Penney L. Miller

The role of fulvic acid composition in the photosensitized degradation of aquatic contaminants

Abstract.Dissolved organic matter (DOM) chemical composition varies depending upon the source of its precursor materials. Results show that the indirect photodegradation rate coefficients for the compounds sulfadimethoxine (SDM) and triclocarban (TCC) differ depending on the source of fulvic acids used as DOM surrogates. For sulfadimethoxine, little to no enhanced photolysis occurred for the terrestrially derived Suwannee River fulvic acid, but the rate coefficients for triclocarban increased 28%. In contrast, a large photo-enhancement (48% for SDM and 45% for TCC) occurred in the presence of Pony Lake and Old Woman Creek fulvic acids, both of which are derived from predominantly autochthonous material. Conversely, the iron-promoted photodegradation of alachlor occurred more quickly in the presence of Suwannee River fulvic acid than another autochthonous fulvic acid isolated from Lake Fryxell, Antarctica. This pathway is dominated by reaction through hydroxyl radicals generated by the photolysis of the fulvic acids. Taken together, these data provide evidence that autochthonous fulvic acids are more reactive than allochthonous fulvic acids in promoting pathways involving triplet dissolved organic matter intermediates, whereas the latter are more reactive than the former in promoting degradation by some reactive oxygen species (ROS). Thus, more systematic studies are needed to determine the full extent of the linkage between fulvic acid composition and its ability to promote indirect photolytic processes and how the presence of other DOM fractions may affect these reactions.

When a habitat freezes solid: Microorganisms over-winter within the ice column of a coastal Antarctic lake

A major impediment to understanding the biology of microorganisms inhabiting Antarctic environments is the logistical constraint of conducting field work primarily during the summer season. However, organisms that persist throughout the year encounter severe environmental changes between seasons. In an attempt to bridge this gap, we collected ice core samples from Pony Lake in early November 2004 when the lake was frozen solid to its base, providing an archive for the biological and chemical processes that occurred during winter freezeup. The ice contained bacteria and virus-like particles, while flagellated algae and ciliates over-wintered in the form of inactive cysts and spores. Both bacteria and algae were metabolically active in the ice core melt water. Bacterial production ranged from 1.8 to 37.9 μg CL(-1) day(-1). Upon encountering favorable growth conditions in the melt water, primary production ranged from 51 to 931 μg CL(-1) day(-1). Because of the strong H(2) S odor and the presence of closely related anaerobic organisms assigned to Pony Lake bacterial 16S rRNA gene clones, we hypothesize that the microbial assemblage was strongly affected by oxygen gradients, which ultimately restricted the majority of phylotypes to distinct strata within the ice column. This study provides evidence that the microbial community over-winters in the ice column of Pony Lake and returns to a highly active metabolic state when spring melt is initiated.

Microbial growth under humic-free conditions in a supraglacial stream system on the Cotton Glacier, Antarctica

During the austral summers of 2004 and 2009, we sampled a supraglacial stream on the Cotton Glacier, Antarctica. The stream dissolved organic matter (DOM) was low (44?48??M?C) and lacked detectable humic fluorescence signatures. Analysis of the excitation emissions matrices (EEMs) indicated that amino-acid fluorophores dominated, consistent with DOM of microbial origin, with little humic-like fluorescence. In most aquatic ecosystems, humic DOM attenuates harmful UV radiation and its absence may represent an additional stressor influencing the microbial community. Nonetheless, the stream contained an active microbial assemblage with bacterial cell abundances from 2.94???104 to 4.97???105?cells?ml?1, and bacterial production ranging from 58.8 to 293.2?ng?C?l?1?d?1. Chlorophyll-a concentrations ranged from 0.3 to 0.53??g?l?1 indicating that algal phototrophs were the probable source of the DOM. Microbial isolates produced a rainbow of pigment colors, suggesting adaptation to stress, and were similar to those from other cryogenic systems (Proteobacteria and Bacteroidetes lineages). Supraglacial streams provide an example of contemporary microbial processes on the glacier surface and a natural laboratory for studying microbial adaptation to the absence of humics.

Characterization of fulvic acid fractions of dissolved organic matter during ice-out in a hyper-eutrophic, coastal pond in Antarctica

Dissolved humic material (HDOM) is ubiquitous to all natural waters and its source material influences its chemical structure, reactivity, and bioavailability. While terrestrially derived HDOM reference materials distributed by the International Humic Substances Society (IHSS) have been readily available to engineering and scientific communities, a microbially derived reference HDOM was not, despite the well-characterized differences in the chemistry and reactivity of HDOM derived from terrestrial versus microbial sources. To address this gap, we collected a microbial reference fulvic acid from Pony Lake (PLFA) for distribution through the IHSS. Pony Lake is a saline coastal pond on Ross Island, Antarctica, where the landscape is devoid of terrestrial plants. Sample collection occurred over a 17-day period in the summer season at Pony Lake. During this time, the dissolved organic carbon (DOC) concentrations increased nearly two-fold, and the fulvic acid fraction (collected using the XAD-8 method) accounted for 14.6% of the DOC. During the re-concentration and desalting procedures we isolated two other chemically distinct fulvic acid fractions: (1) PLFA-2, which was high in carbohydrates and (2) PLFA-CER, which was high in nitrogen. The chemical characteristics (elemental analysis, optical characterization with UV‐vis and fluorescence spectroscopy, and 13 C NMR spectroscopy) of the three fulvic acid fractions helped to explain their behavior during isolation.

Physicochemical and biological dynamics in a coastal Antarctic lake as it transitions from frozen to open water

Abstract Pony Lake, at Cape Royds, Antarctica, is a shallow, eutrophic, coastal lake that freezes solid in the winter. Changes in Pony Lakes physicochemical parameters and microbial community were studied during the transition from ice to open water. Due to rising water temperatures, the progressive melt of the ice column and the gradual mixing of basal brines into the remaining water column, Pony Lake evolved physically and chemically over the course of the summer, thereby affecting the microbial community composition. Temperature, pH, conductivity, nutrients and major ion concentrations reached their maximum in January. Pony Lake was colonized by bacteria, viruses, phytoflagellates, ciliates, and a small number of rotifers. Primary and bacterial production were highest in mid-December (2.66 mg C l-1 d-1 and 30.5 μg C l-1 d-1, respectively). A 16S rRNA gene analysis of the bacterioplankton revealed 34 unique sequences dominated by members of the β- and γ-proteobacteria lineages. Cluster analyses on denaturing gradient gel electrophoresis (DGGE) banding patterns and community structure indicated a shift in the dominant members of the microbial community during the transition from winter ice, to early, and late summer lakewater. Our data demonstrate that temporal changes in physicochemical parameters during the summer months determine community dynamics and mediate changes in microbial species composition.