AUTHORS: Darin Kopp*, Daniel Allen – University of Oklahoma, Department of Biology
ABSTRACT: The redistribution of materials and energy across ecosystem boundaries suggests ex situ factors contribute to local food webs. The significance of terrestrial inputs to stream and river ecosystems has been well documented but comparatively less attention has been devoted to aquatic inputs in terrestrial ecosystems. Emergent insects, develop in aquatic environments and shuttle resources to terrestrial systems as winged adults dispersing overland. The distance they travel from the stream is contingent the production and composition of the local benthic macroinvertebrate community. Here, we control for these sources of variability to assess the role of stream network geometry in determining the spatial extent of aquatic-derived resources in terrestrial environments. At the watershed scale, the configuration of the entire river network could influence the amount of contact between aquatic and terrestrial systems and create areas of locally intensified aquatic inputs when adjacent tributaries are in close proximity to one another. We estimated the proportion of a watershed receiving aquatic inputs for ~1,300 stream networks across the contiguous US and tested the relative roles of network geometry and several hydroclimate variables in defining these patterns. Given high in-stream productivity, we found up to 36% of the watershed could be subjected to 25% of the insect biomass exported form a stream and that the spatial extent was strongly related to stream network drainage density. Confluence density, effective basin width and channel sinuosity were related to the proportion of the watershed receiving inputs from >2 source streams. Further, these watershed characteristics differed between ecoregions and were potentially related to differences in hydroclimatic variables. This work complements theoretical developments with realistic stream networks sampled across a broad spatial extent and demonstrates the hydrogeomorphic template alone could constrain the spatial extent of aquatic resources in terrestrial ecosystems.
