What is the relative influence of bed sediment composition and water chemistry on aquatic macroinvertebrate metrics in agricultural headwater streams?

Authors: SHUMAN, TYLER - Indiana University-Purdue University; GILLESPIE, ROBERT - Indiana University-Purdue University; Smiley, Peter - Rocky; Gonzalez, Javier

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/4/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Macroinvertebrates of channelized headwater streams in agricultural landscapes are exposed to pesticides and altered bed sediments. We hypothesized that macroinvertebrate assemblages inhabiting sediments with a low percentage of gravel and low organic content are less diverse than those with greater gravel and organic content. We further hypothesized that agricultural chemicals in the water column would have less influence on macroinvertebrate assemblages than bed sediment characteristics. We analyzed particle-size distribution, percent organic content, and agricultural chemical concentrations of three channelized headwater streams and one reference site. Water samples were collected weekly, sediment samples were collected three times from May-September, and macroinvertebrate assemblages were sampled twice. Taxon richness was significantly greater at the reference site (mean = 13; 11.33-14.67) than that at channelized sites (mean = 8.4; 7.00-10.67). The percent of sediments with particles greater than 16.0 mm (gravel) was significantly greater at the reference site (mean = 12.2%; 4.70-18.20 %) than that at channelized sites (mean = 2.53%; 0.00-10.33 %). However, organic content did not differ significantly between channelized (mean = 2.2%; 1.1-3.1 %) and reference (mean = 2.8%; 1.7-4.8%) streams. Additionally, mean total concentrations of pesticides did not differ between channelized sites (mean = 0.80 ppb; 0.10-2.06 ppb) and reference sites (mean = 0.07 ppb; 0.02-0.15 ppb). These data support the hypothesis that sites with greater gravel content in sediments have greater macroinvertebrate taxa richness. However, it appears that organic content of sediments had no influence on macroinvertebrate richness. Although, as predicted, pesticide concentrations in water were not associated with taxa richness, it is possible that pesticide concentrations in sediments could negatively influence the diversity of macroinvertebrate assemblages. Multivariate analyses of these independent variables and diversity metrics could determine the relative importance of physical and chemical sediment characteristics on macroinvertebrate diversity of channelized headwater streams.