5). Because core C4 does not lie at either extreme in thickness, the variations throughout

the impoundment tend to cancel out, hence the similarity in the two estimates of total sediment mass reported above. Downstream of the former power plant, core C4 is representative of the sediment deposit (Fig. 4). However, upstream of the former power plant, CCP-bearing sediment is absent and the sandy layers that are present have a higher dry bulk density. Because of these limiting assumptions, we caution that our calculation of mass accumulation for the entire impoundment be viewed as a general constraint on the Middle Cuyahoga River sediment load. The Middle Cuyahoga watershed and river have experienced tremendous anthropogenic impacts during the twentieth century, and the sediment deposited in the Gorge Dam impoundment Pexidartinib records those impacts. Changes R428 clinical trial in sediment characteristics and watershed activities have allowed the sediment record to be divided into the following 3 time periods. The mud accumulating during the First Period (1912–1926) has low amounts of CCP, even though the coal-fired power-plant had begun production in 1912 (Fig. 8). The low CCP concentration may be due to low power plant production or better land containment of the CCP. Pb, Cr, and Zn concentrations

exceed the PEC levels in most samples and reflect the many industries and human activities that were well-established along the Cuyahoga River immediately upstream of the Gorge impoundment (Seguin and Seguin, 2000, Hannibal and Foos, 2003 and Whitman et al., 2010, p. 79; Vradenburg, 2012). Although leaded gasoline use was limited prior to the 1940s, lead use in paint was high in the 1910s and peaked in the 1920s (Filippelli et al., 2005). The Second

Period period (1926–1978) sediments have abundant CCP, high and variable metal concentration, and high magnetic concentration (Fig. 8). The strong direct relationship between CCP-bearing sediment and high magnetic susceptibility (K) values results from the abundant ferrimagnetic particles in CCP ( Rose, 1996). The source of much of the CCP in the sediment is the former coal-burning power-plant, because higher K values Quisqualic acid and thus greater amounts of CCP are found downstream of the former power plant ( Fig. 4). Trace metals are often found in relatively high concentrations in CCP and may become soluble and leached under sulfide rich and low pH conditions ( Jegadeesan et al., 2008 and Jones et al., 2012). The sediment in the Gorge Dam pool is anaerobic, as evidenced by the released of abundant methane gas during coring, and is favorable for sulfide formation. Through targeted sampling, the trace metal concentrations in the black mud were found to be 36–140% greater than in the CCP-bearing sediment. Thus, trace metals originally in the CCP may have leached out and attached to particles in the interbedded mud layers. However, CCP are not the only source of trace metals in the sediments.