WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2004AR74B
Title: Hydrodynamics of a Karst Soil Catena in the Ozark Plateau, USA
Project Type: Research
Focus Categories: Groundwater, Solute Transport, Agriculture
Keywords: Karst hydropedology; hydraulic conductivity; infiltration; nitrate; denitrification; dissolved organic carbon; nutrient processing; poultry litter; silvopastoral agroecosystem; stable isotopes; biogeochemistry
Start Date: 03/01/2004
End Date: 02/28/2005
Federal Funds: $19,500
Non-Federal Matching Funds: $39,000
Congressional District: Third
University of Arkansas
Stephen K. Boss
The rapid expansion of the poultry industry in the Ozark Highlands (and the surfeit of poultry litter available for land application) has enhanced forage production on pasture lands, and led to increased stocking rates of grazing livestock. This regional pattern of intensification of agricultural land use has spawned increasing concern regarding nutrient loads dispensed via runoff to surface water bodies as well as by infiltration and drainage through thin soil veneers to shallow aquifers. Better understanding of the spatial and temporal variations of soil hydraulic and chemical properties, as sampled throughout the vadose zone in a soil catena, is crucial to the development and implementation of management practices that optimize plant water and nutrient use in tandem with minimizing nonpoint source impacts from agricultural landscapes.
The dynamics of nutrient infiltration and subsurface transport and transformation in karst terrains characterized by high soil heterogeneity, multi-level permeability contrasts within the vadose zone (e.g., plowpans, fragipans, and relict chert layers), rapidly fluctuating unconfined aquifers, and preferential flow paths is very poorly known. Despite these gaps in our knowledge of basic soil-water relations and biogeochemical processing, land application of animal manures, in the Ozark Plateau, has intensified over the past five decades. The objectives of the proposed research are fivefold: (1) determine saturated and unsaturated hydraulic conductivities at the soil surface for the three soil series (Nixa, Captina, and Johnsburg) that dominate an experimental silvopastoral field on the University of Arkansas Farm and represent a common soil catena across much of the northern Ozarks; (2) characterize saturated hydraulic conductivity distributions for representative subsoil horizons; (3) track fluctuations in the unconfined aquifer, throughout the year, and produce a probability map for the water table surface; (4) evaluate nutrient (NO3-N) sources, transformations and transport, within a karst catena, using stable isotopes; (5) examine current management practices (i.e., the timing and rate of poultry litter and commercial fertilizer applied per hectare) in light of the hydrodynamic patterns that develop in this field throughout the year (and suggest modifications that should be implemented to enhance fertilizer use efficiency and decrease impacts to stream and ground water quality.
Project objectives will be accomplished using seasonal synoptic sampling events combined with storm-event sampling that will serve to characterize hydrologic shifts and alterations in the biogeochemical processes operating at the soil-karst interface in this small watershed. The approach will capture aspects of the transition from high-flow to base-flow conditions. The concentration and isotopic composition of NO3-N from shallow ground water samples will be explored in tandem with the results of soil tests (i.e., pH, PSA, bulk density, EC, C, N, NO3-N, NH4-N, C:N, CEC and AEC) in order to assess the subsoil denitrification and/or immobilization potentials of the soil series that comprise this catena. In addition, seasonal changes in the infiltrability of Nixa, Captina, and Johnsburg surface soils as well as saturated hydraulic conductivities of representative subsoils proximate to the karst interface will be evaluated. Results of this field-to-small-watershed scale investigation will provide much-needed data on key soil physical properties and processes useful in the development of nutrient management strategies that adequately reflect the “N-loading capabilities” as well as seasonal vulnerabilities of a common toposequence broadly representative of conditions across the Ozark Plateau.