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R. A. Davis

Publications and source records attributed to R. A. Davis.

13 recordsLinked to original sources
USGS2020

Liquid chromatographic determination of chloramine-T and its primary degradation product, p-toluenesulfonamide, in water

N -sodium- N -chloro-ρ-toiuenesulfonamide (chloramine-T) effectively controls bacterial gill disease (BGD) in cultured fishes. BGD, a common disease of hatchery-reared salmonids, causes more fish losses than any other disease among these species. This study describes a liquid chromatographic (LC) method that is capable of direct, simultaneous analysis of chloramine-T and its primary degradation product, ρ-toluenesulfonamide (ρ-TSA), in water. The procedure involves reversed-phase (C 18 ) LC analysis with ion suppression, using 0.01 M phosphate buffer at pH 3. The mobile phase is phosphate buffer-acetonitrile (60 + 40) at 1 mL/min. Both chemicals can be detected with a UV spectrophotometer at 229 nm; the method is linear up to 40 mg chloramine-T or ρ-TSA/L. Mean recoveries were 96.4 ± 6.1% for water samples fortified with 0.03 mg chloramine-T/L and 95.3 ± 4.6% for water samples fortified with 0.005 mg ρ-TSA/L. Limits of detection without sample enrichment for chloramine-T and ρ-TSA are 0.01 mg/L and 0.001 mg/L, respectively.

Journal of AOAC International↗
USGS2003

Patterns and controls of surface sediment distribution: West-central Florida inner shelf

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems. ?? 2003 Elsevier B.V. All rights reserved.

Marine Geology↗
USGS1991

Rotenone persistence in freshwater ponds: Effects of temperature and sediment adsorption

The persistence of rotenone was compared between a cement-lined pond (0.04 hectare) and an earthen-bottom pond (0.02 hectare) treated with 5 μL Noxfish/L (250 μg rotenone/L) during spring, summer, and fall. Water temperatures on the days of treatment in each season were 8, 22, and 15°C, respectively. Both ponds were filled with pond water from a common source 1 week before each of the three treatments. Water samples (filtered and unfiltered) and sediment samples were analyzed by high-performance liquid chromatography to monitor the decrease of rotenone until residues were at or below the detection limit (<2.0 μg/L for water and < 25 ng/g for sediments). The loss of rotenone from water generally followed a first-order rate ofdecay. Rotenone disappeared two to three times faster in the earthen pond than in the concrete pond. The rotenone half-life times in the spring, summer, and fall treatments were 3.7, 1.3, and 5.2 d, respectively, in the concrete pond, and 1.8, 0.7, and 1.8 d in the earthen pond. Rates of decay in both ponds were directly correlated with water temperature. Filtered water samples from both ponds contained less rotenone than unfiltered water, indicating that some rotenone was bound to suspended material. The highest concentration of rotenone in sediment samples was 102 ng/g; residues decreased to below the detection limit within 14 d in the spring treatment and within 3 d in the summer and fall treatments.

North American Journal of Fisheries Management↗