Biological Assessment at the Whole Organism Level : Chironomidae Body Condition Indices Within the Lower Cheyenne River Watershed

The Chironomidae are a taxonomically and functionally diverse family of flies with predominantly aquatic larvae. Due to their diverse habits they are of great value in understanding the condition of water bodies. As a result, several macroinvertebrate community metrics have been devised as indicators of impairment. In addition, several body condition indices have been devised to detect and estimate the impact of potential toxic chemicals. Deformities of head capsule structures are enumerated and scored relative to severity. Parasitism has also been suggested as a useful indicator of stress. Preparasitic larvae of the family Mermithidae must locate and infect host animals in order to mature and hence abiotic variables can directly affect the larvae, thereby influencing observed infection rates. The objectives of this study were to (1) describe the Chironomidae community within the Lower Cheyenne River watershed, (2) examine relationships between Chironomidae body condition and nematode infection frequency, habitat and water quality characteristics and (3) examine relationships between Chironomidae body condition metrics including nematode infection frequency and macroinvertebrate community metrics within these same streams. Samples were collected during the summers of 2007 and 2008 using EPA’s western EMAP Pilot Protocols. Each of the 46 sites (Plains, Black Hills, Badlands and Large River based on portion of the basin) were sampled twice per summer unless completely dry. The 2007 sampling period occurred from May through August, and the 2008 period from April through August. Badlands sites had the fewest Chironomidae genera of the stream classes. Indicator genera of plains streams include Ablabesmyia, Chironomus, Procladius, and Sublettea. Lopecladius was considered to be an indicator genus of large rivers while Micropsectra was considered to be an indicator genus of Badlands streams. Indicator genera of Black Hills streams included Brillia, Diamesa, Eukiefferiella, Orthocladius, and Parametriocnemus. These findings suggest distinct Chironomidae communities among the major landforms. Chironomidae from nine Plains sites were used to evaluate body condition, site water quality and total invertebrate community relationships. Toxic score, Severity Index of Sensitive Species (SISS) and nematode infection frequencies were evaluated for larvae in each sample. Only three samples contained individuals with deformed antennae and no attempt was made to examine relationships between antennae deformity and biological, water quality, or physical habitat metrics. Toxic score of the mentum displayed greater variation among study sites relative to reference sites. Nematode infection rates were found to be positively correlated with substrate embeddedness. Sedimentation may allow these parasitic nematodes to increase, potentially impacting stream arthropod communities. Ten optimized community metrics were used to generate site specific Index of Biotic Integrity (IBI) scores. A significant negative correlation was observed between nematode infection and community Hilsenhoff Biotic Index scores. In general, other biological investigations within the Cheyenne River Watershed would be beneficial. Additional biological data coupled with macroinvertebrate and preexisting fish data would allow investigators and natural resource managers to have a better understanding of the biota and what major impacts are affecting the biota. More work should be carried out investigating relationships between whole organism body condition of midges and abiotic variables. Because midges are frequently abundant, it would be beneficial to know more about how ambient environmental variables such as substrate size influence the onset of deformities. This may help future investigators in studies examining the role of toxic substances and possible complications due to environmental variables. The role of disturbance on parasites needs to be more thoroughly investigated. This would benefit humans in predicting possible disease outbreaks. This may also help explain potential pest outbreaks as a result of low parasite abundance within the ecosystem or whether disturbance can enhance a parasite’s ability to control host populations