River channelization reduces nutrient flow and macroinvertebrate diversity at the aquatic terrestrial transition zone

Abstract

Aquatic and terrestrial ecosystems are linked through lateral interactions that support and maintain biodiversity in both regions. However, in many places, river regulation and channelization have isolated rivers from surrounding riparian areas. We evaluated the effects of channelization on the linkages between aquatic and terrestrial invertebrate assemblages in the Rio Grande, New Mexico via comparison of quantitative macroinvertebrate survey data and analyses of carbon and nitrogen isotopes to test for changes in nutrient flow between channelized and non-channelized reaches of this highly regulated system. Aquatic and terrestrial macroinvertebrates were surveyed in summer 2008 at channelized and non-channelized reaches. Average densities of aquatic macroinvertebrates were 50% lower in the channelized reaches. Taxonomic richness and densities of macroinvertebrates in the transition zone between the river and forested floodplain were also lower in channelized reaches and this effect was especially pronounced for predatory macroinvertebrate species. Carbon isotope ratios in consumers indicated that instream (i.e., benthic algae) production served as the major source of carbon for predaceous arthropods in the transition zone. Our results indicate that river regulation that leads to channelization can reduce diversity and macroinvertebrate densities at the landscape scale by severing linkages between the aquatic and riparian communities. These effects appear especially acute for predaceous macroinvertebrates, perhaps because preferred prey density is lowered. Restoration of natural flow regimes is vitally important to reduce channelization and maintain connectivity between the aquatic and terrestrial environments to conserve the unique assemblage of macroinvertebrates in the transition zone.