Biogeochemical processes and mechanisms

Sverdrup, Harald; Hagen-Thorn, Anna; Holmqvist, Johan; Wallman, P.H.; Wärfvinge, Per; Walse, Charlotta; Alveteg, Mattias

doi:10.1007/978-94-015-9888-0_7

Cited by 21 publications

(12 citation statements)

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“…Their suggestion could not be fully evaluated due to the lack of suitable constraints on both aqueous Al activities and clay mineral abundances at that particular site. The results from this study, which are constrained by the mineral abundances, the aqueous chemistry and thermodynamic saturation states, suggest that the majority of dissolution at Santa Cruz occurs close to equilibrium and as a result the inferred kinetic rate constants and the overall profile mass depletion are highly dependent on the particular form of the rate law, a finding similar to that of Sverdrup et al (2002).…”

Section: 4supporting

confidence: 57%

The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

Maher

Steefel

White

et al. 2009

Geochimica et Cosmochimica Acta

287

269

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ABSTRACT:In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka marine terrace chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized (White et al., 2008, GCA) and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [2006] or the aluminum inhibition model proposed by Oelkers et al. [1994], modeling results are consistent with fieldscale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site.Observed maximum clay abundances in the argillic horizons occur at the depth and time where the reaction fronts of the primary minerals overlap. The modeling indicates that the argillic horizon at Santa Cruz can be explained almost entirely by weathering of primary minerals and in situ clay precipitation accompanied by undersaturation of kaolinite at the top of the profile. The rate constant for kaolinite precipitation was also determined based on model simulations of mineral abundances and dissolved Al, SiO 2 (aq) and pH in pore waters. Changes in the rate of kaolinite precipitation or the flow rate do not affect the gradient of the primary mineral weathering profiles, but instead control the rate of propagation of the primary mineral weathering fronts and thus total mass removed from the weathering profile. Our analysis suggests that secondary clay precipitation is as important as aqueous transport in governing the amount of dissolution that occurs within a profile because clay minerals exert a strong control over the reaction affinity of the dissolving primary minerals. The modeling also indicates that the weathering advance rate and the total mass of mineral dissolved is controlled by the thermodynamic saturation of the primary dissolving phases plagioclase and K-feldspar, as is evident from the difference in propagation rates of the reaction fronts for the two minerals despite their very similar kinetic rate laws.

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Section: 4supporting

confidence: 57%

The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

Maher

Steefel

White

et al. 2009

Geochimica et Cosmochimica Acta

287

269

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“…The results obtained can be compared to those for modelled N‐accumulation in Sweden presented by Sverdrup et al . (2002) in which N‐accumulation varied between 8 and 16 kg ha −1 year −1 in southern Sweden and 0–5 kg ha −1 year −1 in northern Sweden.…”

Section: Discussionmentioning

confidence: 81%

Regionalized nitrogen budgets in forest soils for different deposition and forestry scenarios in Sweden

Akselsson¹,

Westling²

2004

Global Ecology and Biogeography

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Aim The aim of this work was to estimate on a regional scale the effects of nitrogen (N) deposition and harvest intensity on N-budgets in forest soils as a basis for strategies of emission reduction and sustainable forest management methods.Location The calculations were applied to Sweden, a country with a managed forest area of 23 × 10 6 ha.Methods Mass balance calculations, including N-deposition, N-fixation, N-loss through harvest, and N-leaching, were performed on a GIS platform using 5 × 5 km grids. Modelled deposition data together with spatial data obtained from the National Forest Inventory served as the basis for the calculations. Four different scenarios were run: a 'base scenario' involving present deposition and conventional forestry (stem harvest only); a 'whole-tree harvesting scenario' with present deposition and the harvesting of stems, branches and needles; a 'decreased deposition scenario'; and a 'whole-tree harvesting and decreased deposition scenario' .

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“…4). The two latter observations contradict the ideas of slow recovery of soil pH (Beier et al , 1998) and that weathering of temperate forest soils is a very slow process (Sverdrup et al , 2002). Our data also suggest that pH is determined by other factors in addition to the base saturation of the exchange complex.…”

Section: Discussionmentioning

confidence: 89%

Tree growth and soil acidification in response to 30 years of experimental nitrogen loading on boreal forest

Högberg¹,

Fan

Quist³

et al. 2006

Global Change Biology

414

300

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Relations among nitrogen load, soil acidification and forest growth have been evaluated based on short-term (o15 years) experiments, or on surveys across gradients of N deposition that may also include variations in edaphic conditions and other pollutants, which confound the interpretation of effects of N per se. We report effects on trees and soils in a uniquely long-term (30 years) experiment with annual N loading on an unpolluted boreal forest. Ammonium nitrate was added to replicated (N 5 3) 0.09 ha plots at two doses, N1 and N2, 34 and 68 kg N ha À1 yr À1 , respectively. A third treatment, N3, 108 kg N ha À1 yr À1 , was terminated after 20 years, allowing assessment of recovery during 10 years. Tree growth initially responded positively to all N treatments, but the longer term response was highly rate dependent with no gain in N3, a gain of 50 m 3 ha À1 stemwood in N2 and a gain of 100 m 3 ha À1 stemwood in excess of the control (N0) in N1. High N treatments caused losses of up to 70% of exchangeable base cations (Ca 2 1 , Mg 2 1 , K 1 ) in the mineral soil, along with decreases in pH and increases in exchangeable Al 3 1 . In contrast, the organic mor-layer (forest floor) in the N-treated plots had similar amounts per hectare of exchangeable base cations as in the N0 treatment. Magnesium was even higher in the mor of N-treated plots, providing evidence of up-lift by the trees from the mineral soil. Tree growth did not correlate with the soil Ca/Al ratio (a suggested predictor of effects of soil acidity on tree growth). A boron deficiency occurred on N-treated plots, but was corrected at an early stage. Extractable NH 4 1 and NO 3 À were high in mor and mineral soils of on-going N treatments, while NH 4 1 was elevated in the mor only in N3 plots. Ten years after termination of N addition in the N3 treatment, the pH had increased significantly in the mineral soil; there were also tendencies of higher soil base status and concentrations of base cations in the foliage. Our data suggest the recovery of soil chemical properties, notably pH, may be quicker after removal of the N-load than predicted. Our long-term experiment demonstrated the fundamental importance of the rate of N application relative to the total amount of N applied, in particular with regard to tree growth and C sequestration. Hence, experiments adding high doses of N over short periods do not mimic the long-term effects of N deposition at lower rates.

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Biogeochemical processes and mechanisms

Cited by 21 publications

References 0 publications

The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

Regionalized nitrogen budgets in forest soils for different deposition and forestry scenarios in Sweden

Tree growth and soil acidification in response to 30 years of experimental nitrogen loading on boreal forest

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