Stable isotope analysis of carbon cycling in the Perdido Estuary, Florida

Stable carbon isotope (delta(13)C) analysis was used in the Perdido Estuary , Florida U.S. to determine the predominant carbon source that supports the bacterial assemblage. Stable carbon isotope values were measured in the su spended particulate matter (SPM), dissolved organic and inorganic matter, a nd bacteria. Stable nitrogen isotope (delta(15)N) ratios were measured in S PM and nitrate to assist in understanding carbon cycling through the estuar y. Analyses were conducted on samples from riverine, coastal, and anthropog enic sources and compared with samples from the bay. Stable isotope ratio a nalysis was coupled with estimates of mixing of riverine and coastal waters into the bay. Preliminary observation of the delta(13)C data indicates tha t terrestrial organic matter is the primary carbon source that is assimilat ed by bacteria in the ecosystem. Stable isotope data from carbon and nitrog en pools in combination with analysis of estuarine current velocities indic ates that primary production is an important factor in the carbon cycle. Th is study demonstrates the importance of stable isotope analysis of multiple carbon and nitrogen pools to assess sources and cycling of organic matter.