An Investigation of Dissolved Organic Matter in a Shallow Coastal Bay Subject to \u3ci\u3eAureococcus anophagefferens\u3c/i\u3e Blooms

Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, was identified in Chincoteague Bay in 1997 and has “bloomed” there since at least 1998. Aureococcus anophagefferens is capable of using dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) substrates to support growth, and this utilization is hypothesized to give the organism a competitive advantage relative to other phytoplankton when inorganic nutrient concentrations are low or depleted. Because previous studies suggest dissolved organic matter (DOM) is important in initiating and sustaining brown tide blooms, a field study of the variations in DOC concentration and DOM composition was performed at two sites in Chincoteague Bay, one where brown tide blooms had been reported and another where no A. anophagefferens blooms had been reported before. DOM collected before, during, and after brown tide events in 2002 and 2003 was characterized in terms of bulk DOC concentration and ultraviolet/visible light absorption. Stable isotope signatures and direct temperature-resolved mass spectrometry were performed on high-molecular-weight-DOM (HMW-DOM) isolated by ultrafiltration. Results from 2002 suggest that during the brown tide bloom, N-enriched HMW-DOM was released into the surface water and that this material was optically active and more aromatic. Comparison of results from 2002, a drought year, and 2003, a wet year, show that spring DOM pools differed between the two years in DOC concentration and DOM composition; however, brown tide blooms developed in early summer of both years. During all the brown tide blooms monitored, the DOM pool shifted in composition, probably due to input of DOM by Aureococcus anophagefferens. In an attempt to expand the portion of DOM that can be molecularly characterized, the combination of ultrafiltration and C18 disk solid-phase extraction (SPE) for the isolation of DOM was also investigated. Using C18 SPE on LMW-DOM samples (ultrafiltration filtrate) increased the recovery of DOC from the total sample to about 70%, compared to the approximately 50% isolated within the ultrafiltration retentate alone

Composition of dissolved organic matter within a lacustrine environment

Freshwater dissolved organic matter (DOM) is a complex mixture of chemical components that are central to many environmental processes, including carbon and nitrogen cycling. However, questions remain as to its chemical characteristics, sources and transformation mechanisms. Here, we employ 1- and 2-D nuclear magnetic resonance (NMR) spectroscopy to investigate the structural components of lacustrine DOM from Ireland, and how it varies within a lake system, as well as to assess potential sources. Major components found, such as carboxyl-rich alicyclic molecules (CRAM) are consistent with those recently identified in marine and freshwater DOM. Lignin-type markers and protein/peptides were identified and vary spatially. Phenylalanine was detected in lake areas influenced by agriculture, whereas it is not detectable where zebra mussels are prominent. The presence of peptidoglycan, lipoproteins, large polymeric carbo- hydrates and proteinaceous material supports the substantial contribution of material derived from microorganisms. Evidence is provided that peptidoglycan and silicate species may in part originate from soil microbes

Dynamics and Characterization of Refractory Dissolved Organic Matter Produced by a Pure Bacterial Culture in an Experimental Predator-Prey System

We studied the effects of a bacterium (Pseudomonas chlororaphis) and a bactivorous protozoan (Uronema sp.) on transformations of labile dissolved organic carbon (DOC). In 36-day time series experiments, bacteria were grown on glucose both with and without protozoa. We measured bulk organic carbon pools and used electrospray ionization mass spectrometry to characterize dissolved organic matter on a molecular level. Bacteria rapidly utilized glucose, depleting it to nondetectable levels and producing new DOC compounds of higher molecular weight within 2 days. Some of these new compounds, representing 3 to 5% of the initial glucose-C, were refractory and persisted for over a month. Other new compounds were produced and subsequently used by bacteria during the lag and exponential growth phases, pointing to a dynamic cycling of organic compounds. Grazers caused a temporary spike in the DOC concentration consisting of labile compounds subsequently utilized by the bacteria. Grazing did not increase the complexity of the DOC pool already established by the bacteria but did continually decrease the particulate organic carbon pool and expedited the conversion of glucose-C to CO(2). After 36 days, 29% of initial glucose-C remained in pure bacteria cultures, while only 6% remained in cultures where a grazer was present. In this study the bacteria were the primary shapers of the complex DOC continuum, suggesting higher trophic levels possibly have less of an impact on the qualitative composition of DOC than previously assumed