively large areas as well as adequately predict absolute weathering rates values for the sum of base cations, Ca and Mg.

scholarly journals Catchment export of base cations: Improved mineral dissolution kinetics influence the role of water transit time

2019 ◽  
Author(s):  
Martin Erlandsson Lampa ◽  
Harald U. Sverdrup ◽  
Kevin H. Bishop ◽  
Salim Belyazid ◽  
Ali Ameli ◽  
...  
Keyword(s):  
Soil Water ◽  
Transit Time ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Mineral Dissolution ◽  
Catchment Scale ◽  
Major Step ◽  
Weathering Rates ◽  
Catchment Runoff

Abstract. Soil mineral weathering is one of the major sources of base cations (BC), which play a dual role for a forest ecosystem; they function both as plant nutrients, and for buffering against acidification of catchment runoff. On a long-term basis, the soil weathering rates will determine the highest sustainable forest productivity without causing acidification. It is believed that the hydrologic residence time plays a key role in determining weathering rates on a landscape scale. The weathering model PROFILE has been used for almost 30 years to calculate weathering rates in the rooting zone of forest soils. However, the mineral dissolution equations in PROFILE are not adapted for the unsaturated zone, and employing these equations on a catchment scale results in a significant over-prediction of base cation release rates to surface waters. In this study we use a revised set of PROFILE equations which, among other features, include retardation from silica concentrations. Relationships between the water transit time (WTT) and soil water concentrations were derived for each base cation, by simulating the soil water chemistry along a one-dimensional flowpath, using the mineralogy from a glacial till soil. We show how the revised PROFILE equations are able to reproduce patterns in BC- and Si-concentrations, as well as BC-ratios (Ca2+ / BC, Mg2++ / BC and Na+ / BC), observed in soil water profiles and catchment runoff. As opposed to the original set of PROFILE equations, the revised set of equations could reproduce how increasing WTT led to decreasing Na+ / BC, as well as increasing Ca2+ / BC and Mg2+ / BC. Furthermore, the total release of base cations from a hillslope was calculated using a mixing model, where water of different WTT was mixed according to an externally modelled WTT-distribution. The revised set of equations gave a 50 % lower base cation release (0.23 eq m−2 yr−1) than the original PROFILE equations, and are in better agreement with mass balance calculations of weathering rates. The results from this study thus demonstrate that the revised mineral dissolution equations for PROFILE are a major step forward in modelling weathering rates on a catchment scale.

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.

scholarly journals Catchment export of base cations: improved mineral dissolution kinetics influence the role of water transit time

SOIL ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 231-244 ◽  
Author(s):  
Martin Erlandsson Lampa ◽  
Harald U. Sverdrup ◽  
Kevin H. Bishop ◽  
Salim Belyazid ◽  
Ali Ameli ◽  
...  
Keyword(s):  
Soil Water ◽  
Transit Time ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Mineral Dissolution ◽  
Catchment Scale ◽  
Major Step ◽  
Weathering Rates ◽  
Catchment Runoff

Abstract. Soil mineral weathering is one of the major sources of base cations (BC), which play a dual role in forest ecosystems: they function as plant nutrients and buffer against the acidification of catchment runoff. On a long-term basis, soil weathering rates determine the highest sustainable forest productivity that does not cause acidification. It is believed that the hydrologic residence time plays a key role in determining the weathering rates at the landscape scale. The PROFILE weathering model has been used for almost 30 years to calculate weathering rates in the rooting zone of forest soils. However, the mineral dissolution equations in PROFILE are not adapted for the saturated zone, and employing these equations at the catchment scale results in a significant overprediction of base cation release rates to surface waters. In this study, we use a revised set of PROFILE equations which, among other features, include retardation due to silica concentrations. Relationships between the water transit time (WTT) and soil water concentrations were derived for each base cation, by simulating the soil water chemistry along a one-dimensional flow path, using the mineralogy from a glacial till soil. We show how the revised PROFILE equations are able to reproduce patterns in BC and silica concentrations as well as BC ratios (Ca2+/BC, Mg2+/BC and Na+/BC) that are observed in the soil water profiles and catchment runoff. In contrast to the original set of PROFILE equations, the revised set of equations could reproduce the fact that increasing WTT led to a decreasing Na+/BC ratio and increasing Ca2+/BC and Mg2+/BC ratios. Furthermore, the total release of base cations from a hillslope was calculated using a mixing model, where water with different WTTs was mixed according to an externally modeled WTT distribution. The revised set of equations gave a 50 % lower base cation release (0.23 eq m−2 yr−1) than the original PROFILE equations and are in better agreement with mass balance calculations of weathering rates. Thus, the results from this study demonstrate that the revised mineral dissolution equations for PROFILE are a major step forward in modeling weathering rates at the catchment scale.

Acid rain and soils of the Adirondacks. III. Rates of soil acidification in a montane spruce–fir forest at Whiteface Mountain, New York

1994 ◽  
Vol 24 (4) ◽  
pp. 663-669 ◽  
Author(s):  
A.H. Johnson ◽  
A.J. Friedland ◽  
E.K. Miller ◽  
T.G. Siccama
Keyword(s):  
New York ◽  
Soil Acidification ◽  
Forest Floor ◽  
Base Cations ◽  
Base Cation ◽  
Mineral Weathering ◽  
Published Data ◽  
Whiteface Mountain ◽  
The Impact ◽  
Loss Rates

To assess the impact of atmospheric deposition on soil acidification and base cation supplies in montane spruce–fir forest soils at Whiteface Mountain, New York, base cation and proton fluxes were determined for organic and mineral horizons from measurements made at four stands (1020–1090 m above sea level) over a 4-year period. Our best estimates indicate an annual accumulation of H+ and a net loss of base cations from the forest floor of about 0.71 kmolc/ha, a 2.8% per year loss of the total forest floor base cation pool. This high rate of acidification is attributable to base cation leaching by sulfate and organic anions, and uptake by living biomass. From 1986 to 1990, the annual net loss rate of forest floor Ca, the most abundant base cation, was several times greater than historical loss rates as determined by 50-year comparisons of forest floor Ca in nearly identical forests of the Adirondack High Peaks region. Published data on long-term trends in Ca deposition in the U.S. Northeast suggest that the difference between historical and current net loss rates of forest floor Ca may be due to sharply reduced atmospheric inputs of Ca after about 1970, exacerbated by sulfate leaching. In mineral horizons where the total base cation pool (mostly mineral bound) is very large, the net losses of base cations were substantially lower and in the range where losses due to leaching and uptake can be countered by mineral weathering.

Sign in / Sign up

Export Citation Format

Share Document