Publications

Selenium stable isotope ratio measurements should serve as indicators of sources and biogeochemical transformations of Se. We report measurements of Se isotope fractionation during selenate reduction, selenite sorption, oxidation of reduced Se in soils, and Se volatilization by algae and soil samples. These results, combined with previous work with Se isotopes, indicate that reduction of soluble o

Robowell is an automated process for monitoring selected ground water quality properties and constituents by pumping a well or multilevel sampler. Robowell was developed and tested to provide a cost-effective monitoring system that meets protocols expected for manual sampling. The process uses commercially available electronics, instrumentation, and hardware, so it can be configured to monitor gro

Humic substances (HS) form molecular aggregates in solution and on mineral surfaces. Elucidation of the mechanism of formation of these aggregates is important for an understanding of the interactions of HS in soils arid natural waters. The HS are formed mainly by enzymatic depolymerization and oxidation of plant biopolymers. These reactions transform the aromatic and lipid plant components into a

A comprehensive set of soil characteristics were examined to determine the effect of soil on the transport of agrichemicals to ground water. This paper examines the relation of local soil characteristics to concentrations and occurrence of nitrate, atrazine (2-chloro-4 ethylamino-6-isopropylamino-s-trazine), and atrazine residue [atrazine + deethylatrazine (2-amino-4-chloro-6-isopropylamino-s-tria

Washed-cell suspensions of Sulfurospirillum barnesiireduced selenate [Se(VI)] when cells were cultured with nitrate, thiosulfate, arsenate, or fumarate as the electron acceptor. When the concentration of the electron donor was limiting, Se(VI) reduction in whole cells was approximately fourfold greater in Se(VI)-grown cells than was observed in nitrate-grown cells; correspondingly, nitrate reducti

The development and distribution of phytoplankton blooms in estuaries are functions of both local conditions (i.e. the production-loss balance for a water column at a particular spatial location) and large-scale horizontal transport. In this study, the second of a 2-paper series, we use a depth-averaged hydrodynamic-biological model to identify transport-related mechanisms impacting phytoplankton

A device that uses a siphon tube to establish a hydraulic connection between the bottom of an onshore standpipe and a point at the bottom of a water body was designed and tested for monitoring surface-water levels. Water is added to the standpipe to a level sufficient to drive a complete slug of water through the siphoning tube and to flush all air out of the system. The water levels in the standp

No abstract available.

An important gap in the understanding of the hydrology of the Middle Rio Grande Basin, central New Mexico, is the rate at which water from the Rio Grande recharges the Santa Fe Group aquifer system. Several methodologies-including use of the Glover-Balmer equation, flood pulses, and channel permeameters- have been applied to this problem in the Middle Rio Grande Basin. In the work presented here,

The 1997 Annual Report is the fifth Annual Report from the Regional Monitoring Program for Trace Substances (RMP) and contains a comprehensive description of RMP results from the 1997 monitoring year. As in previous years, the report includes results from the Base Program (water, sediment, and bivalve monitoring) and results from Pilot and Special Studies completed in 1997, in addition to an updat

No abstract available.

Sediment chronologies based on radioisotope depth profiles were developed at two sites in the San Francisco Bay estuary to provide a framework for interpreting historical trends in organic compound and metal contaminant inputs. At Richardson Bay near the estuary mouth, sediments are highly mixed by biological and/or physical processes. Excess  penetration ranged from 2 to more than 10 cm at eight