Isotopic constraints on growth conditions of multiphase calcite–pyrite–barite concretions in Carboniferous mudstones

Carbonate concretions in the Lower Carboniferous Caton Shale Formation contain diagenetic pyrite, calcite and barite in the concretion matrix or in different generations of septarian fissures. Pyrite was formed by sulphate reduction throughout the sediment before concretionary growth, then continued to form mainly in the concretion centres. The septarian calcites show a continuous isotopic trend from δ¹³C=?28·7‰ PDB and δ¹⁸O=?1·6‰ PDB through to δ¹³C=?6·9‰ PDB and δ¹⁸O=?14·6‰ PDB. This trend arises from (1) a carbonate source initially from sulphate reduction, to which was added increasing contributions of methanogenic carbonate; and (2) burial/temperature effects or the addition of isotopically light oxygen from meteoric water. The concretionary matrix carbonates must have at least partially predated the earliest septarian cements, and thus used the same carbonate sources. Consequently, their isotopic composition (δ¹³C=?12·0 to ?10·1‰ PDB and δ¹⁸O=?5·7 to ?5·6‰ PDB) can only result from mixing a carbonate cement derived from sulphate reduction with cements containing increasing proportions of carbonate from methanogenesis and, directly or indirectly, also from skeletal carbonate. Concretionary growth was therefore pervasive, with cements being added progressively throughout the concretion body during growth. The concretions contain barite in the concretion matrix and in septarian fissures. Barite in the earlier matrix phase has an isotopic composition (δ³⁴S=+24·8‰ CDT and δ¹⁸O=+16·4‰ SMOW), indicating formation from near‐surface, sulphate‐depleted porewaters. Barites in the later septarian phase have unusual isotopic compositions (δ³⁴S=+6 to +11‰ CDT and δ¹⁸O=+8 to +11‰ SMOW), which require the late addition of isotopically light sulphate to the porewaters, either from anoxic sulphide oxidation (using ferric iron) or from sulphate dissolved in meteoric water. Carbon isotope and biomarker data indicate that oil trapped within septarian fissures was derived from the maturation of kerogen in the enclosing sediments.     

Analytical Solutions for Flow Fields near Drain-and-Gate Reactive Barriers

Permeable reactive barriers (PRBs) are a popular technology for passive contaminant remediation in aquifers through installation of reactive materials in the pathway of a plume. Of fundamental importance are the degree of remediation inside the reactor (residence time) and the portion of groundwater intercepted by a PRB (capture width). Based on a two-dimensional conformal mapping approach (previously used in related work), the latter is studied in the present work for drain-and-gate (DG) PRBs, which may possess a collector and a distributor drain (“full” configuration) or a collector drain only (“simple” configuration). Inherent assumptions are a homogeneous unbounded aquifer with a uniform far field, in which highly permeable drains establish constant head boundaries. Solutions for aquifer flow fields in terms of the complex potential are derived, illustrated, and analyzed for doubly symmetric DG configurations and arbitrary reactor hydraulic resistance as well as ambient groundwater flow direction. A series of practitioner-friendly charts for capture width is given to assist in PRB design and optimization without requiring complex mathematics. DG PRBs are identified as more susceptible to flow divergence around the reactor than configurations using impermeable side structures (e.g., funnel-and-gate), and deployment of impermeable walls on drains is seen to mitigate this problem under certain circumstances.     

Liver lesions in winter flounder (Pseudopleuronectes americanus) from Jamaica Bay,New York: Indications of environmental degradation

Liver sections of winter flounder (Pseudopleuronectes americanus) collected from Jamaica Bay and Shinnecock Bay, New York, in 1989, were examined microscopically to determine the pervasiveness of liver lesions observed previously in Jamaica Bay winter flounder. Neoplastic lesions were not detected in fish from Jamaica Bay or the Shinnecock Bay reference site. Twenty-two percent of Jamaica Bay winter flounder examined (n=103) had unusual vacuolization of hepatocytes and biliary pre-ductal and ductal cells (referred to hereafter as the vacuolated cell lesion). The lesion, identical to that found in 25% of Jamaica Bay winter flounder examined in 1988, has previously been identified in fishes taken from highly polluted regions of the Atlantic coast (e.g., Boston Harbor, Massachusetts, and Black Rock Harbor, Connecticut). Prevalence of the vacuolated cell lesion in winter flounder from Jamaica Bay was significantly greater (p<0.0001) than in 102 specimens collected from Shinnecock Bay. Current scientific literature indicates vacuolated hepatocytes and cholangiocytes are chronically injured and that the extent of their deformity is consistent with the action of a hepatotoxicant. The high prevalence of vacuolated hepatocytes in Jamaica Bay winter flounder and absence of the lesion in flounder from reference sites strongly supports the hypothesis that this impairment is a manifestation of a toxic condition in at least some portions of Jamaica Bay.     

Evaluation of Monod kinetic parameters in the subsurface using moment analysis: Theory and numerical testing

The spatial moments of a contaminant plume undergoing bio-attenuation are coupled to the moments of microbial populations effecting that attenuation. In this paper, a scalable inverse method is developed for estimating field-scale Monod parameters such as the maximum microbial growth rate (μ^max), the contaminant half saturation coefficient (K_s), and the contaminant yield coefficient (Y_s). The method uses spatial moments that characterize the distribution of dissolved contaminant and active microbial biomass in the aquifer. A finite element model is used to generate hypothetical field-scale data to test the method under both homogeneous and heterogeneous aquifer conditions. Two general cases are examined. In the first, Monod parameters are estimated where it is assumed a microbial population comprised of a single bacterial species is attenuating one contaminant (e.g., an electron donor and an electron acceptor). In a second case, contaminant attenuation is attributed to a microbial consortium comprised of two microbial species, and Monod parameters for both species are estimated. Results indicate the inverse method is only slightly sensitive to aquifer heterogeneity and that estimation errors decrease as the sampling time interval decreases with respect to the groundwater travel time between sample locations. Optimum conditions for applying the scalable inverse method in both space and time are investigated under both homogeneous and heterogeneous aquifer conditions.     

Spatial Variation of Rainfall over a Large Watershed in Central Iowa

Summary Rainfall amounts and the distribution across the landscape are critical to decision-making and evaluation of hydrological models. Spatial variation in rainfall has been observed through anecdotal evidence and limited studies; however, there is little quantitative evidence that can be used to assess rainfall variation within a watershed on a daily, monthly, or yearly temporal scale. This study was conducted to quantify the spatial variation within a watershed in central Iowa and to determine if there were consistent differences among rain gages for the period from 1991 through 1998. The study was conducted within Walnut Creek watershed located south of Ames, Iowa on the Des Moines Lobe Landform region. The topography of this 5130 ha watershed is characterized by gently rolling fields with a narrow area of steeper land along the stream in the lower part of the watershed. Twenty-two tipping bucket rain gages were placed throughout the watershed and rainfall was recorded as 5 minute totals and then aggregated into daily totals. Accumulation of errors of the 5 minute values into the daily totals were considered to be random. There was a large coefficient of variation in the average daily totals; however, there was no consistent pattern of variation among rain gages, and coefficient of variation decreased with amount of rain. Each rain gage had an equal chance of receiving the lowest or highest rainfall total for any given storm event. When the daily average was computed over the year, there were no differences among rain gages. Monthly and yearly totals showed a decreased coefficient of variation compared to daily totals. There was no consistent pattern of spottiness within the watershed and if daily rainfall amounts are required for a decision, then direct measurements may be required. Received August 18, 1997 Revised March 1, 1999     

Quantifying atmospheric stability conditions at a swine facility and an adjacent corn field in Iowa, USA

Atmospheric stability conditions in the atmospheric surface layer control the distance and direction of transport of air contaminants. Near confined animal facilities, transport processes significantly impact air quality as these sites typically act as point sources of dust and odor constituents; however, little information is available on atmospheric stability effects. This study was conducted to assess year-round temporal patterns of atmospheric stability at a swine production facility and an adjacent commercial corn field (CF) in the US Midwest. Two towers of 10 and 20?m heights for continuous micrometeorological measurements were deployed within a CF and between swine buildings (BSB), respectively. Each tower was equipped with an eddy-covariance system at 6.8?m height, infrared thermometers, and six cup anemometers with thermocouples installed at log-distributed heights. Overall results from gradient Richardson number and Monin?CObukhov (z/L) calculations revealed a greater prevalence of unstable conditions for BSB compared with CF. During the 13-month measurement period, unstable cases (z/L ranging from ?1 to ?0.01) occurred 1.4 times more frequently for BSB than CF (52 vs. 39%, respectively), while stable cases (0.011?C0.2) were 1.8 times more frequent for CF than BSB (24 vs. 14%, respectively). These patterns were partly associated with higher surface radiometric temperatures for BSB. Relatively greater diurnal heat capture at BSB (ground and roof surfaces) and a cooling effect in CF through active canopy transpiration during the daytime explain these z/L and radiometric temperature results. Prevalent diurnal atmospheric instability at BSB suggests enhanced ascendant vertical transport of air pollutants perhaps causing greater mixing/dilution with the atmospheric layer and/or their facilitated transport over greater distances when sorbed onto particles. This enhanced understanding of the spatio-temporal patterns of atmospheric stability can be subsequently applied in further studies for identifying effective odor mitigation strategies near commercial animal production facilities.     

Energy balance and turbulent flux partitioning in a corn–soybean rotation in the Midwestern US

Quantifying the energy balance above plant canopies is critical for better understanding of water balance and changes in regional weather patterns. This study examined temporal variations of energy balance terms for contrasting canopies [corn (Zea mays L.) and soybean (Glycine max L. Merr.)]. We monitored energy balance for 4 years using eddy-covariance systems, net radiometers, and soil heat flux plates in adjacent production fields near Ames, Iowa. On an annual basis, soybean exhibited 20% and 30% lower sensible heat flux (H) and Bowen ratio than corn, respectively. As canopies developed, a gradual shift in turbulent fluxes occurred with decreasing H and increasing latent heat flux (LE), but with a more pronounced effect for corn. Conversely, during mid-growing season and as both canopies progressively senesced, H in general increased and LE decreased; however, soybean exhibited slightly greater LE and much lower H than corn. These temporal variations in magnitude and partitioning of turbulent fluxes translated into a pronounced energy imbalance for soybean (0.80) and an enhanced closure for corn (0.98) in August and September. These discrepancies could be directly associated with differences in momentum transport as shown by friction velocities of 0.34 and 0.28 m s^?1 for corn and soybean, respectively. These results support influential roles of plant canopy on intensity and mode of surface energy exchange processes.