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 organic 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 bays. The δ13C values of SPOM, lipids, and chlorophylls in these bays varied from − 18 to − 27, − 20 to − 31, and − 18 to − 31‰, respectively. The δ13C values of SPOM, lipids, and chlorophylls, and the pigment composition together suggest that the 13C-depleted organic matter in Corpus Christi Bay in June 1992 resulted from the fixation of 13C-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 were 13C-enriched and most likely derived from local phytoplankton production. The δ13C values of SPOM, lipids and chlorophylls in the bays where salinities were closest to that of seawater were in the range expected for marine phytoplankton, i.e., − 18 to − 24‰. The δ15N values for SPOM, lipids, and chlorophyll a ranged from + 4 to + 14‰ with most between + 6 to + 10‰. These values are similar to the SPOM of marine systems and indicate a common source of nitrogen throughout the estuaries.