ASSESSING SEDIMENTS FROM UPPER MISSISSIPPI RIVER NAVIGATIONAL POOLS USING A BENTHIC INVERTEBRATE COMMUNITY EVALUATION AND THE SEDIMENT QUALITY TRIAD APPROACH

Benthic invertebrate samples were collected from 23 pools in the Upper Mississippi River (UMR) and from one station in the Saint Croix River (SCR) as part of a study to assess the effects of the extensive flood ing of 1993 on sediment contamination in the UMR system. Sediment cont aminants of concern included both organic and inorganic compounds. Oli gochaetes and chironomids constituted over 80% of the total abundance in samples from 14 of 23 pools in the UMR and SCR samples. Fingernail clams comprised a large portion of the community in three of 23 UMR po ols and exceeded abundances of 1,000/m(2) in five of 23 pools. Total a bundance ranged from 250/m(2) in samples from pool 1 to 22,389/m(2) in samples from pool 19. Abundance values are comparable with levels pre viously reported in the literature for the UMR. Overall frequency of c hironomid mouthpart deformities was 3% (range 0-13%), which is compara ble to reported incidence of deformities in uncontaminated sediments p reviously evaluated. Sediment contamination was generally low in the U MR pools and the SCR site. Correlations between benthic measures and s ediment chemistry and other abiotic parameters exhibited few significa nt or strong correlations. The sediment quality triad (Triad) approach was used to evaluate data from laboratory toxicity tests, sediment ch emistry, and benthic community analyses; it showed that 88% of the sam ples were not scored as impacted based on sediment toxicity chemistry, and benthic measures. Benthic invertebrate distributions and communit y structure within the UMR in the samples evaluated in the present stu dy were most likely controlled by factors independent of contaminant c oncentrations in the sediments.