Geology topics

Marjorie S. Schulz

Publications and source records attributed to Marjorie S. Schulz.

23 records · Page 2Linked to original sources

USGS2011

Seasonal dynamics of CO2 profiles across a soil chronosequence, Santa Cruz, California

Concentrations of CO 2 in soil atmosphere and CO 2 efflux were measured across a marine terrace soil chronosequence near Santa Cruz, California. Soil development, specifically the formation of an argillic horizon, has created a two-tier soil gas profile in the older terrace soils. The soil above the argillic horizon has seasonal variations in soil CO 2 associated with plant respiration. The older soils with dense argillic horizons maintain a year round ∼1%CO 2 below the argillic horizon. The CO 2 efflux during the growing season is higher on the older terraces.

California↗

USGS2010

Shifting microbial community structure across a marine terrace grassland chronosequence, Santa Cruz, California

Changes in the biomass and structure of soil microbial communities have the potential to impact ecosystems via interactions with plants and weathering minerals. Previous studies of forested long-term (1000s – 100,000s of years) chronosequences suggest that surface microbial communities change with soil age. However, significant gaps remain in our understanding of long-term soil microbial community dynamics, especially for non-forested ecosystems and in subsurface soil horizons. We investigated soil chemistry, aboveground plant productivity, and soil microbial communities across a grassland chronosequence (65,000–226,000 yrs old) located near Santa Cruz, CA. Aboveground net primary productivity (ANPP) initially increased to a maximum and then decreased for the older soils. We used polar lipid fatty acids (PLFA) to investigate microbial communities including both surface (<0.1 m) and subsurface (≥0.2 m) soil horizons. PLFAs characteristic of Gram-positive bacteria and actinobacteria increased as a fraction of the microbial community with depth while the fungal fraction decreased relative to the surface. Differences among microbial communities from each chronosequence soil were found primarily in the subsurface where older subsurface soils had smaller microbial community biomass, a higher proportion of fungi, and a different community structure than the younger subsurface soil. Subsurface microbial community shifts in biomass and community structure correlated with, and were likely driven by, decreasing soil P availability and Ca concentrations, respectively. Trends in soil chemistry as a function of soil age led to the separation of the biological (≤1 m depth) and geochemical (>1 m) cycles in the old, slowly eroding landscape we investigated, indicating that this separation, commonly observed in tropical and subtropical ecosystems, can also occur in temperate climates. This study is the first to investigate subsurface microbial communities in a long-term chronosequence. Our results highlight connections between soil chemistry and both the aboveground and belowground parts of an ecosystem.

California↗

USGS2010

Seamounts and ferromanganese crusts within and near the U.S. EEZ off California - Data for RV Farnella cruise F7-87-SC

The purpose of this report is to present and briefly describe ship-board and laboratory data for a U.S. Geological Survey (USGS) research cruise aboard the RV Farnella that took place December 3-21, 1987 (cruise F7-87-SC). The purpose of the cruise was to survey seamounts and ferromanganese crusts within and near the U.S. Exclusive Economic Zone (EEZ) off California. Eight seamounts were studied - Rodriguez, San Marcos, Adam, Hoss, Little Joe, Ben, Flint, and Jasper. A geophysical survey of Jasper Seamount took place, but that seamount was not sampled; whereas Adam and Hoss Seamounts were sampled, but not surveyed with geophysics lines.

California↗

USGS2007

Chemical weathering of a marine terrace chronosequence, Santa Cruz, California: Deciphering reaction rates from mineral depth profiles

A soil chronosequence developed on marine terraces along coastal California, exhibits deeper and more intensively weathered mineral profiles with increasing age (65 to 226 kyrs). Feldspar concentrations generally increase linearly with terrace depth. The slope or weathering gradient is defined by the ratio of the weathering rate and the velocity at which the profile penetrates into the regolith.A spread sheet calculator further refines profile geometries, demonstrating that the non-linear regions at low residual feldspar concentrations are dominated by exponential changes in mineral surface to volume and at high residual feldspar concentrations by the approach to thermodynamic saturation.These parameters, in addition to the kinetic rate constant, are of secondary importance to the fluid flux qh which controls the weathering velocity and solute fluxes from the profile. © 2007 Taylor & Francis Group, London.

California↗

USGS2001

Chemical weathering of the Panola Granite: Solute and regolith elemental fluxes and the weathering rate of biotite

Present-day elemental and mineral weathering rates based on solute fluxes are compared quantitatively to past long-term rates determined from solid-state elemental fractionation in a saprolitic granite regolith at Panola, Georgia, USA. Saturated fluid flow across a low-permeability kaolin duripan controls the rate of steady-state unsaturated flow in the underlying saprolite. Water and Cl mass balances and experimental conductivities produce a minimum fluid flux density of 8x10 -2 m yr -1 and a fluid residence time of 12 years. Solute Si flux, based on pore water concentrations and infiltration rates, is 27 mmoles yr -1 , compared to a long-term flux rate of 17 mmoles yr -1 , based on regolith Si loss and reported 36 Cl dating of the regolith surface. Similarities in short- and long-term fluxes imply that parameters influencing silicate weathering, including precipitation, temperature, and vegetative cover, while not necessarily constant, have not significantly impacted Si leaching rates during the last several hundred thousand years. Linear decreases in solid-state Mg with decreasing regolith depth permit the calculation of the long-term biotite weathering rate under isovolumetric steady-state weathering conditions. A rate constant of 3x10 -17 moles m -2 s -1 is up to 5 orders of magnitude slower than that reported for experimental dissolution of biotite, implying very different reaction kinetics during natural weathering. Short-term biotite weathering fails to produce expected increases in solute Mg and K concentrations with increasing depth and fluid residence times in the regolith. This discrepancy indicates that ion exchange disequilibrium and open-system biologic uptake in an aggrading forest ecosystem are of sufficient magnitudes to overwhelm solute fluxes resulting from biotite weathering.

Georgia↗