W4 PM Sediment Quality Assessment
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in Ballroom 4

(BIR-1117-564236) Effects of stream hydrology on sediment toxicity in moderate-gradient systems.

Price, D.¹, Birge, W.¹, ¹ University of Kentucky, Department of Biology, Lexington, KY, USA

ABSTRACT- Special efforts were undertaken to determine the effects of stream hydrology on bioavailability of sediment-sequestered toxicants. The focus was on moderate gradient freshwater systems and PCB was used as the principal "chemical marker" for comparisons of high- and low-flow conditions during a 4-year study. The stoneroller minnow (Campostoma anomalum) was used to quantify PCB uptake (bioavailability). This species routinely disturbs and ingests sediments while feeding on benthic substrates. In a typical third-order stream, subject to runoff of contaminated soils, PCB concentrations decreased in the following order: floodplain soils > stream sediments > water column. PCB (g/Kg) averaged 22.06 in the floodplain soils, 8.92 in the sediments, and generally was non-detectable in the water column. During and soon after sustained high-flow (6.64 to 710.0 cu. ft./sec.), PCB (g/Kg) in the stoneroller minnow averaged 4.16 (n=40), whereas during low-flow this value was 2.20 (n=81). Floodplain soil runoff increased PCB bioavailability, affecting the stoneroller and, presumably, other aquatic biota. This same response was observed in a second order tributary. Furthermore, floodplain soil runoff and the disruption of sediments in the contaminated stream sectors resulted in increased PCB contamination at downstream monitoring stations. In conclusion, sediment PCB was more bioavailable during and soon after high-flow events. Even during average stream discharge, sediment PCB bioavailability was greater that during low-flow. The most pronounced finding involved the near constant fluctuations in daily stream discharges measured at USGS gauging stations. Average daily discharge during the 4-year study was 6.81±30.55. The high standard deviation illustrates the degree of stream variability. For the month of December 2001, the average daily flow was 35.35±100.57. The high variability, characteristic of many important moderate gradient systems, may pose a dilemma for the U.S. EPA endorsement of the "equilibrium partitioning" approach for assessing effects of PAHs and some other organic compounds.

Key words: stream hydrology, sediments, PCB, stoneroller minnow