Publications

PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations; (2) batch-reaction and one-dimensional (1D) transport calculations involving reversible...

No abstract available.

Acid mine drainage from abandoned and inactive mines affects the water quality of the upper reaches of Fisher Creek, Montana. A sodium chloride tracer was added to the stream for 29.5 hours to provide a hydrologic context for synoptic sampling of metal chemistry in the stream and its inflows. The detailed profile of stream discharge obtained from the sampling helped to indicate those...

Concentrations of total lead (Pb) and dissolved Pb exceeded the U.S. Environmental Protection Agency action level of 15 micrograms per liter (mg/L) in approximately 19 percent and 1.3 percent, respectively, of ground-water samples collected during 1991-96 from a statewide network of monitoring wells designed to delineate background water quality of Florida's major aquifer systems...

No abstract available.

Lake‐atmosphere CO2 flux was directly measured above a small, woodland lake using the eddy covariance technique and compared with fluxes deduced from changes in measured lake‐water CO2 storage and with flux predictions from boundary‐layer and surface‐renewal models. Over a 3‐yr period, lake‐atmosphere exchanges of CO2 were measured over 5 weeks in spring, summer, and fall. Observed...

The ability to predict the fate of microorganisms in soil is dependent on an understanding of the process of their sorption on soil and subsurface materials. Presently, we have focused on studying the thermodynamics of sorption of bacteriophages (T-2, MS-2, and φX-174) on clays (hectorite, saponite, kaolinite, and clay fraction of samples collected from a landfill site). The...

The herbicide acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide] was first used on corn (Zea mays L.) in the USA during the growing season of 1994. By 1996, it was the third most heavily used corn herbicide in the midwestern USA. During the growing season of 1997, 78% of 375 samples collected at 32 stream sites in the Mississippi River Basin contained detectable

Dissolved sulfide concentrations in the water column and in sediment pore waters were measured by square-wave voltammetry (nanomolar detection limit) during three cruises to the Santa Barbara Basin in February 1995, November–December 1995, and April 1997. In the water column, sulfide concentrations measured outside the basin averaged 3 ± 1 nM (n= 28) in the 0 to 600 m depth range. Inside...

Under methanogenic conditions, stream-bed sediment microorganisms rapidly degraded [1,2-14C]vinyl chloride to 14CH4 and 14CO2. Amendment with 2-bromoethanesulfonic acid eliminated 14CH4 production and decreased 14CO2 recovery by an equal molar amount. Results obtained with [14C]ethene, [14C]acetate, or 14CO2 as substrates indicated that acetotrophic methanogens were responsible for the...

No abstract available.

Selenium (Se) can be oxidized by nitrate (NO−3) from irrigation on Cretaceous marine shale in western Colorado. Dissolved Se concentrations are positively correlated with dissolved NO−3concentrations in surface water and ground water samples from irrigated areas. Redox conditions dominate in the mobilization of Se in marine shale hydrogeologic settings; dissolved Se concentrations...