Browsing by Author "LeMonte, Joshua J."
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Item Hydrologic Control on Arsenic Cycling at the Groundwater–Surface Water Interface of a Tidal Channel(Environmental Science and Technology, 2023-01-10) Yu, Xuan; LeMonte, Joshua J.; Li, Junxia; Stuckey, Jason W.; Sparks, Donald L.; Cargill, John G.; Russoniello, Christopher J.; Michael, Holly A.Historical industrial activities have resulted in soil contamination at sites globally. Many of these sites are located along coastlines, making them vulnerable to hydrologic and biogeochemical alterations due to climate change and sea-level rise. However, the impact of hydrologic dynamics on contaminant mobility in tidal environments has not been well studied. Here, we collected data from pressure transducers in wells, multi-level redox sensors, and porewater samplers at an As-contaminated site adjacent to a freshwater tidal channel. Results indicate that sharp redox gradients exist and that redox conditions vary on tidal to seasonal timescales due to sub-daily water level fluctuations in the channel and seasonal groundwater–surface water interactions. The As and Fe2+ concentrations decreased during seasonal periods of net discharge to the channel. The seasonal changes were greater than tidal variations in both Eh and As concentrations, indicating that impacts of the seasonal mechanism are stronger than those of sub-daily water table fluctuations. A conceptual model describing tidal and seasonal hydro-biogeochemical coupling is presented. These findings have broad implications for understanding the impacts of sea-level rise on the mobility of natural and anthropogenic coastal solutes.Item Impacts of sea level rise on arsenic mobility and cycling in contaminated coastal soils(University of Delaware, 2016) LeMonte, Joshua J.The impacts of sea level rise (SLR) on biogeochemical processes in contaminated soils and sediments along the world’s coastlines remains poorly understood. Elevated levels of the carcinogen arsenic (As), from both geogenic and anthropogenic sources, are found along many coasts, most notably in south and southeast Asia, but also in the US, particularly along the Mid-Atlantic coast. In this work, a combination of laboratory and field techniques were used to ascertain the potential impacts of impending SLR on As mobility and cycling, and the current state of As mobility in a contaminated coastal zone of Delaware, USA. Advanced biogeochemical microcosm reactors were used to simulate inundation with natural sea and river waters on two historically As-contaminated Delaware coastal soils – a wetland soil and ditch sediment – across a wide range of redox potentials while monitoring chemical variables that are known to impact As mobility. Direct As speciation of the soils after reaction at different Eh values was obtained by bulk X-ray absorption near-edge structure (XANES) spectroscopy, X-ray fluorescence (XRF) imaging, and XANES spectroscopy. Reducing conditions led to As release and partial reduction of solid-phase As for both inundation scenarios and both soils. Sulfur speciation was also determined via XANES spectroscopy and showed evidence of sulfate reduction. Prolonged reducing conditions induced by SLR will drive the release of As from historically contaminated soils, but As release may be tempered when inundated by seawater as compared to river water for some soils (e.g. ditch sediment), possibly due to reduced microbial growth in high salinity conditions or preferential sulfate reduction limiting reductive dissolution of As-bearing Fe oxides. However, other soils (e.g. wetland) may see ionic exchange driving pH shifts as a prominent factor driving As release in addition to Eh levels. To assess the contaminant mobility at one of these former industrial sites along the Christina River, we conducted quantitative comparisons of hydrologic and biogeochemical dynamics across time scales ranging from hours to months, and throughout seasonal environmental variations. The use of synchrotron-based X-ray absorption spectroscopy as a geoforensic tool suggests that As from a neighboring Superfund site is likely contributing to recent accumulation of As at the site studied. Data were collected from pressure transducers in wells, multi-level redox sensors, and porewater samplers. Results indicate that groundwater surface interaction induced a tidally controlled redox gradient. In the tidally impacted variably saturated zone, redox potential varied between oxidizing and reducing conditions depending on the water table elevation. This strong correlation indicates that a rising water table may increase contaminant mobility. Porewater samples also confirm increasing arsenic (As) concentration during the rising tide.Item Polymer Coated Urea in Turfgrass Maintains Vigor and Mitigates Nitrogen's Environmental Impacts(Public Library of Science (PLOS), 2016-01-14) LeMonte, Joshua J.; Jolley, Von D.; Summerhays, Jeffrey S.; Terry, Richard E.; Hopkins, Bryan G.; Joshua J. LeMonte, Von D. Jolley, Jeffrey S. Summerhays, Richard E. Terry, Bryan G. Hopkins; LeMonte, Joshua J.Polymer coated urea (PCU) is a N fertilizer which, when added to moist soil, uses temperature- controlled diffusion to regulate N release in matching plant demand and mitigate environmental losses. Uncoated urea and PCU were compared for their effects on gaseous (N2O and NH3) and aqueous (NO3 -) N environmental losses in cool season turfgrass over the entire PCU N-release period. Field studies were conducted on established turfgrass sites with mixtures of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) in sand and loam soils. Each study compared 0 kg N ha-1 (control) to 200 kg N ha-1 applied as either urea or PCU (Duration 45CR1). Application of urea resulted in 127–476% more evolution of measured N2O into the atmosphere, whereas PCU was similar to background emission levels from the control. Compared to urea, PCU reduced NH3 emissions by 41–49% and N2O emissions by 45–73%, while improving growth and verdure compared to the control. Differences in leachate NO3 - among urea, PCU and control were inconclusive. This improvement in N management to ameliorate atmospheric losses of N using PCU will contribute to conserving natural resources and mitigating environmental impacts of N fertilization in turfgrass.