| 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. This 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 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 (Δ 14C) and stable carbon (δ13C) isotope ratios of peat and porewater dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and methane (CH4) highlighted both temporal and spatial trends in below-ground carbon cycling: seasonality in porewater profiles of δ 13C-DIC and δ13-CH4 (representative of rate and pathway of microbial respiration) was greater in fens than bogs; Δ 14C of peat and DOC, DIC and CH4 indicated microbial utilization of recently-fixed organic matter throughout the peatland, and that modern carbon is more labile in fens and Sphagnum lawns (poor fens) than bogs. The sensitivity of carbon dynamics to vegetation and hydrology is a dominant factor in the carbon storage capacity of this wetland in the face of predicted climate change.; Coastal ecosystems are often characterized by the predominant source of organic carbon driving the system. Florida Bay has been highly impacted by the development and management of south Florida in the last century, and changing conditions in the bay have engendered fears that the system is shifting from dependence on benthic production to water-column production (i.e., phytoplankton). A multiple stable isotope analysis (δ13C, δ 15N and δ34S) 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 that have been fixed in formalin and preserved in formalin or ethanol. This allows evaluation of trophic dynamics of current and historic populations relative to environmental conditions (e.g. temperature, salinity, turbidity, and seagrass distribution). |
