Arsenic, vanadium, iron, and manganese biogeochemistry in a deltaic wetland, southern Louisiana, USA

Geochemical cycling of the redox-sensitive trace elements arsenic (As) and vanadium (V) was examined in shallow pore waters from a marsh in an interdistributary embayment of the lower Mississippi River Delta. In particular, we explore how redox changes with depth and distance from the Mississippi River affect As and V cycling in the marsh pore waters. Previous geophysical surveys and radon mass balance calculations suggested that Myrtle Grove Canal and the bordering marsh receive fresh groundwater, derived in large part from seepage of the Mississippi River, which subsequently mixes with brackish waters of Barataria Bay. Additionally, the redox geochemistry of pore waters in the wetlands is affected by Fe and S cycling in the shallow subsurface (0–20 cm). Sediments with high organic matter content undergo SO42 − reduction, a process ubiquitous in the shallow subsurface but largely absent at greater depths (~ 3 m). Instead, at depth, in the absence of organic-rich sediments, Fe concentrations are elevated, suggesting that reduction of Fe(III) oxides/oxyhydroxides buffers redox conditions. Arsenic and V cycling in the shallow subsurface are decoupled from their behavior at depth, where both V and As appear to be removed from solution by either diffusion or adsorption onto, or co-precipitation with, authigenic minerals within the deeper aquifer sediments. Pore water As concentrations are greatest in the shallow subsurface (e.g., up to 315 nmol kg− 1 in the top ~ 20 cm of the sediment) but decrease with depth, reaching values < 30 nmol kg− 1 at depths between 3 and 4 m. Vanadium concentrations appear to be tightly coupled to Fe cycling in the shallow subsurface, but at depth, V may be adsorbed to clay or sedimentary organic matter (SOM). Diffusive fluxes are calculated to examine the export of trace elements from the shallow marsh pore waters to the overlying canal water that floods the marsh. The computed fluxes suggest that the shallow sediment serves as a source of Fe, Mn, and As to the surface waters, whereas the sediments act as a sink for V. Iron and Mn fluxes are substantial, ranging from 50 to 30,000 and 770 to 4300 nmol cm− 2 yr− 1, respectively, whereas As fluxes are much less, ranging from 2.1 to 17 nmol cm− 2 yr− 1. Vanadium fluxes range from 3.0 nmol cm− 2 yr− 1 directed into the sediment to 1.7 nmol cm− 2 yr− 1 directed out of the sediment

Global Lawyering Skills

Global Lawyering Skills is designed to teach fundamental lawyering skills by introducing students to a broader range of skills than a traditional research and writing textbook. While the book covers basic objective and persuasive legal writing skills, it also addresses other lawyering skills, such as oral argument, ARD, transactional drafting, and client interviewing and counseling. Additionally, students need an understanding of how cross-cultural and transnational considerations impact the practice of law.https://scholarlycommons.pacific.edu/facultyteaching/1036/thumbnail.jp

Global Lawyering Skills

Global Lawyering Skills is designed to teach fundamental lawyering skills by introducing students to a broader range of skills than a traditional research and writing textbook. While the book covers basic objective and persuasive legal writing skills, it also addresses other lawyering skills, such as oral argument, ARD, transactional drafting, and client interviewing and counseling. Additionally, students need an understanding of how cross-cultural and transnational considerations impact the practice of law.https://scholarlycommons.pacific.edu/facultyteaching/1036/thumbnail.jp

Measurements of the separated longitudinal structure function FL from hydrogen and deuterium targets at low Q2

Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the partonic dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available in particular for the longitudinal structure function. Here, we present separated structure functions for hydrogen and deuterium at low four-momentum transfer squared, Q2<1GeV2, and compare them with parton distribution parametrization and kT factorization approaches. While differences are found, the parametrizations generally agree with the data, even at the very low-Q2 scale of the data. The deuterium data show a smaller longitudinal structure function and a smaller ratio of longitudinal to transverse cross section, R, than the proton. This suggests either an unexpected difference in R for the proton and the neutron or a suppression of the gluonic distribution in nuclei