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To minimize the risk of biological invasions associated with commercial shipping, vessels are required to conduct ballast water exchange (BWE)≤200 nautical miles offshore when arriving in the US from foreign ports, and some states require coastal BWE≤50 miles offshore along domestic routes. Previous research suggests that the intensity of fluorescent dissolved organic matter (fDOM) can be used to verify whether BWE was implemented. This study examined seasonal and spatial variability of fDOM in Pacific rim ports and the adjacent seas, using the North American coast as a model system to test whether regional fluorescence intensity thresholds consistently distinguish port sites from coastal and oceanic sites at increasing distances from shore. Over 2000 samples from major port systems on the US Pacific coast and along offshore (perpendicular) and alongshore (parallel) transects were analyzed. Overall, humic fDOM fluorescence intensity (C3*=370/494nm) effectively discriminated port versus oceanic sites located further than 100. miles from shore, but discriminated only a subset of coastal versus oceanic sources within the northeastern Pacific. Data from additional global ports are needed to predict the frequency of false positive or false negative ballast source determinations using fDOM for foreign vessel traffic. © 2012 Elsevier B.V.

Marine chromophoric dissolved organic matter (CDOM) imparts highly variable optical signatures in surface waters over short spatial and temporal scales, but the cause of that variability is poorly understood. A major fraction of dissolved organic matter in seawater is colloidal in size and can cycle quite rapidly, potentially contributing to the observed variability in CDOM. The relationship between marine colloids and CDOM optical variability was examined using flow field-flow fractionation (FlFFF) to partition the colloidal organic phase into a continuum of molecular sizes for optical characterization by excitation emission matrix spectroscopy (EEMS). Colloidal organic matter in surface seawater of the Damariscotta River estuary showed 2 major peaks in apparent abundance, spanning at ∼ 1–5 kDa and ∼ 15–150 kDa in size, respectively. The relative magnitude of these peaks changed systematically with the phase of phytoplankton blooms during 2003 and 2004, implying a relationship between colloid size distribution and bloom dynamics. Of the two colloidal sizes, the 1–5 kDa fraction was far more variable in apparent abundance than the larger colloidal matter. EEMS results reveal a compositional partitioning of protein-like and humic-like fluorescence between size fractions. Protein-like materials occurred primarily in the smallest colloid size fraction while humic-type materials resided mainly in the larger colloidal phase. These findings suggest that the fluorescence signature of bulk dissolved organic matter results from a collage of chromophores having optical characteristics that differ according to size of the molecular constituents. The colloidal-sized fluorescence characteristics of marine derived CDOM were contrasted with bulk CDOM to provide fundamental information on the distribution and forms of CDOM in Maine coastal waters. The findings here indicate that colloidal processes will have significant effects on the character and variability in the optical signature of surface seawaters.

Alterations in colored dissolved organic matter (CDOM) characteristics were examined for an extensive fluorescence data set generated by excitation emission matrix spectroscopy (EEMS). Principal component analysis (PCA) was used to assess changes in fluorescence bandwidth and wavelength shifts of entire peak regions, enhancing previous CDOM characterization that was based on changes observed at a few excitation and emission wavelength pairs. Variability within the data set is expressed as a series of linear terms, which can be used to quantitatively evaluate changes in CDOM fluorescence within the perspective of a single cruise or a large geographic region. In this paper we will present PCA results from a comprehensive fluorescence data set examining seasonal and regional CDOM variability within the Gulf of Mexico.

We examined methods for verifying whether or not ships have performed mid-ocean ballast water exchange (BWE) on four commercial vessels operating in the Pacific and Atlantic Oceans. During BWE, a ship replaces the coastal water in its ballast tanks with water drawn from the open ocean, which is considered to harbor fewer organisms capable of establishing in coastal environments. We measured concentrations of several naturally occurring chemical tracers (salinity, six trace elements, colored dissolved organic matter fluorescence and radium isotopes) along ocean transects and in ballast tanks subjected to varying degrees of BWE (0-99%). Many coastal tracers showed significant concentration changes due to BWE, and our ability to detect differences between exchanged and unexchanged ballast tanks was greatest under multivariate analysis. An expanded dataset, which includes additional geographic regions, is now needed to test the generality of our results.