ABSTRACT: To determine the roles of dissolved organic matter in the onset, duration, and decline of blooms of the “brown tide” pelagophyte,
Aureococcus anophagefferens, nutrient and microbial dynamics, heterotrophic and autotrophic carbon (C) and nitrogen (N) uptake, and peptide hydrolysis
were compared in natural populations: (1) seasonally, among physically similar sites in a mid-Atlantic coastal lagoon, Chincoteague
Bay, (2) at an individual site as a bloom initiated, developed, and declined, and (3) in whole versus size-fractionated water.
Throughout the year, urea was the dominant form of N taken up at both bloom and nonbloom sites. C acquisition in the A. anophagefferens (1.2–5.0μm) size fraction was dominated by bicarbonate uptake during bloom initiation but organic C compounds were taken
up later during and after the bloom. Bacterial productivity was enhanced during and just after the bloom and bacterial abundance
was four times higher at the bloom versus nonbloom site.
Estuaries and Coasts 05/2012; 32(6):1176-1194. · 2.11 Impact Factor
ABSTRACT: Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, occurs in coastal bays along the northeast coast of the United States.
This species was identified in Chincoteague Bay, Maryland, in 1997 and has bloomed there since at least 1998. Time series
of dissolved organic matter (DOM) concentrations and characteristics are presented for two sites in Chincoteague Bay: one
that experienced a brown tide bloom in 2002 and one that did not. Characteristics of the bulk DOM pool were obtained using
dissolved organic carbon (DOC) and ultraviolet-visible (UV-Vis) measurements (spectral slope and specific UV absorbance).
High molecular weight DOM (HMW-DOM) was characterized in terms of DOC concentration, carbon: nitrogen (C:N) ratio, isotopic
signature, and molecular-level characteristics as determined by direct temperature resolved mass spectrometry (DT-MS). Compositional
changes in the DOM pool are associated with brown tide blooms, although a direct relationship between DOM characteristics
and bloom development could not be confirmed. DOC measurements suggest that during the brown tide bloom, HMW-DOM was released
into the surface water. UV-Vis analysis on the bulk DOM and molecular-level characterization of the HMW-DOM using DT-MS show
that this material was optically active and more aromatic in nature. Based upon C:N ratio and HMW-DOC measurements, it appears
that this HMW-DOM was more nitrogen enriched. Whether this material was released as exudates or was due to lysis ofA. anophagefferens could not be determined.
Estuaries and Coasts 04/2012; 27(6):986-998. · 2.11 Impact Factor
ABSTRACT: Direct temperature-resolved mass spectrometry (DT-MS) was used to evaluate the molecular-level photodegradation of dissolved
organic matter (DOM) isolated from three sites in a Chesapeake Bay subestuary (swamp- and marsh-influenced up-river, midestuarine,
and bay mouth). From each site, filtered (<0.1 or <0.2 μm) water samples were irradiated in solarsimulated ultraviolet light
followed by isolation of the DOM using C18-solid-phase extraction and subsequent DT-MS analysis. To provide background DOM photoreactivity data for the water samples,
we also determined dissolved inorganic carbon (DIC) photoproduction and chromophoric dissolved organic matter (CDOM) photobleaching.
DIC photoproduction was correlated with initial DOM light absorbance, initial dissolved organic carbon (DOC) concentration,
and photobleaching. Changes in DT-MS characteristics within the extracts (in particular, the loss of an “aromatic” signal
believed to be from reworked terrestrial material) were found to correlate linearly with the absorbance of the corresponding
water samples. A relationship between photobleaching and DT-MS characteristics was also observed, with the upstream samples
asymptotically approaching a constant “molecular-level” value as photobleaching increased. Both relationships appeared to
be independent of absorbance wavelength in the ultraviolet. Following irradiation, the swamp/marsh-dominated upstream samples
resembled the down-stream samples in terms of absorption spectra and MS-determined molecular-level characteristics. These
shifts indicate that terrestrially-derived DOM may be more difficult to differentiate from marine DOM upon photodegradation,
which has implications regarding evaluating the terrestrial impact within the marine DOM pool.
Aquatic Sciences 11/2007; 69(4):440-455. · 2.11 Impact Factor
ABSTRACT: Characterization of dissolved organic matter (DOM) from aquatic environments has always been constrained by the ability to obtain a representative fraction of the DOM pool for analysis. Ultrafiltration or extraction, commonly using XAD or C18 sorbents, is therefore generally used to concentrate and desalt DOM samples for further analyses. In this study, we compared ultrafiltration and C18 solid-phase extraction disks (SPE) as DOM isolation methods for estuarine samples. We also evaluated the use of the C18 SPE disks to isolate low-molecular-weight DOM (LMW-DOM) in the filtrate from ultrafiltration. The isolates from both methods and the LMW-DOM C18-extracts were characterized using Fourier transform infrared spectroscopy (FTIR) and direct temperature-resolved mass spectrometry (DT-MS).Based on mass balance and blank measurements, we found that the C18 SPE disks can be used to isolate bulk DOM and LMW-DOM from estuarine samples. FTIR and DT-MS analysis show that C18-extracted DOM and ultrafiltered high-molecular-weight DOM (HMW-DOM) differ markedly in chemical composition. The HMW-DOM is enriched in (degraded) polysaccharides along with aminosugars when compared with the C18-extracted DOM. The C18-extracted DOM appears enriched in aromatic compounds, probably from lignin and/or aromatic amino acids in proteins.C18 SPE of LMW-DOM samples from ultrafiltration increases the recovery of DOM from the total sample up to about 70%, compared to around 50% using ultrafiltration alone. Thus, a majority of the DOM can be isolated from estuarine samples by a combination of these techniques.
ABSTRACT: Dissolved organic matter (DOM) composition and dynamics in temperate shallow coastal bays are not well described although these bays may be important as local sources of organic carbon to ocean waters and are often sites of economically-important fisheries and aquaculture. In this study surface water samples were collected on a monthly to bi-monthly basis over two years from a mid-Atlantic coastal bay (Chincoteague Bay, Virginia and Maryland, USA). Dissolved organic carbon (DOC) concentrations and light absorbance characteristics were measured on sterile-filtered water, and high-molecular weight (> 1 kDa) dissolved OM (DOM) was isolated to determine stable isotope composition and molecular-level characteristics. Our time series encompassed both a drought year (2002) and a year of above-average rainfall (2003). During the dry year, one of our sites developed a very intense bloom of the brown tide organism Aureococcus anophagefferens while during the wet year there were brown tide bloom events at both of our sampling sites. During early spring of the wet year, there were higher concentrations of > 1 kDa DOC; this fraction represented a larger proportion of overall DOC and appeared considerably more allochthonous. Based upon colored dissolved organic matter (CDOM) and high-molecular weight DOM analyses, the development of extensive phytoplankton blooms during our sampling period significantly altered the quality of the DOM. Throughout both years Chincoteague Bay had high DOC concentrations relative to values reported for the coastal ocean. This observation, in conjunction with the observed effects of phytoplankton blooms on DOM composition, indicates that Chincoteague Bay may be a significant local source of “recently-fixed” organic carbon to shelf waters. Estimating inputs of DOC from Chincoteague Bay to the Mid-Atlantic Bight suggests that shallow productive bays should be considered in studies of organic carbon on continental shelves.
ABSTRACT: Over the past decade, sinking particulate organic matter (POM) samples from depth profiles in the equatorial Pacific have been analyzed by multiple techniques to evaluate the organic matter preservation mechanisms most dominant in the oceanic water column. How the samples were analyzed strongly influenced which organic matter preservation scheme appeared to dominate. Bulk functional group analysis by solid-state 13C-NMR showed that organic matter composition varied very little in light of the extreme degree of remineralization (>98%) that occurred with water column depth. This indicates preservation by a physical mechanism, such as sorption to mineral grains or protection within a mineral aggregate. However, detailed lipid studies of the characterizable fraction showed that selective preservation was important, with lipid structure being correlated with preservation over depth. However, the characterizable fraction decreases greatly with depth. Therefore, in this paper, direct temperature-resolved mass spectrometry (DT-MS), was used to further characterize POM, with the assumption that this approach could “see” a substantial proportion of the “uncharacterized” organic matter. DT-MS, which provides compositional information at an intermediate level between the detailed wet chemical studies and one-dimensional solid-state C13-NMR, also indicates an intermediate view between the mechanistic extremes of selective preservation and physical protection.
Geochimica et Cosmochimica Acta.