Influences of Urban Light Pollution on Stream-Riparian Invertebrate Food Webs

By the year 2050, over 90% of the United States population will live in urban centers. Dense human populations produce a high intensity of ambient light (i.e., ecological light pollution, ELP) due to artificial light sources. Artificial light has been shown to alter mating success, migration patterns, and predator-prey relationships of aquatic and riparian biota, including mammals, birds, fish, amphibians, arthropods, and zooplankton. Ecological light pollution has significant potential to alter important reciprocal energy exchanges between streams and their adjacent riparian zones. Our research seeks to determine the potential influences of ELP on 1) the magnitude and diversity of stream-riparian arthropod fluxes and 2) the structure of invertebrate food webs (i.e., connectance, linkage density, chain length). At nine, 30-m reaches in small, urban streams of Columbus, OH, representing low, moderate, and high levels of ELP, we collected emergent aquatic insects, benthic macroinvertebrates, and riparian arthropods on a bimonthly basis. Results to date suggest that high light levels are correlated with greater abundance of terrestrial arthropods and aquatic invertebrates, whereas low light levels are correlated with greater diversity. Food web results indicate a simplification of trophic structure at high light levels, and more complex food webs at low-moderate light levels, particularly relative to connectance and linkage density. Given the energetic linkages between invertebrates and stream fishes, we anticipate that our findings will have important implications for stream fish assemblages, including potential shifts in assemblage composition and productivity. This research will add to the understanding of the effects of landscape modification in the context of urban stream ecosystems, which will be crucial for informed stream management.