Chemical and carbon isotopic evidence for the source and fate of dissolved organic matter in the northern Everglades

Surface waters in the Florida Everglades contain high levels ofdissolved organic carbon (DOC) compounds. ¹³C values of DOCsamples collected from the northern Everglades indicate that less than about23%of the DOC was derived from sugarcane (the dominant agricultural crop in thearea), and the amount of DOC from sugarcane was greater during the dry period.Most of the DOC (> 50%) in the northern Everglades was in the low molecularweight (< 1000 Dalton) fraction (LMW-DOC). The relative amount of highmolecular weight DOC (HMW-DOC) was higher in the wet period than in the dryperiod. Radiocarbon ages of the DOC ranged from > modern toabout 2400 years B.P., indicating that DOC was derived from both historic peatdeposits and modern vegetation. At each site, the HMW-DOC had older radiocarbonages than the LMW-DOC, and therefore contained a greater fraction of DOCderivedfrom the historic peat deposits. It appears that at least some of the old DOCcompounds from the historic peat deposits were decomposed during theirresidencein the surface water system in the northern Everglades, and the LMW-DOC wasmoremicrobially labile than the HMW-DOC. Our analysis suggests that accelerateddecomposition of organic matter in the historic peat deposits (due to land-usechange) could be a significant source of DOC and nutrients in the northernEverglades. Our data also suggest that the radiocarbon signature of DOC couldbeused as a sensitive indicator of the overall effectiveness of a wetlandrestoration project.