Single species growth and benthic macroinvertebrate community responses to nickel

Sediment metals may be detrimental to aquatic insect growth and community structures if they are bioavailable and exceed threshold limits.  The objective of this study was to evaluate factors that control Ni bioavailability and flux in sediments.  Single species Ni sediment toxicity was examined in laboratory flow through exposures, and transplanted benthic communities were exposed in a streamside mesocosm for 4 wks.  Stenonema spp., Anthopotamus verticis, Psephenus herricki, Isonychia spp., and Chironomus tentans growth was measured during 7-10 d sediment (low acid volatile sulfide (AVS), low organic carbon (OC)) toxicity tests.  Benthic communities were transplanted to a streamside mesocosm with two sediment types (high AVS, OC, and low AVS, OC) spiked with Ni.  Benthic communities and sediment chemistries were sampled weekly.  Only A. verticis and Stenonema spp. showed growth effects with dry weights, ash-free dry weights, and number of exuvia (Stenonema spp.) (p-value <0.001).  Chironomus tentans lab exposures also showed growth effects (p-value <0.005).  The benthic community responded negatively to increasing Ni concentrations with reference treatments having higher total taxa, % Ephemeroptera, % EPT, and % filterers.  Higher sediment Ni resulted in an increase in % dominant taxon and % tolerant.  Ni toxicity was apparent with indigenous aquatic insects in both lab and field sediment exposures and was related to the metal complexation capacity of the sediments.