Tuesday, June 5, 2007 - 10:30 AM
129

Surface-Subsurface Linkages in a Headwater Stream during Leaf Fall

Alba Argerich1, Eugènia Martí2, Miquel Ribot2, Francesc Sabater1, and Daniel Von Schiller2. (1) Departament d'Ecologia, Universitat de Barcelona, Av. Diagonal 645, Barcelona, 08028, Spain, (2) Limnology Group, Centre d'Estudis Avançats de Blanes (CSIC), Accés a la Cala Sant Francesc 14, Blanes (Girona), 17300, Spain

This study examined the variation of surface-subsurface hydrological and chemical linkages during the accumulation of leaf litter inputs in the channel of a headwater stream. We placed 29 wells to a sediment depth of 25 cm at 5 m intervals along a 140 m stream reach. Whole-reach chloride short-term additions and measurements of the vertical hydraulic gradient at each well were done on several dates during fall of 2004 to evaluate hydrologic connectivity between surface and subsurface water. On each sampling date, we also collected surface and subsurface water samples from each well for nutrient concentration analyses, water temperature and oxygen concentration. Of all 29 wells, 13 were located in upwelling zones, 11 in downwelling zones, and in 5 the direction of the exchange fluctuated with time. In general, hydrologic connectivity increased with stream discharge, but no clear trend related to leaves accumulation was observed. Subsurface water showed higher temperature and nutrient concentrations and lower oxygen concentration than surface water despite of the large variability among wells. These differences tended to increase as leaves accumulate in the channel, especially in downwelling areas, suggesting that leaf inputs into the stream channel increase the chemical decoupling between surface and subsurface stream compartments.

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