Effects of exposure to agricultural drainage ditch water on survivorship, distribution and abundance of riffle beetles (Coleoptera: Elmidae) in headwater streams of the Cedar Creek Watershed, Indiana

Alicia E Conrad, Purdue University

Abstract

Riffle beetles (Coleoptera: Elmidae) are fairly sensitive to agrichemicals and require established streams with riffle habitat and high dissolved oxygen content for survival. Because these beetles require good water quality and habitat quality, they are effective indicators of ecological health in headwater streams. I conducted static-renewal, aquatic bioassays using larval riffle beetles and stream water from three channelized agricultural headwater streams and one reference stream from April 24 through June 26, 2015 to assess the toxicity of typical agricultural receiving streams. We also completed three field surveys for riffle beetles at seven sites in three channelized agricultural headwater streams and two surveys at one reference stream during the spring, summer and fall of 2015. Additionally, instream habitat measurements and physiochemical parameters were recorded. Throughout the study period, water samples were collected daily at agricultural sites and weekly at the reference site and analyzed for concentrations of pesticides and nutrients at the National Soil Erosion Research Laboratory, West Lafayette, IN. Mean Mayfield survival rate of beetles exposed to water from the reference site (84%) was significantly greater than that of beetles exposed to water from channelized agricultural headwater streams (43%). Survivorship was significantly, and negatively correlated with a pesticide toxicity index and evidence suggested that smaller individuals were more sensitive to mortality than larger individuals. Field surveys captured riffle beetles at only site (13/m2) in 2015 within the channelized agricultural headwater stream study area in 2015. On the other hand, surveys at the reference site in 2015 found an average density of beetles during summer and fall of 64/m2. Lower survival of beetles exposed to water from channelized agricultural streams suggests that pesticides are a driving factor of mortality, however, other contaminants, such as ammonia, nitrate, and total suspended solids may also contribute. Riffle beetles were abundant in 2006 at several agricultural headwater stream sites. Results from the bioassay coupled with the lack of beetles at most channelized agricultural streams in 2015 suggests that exposure to toxicants in these streams decreases their survival.

Degree

M.S.

Advisors

Gillespie, Purdue University.

Subject Area

Ecology|Entomology|Toxicology|Surgery

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