The near-shore distribution and macro-molecular contents of the dissolved organic matter of Texas estuarine and Gulf of Mexico waters.




Maurer, L.G.

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University of Texas at Austin


Two hitherto neglected areas of organic marine chemistry have been studied in order to add to the understanding of the carbon cycle in the sea. Dissolved organic carbon (DOC) contents in the estuarine and continental shelf waters of the Texas Gulf of Mexico were measured by a wet oxidation method. The amounts of DOC in estuaries is governed in part by fresh water input and evaporation. The fresh water is generally higher than marine waters giving rise to an inverse DOC to salinity relationship near areas of inflow. Depending on the magnitude of the run-off, this effect disappears a relatively short distance from the area of mixing, and evaporation and in situ production and removal become predominant. In the Laguna Madre, which has little tidal exchange, evaporation has produced a hypersaline and organic-rich environment. Factors other than evaporation must contribute also to the high DOC of this water. Differences in productivity and phytoplankton types are the most likely of these. Near areas of tidal exchange, the water resembles more that of the Gulf of Mexico in salinity and DOC. In turn, little effect from estuarine waters on the Gulf in these areas was found beyond the 20 fathom line. DOC measurements on the continental shelf indicate zones or bands of alternating high and low DOC parallel to the coast. This seems to fit a model proposed for nearshore circulation cells proposed by K-H. Szekielda recently. A form of pressure dialysis, ultrafiltration, which utilizes membranes with approximately defined molecular size cut-offs, was employed to isolate the macromolecular species from the filtered marine waters. Fractions containing components with nominal molecular weights of 1000, 10,000 and 100,000 were examined for their contribution to the total organic carbon, carbohydrate and protein of sea water. While large amounts of the organic carbon behaves as macromolecular, only a small fraction of it can be accounted for as biopolymers. Since most of the dissolved organic matter in the sea is of biological origin, this evidence supports the theory of some investigators that the larger portion of it has been transformed into undefined heteropolycondensates. The composition and nature of such condensates is still under study. Some indications are that it may be analogous to the humates of fresh water. Its incorporation into sediment is still doubtful since comparison of sediment extracts to the organics in the water show no convincing similarities. Since biopolymers are such a small part of the macromolecular material, it is proposed that new biological material is either being added to the water relatively slowly or being transformed rapidly after introduction. Differences observed in samples from different areas and


103 p., Dissertation


dissolved organic matter (DOM), salinity gradients, water analysis