Weathering & Soils

Landscape-Scale Controls on C, N, and exchangeable Ca++, Mg++ and K+ in Soils of the Luquillo CZO Forest

Project Description: 

We sampled soils from 216 profiles representing 24 sites in the El Yunque National Forest to determine amounts C, N and neutral-salt-extractable Ca++, Mg++ and K+. Following the classic paradigm, we assessed the influence of climate (modeled precipitation, modeled temperature and/or elevation as a surrogate variable for both), forest type (tabonuco, colorado, palm), parent material (quartz diorite, volcaniclastics), and topography (catena positions ridge, slope, valley and % slope) on the distribution of these nutrients.

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Quantification of soil production in the Bisley catchment using U-series isotopes.

Project Description: 

The ability to quantify how fast weathering profiles develop is crucial to assessing soil resource depletion and quantifying how landscapes evolve over millennia. Uranium-series isotopes can be used to determine the age of the weathering front throughout a profile and to infer estimates of regolith production rates, because the abundance of U-series isotopes in a weathering profile is a function of chemical weathering and time. This technique is applied to a weathering profile in Puerto Rico developed over a volcaniclastic bedrock.

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Microbial community analysis of Bisley watershed in Puerto Rico

Project Description: 

Biological processes are known to play significant roles in soil formation and surficial weathering. However, the contributions of biological activity to regolith and rock weathering below the root zone are less well understood, especially in humid tropic forests that have shallow root systems and rapid nutrient cycling in surficial layers. In Puerto Rico, thick, highly leached saprolites blanket the landscape, reaching well over 16 m deep on some ridges, often decoupling deep biogeochemical cycles from surface cycles.

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Tracing Biogeochemical Cycles in the Weathering Environment using Mg and Li isotopes.

Project Description: 

Ca and Mg are released from silicate minerals during chemical weathering, react with atmospheric CO2, and are deposited as carbonate in the oceans, regulating global climate on geological time scales. Thus to estimate and predict CO2 consumption rates, it is important to identify and quantify the sources and fluxes of Ca and Mg that are discharged to the world’s oceans via rivers, and the weathering processes that produce those fluxes.

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Weathering Processes on Landslides

Project Description: 

A landslide chronosequence will be instrumented (nested suction lysimeters for collecting soil/saprolite pore waters, rain collectors, runoff collectors) and analyzed (via a suite of geochemical analyses of both solid and aqueous samples) to study the effects of landslides on chemical weathering processes and rates, the spatial and temporal variability of chemical weathering profiles in the LCZO, and to explore hypotheses regarding the establishment and maintenance of steady-state regolith profiles.

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Lithological Influences on Weathering Processes and Rates in the Luquillo Mountains of Puerto Rico

Project Description: 

Rapid weathering and erosion rates in mountainous tropical watersheds lead to highly variable soil and saprolite thicknesses which in turn impact, nutrient fluxes, and biological populations. To understand mineral nutrient cycling in such environments requires tracing nutrients through the entire critical zone: weathering bedrock, saprolite, soil, soil water, precipitation, vegetation, and microorganisms. A thorough understanding of nutrient cycling in tropical uplands is necessary in order to predict the effects of human impacts.

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Parent Material and Topography Determine Soil Phosphorus Status in the Luquillo Mountains of Puerto Rico

Project Description: 

We collected soils from both Icacos and Bisley, in different topographic positions, and analyzed them for phosphorus content.

Abstract from the paper listed below Mage & Porder 2013.

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Core Area(s) and/or Keywords: 

Soil, phosphorus, topography, rock type, granodiorite, volcaniclastic, nutrients, parent material

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Stabilization of soil organic matter in contrasting parent materials

Project Description: 

Critical zone processes contributing to soil development over the contrasting bedrock parent materials in the Luquillo Mountains has resulted in significant differences important to organic C quantity and soil organic matter (SOM) quality. Similar vegetation cover at sites on contrasting slope positions or underlying lithology will likely generate similar surface litter. Once this litter enters the soil, however, we ask: 1) will the resultant SOM be chemically distinct or is it simply protected differently?

Core Area(s) and/or Keywords: 

soil, litter, soil organic matter, organic carbon, carbon, parent material

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