Biogeochemical Cycling of Carbon, Phosphorus, and Trace Metals

Carbon isotopes were used as tracers in the Florida Everglades to investigate the sources and sinks of dissolved organic carbon in natural and constructed wetlands and provide a way to monitor ecosystem restoration efforts. Stable carbon isotopes were used to determine the source of DOC and POC, and in a basic mass balance model to calculate turnover times of DOC in small constructed wetland cells. Radiocarbon was used to distinguish "old" DOC derived from historic peats from "new" DOC derived from modern primary production. Our study suggests that Ä14C measurements can be a useful indicator of the progress of ecosystem restoration in the Everglades. The oxygen isotope of phosphate (P) can also serve as an isotopic tracer in wetlands. Initial method development to use the oxygen isotope of phosphate extracted from natural waters is presented here. Preliminary data indicates that microbial recycling is a major means by which P stays in the water column despite reducing anthropogenic contributions. Stable carbon isotopes were also used to quantify the percent of methane oxidized within Tallahassee landfill soils. Carbon isotope and oxidation data collected over almost 9 months of monitoring methane emissions from landfill surfaces with and without a "biocover" is examined. These measurements, combined with measurements of methane flux, can help monitor the efficiency of various treatments in reducing methane emissions to the atmosphere by enhancing oxidation of methane by methanogenic bacteria. The presence or absence of DOC in the water column can determine whether trace metals will be present as a nutrient or as a toxicant. A novel method coupling capillary electrophoresis with ICP-MS was used to separate metal species and calculate binding constants of rare earth elements and Th, Hf, and Zr with humic substances at a range of pH and ionic strength of 0.1. Equilibrium dialysis ligand exchange was performed to validate the CE-ICP-MS method. Conditional stability constants of tetravalent metal-HA complexes are several orders of magnitude higher than lanthanide-HA complexes. Because thorium is often used as a proxy for the tetravalent actinides, Th-HA binding constants are useful in the study of sequestration of actinides in nuclear repository settings.