Freshwater wetlands and coastal zones are complex ecosystems threatened by direct (e.g., encroachment, water/waste management) and indirect (e.g., climate change) human disturbances. My research evaluates a northern peatland and a subtropical estuary using natural abundance isotopes to trace the origin, transport and transformation of energy through these systems. This information is used in establishing current levels of functioning, comparing present to past status, and constructing models of potential responses to continually changing environmental conditions.

Peat-accumulating wetlands are often characterized by their ability to store carbon. In a northern Minnesota peatland, radiocarbon and stable carbon isotope ratios of peat and of porewater dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and methane (CH4) illustrated both temporal and spatial trends in below-ground carbon cycling: seasonality in porewater profiles of del 13C-DIC and del 13C-CH4 (representative of rate and pathway of microbial respiration) was greater in fens than bogs; radiocarbon content of peat and DOC, DIC and CH4 indicated that recently-fixed organic matter is utilized as substrate for microbial respiration throughout the peatland, and that modern carbon is more labile in fens and non-forested Sphagnum lawns (poor fens) than bogs. Sensitivity of carbon dynamics to local vegetation and hydrology will be a dominant factor controlling the carbon storage capacity of large northern peatlands in the face of predicted climate change.

In contrast, coastal ecosystems are often characterized by the types of primary production driving the system and by the dynamics of higher trophic levels. Florida Bay has been heavily impacted by the development of south Florida, and changing conditions in the bay have engendered fears that the fisheries in this system are shifting from dependence on benthic production (seagrasses) to water-column production (phytoplankton). A multiple stable isotope analysis (del 13C, del 15N and del 34S) of the bay’s biota illustrates a strong dependence on benthic production such as seagrass, seagrass detritus, benthic algae and sedimentary organic matter. Long-term fish preservation experiments indicate that this multiple stable isotope approach is feasible for museum specimens (i.e. specimens that have been fixed in formalin and preserved in formalin or ethanol), allowing evaluation of trophic dynamics of current and historic populations relative to changing environmental conditions (e.g. temperature, salinity, turbidity, and seagrass distribution).