Subsidies of Aquatic Resources in Terrestrial Ecosystems

Abstract

Floods, spatially complex water flows, and organism movements all generate important fluxes of aquatic-derived materials into terrestrial habitats, counteracting the gravity-driven downhill transport of matter from terrestrial-to-aquatic ecosystems. The magnitude of these aquatic subsidies is often smaller than terrestrial subsidies to aquatic ecosystems but higher in nutritional quality, energy density, and nutrient concentration. The lateral extent of biological aquatic subsidies is typically small, extending only a few meters into riparian habitat; however, terrestrial consumers often aggregate on shorelines to capitalize on these high-quality resources. Although the ecological effects of aquatic subsidies remain partially understood, it is clear that ongoing human modification to aquatic ecosystems, riparian habitats and river floodplains affect the magnitude, quality, and spatial and temporal patterning of aquatic subsidies in terrestrial landscapes. These changes will alter the character of aquatic–terrestrial coupling and have consequences for terrestrial organisms that rely on these high-quality and temporally dependable resource subsidies. Homogenization of landscapes and flow regimes, eutrophication, exotic species, and contaminants all represent threats to the vital flows of aquatic-derived resources into terrestrial ecosystems. Research emphasizing that landscapes are integrated terrestrial–aquatic systems, characterized by both biological and hydrological flows among habitats, is needed for understanding the consequences of aquatic subsidies and managing ecological risks of ongoing human development.