Hydrology, Water Resources and Ecology in Headwaters (Proceedings of the HeadWater'98 Conference 4.9 S held at Meran/Merano, Italy, April 1998). IAHS Publ. no. 248, 1998. The Val Roseg project: habitat heterogeneity and connectivity gradients in a glacial flood-plain system JAMES V. WARD, PETER BURGHERR, MARK O. GESSNER, FLORIAN MALARD, CHRISTOPHER T. ROBINSON, KLEMENT TOCKNER, URS UEHLINGER & RAINER ZAH Department of Limnology, EAWAG/ETH, CH-8600 Dubendorf, Switzerland Abstract The Val Roseg Project is a holistic ecological study of an alluvial flood plain in the Swiss Alps. Major geomorphic features consist of a proglacial reach below the terminus of Tschierva Glacier, the outlet stream of a glacial lake at the terminus of Roseg Glacier, and the glacial flood plain. Here we describe the habitat heterogeneity of the glacial flood plain, which is 2.6 km long and up to 510 m wide. Transects were established every 150- 200 m to investigate gradients of turbidity, temperature, nutrients, organic matter, and surface water-groundwater interactions. Six distinct channel types have been identified, based on the correspondence between connectivity and physico-chemical characteristics. Seasonal and diel variations in discharge are marked and play a prominent role in structuring the habitat template. The entire flood plain shifts from dominance by glacial meltwater in summer to a groundwater-controlled system in winter. INTRODUCTION Alpine stream ecosystems have been proposed as sensitive indicators of climate change and anthropogenic impacts (McGregor et al, 1995), yet relatively little is known of their ecology (Ward, 1994). Despite interest in high mountain streams by European limnologists early in this century (Steinmann, 1907; Thienemann, 1912; Steinbeck, 1934; Léger, 1937), we are not aware of a single holistic ecological study that has been conducted on a glacial flood plain. Therefore, we initiated a comprehensive ecological investigation of a pristine glacial flood-plain system in the Swiss Alps (Fig. 1) to determine how spatio-temporal heterogeneity (a) contributes to biodiversity patterns of lotie zoobenfhos, groundwater fauna and periphyton in a harsh environment and (b) influences ecosystem processes such as productivity and decomposition dynamics. In this paper we focus on habitat heterogeneity and connectivity for the surface waters of the flood-plain complex. DESCRIPTION OF STUDY AREA Val Roseg is situated in the Bernina Massif of the Swiss Alps (Fig. 2). In the upper Roseg catchment (49.5 km 2 , 42% covered by glaciers) elevations range from 1990 m a.s.l. at the downstream end of the glacial flood plain to 4049 m at the top of Piz