The interactions of substrate, soil frost, groundwater levels, vegetation, and ongoing landscape-forming processes were studied in a portion of the Saskatchewan River Delta. Representative field transects were used to relate vegetation types to differences in relief and seasonal water table elevation. Seasonal soil temperatures were recorded from common community types, and peat stratigraphy was determined along several field transects.Vegetation zonations, extending from mixed forest on river levees to open lake water obviously reflect moisture gradients. However, increasing moisture availability is paralleled by declining nutrient availability, away from the levees, as peat accumulation prevents rooting in the mineral soil. Nutrient status and type and degree of peat accumulation are thus dependent on landform and water circulation. Three main physiographic divisions were recognized as a means of discussing the dynamics of vegetation/environment interrelationships; alluvial levees, open drainage basins, and closed drainage basins.Alluvial levees, paralleling stream channels, are generally well drained, nutrient-rich, and covered by mixed forest and tall shrub communities. Open drainage basins are characterized by slow circulation of mineral waters, favoring growth of minerotrophic fens and floating sedge mats. Closed drainage basins are more or less completely surrounded by raised levees. Their source of water is limited runoff from the encircling levees and precipitation falling onto the basins. Deep peat deposits are characteristic of these sites. Nutrient levels are lower than in open basins and sphagnum moss commonly occurs above the fen peat deposits. The slightly raised centers of these closed basins often support black spruce bog communities.