Larry Robinson

Relaxed eddy accumulation measurements of ammonia, nitric acid, sulfur dioxide and particulate sulfate dry deposition near Tampa, FL, USA

The relaxed eddy accumulation (REA) method was utilized to measure fluxes of key atmospheric species, specifically ammonia (NH3), nitric acid (HNO3), sulfur dioxide (SO2) and particulate sulfate (SO42−) to vegetation that is characteristic throughout the Tampa Bay Watershed. Three annular denuder systems (ADS), each consisting of two annular denuders and a filter pack in series, were deployed to accumulate gaseous constituents and fine-fraction particulates (Dp<2.5 µm) in updraft and downdraft eddies, as well as in the mid-draft velocity range. Relaxed eddy accumulation samples, which were analyzed by ion chromatography, and continuous meteorological data were collected during the May 2002 Bay Regional Atmospheric Chemistry Experiment (BRACE) near Sydney, FL. For the chemical species of current interest, concentrations were 1.64 ± 0.23 for NH3, 2.06 ± 0.24 for HNO3, 3.49 ± 0.50 for SO2 and 4.64 ± 0.31 µg m−3 for SO42−, and the deposition velocity (Vd) estimates for NH3, HNO3, SO2 and SO42− were 1.27 ± 3.65, 3.63 ± 1.47, 0.45 ± 0.98 and 0.42 ± 1.00 cm s−1, respectively. The results obtained confirm the expectation that the deposition of ammonia, nitric acid and particulate sulfate was controlled by aerodynamic and quasi-laminar layer resistances and that sulfur dioxide is relatively dependent upon stomatal conditions.

Chronology of sediment nutrient geochemistry in Apalachicola Bay, Florida (U.S.A.)

Abstract Land use changes have been shown to alter the balance of nutrient and mineral sources and sinks to coastal systems. These shifts are often preserved in sediment records. In Apalachicola Bay, productivity is dependent on nutrient loading from the Apalachicola-Chattahoochee-Flint (ACF) river basin; alterations to ACF watershed flow by management activities coupled with increased marine water inundation associated with rising sea level threaten this productivity. The objective of this research was to evaluate past changes in nutrient loading to Apalachicola Bay as recorded in sediment history and determine if these changes could be associated with both anthropogenic and natural alterations in the system. Sediment cores from three sites in the bay were collected and analyzed for organic carbon (C), total nitrogen (N), and total phosphorus (P) concentrations and δ13C and δ15N stable isotopic abundances. The three sites are located at the river mouth (S1), mid-bay (S2), and in the northeastern region of the bay (S3). Carbon and nitrogen concentrations, ratios, and stable isotopes coupled with grain-size shifts for the bay suggest a decrease in river organic matter supply and a change in sediment clay content supply and/or distribution for the bay. Overall, the applied indicators suggest an increase in marine influence on the organic matter in the estuary. These shifts appear to be associated with Apalachicola River management practices coupled with sea-level rise in the Gulf of Mexico.

Phenanthrene Emulsification and Biodegradation Using Rhamnolipid Biosurfactants and Acinetobacter calcoaceticus In Vitro

ABSTRACT The ability of biosurfactants and Acinetobacter calcoaceticus to enhance the emulsification and biodegradation of phenanthrene was investigated. Phenanthrene is a polycyclic aromatic hydrocarbon that may be derived from various sources, for example incomplete combustion of petroleum fuel, and thus it occurs ubiquitously throughout the environment. In order to assess the efficacy of a biosurfactant microparticle system, emulsification assays and in vitro biodegradation studies were conducted. Emulsification assays were carried out to assess the stability of phenanthrene emulsions. Emulsion stability was determined by the height of the emulsion layer (Emulsification Index) and turbidity. In vitro biodegradation tests were done to estimate phenanthrene degradation from an aqueous system by A. calcoaceticus supplemented with encapsulated (ERhBS) and nonencapsulated biosurfactants (NERhBS). Results show that phenanthrene emulsifications were stabilized after 48 h with NERhBS and remained stable for 72 additional hours. Phenanthrene emulsifications were stabilized with ERhBS after 216 h and remained stable for an additional 96 h. A. calcoaceticus alone and supplemented with rhamnolipid biosurfactant were able to biodegrade 10 to 50 mg L−1 of phenanthrene within 250 h. When supplemented with NERhBS, A. calcoaceticus degraded phenanthrene significantly faster than when nonsupplemented or supplemented with ERhBS. Addition of exogenous biosurfactants was considered to be a major factor driving the direct correlation between decreasing phenanthrene concentration in the system and increasing bacterial biomass.

The neutron flux of a252Cf neutron activation analysis device using the MCNP code

This report presents results from the application of the Monte Carlo N-Particle (MCNP) computer code to the252Cf neutron activation analysis (NAA) Device in the Technical Physics Institute of the Heilongjiang Science Academy of the Peoples Republic of China. The thermal and epithermal neutron flux at the sample positions and the neutron and photon fluxes on the surfaces of the device were calculated. A comparison between the calculated and experimental thermal and epithermal neutron fluxes at sample positions yield relative errors of less than 10% for the thermal neutron flux.

Characteristics of Nutrient Transport from Tate's Hell State Forest into East Bay in Florida

Abstract From 1988 to 1998, silvicultural activities impacted 5,856 km of rivers and streams in the southern United States. Internal cycling of nutrients from the water column and sediment in a forest can be an important contribution to the nutrient load of aquatic ecosystems. Therefore, understanding nutrient transport in forests can aid efforts to protect aquatic resources. Two watersheds in Tates Hell State Forest in northwest Florida were selected to conduct a study of silvicultural impacts on surface water quality. Of the two sites one had been impacted with ditching and fertilization while the other site was not. From June 2003 to May 2005 a field study determined nutrient [nitrate-nitrogen (NO3-N); ammonia-nitrogen (NH3-N) and ortho-phosphate (PO4−)] concentrations in run-off water and sediment in these watersheds. Results showed NO3-N, NH3-N and ortho-phosphate concentrations in water and sediment, were higher at the impacted site verses the non-impacted site. At the impacted site NO3-N, NH3-N and ortho-phosphate concentrations in the water column were 16% to 33%, 39% to 47% and 66% higher, respectively. Nutrient concentrations in sediment from the impacted site were significantly (p< 0.05) higher than those from the un-impacted site and ranged (in mg kg−1) from 0.25 ± 0.01 to 0.44 ± 0.03 for NO3-N; 6.41 ± 0.19 to 12.77 ± 0.45 for NH3-N; and 1.01± 0.02 to 1.50 ± 0.02 for PO4−. In this ecosystem sediment acted as a source of NH3-N and ortho-phosphate and as a sink for NO3-N. These results indicate that proper management of inactive silvicultural sites is necessary to mitigate nutrient transport to aquatic systems.