Urban Land Use,Channel Incision,and Water Table Decline Along Coastal Plain Streams,North Carolina1

Abstract: This study evaluates the effects of urban land use on stream channels and riparian ground‐water levels along low‐order Inner Coastal Plain streams in North Carolina. Six sites with stream catchments of similar size (1.19‐3.46 km²) within the Tar River Basin were selected across an urban land use gradient, as quantified by a range of catchment total impervious area (TIA; 3.8‐36.7%). Stream stage and ground‐water levels within three floodplain monitoring wells were measured manually and using pressure transducers from May 2006‐June 2007. Channel incision ratio (CIR), the ratio of bank height to bankfull height, was also measured at each monitoring site and along stream reaches within the study area (12 urban and 12 rural sites). Riparian ground‐water levels were inversely related to catchment TIA (%). As TIA (%) and stormwater runoff increased, the degree of stream channel incision increased and riparian ground‐water tables declined. In urban floodplains (>15% TIA), the median ground‐water level was 0.84 m deeper than for the rural settings (<15% TIA). This has resulted in a shift to drier conditions in the urban riparian zones, particularly during the summer months. CIR was found to be a reliable surface indicator of “riparian hydrologic drought” in these settings.     

Spatial and temporal analysis of pharmaceutical concentrations in the upper Tennessee River basin

The behavior of pharmaceutical compounds in aquatic ecosystems is not well defined. In order to determine spatial and temporal variations in concentrations of pharmaceuticals in the Tennessee River, water samples were collected from multiple points along the river and at the inflow of major tributaries. Sampling structure was designed to investigate trends between surface and subsurface samples, seasonal trends (winter, spring, summer, and fall), the direct influence of sewage treatment plants (upstream versus downstream), and the effect of downstream distance on pharmaceutical concentrations. All samples were quantified via solid phase extraction followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method yielded reproducible quantitation at low parts per trillion (ng L(-1)) levels for all 14 analytes (acetaminophen, atorvastatin, caffeine, carbamazepine, ciprofloxacin, diltiazem, fluoxetine, levofloxacin, lovastatin, norfluoxetine, ranitidine, sertraline, sulfamethoxazole, and trimethoprim). Correlation analyses (depth, distance) and repeated-measures ANOVAs (season, sewage treatment plant proximity) were used to determine statistically significant trends for frequently detected pharmaceuticals (caffeine, carbamazepine, sulfamethoxazole). Caffeine and sulfamethoxazole were found to vary by season in subsurface samples; spring exhibited the highest concentrations. Carbamazepine varied in proximity to sewage treatment plant outfall with subsurface samples yielding greater concentrations downstream than upstream. In addition, individual pharmaceuticals displayed positive correlation between surface and subsurface samples and negative correlation with downstream distance from the headwaters.     

The effect of nitrogen additions on oak foliage and herbivore communities at sites with high and low atmospheric pollution

To evaluate plant and herbivore responses to nitrogen we conducted a fertilization study at a low and high pollution site in the mixed conifer forests surrounding Los Angeles, California. Contrary to expectations, discriminant function analysis of oak herbivore communities showed significant response to N fertilization when atmospheric deposition was high, but not when atmospheric deposition was low. We hypothesize that longer-term fertilization treatments are needed at the low pollution site before foliar N nutrition increases sufficiently to affect herbivore communities. At the high pollution site, fertilization was also associated with increased catkin production and higher densities of a byturid beetle that feeds on the catkins of oak. Leaf nitrogen and nitrate were significantly higher at the high pollution site compared to the low pollution site. Foliar nitrate concentrations were positively correlated with abundance of sucking insects, leafrollers and plutellids in all three years of the study.     

Groundwater Denitrification Capacity of Riparian Zones in Suburban and Agricultural Watersheds1

Watson, Tara K., Dorothy Q. Kellogg, Kelly Addy, Arthur J. Gold, Mark H. Stolt, Sean W. Donohue, and Peter M. Groffman, 2010. Groundwater Denitrification Capacity of Riparian Zones in Suburban and Agricultural Watersheds. Journal of the American Water Resources Association (JAWRA) 46(2):237-245. DOI: 10.1111/j.1752-1688.2010.00418.x Abstract: We evaluated the relationship of dominant watershed land use to the structure and nitrogen (N) sink function of riparian zones. We focused on groundwater denitrification capacity, water table dynamics, and the presence and pattern of organically enriched deposits. We used the push-pull method (measurement of ¹⁵N-enriched denitrification gases derived from an introduced groundwater plume of ¹⁵N-enriched nitrate) to evaluate groundwater denitrification capacity on nine forested wetland riparian sites developed in alluvial or outwash parent materials in southern New England. Three replicate sites were located in each of the three watershed types, those with substantial (1) irrigated agriculture, (2) suburban development, and (3) forest. Soil morphology and water table dynamics were assessed at each site. We found significantly lower mean annual water tables at sites within watersheds with substantial irrigated agriculture or suburban development than forested watersheds. Water table dynamics were more variable at sites within suburban watersheds, especially during the summer. Groundwater denitrification capacity was significantly greater at sites within forested watersheds than in watersheds with substantial irrigated agriculture. Because of the high degree of variability observed in riparian sites within suburban watersheds, groundwater denitrification capacity was not significantly different from either forested or agricultural watersheds. The highly variable patterns of organically enriched deposits and water tables at sites within suburban watersheds suggests that depositional events are irregular, limiting the predictability of groundwater N dynamics in these riparian zones. The variability of riparian N removal in watersheds with extensive suburbia or irrigated agriculture argues for N management strategies emphasizing effective N source controls in these settings.     

Remediation of MTBE-Contaminated Water and Soil

As the number of leaking underground fuel tank sites with methyl tertiary butyl ehter (MTBE) contamination continues to grow, there is a need to develop cost-effective solutions for treatment of soil and water contamination. MTBE poses special challenges because of its physicochemical properties, in particular high solubility and low Henry's constant, low affinity for sorption, and very slow rate of microbial degradation. Advanced oxidation processes tend to generate undesirable by-products. Based on laboratory studies with hollow fiber membranes (HFM), a field-scale unit was constructed and tested at a number of sites, to determine the effectiveness of this technology in dealing with MTBE contamination. In addition, to treat the soil contamination, the HFM unit was coupled with a Spray Aeration Vapor Extraction (SAVE) unit, which is based on an internal combustion engine. The engine provides the means to treat soil vapors, as well as organic vapors from the spray aeration and HFM units. The overall treatment objectives of 5μg/l for MTBE and 1 μg/l for benzene were achieved with a treatment train consisting of an ion exchange unit, a spray aeration system, a hollow fiber membrane module and two granular activated carbon (GAC) units, for flowrates ranging from 3.8 to 30 l/min (1 to 8 gal/min). The ion exchange unit sewed to reduce water hardness and avoid scaling in the subsequent treatment units, extending the run-time of the entire system. Overall removal efficiencies for the spray aeration system and hollow fiber membrane module ranged from 85 to over 99 percent. High removal efficiencies (> 97%) were obtained at elevated water temperatures (54°C) or lower flowrates (up to 11 l/min). The GAC units were used only to polish the effluent and meet the discharge requirements. Soil, water, and gas phases are treated with this system. Cost estimates are provided for similar treatment processes, for water flowrates up to 38 l/min (10 gal/min). © 1999 John Wiley & Sons, Inc.     

Field evaluation of digital optical method to quantify the visual opacity of plumes

Visual Determination of the Opacity of Emissions from Stationary Sources (Method 9) is a reference method established by U.S. Environmental Protection Agency (EPA) to quantify plume opacity. However, Method 9 relies on observations from humans, which introduces subjectivity. In addition, it is expensive to teach and certify personnel to evaluate plume opacity on a semiannual basis. In this study, field tests were completed during a "smoke school" and a 4-month monitoring program of plumes emitted from stationary sources with a Method 9 qualified observer to evaluate the use of digital photography and two computer algorithms as an alternative to Method 9. This Digital Optical Method (DOM) improves objectivity, costs less to implement than Method 9, and provides archival photographic records of the plumes. Results from "smoke school" tests indicate that DOM passed six of eight tests when the sun was located in the 140 degrees sector behind one of the three cameras, with the individual opacity errors of 15% or less and average opacity errors of 7.5% or less. DOM also passed seven of the eight tests when the sun was located in the 216 degrees sector behind another camera. However, DOM passed only one of the eight tests when the sun was located in the 116 degrees sector in front of the third camera. Certification to read plume opacity by a "smoke reader" for 6 months requires that the "smoke reader" pass one of the smoke school tests during smoke school. The average opacity errors and percentage of observations with individual opacity errors above 15% for the results obtained with DOM were lower than those obtained by the smoke school trainees with the sun was located behind the camera, whereas they were higher than the smoke school trainee results with the sun located in front of the camera. In addition, the difference between plume opacity values obtained by DOM and a Method 9 qualified observer, as measured in the field for two industrial sources, were 2.2%. These encouraging results demonstrate that DOM is able to meet Method 9 requirements under a wide variety of field conditions and, therefore, has potential to be used as an alternative to Method 9.     

Screening and selection of sites for CO2 sequestration based on pressure buildup

This paper presents a simple methodology for estimating pressure pressure buildup due to the injection of supercritical CO₂into a saline formation, and the limiting pressure at which the formation starts to fracture. Pressure buildup is calculated using the approximate solution of Mathias et al. [Mathias, S.A., Hardisty, P.E., Trudell, M.R., Zimmerman, R.W., 2009. Approximate solutions for pressure buildup during CO₂ injection in brine aquifers. Transp. Porous Media. doi:10.1007/s11242-008-9316-7], which accounts for two-phase Forchheimer flow (of supercritical CO₂ and brine) in a compressible porous medium. Compressibility of the rock formation and both fluid phases are also accounted for. Injection pressure is assumed to be limited by the pressure required to fracture the rock formation. Fracture development is assumed to occur when pore pressures exceed the minimum principal stress, which in turn is related to the Poisson’s ratio of the rock formation. Detailed guidance is also offered concerning the estimation of viscosity, density and compressibility for the brine and CO₂. Example calculations are presented in the context of data from the Plains CO₂ Reduction (PCOR) Partnership. Such a methodology will be useful for screening analysis of potential CO₂ injection sites to identify which are worthy of further investigation.     

Effect of clays, metal oxides, and organic matter on rhamnolipid biosurfactant sorption by soil

Rhamnolipids produced by Pseudomonas aeruginosa have been proposed as soil washing agents for enhanced removal of metal and organic contaminants from soil. A potential limitation for the application of rhamnolipids is sorption by soil matrix components. The objective of this study is to empirically determine the contribution of representative soil constituents (clays, metal oxides, and organic matter) to sorption of the rhamnolipid form most efficient at metal complexation (monorhamnolipid). Sorption studies show that monorhamnolipid (R1) sorption is concentration dependent. At low R1 concentrations that are relevant for enhancing organic contaminant biodegradation, R1 sorption followed the order: hematite (Fe(2)O(3))>kaolinite>MnO(2) approximately illite approximately Ca-montmorillonite>gibbsite (Al(OH)(3))>humic acid-coated silica. At high R1 concentrations, relevant for use in complexation/removal of metals or organics, R1 sorption followed the order: illite>humic acid-coated silica>Ca-montmorillonite>hematite>MnO(2)>gibbsite approximately kaolinite. These results allowed prediction of R1 sorption by a series of six soils. Finally, a comparison of R1 and R2 (dirhamnolipid) shows that the R1 form sorbs more strongly alone than when in a mixture of both the R1 and R2 forms. The information presented can be used to estimate, on an individual soil basis, the extent of rhamnolipid sorption. This is important for determining: (1) whether rhamnolipid addition is a feasible remediation option and (2) the amount of rhamnolipid required to efficiently remove the contaminant.