Modern analytical and remote sensing approaches allow for detailed characterization of the composition, chemistry, and spatial distributions of dissolved organic matter (DOM) in aquatic systems. Here, the utility of these approaches for assessing the influences of riverine sources on DOM in the Gulf of Maine is presented. DOM exported from the Gulf of St. Lawrence and by rivers in Maine, Nova Scotia, and New Brunswick is being studied to quantify and characterize optical proxies in the receiving waters of the GoM. Measurements of DOC concentrations, absorption coefficients (254 nm, 350 nm and 412 nm), specific ultraviolet absorbance (SUVA254), spectral slope, fluorescence, DOC fractionation and isotopic composition were used to determine the amount and nature of DOM from major inflowing rivers and the GoM. In addition, lignin phenols, 14C-age, 13C-NMR and FTICR-MS analyses were performed on the hydrophobic and transphilic organic acid fractions of the DOM isolated using XAD resins for a smaller subset of samples from the Penobscot River, Penobscot Bay, GoM waters in the Western Maine Coastal Current (WMCC), a sample from the eastern portion of the GoM (Scotian Shelf waters), and the Pacific Ocean. These samples provide detailed DOM compositional data in support of the more easily collected concentration and optical data obtained from discrete samples, optical data obtained by an in situ glider, and remotely-sensed satellite observations. Optical measurements, 13C-NMR, and lignin phenol analyses showed that DOM associated with inflowing rivers to the GoM is rich in aromatic compounds resulting in a large flux of terrestrially-derived chromophoric DOM (CDOM). As a result, GoM DOM is more aromatic and younger than open ocean samples collected from the Sargasso Sea and from the Pacific Ocean near Hawaii. This observation is consistent with isotopic data that indicate δ 13C values for the HPOA fractions from the Gulf samples (δ 13C= -27‰ and -25‰) were considerably depleted in comparison to the whole DOM sample (δ 13C = -19‰; which also includes algal-produced DOM) and are more similar to those from the terrestrial sources. Samples from the WMCC were the most heavily influenced by terrestrial sources. Results from this study are being used to ground-truth and calibrate remote sensing optical data and develop relationships for predicting DOC concentration in the GoM.

From molecular analyses to remote sensing: Characterization of dissolved organic matter in the Gulf of Maine

249th National Meeting (2015)

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