Physico-chemical heterogeneity in a glacial riverscape

Spatio-temporal heterogeneity in physico-chemical conditions associated wit h the annual expansion/contraction cycle in a complex glacial flood plain o f the Swiss Alps was investigated employing a landscape approach. The diver se and dynamic aquatic habitats of the flood plain were visualized as an aq uatic mosaic or riverscape. Based on samples collected at ca. monthly inter vals for 1.5 yr along 17 floodplain transects, the 3 components of riversca pe heterogeneity, extent, composition, and configuration, were quantified u sing categorical maps and indices of landscape patterns for turbidity and s pecific conductance. Changes in the spatial heterogeneity of 13 other physi co-chemical parameters were further analyzed by means of a within-dates pri ncipal component analysis. Riverscape heterogeneity (RH), quantified by app lying several indices of landscape pattern to turbidity and specific conduc tance data, was minimum during groundwater-dominated base flow in winter. D espite an increase in surface connectivity in the channel network with risi ng discharge, RH rose in spring and summer as additional chemically-distinc t water sources (i.e., snowmelt runoff and glacial ablation) contributed to surface flow within the flood plain. Most other physico-chemical variables measured during this study exhibited the same spatio-temporal heterogeneit y as turbidity and specific conductance. Overall, the glacial flood plain s hifted from a monotonous physico-chemical riverscape in winter to a complex mosaic in summer, this seasonal pattern being clearly driven by hydrologic al factors operating at the catchment scale rather than by autogenic proces ses within individual water bodies. Although RH exhibited a predictable ann ual pattern in response to the seasonal flow regime, we expect the channel network to undergo future modifications from stochastic factors associated with flood events and long-term changes reflecting movements of the glacier s.