Publications

Sediment cores of known chronology from Richardson and San Pablo Bays in San Francisco Bay, CA, were analyzed for a suite of chlorinated hydrocarbon pesticides and polychlorinated biphenyls to reconstruct a historic record of inputs. Total DDTs (DDT = 2,4'- and 4,4'-dichlorodiphenyltrichloroethane and the metabolites, 2,4'- and 4,4'-DDE, -DDD) range in concentration from 4-21 ng/g and...

A new method for direct determination of dissolved Fe(III) in acid mine water has been developed. In most present methods, Fe(III) is determined by computing the difference between total dissolved Fe and dissolved Fe(II). For acid mine waters, frequently Fe(II) ≫ Fe(III); thus, accuracy and precision are considerably improved by determining Fe(III) concentration directly. The new method...

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...

Recently, methods have been developed to analyze NO3- for δ15N and δ18O, improving our ability to identify NO3- sources and transformations. However, none of the existing methods are suited for waters with low NO3- concentrations (0.7-10 µM). We describe an improved method for collecting and recovering NO3- on exchange columns. To overcome the lengthy collection loading times imposed by...

A model for trace metals that considers in-stream transport, metal oxide precipitation-dissolution, and pH-dependent sorption is presented. Linkage between a surface complexation submodel and the stream transport equations provides a framework for modeling sorption onto static and/or dynamic surfaces. A static surface (e.g., an iron- oxide-coated streambed) is defined as a surface with a

Periphyton samples from Water Conservation Areas, Big Cypress National Preserve, and Everglades National Park in south Florida were analyzed for concentrations of total mercury, methylmercury, nitrogen, phosphorus, organic carbon, and inorganic carbon. Concentrations of total mercury in periphyton decrease slightly along a gradient from north‐to‐south. Both total mercury and...

Precipitation and aggregation of metacinnabar (black HgS) was inhibited in the presence of low concentrations (≥3 mg C/L) of humic fractions of dissolved organic matter (DOM) isolated from the Florida Everglades. At low Hg concentrations (≤5 × 10-8 M), DOM prevented the precipitation of metacinnabar. At moderate Hg concentrations (5 × 10-5 M), DOM inhibited the aggregation of colloidal

Soil water collected from suction lysimeters and wick samplers buried in the unsaturated zone of a sand and gravel aquifer and extracted from soil cores were analyzed for stable oxygen and hydrogen isotope values. Soil water isotopic values differed among the three sampling methods in most cases. However, because each sampling method collected different fractions of the total soil-water...

The formation and spatial distribution of phytoplankton blooms in estuaries are controlled by (1) local mechanisms, which determine the production-loss balance for a water column at a particular spatial location (i.e. control if a bloom is possible), and (2) transport-related mechanisms, which govern biomass distribution (i.e. control if and where a bloom actually occurs). In this study...

A 1,000-Dalton tangential-flow ultrafiltration (TFUF) membrane was used to isolate dissolved organic matter (DOM) from several freshwater environments. The TFUF unit used in this study was able to completely retain a polystyrene sulfonate 1,800-Dalton standard. Unaltered and TFUF-fractionated DOM molecular weights were assayed by high-pressure size exclusion chromatography (HPSEC). The...

Sediments sampled at a hydrocarbon-contaminated, glacial-outwash, sandy aquifer near Bemidji, Minnesota, were analyzed for sediment-associated Fe with several techniques. Extraction with 0.5 M HCl dissolved poorly crystalline Fe oxides and small amounts of Fe in crystalline Fe oxides, and extracted Fe from phyllosilicates. Use of Ti-citrate-EDTA-bicarbonate results in more complete...

Polarities of the soiL/sediment organic matter (SOM) in 19 soil and 9 freshwater sediment sam pies were determined from solid-state 13C-CP/MAS NMR spectra and compared with published partition coefficients (K(oc)) of carbon tetrachloride (CT) from aqueous solution. Nondestructive analysis of whole samples by solid-state NMR permits a direct assessment of the polarity of SOM that is not...