The aeolian transport of aerosols (mineral dust from desert areas, smoke and ash from biomass burning, and from anthropogenic emissions) is an important process for introducing bioactive trace elements to the surface ocean and can have a large impact on marine primary production. All material that enters the ocean from the atmosphere must pass through the air-sea interface, or sea surface microlayer. The microlayer is the physical link between the sea surface and lower atmosphere and is therefore tied to the global biogeochemical cycling of trace elements. The microlayer (50 – 200 µm thickness) is a unique environment with different physical, chemical, and biological properties compared to the underlying water column. The microlayer is dynamic in nature due to numerous non-equilibrium processes such as temperature fluctuations, salinity gradients, irradiance, and wind and wave actions that influence its biogeochemical properties. However, the microlayer is mechanically more stable than the underlying water column due to the higher concentration of surface-active organic compounds; creating a more rigid film-like layer over the surface of the ocean. It is an important, yet often ignored component in the biogeochemical cycling of trace elements in the marine environment due to the lack of trace element clean sampling and analysis methods. A novel technique, a hollow cylinder of ultra-pure SiO₂ (quartz glass) with a plastic handle, was developed to sample the microlayer for trace elements. This research also developed and optimized clean trace element techniques to accurately measure nine trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in the dissolved and particulate fractions of the microlayer and underlying water column. Initially, our research focused on the behavior of dissolved and particulate Al, Mn, Fe, Co, Cu, Zn, Cd, and Pb in the microlayer in a controlled tank experiment using a Saharan dust source. The residence times of the dissolved trace elements ranged from 1.8 hours for Fe to 15 hours for Cd. The residence times for the particulate trace elements ranged from 1.0 minutes for Al and Fe to 1.4 minutes for Mn. There was an initial release of dissolved trace elements to the microlayer from the Saharan dust. However, the reactive fraction of the suspended particles increased over time, indicative of scavenging. Based on the artificial dust deposition experiment, aerosols should be retained in the sea surface microlayer long enough to undergo chemical and physical alteration that affects the bioavailability of trace elements. Opportunistic bacteria (example: Vibrio spp.) have been shown to experience rapid growth during dust deposition events. Aerosols and microlayer samples were collected in the Florida Keys over the course of two years for analysis of dissolved and particulate Al, Mn, Fe, Co, Ni, Cu, Zn, and Pb. Trace element concentrations increased by factors of 2 to 5 in the microlayer during significant Saharan dust events. Residence times of dissolved trace elements ranged from 0.12 hours for Mn to 2.4 hours for Cu. Residence times of particulate trace elements ranged from 1.1 minutes for Co to 2.4 minutes for Mn. The particulate residence times were comparable between the artificial deposition experiment and the natural deposition event observed in the Florida Keys. The relatively short residence times for dissolved trace elements compared to the artificial deposition event suggest external forces, such as wind and wave actions, mixed the dissolved metals faster than by simple molecular diffusion. Despite the short residence times, Vibrio spp. in the microlayer increased by factors of 2 to 10 after the passage of a Saharan dust event, which suggests that there was an initial pulse of bioavailable trace elements and other nutrients to the system. These findings demonstrate the dynamic nature of the sea surface microlayer and the large role atmospheric deposition can play when introducing trace elements to the surface oceans. It also sheds light on the need for more interdisciplinary research to deconvolute and quantify the processes occurring in the microlayer. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Fall Semester 2016. / December 9, 2016. / atmospheric deposition, sea surface microlayer, trace elements / Includes bibliographical references. / William M. Landing, Professor Directing Dissertation; Albert E. Stiegman, University Representative; Angela N. Knapp, Committee Member; Sven A. Kranz, Committee Member; Vincent J. M. Salters, Committee Member.

Traditional measurements of phytoplankton N uptake have been confounded by bacterial retention on filters used in 15N uptake studies, and such methodological obstacles have limited our understanding of phytoplankton-bacterial interactions regarding N cycling. In this research, uptake of various inorganic and organic N substrates by phytoplankton and bacteria was measured in several marine ecosystems using two distinct approaches: size fractionation into phytoplankton and bacterial size classes, and flow cytometric (FCM) sorting of autotrophic cells. Comprehensive assessments of N uptake dynamics were conducted in Chesapeake Bay, the Mid-Atlantic Bight, and Raunefjord, Norway, with supplementary data collected from the York River, Virginia and the Gulf of Mexico. In Chesapeake Bay, the composition of the dissolved N pool shifted from being dominated by dissolved inorganic N (DIN) in the upper bay to mostly dissolved organic N (DON) in the lower bay. Accordingly, phytoplankton nitrate uptake was highest near the head, whereas uptake of urea and dissolved free amino acids generally increased southward. Nonetheless, ammonium was the dominant form of N used by phytoplankton and bacteria throughout the bay. In the Mid-Atlantic Bight, the surface layer was devoid of DIN but ambient urea concentrations were relatively high and this organic substrate supported a large majority of total measured N uptake. The dissolved N pool in the bottom water consisted of about two-thirds DIN, with ammonium contributing most to total uptake. Bacteria were especially active in the bottom water and contributed over half of the total DIN uptake, and there was evidence of bacterial urea uptake in the surface water. In Raunefjord, a mesocosm approach was used to examine N uptake by a bloom of colonial Phaeocystis as well as the competition between phytoplankton and bacteria for limited N resources. Despite amending with nitrate, ammonium was the primary N form supporting the bloom. In the unfertilized mesocosm, bacteria were responsible for about half the urea uptake, most of the DFAA uptake, and at least a third of DIN uptake. Overall, total dissolved N concentrations and total N uptake decreased from estuarine to oceanic waters, although uptake rates were highly variable within each ecosystem. The reduced N forms, ammonium and urea, were most important to phytoplankton N nutrition, and contrary to traditional belief, urea at times played an important role in bacterial N uptake. With respect to methodological approaches, traditional filtration resulted in significant overestimation of phytoplankton N uptake due to the inclusion of, and 15N enrichment in, bacterial biomass retained on filters. This research represents the first comprehensive assessment of phytoplankton-specific N uptake across various ecosystems. It highlights not only the need for careful qualification of uptake rates measured using traditional approaches, but also the potential application of FCM sorting to more detailed examination of N uptake by phytoplankton in general, but also by specific taxa in various marine ecosystems.

The potential for in situ anaerobic benzene degradation in petroleum-contaminated aquifers was investigated. Sediments collected from a contaminated aquifer near Bemidji, MN in which Fe(III)-reduction was the dominant microbial process readily mineralized benzene when incubated with [U-14C]benzene while sediments from other aquifers did not. Benzene mineralization was localized within a narrow zone at the downgradient edge of the Fe(III) reduction zone. Analysis of MPN cultures and sediment by a variety of 16S rRNA-based techniques indicated a selective enrichment of Geobacteraceae in benzene degrading, Fe(III)-reducing sediments. Members of the Geobacteraceae are known to couple the oxidation of aromatic compounds to the reduction of Fe(III) and could be responsible for the observed benzene degradation at this site. Bemidji sediments also mineralized other aromatic compounds commonly found in hydrocarbon-contaminated groundwaters. Benzene-degrading sediments readily mineralized toluene and naphthalene indicating that these compounds were also being oxidized in situ. The unusual aromatic degradation activity at the Bemidji site could not be attributed to the presence of Fe(III)-chelators and/or electron shuttling compounds in the groundwater. Uncontaminated sediments could be adapted to benzene suggesting that Bemidji sediments naturally contain a microbial population capable of anaerobic benzene degradation. Results obtained from the Bemidji aquifer encouraged the investigation of anaerobic treatment alternatives for contaminated aquifers. Anaerobic bioremediation of benzene was evaluated at a petroleum-contaminated aquifer in Oklahoma. The injection of sulfate into the subsurface stimulated benzene degradation within a treatment zone located downgradient from an injection gallery. Benzene concentrations in the groundwater decreased by an average of 90% (100% in one well) during the study period. Sulfate concentrations, relative to a bromide tracer, decreased with distance from the injection gallery suggesting that benzene removal was coupled to the removal of sulfate from the groundwater. [U-14C]Benzene mineralization and [2-14C]acetate analysis of sediments confirmed that benzene degradation was indeed coupled to sulfate reduction within treatment zone sediments. Mass balance calculations suggested that as much as 42% of the removed sulfate within the treatment zone could be attributed to the anaerobic oxidation of benzene. The results demonstrate that stimulation of anaerobic processes can be an effective treatment alternative for heavily contaminated aquifers.

The research presented in this dissertation describes the influence of planktonic bacterial growth on upper ocean organic matter dynamics in the North Pacific Subtropical Gyre (NPSG). Examination of the temporal dynamics in dissolved organic matter (DOM) was coupled with investigations that targeted the influence of heterotrophic bacterial production (HBP) on organic matter fluxes in the NPSG. Nine cruises to the Hawaii Ocean Time-series field site Station ALOHA revealed that HBP accounted for a large flux of organic carbon in the upper ocean of the NPSG. HBP was significantly enhanced by sunlight, with photoenhancement of HBP accounting for 3.2 mol C m-2 yr-1, equivalent to 21% of the annual photoautotrophic production in this ecosystem. These observations suggest that HBP in the upper ocean of the oligotrophic NPSG exerts a large influence over organic matter fluxes in this ecosystem, and that a large fraction of HBP depends on sunlight. Several experiments were conducted to asses the response of heterotrophic protein production to irradiance at Station ALOHA. The results of these experiments revealed that HBP responded to irradiance similar to the response of photosynthesis to irradiance in this ecosystem. Upper ocean HBP increased with light intensity at low light fluxes (<200 mumol quanta m-2 s -1), but saturated or declined with increasing irradiance. Experiments conducted in the upper and lower photic zone revealed significant photoinhibition of bacterial production in the lower photic zone. Overall, the heterotrophic response was similar to the photosynthetic response, suggesting light-driven HBP could result from mixotrophic growth by the photoautotrophic unicellular cyanobacteria Prochlorococcus. Analyses of dissolved organic matter (DOM) inventories from 1988 to 1999 revealed multiyear increases in the inventories of dissolved organic carbon, nitrogen, and phosphorous (DOC, DON, and DOP) in the upper ocean of the NPSG. During the latter half of the observation period, rates of DOP accumulation declined, coincident with significant DOC and DON accumulation. Analyses of bacterial population dynamics between 1992 and 1999 revealed an apparent shift in the abundance of Prochlorococcus during the period of observation. These results suggest that prokaryote population structure directly influences the cycling of organic matter in this ecosystem.

The impact of the Deepwater Horizon blowout on coastal wetlands can be understood through investigating carbon loading and microbial activity in salt marsh sediments. Carbon influx causes pore water sulfide to increase in wetland sediment, making it toxic and inhospitable to marsh vegetation. High sulfide levels due to increased microbial activity can lead to plant browning and mortality. Preliminary analyses at Marsh Point, Mississippi indicated that sulfate reducing bacteria are more active in contaminated marsh, producing sulfide concentrations 100x higher than in noncontaminated marsh. Sediment electrode profiles, hydrocarbon contamination, and microbial community profiles were measured at three additional locations to capture the spatial sedimentary geochemical processes impacting salt marsh dieback. Findings indicate that response to contamination is variable due to physical and biogeochemical processes specific to each marsh. Temporal evaluation indicates that there is a lag in maximum response to contamination due to seasonal effects on microbial activity.

No description available.

No description available.

No description available.

No description available.

No description available.