Landscape Ecology 15: 679–695, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 679 Physico-chemical heterogeneity in a glacial riverscape Florian Malard ∗ , Klement Tockner and J. V. Ward Department of Limnology, EAWAG/ETH, Ueberlandstrasse 133 CH-8600 Duebendorf, Switzerland; ∗ (Corresponding author: Present address: Florian Malard Hydrobiologie et Ecologie Souterraines, ESA CNRS 5023, Universit´ e Claude Bernard, Lyon 1, Bat. 403, 43 Bd du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France, Fax: (33) 4 72 43 15 23 E-mail: malard@univ-lyon1.fr) Received 4 May 1999; Revised 24 March 2000; Accepted 5 June 2000 Key words: flow path, flood pulse, glacial river, hydrological connectivity, riverscape heterogeneity, water chemistry, water source Abstract Spatio-temporal heterogeneity in physico-chemical conditions associated with the annual expansion/contraction cycle in a complex glacial flood plain of the Swiss Alps was investigated employing a landscape approach. The diverse and dynamic aquatic habitats of the flood plain were visualized as an aquatic mosaic or riverscape. Based on samples collected at ca. monthly intervals for 1.5 yr along 17 floodplain transects, the 3 components of riverscape heterogeneity, extent, composition, and configuration, were quantified using categorical maps and indices of landscape patterns for turbidity and specific conductance. Changes in the spatial heterogeneity of 13 other physico-chemical parameters were further analyzed by means of a within-dates principal component analy- sis. Riverscape heterogeneity (RH), quantified by applying several indices of landscape pattern to turbidity and specific conductance data, was minimum during groundwater-dominated base flow in winter. Despite an increase in surface connectivity in the channel network with rising discharge, RH rose in spring and summer as additional chemically-distinct 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 heterogeneity as turbidity and specific conductance. Overall, the glacial flood plain shifted from a monotonous physico-chemical riverscape in winter to a complex mosaic in summer, this seasonal pattern being clearly driven by hydrological factors operating at the catchment scale rather than by autogenic processes within individual water bodies. Although RH exhibited a predictable annual 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 glaciers. Introduction River-floodplain systems as defined by Junk et al. (1989) comprise a variety of permanent aquatic habi- tats (e.g., main channel, cut-off channels, oxbow lakes) and the floodplain surface, that is the area peri- odically inundated by the lateral overflow of the river. Natural river-floodplain systems are never static, their aquatic habitats are in constant temporal and spatial change. Non-erosive flooding temporarily modifies environmental conditions in pre-existing water bodies and increases the extent of ephemeral aquatic habi- tats, while erosive floods can rejuvenate, create, or eliminate water bodies (Bayley 1995; Ward 1997). Thus, from a landscape perspective (Turner and Gard- ner 1991; Wiens 1995), the different aquatic habitats of river-floodplain systems form a spatially heteroge- neous area, i.e., an aquatic mosaic or riverscape, where physico-chemical characteristics vary through space and time in response to biotic and abiotic processes. Studies emphasizing physico-chemical hetero- geneity of surface water in river-floodplain systems have reported either on seasonal changes of individual water bodies or on differences among various aquatic