Publications

Transport of dissolved material in streams and small rivers may be characterized using tracer-dilution methods and solute transport models. Recent studies have quantified stream/substream interactions using models of transient storage. These studies are based on tracer-dilution data obtained during periods of steady flow. We present a modeling framework for the analysis of transient...

The 1500 km Upper Mississippi River (UMR) consists of 29 navigation pools and can be divided into the upper reach (pools 1-4), the middle reach (pools 5-13), and the lower reach (pools 14-26). Comparison of composite bed sediment samples collected from the downstream third of 24 pools before and after the 1993 UMR flood provides fieldscale data on the effect of the flood on sediment...

A facultatively methylotrophic bacterium, strain IMB-1, that has been isolated from agricultural soil grows on methyl bromide (MeBr), methyl iodide, methyl chloride, and methylated amines, as well as on glucose, pyruvate, or acetate. Phylogenetic analysis of its 16S rRNA gene sequence indicates that strain IMB-1 classes in the alpha subgroup of the class Proteobacteria and is closely...

Pinal Creek, Arizona receives an inflow of ground water with high dissolved inorganic carbon (57-75 mg/l) and low pH (5.8-6.3). There is an observed increase of in-stream pH from approximately 6.0-7.8 over the 3 km downstream of the point of groundwater inflow. We hypothesized that CO2 gas-exchange was the most important factor causing the pH increase in this stream-aquifer system. An...

A ground water basin is defined as the volume of subsurface through which ground water flows from the water table to a specified discharge location. Delineating the topographically defined surface water basin and extending it vertically downward does not always define the ground water basin. Instead, a ground water basin is more appropriately delineated by tracking ground water flowpaths...

Anaerobic oxidation of [1,2-14C]vinyl chloride and [1,2-14C]dichloroethene to 14CO2under humic acid-reducing conditions was demonstrated. The results indicate that waterborne contaminants can be oxidized by using humic acid compounds as electron acceptors and suggest that natural aquatic systems have a much larger capacity for contaminant oxidation than previously thought.

Contamination of shallow ground water by sewage effluent typically contains reduced chemical species that consume dissolved oxygen, developing either a low oxygen geochemical environment or an anaerobic geochemical environment. Based on the load of reduced chemical species discharged to shallow ground water and the amounts of reactants in the aquifer matrix, it should be possible to...

The contribution of hydroxylated atrazine degradation products (HADPs) to the total atrazine load (i.e., atrazine plus stable metabolites) in streams needs to be determined in order to fully assess the impact of atrazine contamination on stream ecosystems and human health. The objectives of this study were (1) to determine the contribution of HADPs to the total atrazine load in streams...

Under some conditions, a first-order kinetic model is a poor representation of biodegradation in contaminated aquifers. Although it is well known that the assumption of first-order kinetics is valid only when substrate concentration, S, is much less than the half-saturation constant, K(s), this assumption is often made without verification of this condition. We present a formal error...

The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Ground water ages within the aquifer could not be accurately determined from the measured distribution of 3H and as a result, chlorofluorocarbon (CFC) and 3H/3He dating techniques were applied. Beneath a 25 m...

There are spatial differences in methyl mercury (MeHg) concentrations in biota in Water Conservation Areas 2 and 3 in the Everglades, with higher concentrations generally found in the southern areas. Fish and hemipterans had the most MeHg on a wet weight basis, with levels exceeding 30 ng g-1. The magnitude of MeHg accumulation in biota varies seasonally and does not always appear to be...

The objective of this study was to examine chemical changes in porewaters that occur over small scales (cm) as groundwater flows through the hyporheic zone and discharges to a stream in a temperate forest of northern Wisconsin. Hyporheic-zone porewaters were sampled at discrete depths of 2, 10, 15, 61, and 183 cm at three study sites in the study basin. Chemical profiles of dissolved...