Responses ofHyalella aztecaandchironomus tentansto particle‐size distribution and organic matter content of formulated and natural freshwater sediments

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Abstract
The freshwater amphipod,Hyalella azteca(Saussure), and midge,Chironomustentans (Fabricius), were exposed to formulated sediments and nontoxic field collected sediments for 10 d to determine their responses to varying sediment particle sizes (0 to 100% sand, 0 to 100% silt, 0 to 60% clay) and organic matter content (0 12 to 7 8%) of freshwater sediments In experiments with formulated sediments, H azteca survival was >80% when exposed for 10 d to all particle size regimes exammed Subsequent exposures of H azteca to field collected sediments resulted in >80% H azteca survival in all sediments Field collected sediments with organic matter content ranging from 0 12 to 7 8% yielded no observed effects on amphipod survival, which ranged from 84 to 100% Survival of C tentans ranged from 4 to 56% when exposed to formulated sediments for 10 d with 0% particulate organic matter content A threshold organic matter content between 0 76 and 0 91% was observed for C tentans exposed to formulated and field collected sediments Chironomus tentans survival was >80% in all cases when exposed to various particle size regimes in formulated sediments containing 2 5% particulate organic matter Formulated sediments were suitable for determining H azteca and C tentans responses to particle size regimes and organic matter content of sediments, as test results using formulated and natural sediments were in agreement Except for C tentans observed intolerance of <0 76 to 0 91% organic matter content of sediments, C tentans and H azteca are suitable benthic toxicity testing organisms for determining the potential toxicity of sediments with a wide range of particle size regimes and organic matter content