Mussel assemblages in a developing oxbow and a newly-cut channel of the Neosho River, Kansas

Abstract

I compared freshwater mussel assemblages (Bivalvia: Unionidae) in a developing oxbow (old channel) and a newly-cut (new) channel of the Neosho River, Neosho County, Kansas, during 2001. I sampled mussels at approximately 1.5 km intervals, totaling 19 sites in the old channel and seven sites in the new channel, by groping substrate from bank to bank in a zigzag fashion along a 100 m reach. I found 1,239 live individuals of 20 mussel species in the old channel and 20 live individuals ofsix species in the new channel. Mussel abundance, diversity, and current species richness were significantly greater in the old channel than in the new. Abundance, diversity, and historic and current species richness all declined significantly from upstream to downstream in the old channel. Historic richness was greater than current richness in the old channel, but both decreased from upstream to downstream at the same rate. Loss of historic species from the old channel was no different from that in the rest of the Neosho River in Kansas; however, a decrease in lotic species will likely occur as the channel continues to evolve into an oxbow. Canonical correspondence analysis illustrated mussel assemblage variation with environmental differences between the old and new channels, and a substrate compaction, substrate composition, and depth gradient in the old channel, including lotic species in flowing waters with sand and gravel substrate and lentic species in still waters with silt substrate.