Role of Seasonal and Interannual Variability on the Cycling and Transport of DOC and Trace Metals Across the Wetland-Stream Transition
Abstract
Dissolved concentrations were determined for Fe, Mn, Cu, Zn, U, Th, REE and organic carbon (DOC) in a wetland zone and its recipient stream (Kervidy stream, France) during a two year period (from October 1999 to September 2001) to unravel the effects of seasonal and interannual changes in environmental conditions on solute cycling and transport across the wetland-stream transition. Time series results from wetland groundwater (weekly sampling frequency) reveal major differences in water chemical dynamics between the two investigated hydrologic years, samples collected during hydrologic year 99-00 showing strong winter-spring concentration increases for all solutes (except Zn and Cu), while those recovered during hydrologic year 00-01 follow an opposite trend showing constant, or decreasing solute concentrations. This interannual difference in wetland groundwater chemistry appears to play an important role in determining the variability of solute concentrations in the recipient stream, especially during storm events when the contribution of wetland water to streamflow is important. Indeed, while storm events occurring during year 99-00 resulted in a stream water showing positive concentration peaks of roughly constant amplitude for all solutes (except Zn), concentration peaks accompanying storm events occurring during hydrologic year 00-01 were found to have amplitudes that regularly decreased from the beginning to the end of the hydrologic year. Nitrate concentration and redox potential data indicate that reducing processes were likely to be responsible of the winter-spring build up of solute concentrations observed in the wetland during hydrologic year 99-00. As regards to the cause of the difference in wetland chemical dynamics between hydrological years 99-00 and 00-01, we suggest here that the latter is due to hydro-climatic factors. Actually, the 00-01 time series encompassed an extended period of extreme rainfalls which resulted in the wetland soil water being continuously recharged in oxygen and nitrate, preventing whereby the installation of the seasonal reducing conditions observed during hydrologic year 99-00. These results demonstrate that redox processes can cause the release of a wide variety of solutes in wetland soil solution. However, any attempt to model and quantify the transport of these solutes across the wetland-stream transition should take into account the seasonal variations of biogeochemical reactions in wetlands, as well as the possible interannual or decadal variability of hydro-climatic conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.H11B0241G
- Keywords:
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- 1806 Chemistry of fresh water;
- 1890 Wetlands