Ambient Toxicity Assessments in the Minnesota River Basin

The ambient toxicity of the Minnesota River is the subject of this section of MRAP Volume III. To gain an understanding of this researchers conducted five toxicity tests and a series of analyses on selected sites throughout the basin. The toxicity tests included sediment pore water with Ceriodaphnia dubia, Selenastrum capriconutum. Mitochondria were also tested on these subjects. Hyalella were used as test subjects in bulk sediment. Analyses included 20 cations, 6 anions, total ammonia-nitrogen, total phosphorus and total organic carbon. Ceriodaphnia was found at 5 of the 24 sample sites. Selenastrum toxicity was found at 8 of the 15 locations sampled. These two tests show the most toxic locations to be Fort Snelling, Henderson and the Rapidan and Lac Qui Parle Reservoirs. Lac Qui Parle showed the greatest toxicity. Mitochondrial tests showed the most inhibitory response at the Fort Snelling site. The Hyalella tests were made invalid through the poor survival of one of the controls. Analyses of the sediment pore water showed a high level of variability in many of the parameters. The reservoir sediment samples did show a high concentration of ammonia and lower concentration of nitrates than the tributary sites. Multiple regression analyses were conducted and the best relationships were found with the Ceriodaphnia and total ammonia nitrogen.