Effects of water loss on primary production: A landscape-scale model

Water loss from stream ecosystems has profound effects on primary producers. The small body of literature on algal responses to desiccation has emphasized mechanisms of resistance to desiccation, recovery of metabolic activity upon rewetting, and small spatial scales. Unfortunately, small-scale patterns are difficult to interpret because of the high degree of variability in both hydrologic patterns of drying and ecological processes within individual drainage basins. Consequently, effects of drying are best examined at larger spatial scales because variation that appears random at smaller scales become incorporated into larger, more predictable patterns across an entire catchment. We present a conceptual model of the effects of water loss on primary producers applicable to the scale of the entire catchment. This perspective describes differences in susceptibility to water loss, and differential rates of decline and recovery in primary production as a function of location within the catchment. Future considerations of drying on ecosystem attributes such as primary production will be facilitated by treating streams as patchy, interconnected landscapes in space and time and recognizing spatially explicit effects of disturbance. It is likely that streams of different regions vary widely in terms of the occurrence of drought, the geophysical template, and response variables (types of organisms present and their collective metabolism). The challenge in drought research today is to determine what phenomena are general and of widespread application and which are peculiar to given regions.