Abstract/Summary

Wetlands are ecosystems capable of improving or maintaining water quality in surface water bodies. River water quality issues include long-term dissolved organic matter (DOM) increases that can affect the ecology of aquatic ecosystems. As such, a more detailed understanding of DOM in wetlands and its association with adjoining water bodies are required. This study investigates the concentration dynamics and chemical composition of DOM in riparian wetlands. Furthermore, an assessment is made of the impact the studied wetlands have on the adjacent streams with respect to DOM and inorganic nutrient concentrations as well as metal toxicity. Two riparian wetlands with contrasting characteristics, and their adjoining streams, were selected for the study. One of the wetlands was a peat-forming, groundwater-fed wetland, located at a hillslope within an undisturbed surrounding area. The other was an ephemeral valley bottom wetland, located within an arable catchment. Results show that DOM varies in time and space, quantity and character, within and among different wetlands. The drivers of this variation included wetland type, land use, land elevation, soil depth and temperature. Both wetlands demonstrated a capacity to act as DOM sources. Acute toxicity tests with Daphnia magna, showed that DOM exported from the peat-forming wetland can reduce tungsten toxicity. The ability of the ephemeral wetland to reduce or buffer phosphorus reaching the adjacent stream was challenged. Findings of this study showed that wetlands should not be considered as an effective mitigation measure for targeting diffuse pollution. Extrapolation from studied to non-studied wetlands should therefore be treated with extreme caution.