Input of terrestrial invertebrates to streams during monsoon-related flash floods in the southwestern United States

Abstract Annual monsoons produce violent thunderstorms in the southwestern USA and can result in significant overland flow and flash floods in stream channels, washing many invertebrates into the streams. We identified >140 taxa of terrestrial invertebrates in samples collected from receding flows in ephemeral stream channels after monsoon-related flash floods at 14 sites in Arizona and New Mexico. Relative to the number of aquatic organisms, proportions of terrestrial individuals and terrestrial taxa were initially high but decreased over time. The initial flush of water during the flows appeared to be very destructive, such that the average organism was 40% intact 24 h after waters began to recede. On the second day, the average individual was 90% intact, but the proportion of intact organisms declined over time. These results suggest high inputs of terrestrial invertebrates to these stream ecosystems during the monsoon.