Gauging macroinvertebrate response to restoration-induced disturbance using recolonization traps in a western Colorado stream

Background/Question/Methods

Streams are imperiled in anthropogenically dominated landscapes and have become the focus of numerous restoration projects. Although restoration goals vary, they often include the improvement of in-stream habitat which usually involves the physical manipulation of the stream bed. The restoration process is potentially a disturbance on an already impacted system and may negatively affect the biota, yet our understanding of the ability of the biotic community to recover after these perturbations is lacking. We assessed modes of benthic macroinvertebrate recolonization at two sites of varying degradation (low vs. high impact) in an agriculturally impacted 3^rdorder stream in western Colorado, USA, in order to gage the ability of the macroinvertebrate community to recover from disturbances related to restoration. Traps designed to allow recolonization from each of the four main routes (upstream, downstream, aerial, and hyporheic), in addition to a control trap (open to all routes), were set at both sites for three weeks during July 2012. We compared overall abundance, biomass, diversity, and functional group composition to determine differences between recolonization routes among sites. These data will be used to evaluate the ability of species with different dispersal modes to recolonize after restoration and better manage the restoration process.

Results/Conclusions

Trap richness and Shannon diversity varied little between traps and sites. Total abundance and biomass were also similar between traps and sites, except for upstream traps at the low impact site that were nearly 2x as high as controls due to an increased number of larval Chironomidae.  Non-metric Multidimensional Scaling (NMDS) revealed differences in community composition between trap types and sites in regard to abundance but not biomass. Overall functional feeding group composition was similar between sites as shown by the controls. However, grazing snails (Physa sp.) and microcaddisflies (Hydroptila sp.) dominated abundance and biomass in all traps at the high impact site, while more functionally diverse communities colonized traps at the low impact site (ie., shredders, filterers, and collector-gatherers). Predators were highly variable and contributed 11-33% of recolonization biomass among traps at both sites. Our results indicate that macroinvertebrate communities have the ability recolonize quickly and dispersal from upstream sources may have the greatest influence on community composition. Additionally, the changes in functional feeding groups suggest that recolonization may be driven by available resources. Thus, restorations should maintain undisturbed upstream sites as a potential source of both biota and resources, although other modes of availability should still be considered.