SUSPENDED PARTICULATE ORGANIC-MATTER (SPOM) IN GULF-OF-MEXICO ESTUARIES - COMPOUND-SPECIFIC ISOTOPE ANALYSIS AND PLANT PIGMENT COMPOSITIONS

Pigment and stable isotopic compositions of suspended particulate orga nic matter (SPOM) were determined in several estuaries along the Texas coast of the Gulf of Mexico. Analysis of the composition of accessory pigments suggested that the phytoplankton taxa varied among these bay s. The delta(13)C values of SPOM, lipids, and chlorophylls in these ba ys varied from - 18 to - 27, - 20 to - 31, and - 18 to - 31 parts per thousand, respectively. The delta(13)C Values of SPOM, lipids, and chl orophylls, and the pigment composition together suggest that the C-13- depleted organic matter in Corpus Christi Bay in June 1992 resulted fr om the fixation of C-13-depleted CO2 derived from riverine water or in Situ remineralization of organic matter. The lipids and chlorophyll a isolated from the nearly freshwater system of Aransas Bay in 1992 wer e C-13-enriched and most likely derived from local phytoplankton produ ction. The delta(13)C values of SPOM, lipids and chlorophylls in the b ays where salinities were closest to that of seawater were in the rang e expected for marine phytoplankton, i.e., - 18 to - 24 parts per thou sand. The delta(13)N values for SPOM, lipids, and chlorophyll a ranged from + 4 to + 14 parts per thousand with most between + 6 to + 10 par ts per thousand. These values are similar to the SPOM of marine system s and indicate a common source of nitrogen throughout the estuaries. C opyright (C) 1996 Elsevier Science Ltd