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This article discusses the amount of nitrogen which is contributed to ground water from tile-drained corn belt watersheds with fine grained soil in central Illinois. The authors argue that a significant amount of nitrogen reached shallow ground water by transportation past the tile drains. The results also showed that significant levels of nitrogen were added to groundwater by denitrifying bacteria found at depth throughout the watershed. Laboratory tests showed that a nitrate could be rapidly denitrified. They conclude that fine grained soils may act as a significant nitrogen sink in groundwater compared to surface water.

Examines the isotopic ratios of Uranium 234 and 238 in a freshwater, fracture-flow aquifer, the eastern Snake River Plain aquifer in Idaho. Interpretation of results in conjunction with strontium isotope and solute concentration data; Implications for groundwater flow patterns and geochemical evolution of the aquifer.

Examines the effectiveness of radiogenic isotopes ratios in tracing groundwater preferential flow paths of Snake River Plain aquifer in Idaho. Characteristic of radiogenic isotope ratios; Role of flow paths in contaminants transportation; Applicability of the ratio as compared to solute-concentration data; Identification of path slow and fast-flow zones.

Analyzes the effectiveness of selenium stable isotope ratios as indicators of selenium sources and reduction of selenium oxyanions in the San Francisco Bay Estuary in California. Environmental samples; Reduction of soluble selenium from the overlying water; Consistent isotopic differences between riverine and refinery inputs with selenium isotopes.

The attenuation of groundwater contamination via chemical reaction is traditionally evaluated by monitoring contaminant concentration through time. However, this method can be confounded by common transport processes (e.g., dilution, sorption). Isotopic techniques bypass the limits of concentration methods, and so may provide improved accuracy in determining the extent of reaction. We apply measurements of 238U/235U to a U bioremediation field experiment at the Rifle Integrated Field Research Challenge Site in Rifle, Colorado. An array of monitoring and injection wells was installed on a 100 m² plot where U(VI) contamination was present in the groundwater. Acetate-amended groundwater was injected along an up-gradient gallery to encourage the growth of dissimilatory metal reducing bacteria (e.g., Geobacter species). During amendment, U concentration dropped by an order of magnitude in the experiment plot. We measured 238U/235U in samples from one monitoring well by MC-ICP-MS using a double isotope tracer method. A significant ∼1.00‰ decrease in 238U/235U occurred in the groundwater as U(VI) concentration decreased. The relationship between 238U/235U and concentration corresponds approximately to a Rayleigh distillation curve with an effective fractionation factor (α) of 1.00046. We attribute the observed U isotope fractionation to a nuclear field shift effect during enzymatic reduction of U(VI)(aq) to U(IV)(s). [ABSTRACT FROM AUTHOR]

Abstract: Strontium isotope values (87Sr/86Sr) in bone and tooth enamel have been used increasingly to identify non-local individuals within prehistoric human populations worldwide. Archaeological research in the Midwestern United States has increasingly highlighted the role of population movement in affecting interregional cultural change. However, the comparatively low level of geologic variation in the Midwestern United States might suggest a corresponding low level of strontium variation, and calls into question the sensitivity of strontium isotopes to identify non-local individuals in this region. Using strontium isotopes of archaeological fauna, we explore the degree of variability in strontium ratios across this region. Our results demonstrate measurable variation in strontium ratios and indicate the potential of strontium analysis for addressing questions of origin and population movement in the Midwestern United States. [Copyright &y& Elsevier]

Purpose/objectives: The objectives of this study were to assess the influence of learner- and education-related factors on standardized in-service examination performance and determine whether in-service examination scores predict residency outcomes., Methods: American Academy of Periodontology (AAP) In-service Examination (AIE) scores from 10 periodontics residency classes at a single center were recorded and compared against a panel of learner- and education-related variables using multiple linear regression models. Defined residency outcome measures were analyzed against AIE scores using binomial logistic regression., Results: No evaluated learner- or education-related variable was a statistically significant predictor of AIE score in this study sample. Likewise, AIE score was not a statistically significant predictor of any assessed residency outcome., Conclusions: The AAP has performed a tremendous service to periodontics residents and programs by marshaling the leadership and expertise necessary to offer a professionally constructed assessment instrument. However, in the current study, no relationship could be identified between AIE score and any outcome, including first-attempt board certification. The AAP In-service Committee appears well situated to provide additional leadership focusing on exam implementation, which may enhance AIE value in competency decision making., (Published 2024. This article is a U.S. Government work and is in the public domain in the USA.)