AN ALTERNATIVE APPROACH FOR USING CHIRONOMIDAE TO MONITOR WATER QUALITY IN TRIBUTARY STREAMS OF THE SAINT CROIX RIVER

Leonard C. Ferrington, Jr., University of Minnesota, Depatment of Entomology
Marcey Westrick, Emmons and Olivier Resources, Inc.
Byron Karns, National Park Service, St. Croix National Scenic Riverway
Tony DeMars, Emmons and Olivier Resources, Inc.

Aquatic insects have been used routinely in biological assessments and monitoring of surface water quality. Aquatic insects of the family Chironomidae typically represent 50% or more of the insect species richness in streams and rivers and are usually among the most common groups occurring in waterbodies across a broad range of water quality conditions. However, they are not utilized adequately in most routine biological monitoring programs because of the time and expense required to sort and identify larvae. We have tested an alternative sampling approach based on collections of surface-floating pupal exuviae (SFPE) for use in biological monitoring in small, spring-fed tributary streams of the Saint Croix River. This approach is commonly employed in England, where it has been codified into standard operating procedures for rapid bioassessments required by law. Our results confirm that this approach can be applied in small streams in the Saint Croix National Scenic Waterway, and is more cost effective than traditional methods using dip-nets (DN) designed for collections of larvae. We have determined that species richness estimates based on SFPE collections are strongly correlated with, but typically exceed, richness estimates for non-chironomid aquatic insect species for 20 tributary streams when sampled on a seasonal basis over a one-year period. The richness estimate for Chironomidae using SFPE collections also exceeded the richness estimate for Chironomidae derived from DN collections. In our study, 75 species of Chironomidae were detected, including several species that are undescribed, rarely collected or have poorly known biologies. By contrast the cumulative richness estimate that we obtained from DN collections for all other groups of aquatic insects only amounted to 64 species. We feel that collections of SFPE can be a cost-efficient adjunct to DN collections and would result in improved estimates of the biological diversity of insect communities in small tributaries to the Saint Croix River. In this presentation we will describe the SPFE collection protocol, provide an overview of our study results, and speculate on the relative merits and possible limitations of the methodology for application in routine water quality monitoring within the Saint Croix National Scenic Waterway.