Spatial and temporal variation in benthic macroinvertebrate assemblages at tributary confluences of the Pecos River

Authors: Kelbi Delaune, Connor Brown, Allison Pease

Year: 2019

Abstract

Tributary streams offer basal resources for aquatic food webs and unique habitats to taxa that differ from the main stem of the river. Because of this, many stream tributaries are known to be biological “hot spots” for species diversity, making them important for river conservation strategies. The Pecos River flows from New Mexico through Texas and offers an ideal study system to investigate diversity in stream tributary junctions across both natural and impacted conditions. In this study, we explored seasonal (summer 2016, fall 2016, and spring 2017) effects of tributary confluences in the Middle and Lower Pecos on the diversity of benthic macroinvertebrate assemblages across sites that encompass a range of habitat conditions. Longitudinally, specific conductivity, substrate, and discharge varied, and sites were significantly different when comparing macroinvertebrate density, Shannon- Weiner diversity, and species evenness. Post-hoc analyses revealed that the Middle Pecos confluence sites of Taiban Creek and Rio Hondo had lower benthic macroinvertebrate density than the Permian Basin site of Delaware River. Additionally, the Taiban Creek and Independence Creek, the most northern and southern sites, were significantly different when comparing Shannon-Weiner diversity. Seasonal differences also existed in the density of macroinvertebrates and the functional feeding groups present across sites. Nonmetric multidimensional scaling analysis revealed that confluences within the same region had similar community structure, and indicator species analysis showed that some taxa were strongly associated with particular regions (e.g., Psephenidae and Naucoridae in the Edwards Plateau). Taken together, these findings indicate that tributary confluences are important sites for benthic macroinvertebrate production in the highly altered Pecos River, and ecoregion-scale physiographic variation strongly influences local confluence community structure.