CHARACTERIZATION OF TOXIC CONDITIONS ABOVE WILSONS-CREEK-NATIONAL-BATTLEFIELD-PARK, MISSOURI

Wilson's Creek has an extensive history of toxicity from both point an d nonpoint sources. Seven-day chronic daphnid (Ceriodaphnia dubia) bio assays identified one toxic site in the Wilson's Creek watershed. Proc edures for the characterization phase of a Toxicity Identification Eva luation (TIE) were modified for chronic assessment and performed on fo ur water samples from the toxic site. The characterization involved ch emical/physical alterations of samples, combined with bioassays, to he lp in identification of the class(es) of toxicants; followed by chemic al analyses. To help understand the additivity of mixtures, toxic unit s were derived. Successive samples contained concentrations of copper, cadmium, nickel and zinc that literature values describe as being chr onically toxic to daphnids. Summed chronic toxic units for these value s greatly exceeded ambient toxic units, and more than accounted for ob served toxicity. Substantial fluctuations in water quality occurred ov er the five sampling periods of the characterization studies and a Tes t of Methods, June through August, 1991. This variability illustrates the difficulty in detecting and documenting nonpoint sources of pollut ion. Tests using living organisms, in conjunction with toxicity identi fication methods, on samples taken over time appear to be appropriate for detecting acute and chronic toxicity in areas impacted by intermit tent point and nonpoint-source toxicity.