College of Science
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Browsing College of Science by Author "Abdulla, Hussain"
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Item A dissolved organic carbon (DOC) analyzer capable of detecting sub-μM DOC differences in natural fresh waters: A proof of concept study(ASLO, 2018-05-11) Jennings, Meredith; Abdulla, Hussain; Stubbins, Aron; Sun, Luni; Wang, Rui; Mopper, Kennethhis study reports the development of a new type of organic carbon (OC) analyzer that combines flow through analysis and ultraviolet-wet chemical oxidation (UV-WCO). Total or dissolved OC (TOC or DOC, respectively) is determined through detection of CO2 as the oxidation product using a vibration insensitive nondispersive infrared (NDIR) gas analyzer. Aided by heat and UV, OC is oxidized by continuously pumping the liquid sample in-line with a carbon-free acidic persulfate reagent at a constant flow rate through the system. The CO2 produced from oxidation of OC is sparged from solution at a precise flow rate and is continuously detected, producing a stable signal plateau with high signal-to-noise ratio. A low carbon blank/baseline for the analysis is achieved by recycling persulfate reagent alone through the system until minimal CO2 is detected. We show progress in the optimization of this novel instrument that, unlike standard high temperature combustion (HTC) instrumentation that is subject to high blank variability and micromolar resolution (typical coefficient of variation (CV) ∼ 1–2%), has potential applications for studies of DOC net production and consumption by various mechanisms that typically require sub-micromolar precision.Item Spatial variation and availability of nutrients at an oyster reef in relation to submarine groundwater discharge(Elsevier, 2019-12-27) Spalt, Nicholas A.; Murgulet, Dorina; Abdulla, HussainSubmarine groundwater discharge (SGD) is often an overlooked component of the solute budgets in coastal embayments and is not considered in oyster restoration, conservation, and management plans. A combination of spatial and temporal geochemistry (nutrients, trace metals, alkalinity components, stable isotopes, and major ions) of porewater and surface water combined with SGD-derived solute fluxes and turnover times was used to examine the significance of SGD in delivering nutrients to paleovalley systems in coastal embayments, thus sustaining the health and productivity of oyster reefs. A 1-km2 area encompassing a paleovalley system, in Copano Bay, Texas, exhibited significant differences in the spatial and temporal hydrogeochemical characteristics (major ions, stable isotopes and nutrients) along the reef when compared to the other environments (i.e., paleovalley, estuary-wide). Solute fluxes (i.e., dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN), total alkalinity, DIC, etc.) are slightly larger at the reef, followed by the margin and shoreline. During dry conditions, SGD from the 1-km2 area was estimated to supply anywhere between two-fold to one order of magnitude more nitrogen (in the form of DIN) than the riverine inputs to Copano Bay. During a wet year SGD equates the river input in the form of DIN. In addition, SGD-based turnover times, averaging <11 days for all nutrients, are significantly shorter than the average estuary flushing time (i.e., 38 days). Results from this study suggest that SGD within a paleovalley system is an important component in the estuarine nutrient budget through significant inputs and cycling processes between the subsurface and water column, particularly during low surface flows. Thus, estuarine environments such as paleovalley margins and interfluves provide favorable conditions to oysters through preferably enhanced SGD solute fluxes and should be considered in oyster restoration efforts.