Physico-chemical characterization of channel types in a glacial floodplain ecosystem (Val Roseg, Switzerland)

Abstract

Val Roseg in the Swiss Alps is a complex alluvial valley formed in glacial outwash. The braided flood plain, 2.6km long and 130-510 m wide, begins 1.2 km downstream of the glacier terminus and extends to a knickpoint at 1990 m a.s.l. where water upwells before entering a constrained reach. A long-term study has been initiated to investigate habitat heterogeneity and how such heterogeneity (1) contributes to the biodiversity of benthos, groundwater fauna, and periphyton in a harsh environment and (2) influences ecosystem processes such as productivity and decomposition dynamics. As a first step we have distinguished different channel types based on the correspondence between hydrological connectivity and physico-chemical attributes. This functional characterization will serve as a habitat template to structure future ecological research in the Val Roseg flood plain. Six distinct channel types have been identified within the floodplain ecosystem: (i) Main channel, (ii) Side channels, (iii) Intermittently-connected channels, (iv) Mixed channels, (v) Groundwater channels, and (vi) Tributaries. Distinct seasonal and daily runoff patterns, caused by ice melt, change the hydrological connectivity between individual channel types. Results clearly demonstrate that the whole flood plain shifts from dominance by surface water at high summer discharge to a groundwater-controlled system in winter. Temporal variability, rather than the means of environmental values, has been used to differentiate between individual floodplain channel types. Groundwater channels exhibit the highest spatial but the lowest temporal variability. In contrast, intermittently-connected channels are characterized by a low spatial but an extraordinary temporal variability. High spatio-temporal heterogeneity resulting from a diversity of channel types is believed to play a major role in maintaining what appears to be remarkably high biodiversity in this glacial flood plain.