Clyde L. Munster

The use of vegetation to remediate soil freshly contaminated by recalcitrant contaminants

The use of vegetation to remediate soil contaminated by recalcitrant hydrocarbons was tested under field conditions. Specifically, an evaluation was made of the effectiveness of deep rooting grasses, Johnsongrass and Canadian wild rye in the dissipation of TNT and PBBs in the soils freshly contaminated to an initial concentration of 10.17+/-1.35 for TNT and 9.87+/-1.23 mg/kg for PBB. The experiment used 72 (1.5m long and 0.1m diameter) column lysimeters with four treatments: Johnsongrass; wild rye grass; a rotation of Johnsongrass and wild rye grass; and unplanted fallow conditions. In the laboratory, immunoassay test procedures determined the TNT and PBB concentrations in the soil, leachate, herbage and root samples. The root characteristics such as total root length, rooting density, and root surface area were quantified to a depth of 1.5m. Changes in microbial biomass were assessed for both rhizosphere soil and the bulk soil during the 2-year study. The largest and most rapid loss in soil chemical concentration was for TNT, which decreased to less than 250 microg/kg, the detection limit, by 93 days after germination. The PBB was at or near the detection limit of 500 microg/kg by 185 days after germination. There was no perceptible difference in contaminant concentration in the soil between the vegetation treatments and/or with depth.

Subsurface stormflow is important in semiarid karst shrublands

[1] In this paper we describe hillslope-scale, rainfallsimulation experiments on karst shrublands dominated by Ashe juniper. These simulations, designed to mimic floodproducing rainfall events, were carried out at two sites separated by 206 km within the Edwards Plateau of Central Texas. Five hillslope plots were instrumented—two shrubcovered (canopy) plots and three intercanopy plots measuring 12–14 m in length. We repeated the experiments on the canopy plots after removing the shrubs. For the canopy plots, both before and after shrub removal, 50% or more of the water applied exited the plots as subsurface stormflow and no overland flow occurred. For the intercanopy plots, subsurface stormflow amounted to less than 10% of the water applied and overland flow was between 10 and 50%. These experiments demonstrate the importance of subsurface stormflow in semiarid karst shrublands during flood events, and more generally highlight the fact that subsurface stormflow is important in some semiarid landscapes. Citation: Wilcox, B. P., P. I. Taucer, C. L. Munster, M. K. Owens, B. P. Mohanty, J. R. Sorenson, and R. Bazan (2008), Subsurface stormflow is important in semiarid karst shrublands, Geophys. Res. Lett., 35, L10403, doi:10.1029/2008GL033696.

SIMULATING WATER QUALITY IMPROVEMENTS IN THE UPPER NORTH BOSQUE RIVER WATERSHED DUE TO PHOSPHORUS EXPORT THROUGH TURFGRASS SOD

The Upper North Bosque River (UNBR) watershed is under a total maximum daily load (TMDL) mandate to reduce loading of soluble phosphorus (P) in impaired river segments. To address these problems, Texas A&M University researchers have developed a Best Management Practice (BMP) that removes excess nutrients from impaired watersheds through turfgrass sod. Harvest of manure-grown sod removes a thin layer of topsoil along with any residual P in this soil layer. In order to assess the impact of the turfgrass BMP on a watershed scale, the Soil and Water Assessment Tool (SWAT) was used to predict water quality changes among four scenarios in the UNBR watershed. The SWAT model was modified to incorporate turfgrass harvest routines for simulation of manure and soil P export during harvest of turfgrass sod. SWAT simulations of the four BMP scenarios predicted reductions of 20% to 36% for instream P loads in the UNBR depending on manure P rate and areas allotted to sod. In addition, total N load was reduced on average by 31% and sediment load declined on average 16.7% at the watershed outlet. The SWAT model predicted up to 176 kg/ha P was removed per harvest of sod top-dressed with 100 kg manure P/ha. Export increased to 258 kg/ha of P per harvest for the manure P application rate of 200 kg/ha. Depending on the implementation scenario, simulations indicated the turfgrass BMP could export between 262 and 784 metric tons of P out of the UNBR watershed every year.

Capacity of biochar application to maintain energy crop productivity: soil chemistry, sorghum growth, and runoff water quality effects.

Pyrolysis of crop biomass generates a by-product, biochar, which can be recycled to sustain nutrient and organic C concentrations in biomass production fields. We evaluated effects of biochar rate and application method on soil properties, nutrient balance, biomass production, and water quality. Three replications of eight sorghum [ (L.) Moench] treatments were installed in box lysimeters under greenhouse conditions. Treatments comprised increasing rates (0, 1.5, and 3.0 Mg ha) of topdressed or incorporated biochar supplemented with N fertilizer or N, P, and K fertilizer. Simulated rain was applied at 21 and 34 d after planting, and mass runoff loss of N, P, and K was measured. A mass balance of total N, P, and K was performed after 45 d. Returning 3.0 Mg ha of biochar did not affect sorghum biomass, soil total, or Mehlich-3-extractable nutrients compared to control soil. Yet, biochar contributed to increased concentration of dissolved reactive phosphorus (DRP) and mass loss of total phosphorus (TP) in simulated runoff, especially if topdressed. It was estimated that up to 20% of TP in topdressed biochar was lost in surface runoff after two rain events. Poor recovery of nutrients during pyrolysis and excessive runoff loss of nutrients for topdressed biochar, especially K, resulted in negative nutrient balances. Efforts to conserve nutrients during pyrolysis and incorporation of biochar at rates derived from annual biomass yields will be necessary for biochar use in sustainable energy crop production.

Large-Scale Rainfall Simulation Experiments on Juniper Rangelands

The effects of shrub clearing on surface and subsurface water movement in the Edwards Aquifer region were investigated using two large-scale rainfall simulation plots. Multiple replications of a large (168 mm) rainfall event were applied at an ashe juniper covered plot before and after shrub removal and at a plot with longstanding herbaceous cover. The study sites were equipped for monitoring of throughfall, stemflow, surface runoff, and soil water. Lateral subsurface flow was measured in a trench at the downhill end of each plot. The canopy plot produced high lateral subsurface flow during rainfall but no surface runoff, even for high rainfall intensities. In contrast, hydrologic response at the inter-canopy plot was dominated by rapid surface runoff. Following shrub removal at the canopy plot, water movement beyond the soil layer increased due to reduced canopy interception. Soil water storage capacity at the shrub plot remained small for both conditions, with much water apparently bypassing the litter and soil layers via macropore pathways. This additional water could move off site as macropore flow or remain on site as matrix and conduit storage. Differences in surface runoff and subsurfaceflow are attributable to vegetation and geologic differences.

AN APPROACH FOR SIMULATING RAINFALL ABOVE THE TREE CANOPY AT THE HILLSLOPE SCALE

Rainfall simulation is a valuable experimental approach to study hydrologic and erosion processes. Most of the rainfall simulation studies done on arid or semi-arid rangelands have been at the small-plot scale, and rarely with water applied above the tree canopy. A new methodology for simulating rainfall above tree canopies at the hillslope scale is presented. The rainfall simulator that was developed consisted of modular components that are easily transported and installed at remote sites on rugged, brush-covered hillslopes. The simulator manifolds, which are equipped with four sprinkler heads, are supported by individual, telescoping masts that can be extended up to 11 m. The masts that support the manifolds are mounted on base plates, designed to facilitate installation on steep hillslopes. the sprinkler-head manifolds are easily installed on the masts using a quick-connect mounting bracket. The rainfall simulator is capable of simulating rainfall from 25 to 250 mm/h at a height of 11 m. The rainfall simulator was field tested on a 7 × 14 m plot with the masts set at a height of 5 m. For simulated rainfall rates of 25, 51, 76, 102, 127 and 153 mm/h, coefficients of uniformity ranged from 58% to 73%. Median raindrop diameters ranged from 1.7 to 2.4 mm, and associated kinetic energies varied from 16.8 to 25.9 J/m2-mm. The rainfall simulator has performed well with minimum maintenance and proved to be a cost-effective and efficient research tool for replicating natural, above-canopy rainfall in arid and semiarid environments.

Changes in Ecological Properties of Petroleum Oil-Contaminated Soil After Low-Temperature Thermal Desorption Treatment

Effects of low-temperature thermal desorption (LTTD) treatment on the ecological properties of soil contaminated by petroleum hydrocarbons were assessed. For this purpose, various ecological properties related to soil health and physicochemical properties of the oil-contaminated soil before and after LTTD treatment were investigated. Total petroleum hydrocarbon concentration, electrical conductivity, organic matter, and total nitrogen decreased while water-holding capacity and available P2O5 increased. The soil color was also changed but textural class was not changed after LTTD. The microbial number and dehydrogenase activity increased following LTTD, but there was no significant difference in the β-glucosidase and acid phosphatase activities. Seed germination succeeded after LTTD, but the germination rate was still lower than that in non-contaminated soil as the growth of plants and earthworms was. The results showed that overall soil health related to biological productivity and environmental functions was improved after LTTD and suggested that LTTD could be a better alternative to other harsh remediation methods. However, ecological indicators still show differences to the adjacent non-contaminated level. Therefore, to ensure safe soil reuse, the change in eco-physiochemical properties as well as contaminant removal efficiency during the remediation process should be considered.

Phytoremediation and Modeling of Contaminated Soil using Eastern Gamagrass and Annual Ryegrass

The effectiveness of a warm season grass (eastern gamagrass), a cool season grass (annual ryegrass) and a rotation of warm and cool season grasses in the remediation of soil freshly contaminated with trinitrotoluene (TNT) and polybrominated biphenyls (PBBs) was evaluated. A total of 96 columns were filled with a Weswood silt loam soil that was mixed with TNT and PBB compounds to a target concentration of 10 mg of each contaminant. Chemical losses during this two-year field lysimeter experiment were similar for all experimental treatments and at all depths. Although higher microbial biomass was found in the rhizosphere soil, enumeration of soil microorganisms revealed a robust population in both the bulk and rhizosphere soils and the microbial growth was not dependent on root exudates only. Microbial degradation rates in the freshly contaminated soil were more affected by soil properties and the chemical characteristics of the contaminant than the presence of roots. The field data collected from the lysimeter experiment was used to calibrate a recently developed phytoremediation model. The phytoremediation computer model successfully simulated TNT soil concentrations in the column lysimeters. The model may be a valuable tool for the selection and optimization of phytoremediation methods at contaminated field sites.

Assessing the hydrologic and water quality impacts of biofuel-induced changes in land use and management

The Southern High Plains (SHP) of Texas, where cotton (Gossypium hirsutum L.) is grown in vast acreage, and the Texas Rolling Plains (TRP), which is dominated by an invasive brush, honey mesquite (Prosopis glandulosa) have the potential for biofuel production for meeting the U.S. bioenergy target of 2022. However, a shift in land use from cotton to perennial grasses and a change in land management such as the harvesting of mesquite for biofuel production can significantly affect regional hydrology and water quality. In this study, APEX and SWAT models were integrated to assess the impacts of replacing cotton with Alamo switchgrass (Panicum virgatum L.) and Miscanthus × giganteus in the upstream subwatershed and harvesting mesquite in the downstream subwatershed on water and nitrogen balances in the Double Mountain Fork Brazos watershed in the SHP and TRP regions. Simulated average (1994–2009) annual surface runoff from the baseline cotton areas decreased significantly (P < 0.05) by 88%, and percolation increased by 28% under the perennial grasses scenario compared to the baseline cotton scenario. The soil water content enhanced significantly under the irrigated switchgrass scenario compared to the baseline irrigated cotton scenario from January to April and August to October. However, the soil water content was depleted significantly under the dryland Miscanthus scenario from April to July relative to the baseline dryland cotton scenario. The nitrate‐nitrogen (NO3‐N) and organic‐N loads in surface runoff and NO3‐N leaching to groundwater reduced significantly by 86%, 98%, and 100%, respectively, under the perennial grasses scenario. Similarly, surface runoff, and NO3‐N and organic‐N loads through surface runoff reduced significantly by 98.9%, 99.9%, and 99.5%, respectively, under the post‐mesquite‐harvest scenario. Perennial grasses exhibited superior ethanol production potential compared to mesquite. However, mesquite is an appropriate supplementary bioenergy source in the TRP region because of its standing biomass and rapid regrowth characteristics.

GIS analysis to identify turfgrass sod production sites for phosphorus removal

Erath County in the North Bosque River (NBR) watershed of central Texas hosts a large portion of dairy production in the state. In recent years, the Texas Commission on Environmental Quality (TCEQ) has approved a total maximum daily load (TMDL) program for soluble phosphorus (P) for two segments of the NBR. The TMDL program affects dairy producers in the region who contribute to the nonpoint-source (NPS) phosphorus loading in the watershed. Best management practices (BMPs) are now necessary to remedy the issue of excess P. One proposed BMP calls for the production of turfgrass sod using composted dairy manure. The turfgrass sod would be transported out of the watershed, thus exporting nutrients and reducing P loadings to the NBR. The objective of this project was to determine, using geospatial databases, if there was enough land in Erath County suitable for turfgrass sod production to make this proposed BMP economically feasible. Our analysis identified over 5,000 ha of land suitable for turfgrass sod production.