Photomineralization of organic carbon in a eutrophic, semiarid estuary

The effect of photomineralization on the carbon cycle in a eutrophic, semiarid estuary (Baffin Bay, Texas) was investigated using closed-system incubations. Photochemical production rate of dissolved inorganic carbon ranged from 0.16 to 0.68 µM hr-1, with a daily removal of 0.3%~1.5% of the standing stock of dissolved organic carbon (DOC). The photomineralization rate was negatively correlated with the chlorophyll a concentration, suggesting that the plankton-derived DOC was less photoreactive to solar radiation. The stable carbon isotope composition (δ13C~-18.6‰) of degraded DOC, as calculated using the DIC “Keeling” plot, further indicated that the high photochemical lability of 13C-enriched DOC in this semiarid environment. Our finding showed that the photomineralization of 13C-enriched DOC is an important component of the carbon cycle in this system, and this process does not necessarily remove 13C-depleted organic carbon as observed in other coastal areas.