Kevin J. McInnes

Soil and canopy energy balances in a west Texas vineyard

Water use in vineyards is controlled by energy absorbed by plants and the soil surface. An 8 day field experiment was conducted in a commercial vineyard near Lamesa, TX, to evaluate soil and canopy energy balances, and to examine energy exchange between canopy and soil. Grape- vines in the vineyard were wrapped tightly to trellis wires, creating compact hedgerows that were 3 m apart and of 1.6 m height and 0.4 m width, with little foliage below 1 m above the soil surface. The Bowen ratio method was used to measure the vineyard energy balance including total latent heat flux (AE). Latent heat flux from the canopy (,~Ec) was determined from sap flow measurements of transpiration. Soil latent heat flux (AEs) was calculated as the difference between AE and AE c. These measurements were combined with measurements of soil net irradiance to partition the vineyard energy balance into soil and canopy components. During the study, AEs accounted for 44-68% of AE. Unstable conditions predominated during the study, with the soil generating sensible heat that was transferred to the canopy, producing values of AE c that were greater than canopy net irradiance. Within-row advection of sensible heat was 17-36% of AEc. Although the canopy was cooler than within- and above-canopy air, it was not a strong enough sink for sensible heat to produce stable conditions above the canopy. The narrow hedgerows created an unusual diurnal pattern of canopy net irradiance, having midmorning and midafternoon peaks, and a low midday plateau. Morning and afternoon peaks occurred during times of maximum direct beam irradiance on east and west sides of the hedgerows. Results also showed that within-canopy wind speed and air temperature were affected by wind direction.

Impact of bulking agents, forced aeration, and tillage on remediation of oil-contaminated soil

Abstract Bioremediation is a relatively new technology used to remediate contaminated soil that involves oil degrading microorganisms. Adequate aeration is essential for oil degrading microorganisms to be active. Methods of promoting aeration are tillage, pumping air into the soil, and adding bulking agents to increase porosity. More knowledge is needed regarding the interaction between bulking agents and other technologies in enhancing aeration for bioremediation of oil-contaminated soil. An experiment was undertaken using oil-contaminated soil from an oil production site in east Texas to evaluate different methods to promote aeration. Each treatment contained 10% total petroleum hydrocarbons (TPH) on a dry weight basis. Treatments were bulking agents (non-bulked control, chopped bermudagrass hay, sawdust, and vermiculite) and aeration (static, tillage, and forced aeration). Treatments were arranged in a 4 × 3 factorial with three replications in a completely randomized design. Sawdust and vermiculite were added at equal volumes with the contaminated soil and chopped bermudagrass hay at a ratio of 1 volume of hay to 2 volumes of contaminated soil. Experimental units were 100 1 barrels open at the top. The TPH content was determined every 6 weeks during a 30 week period. During this time the TPH content decreased in all treatments. Bulked soils showed a more rapid reduction in TPH compared to the non-bulked control. Tilling increased the rate and extent of remediation more than soil receiving forced aeration or left static. The most rapid rate of remediation occurred during the first 12 weeks from the tilled-hay treatment, where the TPH decreased 82%. The slowest remediation rate occurred in the non-bulked-static treatment where the TPH content decreased 33% in 12 weeks. By week 30 the TPH content of the treatments ranged from 90% degraded in the tilled-hay and tilled-vermiculite treatments to 77% degraded for the non-bulked-static treatment. Tillage and adding bulking agents enhanced remediation of oil-contaminated soil.

Influence of salinity on bioremediation of oil in soil.

Spills from oil production and processing result in soils being contaminated with oil and salt. The effect of NaCl on degradation of oil in a sandy-clay loam and a clay loam soil was determined. Soils were treated with 50 g kg(-1) non-detergent motor oil (30 SAE). Salt treatments included NaCl amendments to adjust the soil solution electrical conductivities to 40, 120, and 200 dS m(-1). Soils were amended with nutrients and incubated at 25 degrees C. Oil degradation was estimated from the quantities of CO(2) evolved and from gravimetric determinations of remaining oil. Salt concentrations of 200 dS m(-1) in oil amended soils resulted in a decrease in oil mineralized by 44% for a clay loam and 20% for a sandy-clay loam soil. A salt concentration of 40 dS m(-1) reduced oil mineralization by about 10% in both soils. Oil mineralized in the oil amended clay-loam soil was 2-3 times greater than for comparable treatments of the sandy-clay loam soil. Amending the sandy-clay loam soil with 5% by weight of the clay-loam soil enhanced oil mineralization by 40%. Removal of salts from oil and salt contaminated soils before undertaking bioremediation may reduce the time required for bioremediation.

Macroporosity and initial moisture effects on infiltration rates in vertisols and vertic intergrades

In Vertisols and vertic intergrades, spatial and temporal variability remains a challenge in water flow and chemical transport studies. Infiltration measurements were made with tension infiltrometers operating at supply potentials ≥ −0.24 m in 42 clay-textured horizons from seven Vertisols and three

Estimating parameters for a dual-porosity model to describe non-equilibrium, reactive transport in a fine-textured soil.

Several models have recently been proposed to describe solute transport in two or more mobile regions, yet there have been relatively few attempts to calibrate these models for a particular soil. In this study, a dual-porosity approach is used to describe the steady-state reactive transport of a Br− tracer through a fine-textured Ultisol over a range of pore-water velocities and levels of soil-water saturation. This model partitions the soil into two mobile regions that represent the soil matrix and macropores. Theory and methodology are presented to estimate dispersive transport and adsorption in each region and diffusive exchange between regions for soil columns subjected to steady-state water flow. Numerical inversion of the governing transport equations was used in conjunction with non-linear least-squares optimization to estimate transport parameters for displacement experiments. Pore-water velocity and water content were independently estimated for each region using a pair of displacement experiments conducted on the same column but at different degrees of saturation. Results suggest that the fitted mass exchange coefficient represents a lumped process resulting from the combined effects of intra-aggregate diffusion and local flow variations. We also conclude that when there is limited interaction between regions, the mass transfer coefficient should be estimated independently. A principal difficulty of the application of the dual-porosity model was the non-linear behavior of the diffusive exchange term at early times after a step change in inlet concentration. Another problem was that fitted solutions predicted nearly all adsorption sites to be in equilibrium with solute in the macropore region rather than with solute in the matrix region. Despite these difficulties, the dual-porosity model led to differentiation of transport processes that corresponded to observed structural differences in soil horizons.

Effects of trellising on the energy balance of a vineyard

Abstract Field experiments were conducted in 1992 and 1993 in a commercial vineyard near Lamesa, TX, to evaluate soil and canopy energy balances. In 1992, grapevines were wrapped tightly to trellis wires, creating compact hedgerows that were 3 m apart, 1.6 m high and 0.4 m wide with little foliage below 1 m above the soil surface. In 1993, vines were allowed to grow outward and downward from the trellis because of concerns that excess shading of vines and fruit had occurred the previous year. This change in trellising created wider, less dense hedgerows that increased sunlit leaf area and reduced sunlit soil area from the previous year. Leaf area was also 55% larger in 1993. We examined how the change in trellising affected soil and canopy energy balances. The Bowen ratio method was used to measure the vineyard energy balance including total latent heat flux (λE). Latent heat flux from the canopy (λEc) was determined from sap flow measurements of transpiration. Soil latent heat flux (λEs) was calculated as the difference between λE and λEc. These values were combined with measurements of soil net irradiance to partition the vineyard energy balance into soil and canopy components. The change in trellising in 1993 had little effect on vineyard net irradiance (Rn) and λE, but did alter the partitioning of Rn and λE into soil and canopy components. Canopy Rn and λE were substantially higher for the open hedgerows in 1993 whereas soil Rn and λE were lower than for the dense hedgerows in 1992. Both trellising and leaf area contributed to changes in the energy balance. A comparison of λEc per unit land area with λEc per unit leaf area suggested that roughly 60% of the difference in λEc between years was caused by the change in trellising.

Diel and seasonal variation in CO2 flux of irrigated rice

Abstract Rice is a primary food source for half the world’s population, but little is known of how temporal changes in the field-scale physical environment affect carbon dioxide exchange rate (CER), biomass accumulation, and crop yield. Experiments were conducted in 1998 and 1999 in a commercial field near El Campo, TX, to evaluate interactions between CER and the physical environment. Tower-based conditional sampling was used to measure CER. Environmental parameters such as photosynthetically active radiation (PAR), net radiation, and temperature were measured along with CER. Whole-plant biomass was also collected throughout both seasons. Fluctuations in diel CER were correlated with changes in PAR, while season-long trends in CER were associated with changes in leaf area index and stage of development. Crop yield was found to be directly related to total carbon-dioxide exchange after heading, and may have been affected by environmental conditions at anthesis, such as temperature and wind speed, or leaf nitrogen status, both of which differed considerably between the two seasons. Data showed a positive correlation between biomass accumulation and cumulative CER for both years of the study.

PATHWAYS OF DYE TRACER MOVEMENT THROUGH STRUCTURED SOILS ON A MACROSCOPIC SCALE

Structural features, biopores, and slickensides have been reported to be important features impacting bypass flow of pollutants to shallow groundwater aquifers. The objectives of this research were to identify the pathways of water and solute transport at a macroscopic scale and to identify visible characteristics of solute flow in two Vertisols and one Alfisol. Relative involvement of structural features in solute transport, such as ped interfaces, root channels, and slickenside planes, were studied by mapping dye flow paths. Roots and interpedal pores served as major pathways of transport in all three soils. Slickenside fissures in Vertisols served as minor pathways of solute transport. Solute flow along slickenside surfaces was observed primarily when the dye solution was delivered to the surface of the slickenside via the adjacent root channel. The differences in observed distribution of dye pathways were related to the abundance of different types of structural features, their apparent continuity, interconnectivity, and macropore access to the infiltrating dye front. Lateral transport was identified as one of the major components of the flow, even though the sites were located on nearly-level to gently sloping geomorphic surfaces.

Aerodynamic conductances along a bare ridge-furrow tilled soil surface

Spatial dependence of aerodynamic conductances for heat and mass between the atmosphere and positions along the surface of ridge-furrow tilled soil has been ignored in modeling efforts. Aerodynamic conductances may vary with both wind speed and wind direction. This research was conducted to determine the effect of wind direction on aerodynamic conductances for heat transport gh from small sensors placed along a bare ridge-furrow tilled soil surface relative to the spatial mean value (gh). Aerodynamic conductances were determined from an energy balance of a pair of adjacent sensors, heated and unheated, placed flush with the soil surface. Twelve minute average gh values, 1 m wind speeds, and wind directions, were measured over a 4 week period in a ridge-furrow tilled field near College Station, Texas. The average vertical distance from the furrow bottoms to the ridge tops was 0.24 m and the horizontal distance between ridges was 1 m. Sensors were placed flush with ridge tops, ridge-furrow sides, and furrow bottoms. To minimize the influence of free convection on gh, only measurements that were taken when 1 m wind speeds were greater than 0.5 m s−1 were analyzed. Values of gh/(gh) at the ridge top were 5–10% higher than those at the furrow bottom when the wind was parallel to ridge orientation. When wind was perpendicular to ridge orientation, aerodynamic conductances from sensors on the windward ridge-furrow side were about 5–15% higher than (gh), and those from sensors on the leeward side, were about 5–15% lower than (gh). Differences in gh/(gh) between ridge top and furrow bottom were smaller than differences between windward and leeward sides when wind was not parallel to the ridge orientation. Results from this research could be used to assign spatially dependent conductances from the surface to the atmosphere when modeling two or three dimensional energy and mass transport in ridge-furrow systems.

Microalgal productivity, community composition, and pelagic food web dynamics in a subtropical, turbid salt marsh isolated from freshwater inflow

Carbon entering the food web originating from microalgal productivity may be as important to salt marsh consumers as carbon originating from vascular plant production. The objective of this study was to further our understanding of the role played by microalgae in salt marshes. We focused on microalgal productivity, community dynamics, and pelagic food web linkages. Across three consecutive springs (2001–2003), we sampled the upper Nueces Delta in southeast Texas, United States; a shallow, turbid system of ponds and elevated vegetated areas stressed by low freshwater inflow and salinities ranging from brackish (11) to hypersaline (300). Despite high turbidity and low external nutrient loadings, microalgal productivity was on the order of that reported for vascular plants. Primary productivity in surface waters ranged from 0 to 2.02 g C m−2 d−1 and was usually higher than primary productivity associated with the benthos, which ranged from 0 to 1.14 g C m−2 d−1. This was likely due to high amounts of wind-driven resuspended sediment limiting production at greater depths. Most of the water column microalgal biovolume seemed to originate from the benthos and was comprised mostly of pennate diatoms. But true phytoplankton taxa were also observed, which included cryptomonads, chlorophyhtes dinoflagellates, and cyanobacteria. Succession from r-selected to K-selected taxa with the progression of spring, a common phenomena in aquatic systems, was not observed. Codominance by both potentially edible and less edible taxa was found. This was likely due to decreased grazing pressure on r-selected taxa as salinity conditions became unfavorable for grazers. In addition to a decoupled food web, reduced primary and net productivity, community respiration, and microalgal and zooplankton population densities were all observed at extreme salinities. Our findings suggest that a more accurate paradigm of salt marsh functioning within the landscape must account for microalgal productivity as well as production by vascular plants. Because the value of microalgal productivity to higher trophic levels is taxa specific, the factors that govern microalgal community structure and dynamics must also be accounted for. In the case for the Nueces Delta, these factors included wind mixing and increasing salinities.