Bedrock fracture systems facilitate weathering, allowing fresh mineral surfaces to interact with corrosive waters and biota from Earth's surface, while simultaneously promoting drainage of chemically ...equilibrated fluids. We show that topographic perturbations to regional stress fields explain bedrock fracture distributions, as revealed by seismic velocity and electrical resistivity surveys from three landscapes. The base of the fracture-rich zone mirrors surface topography where the ratio of horizontal compressive tectonic stresses to near-surface gravitational stresses is relatively large, and it parallels the surface topography where the ratio is relatively small. Three-dimensional stress calculations predict these results, suggesting that tectonic stresses interact with topography to influence bedrock disaggregation, groundwater flow, chemical weathering, and the depth of the "critical zone" in which many biogeochemical processes occur.
Investigations to understand linkages among climate, erosion and weathering are central to quantifying landscape evolution. We approach these linkages through synthesis of regolith data for granitic ...terrain compiled with respect to climate, geochemistry, and denudation rates for low sloping upland profiles. Focusing on Na as a proxy for plagioclase weathering, we quantified regolith Na depletion, Na mass loss, and the relative partitioning of denudation to physical and chemical contributions. The depth and magnitude of regolith Na depletion increased continuously with increasing water availability, except for locations with mean annual temperature <
5
°C that exhibited little Na depletion, and locations with physical erosion rates <
20
g
m
−
2
yr
−
1
that exhibited deep and complete regolith Na depletion. Surface Na depletion also tended to decrease with increasing physical erosion. Depth-integrated Na mass loss and regolith depth were both three orders of magnitude greater in the fully depleted, low erosion rate sites relative to other locations. These locations exhibited strong erosion-limitation of Na chemical weathering rates based on correlation of Na chemical weathering rate to total Na denudation. Sodium weathering rates in cool locations with positive annual water balance were strongly correlated to total Na denudation and precipitation, and exhibited an average apparent activation energy (
Ea) of 69
kJ
mol
−
1
Na. The remaining water-limited locations exhibited kinetic limitation of Na weathering rates with an
Ea of 136
kJ
mol
−
1
Na, roughly equivalent to the sum of laboratory measures of
Ea and dissolution reaction enthalpy for albite. Water availability is suggested as the dominant factor limiting rate kinetics in the water-limited systems. Together, these data demonstrate marked transitions and nonlinearity in how climate and tectonics correlate to plagioclase chemical weathering and Na mass loss.
► The depth and magnitude of regolith Na depletion increased with water availability. ► Cold and low erosion rate location Na depletion unrelated to water availability. ► Grade from kinetic to erosion limited weathering with increased water availability. ► Variable sodium activation energy for erosion- and kinetic-limited locations.
Ecology Letters (2010) 13: 284-291 Atmospheric CO₂ enrichment generally stimulates plant photosynthesis and nutrient uptake, modifying the local and global cycling of bioactive elements. Although ...nutrient cations affect the long-term productivity and carbon balance of terrestrial ecosystems, little is known about the effect of CO₂ enrichment on cation availability in soil. In this study, we present evidence for a novel mechanism of CO₂-enhancement of cation release from soil in rice agricultural systems. Elevated CO₂ increased organic C allocation belowground and net H⁺ excretion from roots, and stimulated root and microbial respiration, reducing soil redox potential and increasing Fe²⁺ and Mn²⁺ in soil solutions. Increased H⁺, Fe²⁺, and Mn²⁺ promoted Ca²⁺ and Mg²⁺ release from soil cation exchange sites. These results indicate that over the short term, elevated CO₂ may stimulate cation release from soil and enhance plant growth. Over the long-term, however, CO₂-induced cation release may facilitate cation losses and soil acidification, negatively feeding back to the productivity of terrestrial ecosystems.
Early growth performance of four native and two introduced tree species was studied during six years at 13 sites in the southern region of Costa Rica. Selected study sites represent a wide ...environmental gradient.The selected species were:
Pinus caribaea Morelet var
hondurensis (Barret y Golfari)
and Gmelina arborea Roxb as the introduced species, and
Terminalia amazonia (J.F. Gmelin) Exell,
Vochysia ferruginea Mart.,
Vochysia guatemalensis Donn. Sm. and
Hieronyma alchorneoides Fr. Allemao. A study about the distribution of aboveground biomass, nutrients and total carbon content of these young plantations by compartments (branches, stem, bark and leaves) was also conducted. Biomass equations for tree compartments were fitted simultaneously using the data corresponding to 24 trees felled. Total export quantities of nutrient from stem and bark biomass were estimated in order to conduct an evaluation of the potential effect of harvesting these species on soil nutrient reserves. The data presented in this study related to plantation growth, aboveground biomass and nutrient concentration and C content by tree compartment, aboveground biomass equations by tree compartment, soil nutrient reserves, stability indices can be used as a reference for: a) selection of tree species
vs site characteristics, b) estimation of nutrient export by stem + bark harvesting, c) planning for a second rotation, c) maintenance of site productivity and d) generate better carbon sequestration estimations.
Although soil erosion has often been considered a net source of atmospheric carbon (C), several recent studies suggest that erosion serves as a net C sink. We have developed a spreadsheet‐based model ...of soil organic C dynamics within an eroding profile (Soil Organic Carbon, Erosion, Replacement, and Oxidation (SOrCERO)) that calculates effects of soil organic carbon (SOC) erosion and altered SOC oxidation and production on the net exchange of C between the eroding profile and atmosphere. SOrCERO suggests that erosion can induce a net C sink or source, depending on management practices, the extent to which SOC oxidation and production characteristics change with erosion, and the fate of eroded SOC. Varying these parameters generated a wide range of C source and sink estimates (maximum net source and sink of 1.1/3.1 Pg C yr−1 respectively, applying results globally), highlighting research needs to constrain model estimates. We invite others to download SOrCERO (http://www.kbs.ku.edu/people/staff_www/billings/index.html) to test conceptual models and eroding soil profiles of interest in a consistent, comparable fashion.
In the ancient and acidic Ultisol soils of the Southern Piedmont, USA, we studied changes in trace element biogeochemistry over four decades, a period during which formerly cultivated cotton fields ...were planted with pine seedlings that grew into mature forest stands. In 16 permanent plots, we estimated 40-year accumulations of trace elements in forest biomass and O horizons (between 1957 and 1997), and changes in bioavailable soil fractions indexed by extractions of 0.05 mol/L HCl and 0.2 mol/L acid ammonium oxalate (AAO). Element accumulations in 40-year tree biomass plus O horizons totaled 0.9, 2.9, 4.8, 49.6, and 501.3 kg/ha for Cu, B, Zn, Mn, and Fe, respectively. In response to this forest development, samples of the upper 0.6-m of mineral soil archived in 1962 and 1997 followed one of three patterns. (1) Extractable B and Mn were significantly depleted, by -4.1 and -57.7 kg/ha with AAO, depletions comparable to accumulations in biomass plus O horizons, 2.9 and 49.6 kg/ha, respectively. Tree uptake of B and Mn from mineral soil greatly outpaced resupplies from atmospheric deposition, mineral weathering, and deep-root uptake. (2) Extractable Zn and Cu changed little during forest growth, indicating that nutrient resupplies kept pace with accumulations by the aggrading forest. (3) Oxalate-extractable Fe increased substantially during forest growth, by 275.8 kg/ha, about 10-fold more than accumulations in tree biomass (28.7 kg/ha). The large increases in AAO-extractable Fe in surficial 0.35-m mineral soils were accompanied by substantial accretions of Fe in the forest's O horizon, by 473 kg/ha, amounts that dwarfed inputs via litterfall and canopy throughfall, indicating that forest Fe cycling is qualitatively different from that of other macro- and micronutrients. Bioturbation of surficial forest soil layers cannot account for these fractions and transformations of Fe, and we hypothesize that the secondary forest's large inputs of organic additions over four decades has fundamentally altered soil Fe oxides, potentially altering the bioavailability and retention of macro- and micronutrients, contaminants, and organic matter itself. The wide range of responses among the ecosystem's trace elements illustrates the great dynamics of the soil system over time scales of decades.
•LiDAR scanning enables identification of previously undetectable erosional features.•Smoothing-via-Filling-Rough-Depressions (SvFRD) effectively quantifies gully volumes.•SvFRD estimates a pre-gully ...terrain surface based on local & landscape microtopography.•SvFRD was developed entirely using free software facilitating further development.
Gully mapping techniques successfully identify gullies over a large range of breadths and depths in complex landscapes but practices for estimating gully volumes need further development. Gully gap-interpolation for estimation of gully volume does not often factor in landscape microtopography in the generation of the new surface. These approaches can thus overestimate large classical gully volumes, averaging over depressions, or underestimate volumes by creating overly-smooth highly curved surfaces. Microtopographic methodology was developed to estimate the pre-gully surface and gully volume across the Calhoun Critical Zone Observatory (CCZO) in South Carolina, USA. The CCZO is a Southern Piedmont landscape severely gullied by historic agriculture with upland Ultisols many meters deep. Our gully-mapping and gully-filling approaches used 1 m2 LiDAR elevation data and is based on the premise that gullies are local depressions on uplands which are deeply incised with high microtopographic roughness. Our smoothing-via-filling-rough-depressions (SvFRD) algorithm iteratively fills gullies until landscape microtopographic roughness is reduced and unchanging after a subsequent iteration. Results were evaluated in the context of prior landscape bulk erosion estimates ranging from 1483 to 3708 m3/ha as well as field surveys of gullies. Minimally eroded reference and highly-eroded post-agricultural terrain were compared to test gully-mapping and volume accuracy. Comparing gully-volume estimation techniques, inverse-distance-weighting (IDW) yielded the highest volume (1072 m3/ha) followed by ANUDEM (638 m3/ha) while spline-interpolation yielded the lowest estimate (555 m3/ha). SvFRD landscape gully volume estimates (615.5 m3/ha) were most similar to ANUDEM interpolation with roughness and gully extent results most similar to spline interpolation. Spline interpolation is effective and easily implemented but if microtopographic accuracy and mapping of fine-scale erosions features is desired to hindcast pre-gully terrain conditions, our depression-filling approach, implemented using free GIS and statistical software, is an effective method to estimate reasonable erosion volumes.
Wetlands are valuable for buffering waterways from excess nitrogen, yet these habitats are often dominated by invasive plant species. There is little understanding as to how various invasive species ...alter ecosystem nitrogen cycling, especially if one invasive overtakes an entire community of plants.
Microstegium vimineum
is a nonnative annual grass from Asia that is dominating riparian wetlands in the southeastern United States. To evaluate
M. vimineum
impacts on the N cycle, we used six paired plots, one invaded by
M. vimineum
and the other carefully weeded of
M. vimineum
; removal allowed the establishment of a diverse plant community consisting of
Polygonum
,
Juncus
, and
Carex
species. In the paired plots, we estimated (1) N uptake and accumulation in vegetation biomass, (2) rates of decomposition and N release from plant detritus, (3) mineral soil N mineralization and nitrification, (4) root zone redox potential, and (5) soil water concentrations of inorganic N. The
M. vimineum
community accumulated approximately half the annual N biomass of the diverse community, 5.04 vs. 9.36 g N·m
−2
·yr
−1
, respectively (
P
= 0.05). Decomposition and release of N from
M. vimineum
detritus was much less than in the diverse community, 1.19 vs. 5.24 g N·m
−2
·yr
−1
. Significantly higher inorganic soil N persisted beneath
M. vimineum
during the dormant season, although rates of soil N mineralization estimated by in situ incubations were relatively similar in all plots.
Microstegium vimineum
invasion thus appears to greatly diminish within-ecosystem circulation of N through the understory plants of these wetlands, whereas invasion effects on ecosystem N losses may derive more from enhanced denitrification (due to lower redox potential under
M. vimineum
plots) than due to leaching.
Microstegium vimineum
's dominance and yet slower internal cycling of N are counterintuitive to conventional thinking that ecosystems with high N contain vegetation that quickly uptake and release N.
Field-scale observations of two upland soils derived from contrasting granite and basalt bedrocks are presented to hypothesize that redox activity of rhizospheres exerts substantial effects on ...mineral dissolution and colloidal translocation in many upland soils. Rhizospheres are redox-active microsites and in the absence of O₂, oxidation of rhizodeposits can be coupled by reduction of redox-active species such as Fe, a biogenic reduction that leads to Fe translocation and oxidation, accompanied by substantial proton flux. Not only do rhizogenic Fe-C redox cycles demonstrate a process by which the rhizosphere affects an environment well outside the near-root zone, but these redox processes are also hypothesized to be potent weathering systems, such that rhizogenic redox-reactions complement acid- and ligand-promoted reactions as major biogeochemical processes that control crustal weathering. The potential significance of Fe-C redox cycling is underscored by the deep and extensive rooting and mottling of upland subsoils across a wide range of plant communities, lithologies, and soil-moisture and temperature regimes.
Soil in the Anthropocene Richter, Daniel deB; Bacon, Allan R; Brecheisen, Zachary ...
IOP conference series. Earth and environmental science,
01/2015, Letnik:
25, Številka:
1
Journal Article
Recenzirano
Odprti dostop
With scholars deliberating a new name for our geologic epoch, i.e., the Anthropocene, soil scientists whether biologists, chemists, or physicists are documenting significant changes accruing in a ...majority of Earth's soils. Such global soil changes interact with the atmosphere, biosphere, hydrosphere, and lithosphere (i.e., Earth's Critical Zone), and these developments are significantly impacting the Earth's stratigraphic record as well. In effect, soil scientists study such global soil changes in a science of anthropedology, which leads directly to the need to transform pedostratigraphyinto an anthro-pedostratigraphy, a science that explores how global soil change alters Earth's litho-, bio-, and chemostratigraphy. These developments reinforce perspectives that the planet is indeed crossing into the Anthropocene.
PDF
