Hydrologic and water quality models are very sensitive to input parameter values, especially precipitation input data. With several different sources of precipitation data now available, it is quite difficult to determine which source is most appropriate under various circumstances. We used several sources of rainfall data in this study including single gauge rainfall data located outside the watershed boundary, and next generation radar (NEXRAD) rainfall data with different corrections, to examine the impact of such sources on Soil and Water Assessment Tool (SWAT) model streamflow predictions tor a 50 km 2 watershed located in the coastal plain of Maryland. For a watershed of that size with annual average precipitation of 43 inches, at least 3 rain gauges within the watershed would reduce the percentage error in measured average watershed rainfall amounts to less than 23% (for 0.5 inch storm events). The larger the amount of storm rainfall the less error was associated with its measurement. Model simulation results indicated that distance and location of the single rain gauge located outside the watershed boundary has a significant impact in simulating hydrologic and water quality response of the watershed in the temperate region of Maryland. In the absence of a spatially representative network of rain gauges within the watershed, NEXRAD data produced more accurate estimates of streamflow than using single gage data. This study concludes that one has to be mindful of the source and methods of interpolation of rainfall data for input into hydrologic and water quality models if simulation accuracies are desired.
Wetlands are an integral part of many agricultural watersheds. They provide multiple ecosystem functions, such as improving water quality, mitigating flooding, and serving as natural habitats. Those functions are highly depended on wetland hydrological characteristics and their connectivity to the downstream waters. However, wetland hydrology has been poorly understood at the watershed scale. In this study, we simulated the Soil and Water Assessment Tool (or SWAT) model along with the inclusion of a Riparian Wetland Module (RWM) at Tuckahoe Creek, a sub-watershed within the Choptank River watershed on the Coastal Plain of the Chesapeake Bay watershed. The RWM, a SWAT extension module, was adopted to better simulate interactions between riparian wetlands and nearby streams. The SWAT-RWM was calibrated and validated against observed streamflow collected at the outlet of the watershed and then applied for assessing wetland hydrological benefits. The poster will demonstrate the hydrological benefits of wetlands to stabilize overall flow pattern and reduce peak flow at the storm event. The outcomes of this study will contribute to the enhanced understanding of the hydrological role of wetlands in the watershed. © 2016 American Society of Agricultural and Biological Engineers. All rights reserved.
Elevated C02 concentration, temperature, and change in precipitation patterns driven by climate change are expected to cause significant environmental effects in the Chesapeake Bay Watershed (CBW). Although the potential effects of climate change are widely reported, few studies have been conducted to understand implications for water quality and the response of agricultural watersheds to climate change. The objective of this study is to quantify changes in hydrological processes and nitrate cycling, as a result of climate variability, using the Soil and Water Assessment Tool (SWAT) model. Specifically we assessed the performance of winter cover crops (WCC) as a means of reducing nutrient loss in the realm of climate change and evaluate its impacts on water quality at the watershed scale. WCC planting has been emphasized as the most cost-effective means for water quality protection and widely adopted via federal and state cost-share programs. Climate change data were prepared by modifying current climate data using predicted mean temperature and precipitation change for the future periods (2070-2099) predicted by four global climate models. Current CO2 concentration, temperature, and precipitation increased by 850 ppm, 4.5 °C, and 23%, respectively. Although temperature increase reduced the water and nitrate loads, nitrate loads were found to increase by 40% under baseline land management and WCC were found to be less effective at reducing nitrate (nitrate increased by 4.6 kg/ha). Therefore agricultural conservation practices are likely to be even more important in the future, but acreage goals may need to be adjusted to maintain baseline effects.
Concern over chemical loadings to unconfined aquifers and into the surface water sources through drain tiles and subsurface groundwater flow has directed researchers to focus on the pathways that speed up the pollutant arrival to such sources. Preferential flow of water and chemical transport though porous media has attracted the attention of scientists and engineers working in the environmental field. Research has indicated that structured soils promote bypass flow (a form of preferential flow induced by macropores formed due to shrinking and swelling of soils) that results in fast movement of solutes, whereas piston flow is mostly responsible for the flow of water and solutes in nonstructured homogeneous (e.g., homogeneous sand-textured) soils (Skopp, 1981; Schumacher, 1864; Bergstrom and Shirmohammadi, 1999). Nieber (2001) stated that preferential flow includes macropore flow, gravity-driven unstable flow, heterogeneity-driven flow, oscillatory flow, and depression-focused recharge. Flow systems such as fingering caused by a sequence of texturally different layers (Hill and Parlange, 1972), hydrophobicity (Ritsema et al., 1983), and funnel flow due to texturally different lenses (Kung, 1990) are examples of preferential flow mechanisms. Such multiple transport behavior has created a multitude of difficulties in modeling solute leaching in vadose zone. © 2005 by CRC Press.
Agricultural and Forest Meteorology (01681923)33(2-3)pp. 225-238
A field evaporation-drainage study was conducted to compare three methods of predicting evaporative losses from a bare soil. Two of the methods (modified Penman combination and Idso-Jackson) are dependent only on measurements of atmospheric parameters whereas the third method (plane of zero flux) is dependent only on measurements of soil parameters. A Captina soil profile was wet up and allowed to dry by evaporation and drainage. For the initial two days after infiltration ceased all three methods predicted similar evaporative losses. Differences between the three methods occurred when the soil moisture content at the soil surface controlled the evaporation rates. Under the three drying conditions the three methods behaved somewhat differently in the prediction of the amounts of water evaporated from the soil surface. Lower losses by evaporation were predicted by the Idso-Jackson and zero-flux methods. In the case of the Idso-Jackson method this result was attributed to the influence of clouds on albedo, the impact of wind and the importance of albedo in the predictive equation. For the zero-flux method the decrease in evaporation was due to lower soil water contents and matrix potentials near the surface which resulted in lower transport rates of water to the surface. © 1984.
The use of tile drains for alleviating soluble salt accumulation on silt loam soil was investigated during 1984. Although the chemical analyses of the floodwater and tile drainage water were very similar suggeting that the floodwater was moving to the tile drain, the overall results so far indicate that this is not a feasible solution owing to lack of significant drainage. Application of DRAINMOD utilizing soil and weather data from Arkansas showed no significant effluent from the tile drains for our experimental site during rice production. This was attributed to the extremely slow saturated hydraulic conductivity values for this particular soil. However, more observations (concerning the operation of the tile field) are needed before it can be concluded that tile drain fields are not a viable solution to the problem.
IEEE Transactions on Geoscience and Remote Sensing (01962892)22pp. 394-405
Results are presented of an experimental program to determine the functional dependence of the microwave reflectivity of nonvegetated soil surfaces upon volumetric soil moisture and matric potential. A combination evaporation-drainage field experiment was conducted on a bare Captina silt loam with reflectivity, soil moisture content, and matric potential monitored for extended time periods. Results show that for a restricted pressure range (approximately -0.05 to -0.75 bar) there is excellent linear correlation between the log of bistatic reflectivity and both volumetric moisture content and matric potential. Layering effects due to steep moisture content (and matric potential) gradients in the profile are demonstrated to have two distinct and significant effects on the reflectivity response. At near saturation of rough surfaces a very thin dry surface layer appears to modify the effective roughness. This leads to a saturation of reflectivity at high moisture contents. As the surface proceeds to dry further, deeper layers produce coherent interference patterns in the reflectivity response, particularly at the higher frequencies. © 1984 IEEE
Sadeghi, A.,
Hancock g.d., ,
Waite w.p., W.P.,
Scott h.d., ,
Rand j.a., Water Resources Research (00431397)20(7)pp. 927-934
Laboratory and field experiments were conducted to investigate the ability of microwave remote sensing systems to detect the moisture status of a silt loam soil exhibiting abrupt changes in moisture content near the surface. Laboratory soil profiles were prepared with a discontinuous moisture boundary in the subsurface. Reflectivity measurements of these profiles were made with a bistatic reflectometer operating over the frequency ranges of 1–2 and 4–8 GHz (wavelength ranges of 30–15 and 7.5–3.75 cm, respectively). These measurements exhibited a well‐developed coherent interference pattern in good agreement with a simple two‐layer reflectivity model. Field measurements of bare soil surfaces were conducted for initially saturated profiles and continued for extended periods of drying. During drying, coherent interference patterns similar to those observed in the laboratory were detected. These appear to be due to steep moisture gradients occurring between drying layers near the surface. The field results were modeled by a five‐segment linear moisture profile with one or two steep segments and a multilayer reflectivity program. Agreement between model and field response over the frequency range was used to estimate the depth of drying layers within the soil. These depths were monitored over the second and third drying cycles. Formation of the drying layers under field conditions appears to be influenced by drying time, tillage, and evaporative demand. In any case, it appears that the coherent effects caused by nonuniform moisture profiles may substantially affect the reflectivity of even rough soil surfaces. Copyright 1984 by the American Geophysical Union.
IEEE Transactions on Geoscience and Remote Sensing (01962892)26(4)pp. 490-493
Field studies were conducted to evaluate the application of radar reflectivity as compared with the shortwave reflectivity (albedo) used in the Idso-Jackson equation for the estimation of daily evaporation under overcast sky and subhumid climatic conditions. Soil water content, water potential, shortwave and radar reflectivity, and soil and air temperatures were monitored during three soil drying cycles. The data from each cycle were used to calculate daily evaporation from the Idso-Jackson equation and from two other standard methods, the modified Penman and the plane of 7ero-flux. All three methods resulted in similar estimates of evaporation under clear sky conditions; however, under overcast sky conditions, evaporation fluxes computed from the Idso-Jackson equation were consistently lower than the other two methods. The shortwave albedo values in the Idso-Jackson equation were then replaced with radar reflectivities and a new set of total daily evaporation fluxes were calculated. This resulted in a significant improvement in computed soil evaporation fluxes from the Idso-Jackson equation, and a better agreement between the three methods under overcast sky conditions. © 1988 IEEE
Soil Science Society of America Journal (03615995)52(1)pp. 46-49
Urea fertilizer is often applied at the soil surface, where it hydrolyzes and can form NH//3. To quantify the volatilization of NH//3, the molecular diffusion of urea into the soil must be described. The diffusion coefficient of urea in soil is related to its diffusion coefficient in water, which varies with temperature. We initially regressed the value of the urea diffusion coefficient in water from the international critical tables (ICT) on temperature for the range of 10 to 20 degree C. Since surface soil temperatures often fall outside this range, additional values for the urea diffusion coefficients were needed. The capillary tube method of Phillips and Ellis was used to measure the diffusion coefficient of urea in water at temperatures ranging from 0 to 50 degree C. The new regression equation allowed a better agreement between actual and simulated urea concentrations in soil.
Soil Science Society of America Journal (03615995)53(1)pp. 15-18
The objective of this study was to modify the parameters in an empirical equation of R.J. Papendick and G.S. Campbell and, if necessary, develop a new relationship to estimate the value of the molecular diffusion coefficient of urea in soil (Ds) in soils. Laboratory studies were conducted on seven soils in which the clay content ranged from 10 to 51%. Urea concentrations with depth at 48 h following surface-application were measured and also computed using numerical techniques with an initial estimate for Ds instead of computing it using Papendick and Campbell's equation. The Ds was modified incrementally, until the difference between computed and measured concentrations was minimized. In all seven soils, good agreement was obtained between measured and computer urea concentrations with depth.
Journal of Geochemical Exploration (03756742)32(1-3)pp. 279-286
Three hundred and thirty-five stream sediment samples (<75×10-3 mm diameter) from 3275 km2 in central Arkansas, U.S.A. were utilized to evaluate geochemistry as an exploration method for carbonatite and U in this geologically diverse area. Approximately one-half of the area is located in the Ouachita Mountains and the other half is located in the Gulf Coastal Plain. Alkalic igneous intrusions are located in both regions; however, shale, sandstone, novaculite and unconsolidated sediments are the major lithologies. The areas was divided into four geochemical regions based on similarities in geology and geochemistry. Neutron activation analysis was used to analyze for rare earth elements (REE), Ti, F, U, and 17 other elements. A REE+Ti+ F map based on an enrichment index and a U concentration map delineate two anomalous areas. One of these anomalous areas is near the Magnet Cove intrusion which contains carbonatite, and the other is near lignite deposits that contain U and unusually high concentrations of REE. R-mode cluster analysis indicates that these two areas are distinctly different geochemical environments. Less anomalous samples are associated with syenite intrusions and shale. Anomalous samples associated with the carbonatite are enriched in light REE relative to anomalies associated with syenite intrusions and are enriched in light REE and Ti compared to anomalies associated with sedimentary rocks and lignite. © 1989.
Soil Science (0038075X)152(5)pp. 333-339
A small core of intact soil provided information about the lateral transport and diminution of nitrate in the presence and absence of a carbon source capable of supporting microbial growth. The core (6.2 cm in diameter by 15 cm in length) was obtained by pushing a plastic cylinder horizontally into the wall of a trench excavated in a riparian zone where water moves laterally. Under conditions favorable for nitrate diminution, pulses of nitrate solution containing carbon were passed through the core and leached with water. Effluents were collected at fixed intervals and analyzed. Nitrate losses ranged from 4% to 72%, presumably via denitrification. Effluent nitrate concentrations and pore water velocities were entered into a model developed by Parker and van Genuchten for one-dimensional convective-dispersive solute transport and for solute decay and production. The model accounted for the experimentally determined transport and loss of nitrate (r2= 0.92–0.98). The model also provided values for dispersion coefficient, nitrate exclusion factor, and nitrate decay rate constant. Nitrate loss was reasonably accounted for by a decay rate constant (avg. = 2.75/day) that increased as observed nitrate loss increased from 53% to 72%. A sizable factor for anion exclusion and/or the presence of immobile-water regions was necessary to account for the rapid passage of nitrate through the soil core. Peclet numbers, which are inversely related to dispersion coefficient, were low. These low numbers and a retardation factor of less than 1 suggested that the flow through the soil core may have been heterogeneous. © 1991 Williams & Wilkins.
Mezrow, C.K.,
Sadeghi, A.,
Gandsas, A.,
Shiang, H.H.,
Levy, D.,
Green, R.,
Holzman, I.R.,
Griepp r.b., R.B. The Annals of Thoracic Surgery (00034975)54(4)pp. 609-616
Although hypothermic circulatory arrest has been accepted for use in cardiovascular operations, the potential for cerebral injury exists. The mechanism of the cerebral injury remains unclear. To address these questions we studied cerebral blood flow and metabolism. Sixteen puppies were randomly assigned to undergo either 45 or 90 minutes of hypothermic circulatory arrest after perfusion/surface cooling to 13 °C. Cerebral blood flow, cerebral oxygen and glucose metabolism, and cerebral vascular resistance measurements were obtained at 37 °C, 13 °C, 10 minutes after reperfusion, 30 °C and 2 and 4 hours after hypothermic circulatory arrest. No neurologic or behavioral changes were observed in any of the long-term survivors ( 11 16). Metabolic and cerebral blood flow data did not differ between groups. Cerebral blood flow was significantly lower in the late postarrest measurements, whereas oxygen and glucose consumption had returned to baseline values. In the presence of low cerebral blood flow and high cerebral vascular resistance it is notable that control levels of oxygen consumption were attained by abnormally high oxygen extraction. These data strongly suggest a vulnerable interval after hypothermic circulatory arrest in which cerebral metabolism is limited by cerebral blood flow. © 1992.
Journal of Environmental Quality (00472425)21(3)pp. 464-469
High variability of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5 triazine) residues in soil and shallow groundwater have been reported under various agricultural management systems. This 2-yr study was conducted to evaluate atrazine residue levels in soil as influenced by no-till (NT) vs. conventional-till (CT) under natural rainfall conditions. Atrazine was applied annually (at 1.34 kg/ha), 1 d after corn (Zea mays L.) planting, to two NT and two CT plots. Atrazine residues within the 0- to 10-cm soil depth of CT plots were higher than in the NT plots, regardless of the difference in the rainfall patterns. Higher (ca. 61%) mean atrazine residues in the CT plots over NT plots in 1988 was most likely related to the rainfall that began 12 h after application. In contrast, in 1987, it rained 3 to 4 d after application and the residues in the CT were only 31% higher than in NT. These results indicate that even a subtle difference in rainfall distribution (temporal) can result in marked spatial variability in the distribution of atrazine.
Chemosphere (00456535)25(4)pp. 581-590
This paper describes the design, construction, operation, and performance of an apparatus useful for studying pesticide leaching through intact soil cores. A technique is described for rapidly mounting intact soil cores. A turntable is used to support and rotate 12 or more soil cores under an oscillating dripper unit capable of simulating rainfall intensities of 1 to 30mm/h. Each soil core is attached to a filtration flask which is connected to a -10 to -20 Kpa vacuum supply. The CV of the rainfall delivery rate over a range of 2-12mm/h averaged 3.7%. Dye studies using intact soil cores indicated that water movement at the soil-wall interface was not faster than through the soil matrix. An experiment conducted to evaluate atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] leaching through soil cores obtained from no-till(NT) and conventional-till(CT) fields indicated consistently greater leaching through CT cores. The capability of precise application of simulated rain, accommodation of large number of soil cores, and ease of modification to meet a wide range of research parameters make this apparatus useful for the laboratory evaluation of soil-water-pesticide interactions. © 1992.
Soil Science Society of America Journal (03615995)56(2)pp. 600-603
A chamber was designed and used to simulate shallow groundwater flow in the field. The chamber, made of Plexiglas with dimensions 120 by 60 by 60cm, was filled to a depth of 30cm with sand and had a multiport arrangement of 10mm-diam. holes on a 5 by 5cm grid on both end walls. As a first approximation, the flow and transport were assumed to be one dimensional, and a convective-dispersive solute-transport model was applied to the Cl breakthrough data of each of the 50 outlet ports in order to quantify the spatial distribution of the dispersion-coefficient values at the outlet plate. Based on the inconsistency observed between measured and estimated pore-water velocities and dispersion coefficients of each of the 50 outlet ports, it appears that the one-dimensional model is not appropriate to adequately characterize transport parameter in this horizontal flow system. -from Authors
Mezrow, C.K.,
Midulla, P.S.,
Sadeghi, A.,
Dapunt, O.E.,
Gandsas, A.,
Shiang, H.H.,
D'alessandro, D.A.,
Griepp r.b., R.B. Cardiology in the Young (10479511)3(3)pp. 287-298
Over the past two decades, advances in equipment used for cardiopulmonary bypass and in operative techniques have resulted in a tremendous decrease in the mortality of patients undergoing surgical repair of congenital heart disease utilizing hypothermic circulatory arrest. Despite the widespread use of hypothermic arrest, opinion is not unanimous with regard to its safety. Previous studies which have examined neurological outcome following repair of congenital heart disease in infancy have generally agreed that when the period of arrest exceeds 60 minutes, there is increasing risk of cerebral injury. © 1993, Cambridge University Press. All rights reserved.
Journal of Environmental Quality (00472425)22(3)pp. 389-391
To meet the global needs of a growing population, both increased productivity and additional land may need to be dedicated to agriculture. However, to effectively evaluate the impact of new farming strategies and agricultural chemicals on the environment, a broad perspective is needed to prevent simply shifting pollution from one part of the hydrologic cycle to another. The loss of agricultural chemicals to the environment may include a combination of processes such as volatilization, runoff and leaching, each exhibiting considerable spatial and temporal dependency. Subsequent losses of agricultural chemicals to the environment may also be transported offsite,having a potential detrimental effect on the environment. This overview provides a brief introduction to the papers presented at a special USDAARS symposium entitled″Agricultural Water Quality Priorities, A Team Approach to Conserving Natural Resources″.
Journal of Agricultural and Food Chemistry (00218561)41(7)pp. 1134-1138
Losses of efficacy are due to rates of microbial degradation which exceed rates of granular leaching/dissolution, resulting in carbofuran concentrations below the lethal threshold needed for rootworm control. Previous studies have documented enhanced rates of carbofuran biodegradation and concentrations required for corn rootworm control; however, little information is available on rates of release of carbofuran from granules. Rates of carbofuran leaching from granules as a function of rainfall intensity/infiltration rate, and of granular dissolution as a function of time, were estimated using a rain simulation device. Rates of leaching (1.5 µg (mg of granule)−1 (cm of rainfall)−1) were positively correlated with rainfall/infiltration, and rates of granular dissolution were linear with time (0.28 µg (mg of granule)−1 h−1). Adjusted for field conditions, ca. 50 h of rainfall would be required to leach carbofuran from granules or ca. 11 days (at field capacity) for dissolution of granules (assuming linear rates). Soil solution concentrations would be ca. 16 µg mL−1, or 4 µg (g of bulk soil)−1 (at field capacity and a partition coefficient of 0.1). Rates of spherical carbofuran diffusion from a theoretical granule were calculated. High carbofuran concentrations in the vicinity of granules may result in localized high population densities of carbofuran-degrading microorganisms. In combination with previous studies, these data suggest that losses of efficacy may potentially result either from the complete leaching/dissolution of granules and biodegradation before larvae hatch or from rates of biodegradation which exceed rates of granular leaching/dissolution after larvae hatch. © 1993, American Chemical Society. All rights reserved.
Journal of Soil and Water Conservation (00224561)48(6)pp. 523-527
Soil Science (0038075X)156(4)pp. 225-232
Pesticide leaching may be affected by rainfall parameters and the amount and type of vegetation on the soil surface. This study was conducted to determine the effect of rainfall intensity and crop residue on the movement of [ring14C]atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and bromide (Br) through no-till (NT) cores. Undisturbed soil cores (10 cm diameter by 8 cm depth) were taken from the surface horizon of a NT corn (Zea mays L.) field. The cores were surface treated with 1.3 kg ai ha−1 atrazine and 150 kg ha−1 of Br and subjected to simulated rainfall at 3, 6, 9, or 12 mm h−1. The amount of crop residue on the surface of another set of soil cores was adjusted to 0, 2000, 4000, and 8000 kg ha−1, then treated with atrazine and subjected to 9 mm h−1 of simulated rain. Overall, the transport of atrazine and Br were significantly (P < 0.01) affected by rainfall intensity. An average of 92% (Br) and 52% (atrazine) of the total amount applied was leached through the soil cores by 2 pore volumes (520 ml) of simulated rain applied at 12 mm h−1 compared with 61% for Br and 33% for atrazine at the 3-mm h−1 rate. Covering soil cores with 2000 or 8000 kg ha−1 of crop residue reduced atrazine leaching by 26 to 37%, respectively, compared with soil cores without crop residue. Soil cores covered with recently harvested vegetation reduced atrazine leaching by 39% compared with cores covered with aged crop residue. © 1993 Williams and Wilkins.
Journal of Ferrocement (01251759)23(4)pp. 289-299
Ferrocement has been increasingly used as a structural material which competes favorably with reinforced concrete and other building materials. The durability of ferrocement depends on several factors including the quality of ferrocement, mesh type, depth of cover over the mesh, the direction and magnitude of applied load(s) and its resistance to corrosion. Corrosion of mesh reinforcement in ferrocement is one of the important aspects which has not received sufficient attention from research workers. This paper presents the results of monitoring the corrosion performance of ferrocement specimens exposed to extremely aggressive conditions (6% NaCl solution at 60°C). Several parameters have been considered in this study, including type and arrangement of mesh reinforcement and depth of mortar cover over the meshes. Four methods were used for corrosion examination of the specimens; visual examination, corrosion potential, corrosion rate and microscopic examination.
Journal of Environmental Quality (00472425)22(1)pp. 162-166
Volatilization of agricultural chemicals is one process whereby chemicals may enter into parts of the environment where they were not intended. Starch encapsulation of pesticides has been proposed as way of modifying pesticide behavior in the soil environment. This study was conducted to assess how starch encapsulation and temperature affect volatilization of atrazine [6-chloro-N-ethyl-N'-(1 -methylethyl)-1,3,5-triazine-2,4-diamine] and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide]. Volatilization was measured using agroecosystem chambers as model systems. Herbicides were applied at rates of 1.7 kg ha-1 for atrazine and 2.8 kg ha-1 for alachlor, as either a commercial formulation or a starch encapsulated formulation, to the surface of moist soils maintained at temperatures of 15, 25 and 35° C. Air was drawn through the chambers (2.5 m3 min-1) and herbicide in the vapor phase was trapped in polyurethane foam plugs. Volatilization of both herbicides increased as temperature increased. Volatilization of atrazine was less when applied as starch-encapsulated formulation than the commercial formulation. After 35 d cumulative volatilization of atrazine ranged from < 1% of that applied as starch-encapsulated formulation at 15° C, to 14% of that applied as the commercial formulation at 35° C. Cumulative volatilization of alachlor was greater when applied as starch-encapsulated formulation than as the commercial formulation. After 35 d, cumulative volatilization of alachlor ranged from >2% of that applied as either formulation at 15 °C to 32% of that applied as starch encapsulated formulation at 35 °C. Differences in volatilization behavior between these herbicides are likely to be due to differences in chemical properties of these herbicides.
Galla, J.D.,
Ergin, M.A.,
Sadeghi, A.,
Lansman, S.L.,
Danto, J.,
Griepp r.b., R.B. Journal of Cardiac Surgery (08860440)9(6)pp. 662-672
Recent work in our laboratory has demonstrated the effectiveness of somatosensory evoked potentials (SEPs) In identifying the critical intercostal arteries (CICAs) for preserving spinal cord integrity during simulated aortic aneurysm repairs in the pig. Further studies have also demonstrated increased preservation of neurological function during prolonged aortic clamping if ClCAs are perfused until ligation or clipping, as opposed to transaortic identification of back‐bleeding intercostals and their subsequent ligation. We have developed a technique of repair of descending thoracic and thoracoabdominal aortic aneurysms and dissections that uses these principles. Since January 1993, 26 patients have undergone repair of their aortas using this new technique and SEP directed intercostal artery ablation. There were 22 (85%) long‐term survivors among 10 thoracoabdominal and 16 descending aortic repairs. All patients with uncorrected abnormal SEP recordings developed paralysis; one patient who required reimplantatlon of an intercostal artery island into the aortic graft had normal neurological function postoperatively. Paraplegia was seen in only one of the surviving patients, but this patient had normal intra‐ and postoperative SEPs (4% false negative). Our experience suggests that SEP‐guided obliteration of intercostal arteries while maintaining perfusion may be a useful approach to the surgical repair of descending and thoracoabdominal aortic disease. (J Card Surg 1994;9:662–672) Copyright © 1994, Wiley Blackwell. All rights reserved
Midulla, P.S.,
Dapunt, O.E.,
Sadeghi, A.,
Quintana c.s., C.S.,
Griepp r.b., R.B. The Annals of Thoracic Surgery (00034975)58(3)pp. 874-875
We report the successful surgical treatment of a 67-year-old man with a double aortic arch, right descending aorta, and a subacute dissection of the descending thoracic aorta using hypothermic circulatory arrest. © 1994.
Neustein, S.M.,
Dimich, I.,
Sampson, I.,
Sadeghi, A.,
Mezrow, C.K.,
Shiang, H.H. Canadian Journal of Anaesthesia (14968975)41(6)pp. 542-546
Dopexamine hydrochloride (Dopacard®) is the novel synthetic catecholamine designed for use in the acute management of a low cardiac output status. In addition to dopaminergic receptor stimulation, dopexamine hydrochloride is a potent β2 adrenoreceptor agonist with negligible direct β1 and no alpha adrenergic effect. The objective of this study was to compare the arrhythmogenic effects of dopexamine hydrochloride and dopamine in dogs anaesthetized with halothane (1.2 MAC). The starting dose for dopexamine hydrochloride was 3.5 μg · kg-1 min-1 and for dopamine was 5 μg · kg-1 min-1. Concentrations of the drugs were increased until four or more premature ventricular contractions within 15 seconds were produced. All dogs developed ventricular tachycardia when dopamine was administered in concentrations ranging between 18-20 μg · kg-1 · min-1. Unlike dopamine, dopexamine hydrochloride even at concentrations as high as 50 μg · kg-1· min-1 did not induce any atrial or ventricular ectopic beats. Lack of β-1 and alpha adrenergic agonist effects is a likely explanation for low arrhythmogenicity of dopexamine hydrochloride. Both drugs increase cardiac output; dopexamine hydrochloride primarily by a dose-related increase in heart rate and increased aflerload. At the maximal concentration dopexamine hydrochloride increased heart rate from 114 to 150 beat · min-1, mean arterial pressure decreased from 81 mmHg to 45 mmHg and SVR decreased from 2418 to 962 dyne · sec-1cm-5. Myocardial contractility increased only moderately, as evaluated by dP/dt, which increased from 1290 to 1696 mmHg · sec-1. Dopamine had a more marked inotropic effect: the dP/dt increased, at the maximal concentration, from 1480 to 2570 mmHg · sec-1. Dopamine also produced vasoconstriction: SVR increased from 2325 to 2683 dyne · sec · cm-5 and mean arterial pressure from 86 mmHg to 110 mmHg. In conclusion, dopexamine hydrochloride is less arrhythmogenic than dopamine, has less of an inotropic effect, and a greater effect on aflerload. © 1994 Canadian Anesthesiologists.
Mezrow, C.K.,
Sadeghi, A.,
Gandsas, A.,
Dapunt, O.E.,
Shiang, H.H.,
Zappulla, R.,
Griepp r.b., R.B. The Annals of Thoracic Surgery (00034975)57(3)pp. 532-539
Although both hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (CPB) are accepted techniques for the operative management of complex cardiovascular pathology, the potential for neurologic sequelae is still a concern. To assess the relative safety of these techniques, we compared cerebral hemodynamics and clinical outcome in two groups of puppies. Sixteen puppies underwent 45 minutes of either HCA or low-flow CPB (25 mL · kg-1 · min-1) after cooling to 13 °C. Methodology included radioactive microsphere determination of cerebral blood flow; calculation of cerebral oxygen extraction (arteriovenous oxygen content difference) and consumption; measurement of glucose consumption, and determination of cerebrovascular resistance. Measurements were obtained at baseline (37 °C, 13 °C, and 30 °C and at 2, 4, and 8 hours after HCA or low-flow CPB. No neurologic deficits were observed in any of the survivors ( 15 16). In both groups, cerebral metabolic rate of oxygen was maintained at baseline or greater levels postoperatively. Cerebrovascular resistance rose slightly in the low-flow CPB group postoperatively in contrast to a marked elevation in the HCA group. During the period of high cerebrovascular resistance after HCA, cerebral metabolic rate of oxygen was maintained by increased oxygen extraction. After low-flow CPB, oxygen extraction was not significantly different from baseline, presumably because of less severe changes in cerebrovascular resistance. Glucose metabolism followed the same trends as oxygen metabolism in both groups. These data suggest that after HCA there is a vulnerable interval, lasting as late as 8 hours postoperatively, in which cerebrovascular resistance remains high and cerebral metabolism is maintained primarily by high oxygen and glucose extraction. Any additional stress during this interval (a decrease in arterial oxygen content or perfusion pressure) could result in cerebral injury. © 1994.
