Ponar grab. Collected sediment was placed in prevvashed high-density polypropylene ice chests 

 (Coleman®) and then covered with river water with no or minimum air space. Sediments were 

 stored in the ice chests for less than two weeks before testing. 



Porewater was extracted from the collected sediments by centrifugation. Sediment 

 (approximately 250-300 g) was placed in high-density polypropylene centrifuge bottles and 

 spun for 30 minutes at 4,000 X g and 4°C. The collected porewater was placed in prewashed 1- 

 L cubitainers with no head space and stored at 4°C for a maximum of one week. Prior to 

 testing, porewaters were poured through a 1 10-um mesh screen to remove any large particulates 

 and extraneous organisms (i.e., copepods and midge larvae) and allowed to reach test 

 temperature (20 ± 1°C). 

 2.1.2. Control Solutions 



Standard reconstituted water (pH = 7.6-8.0, hardness = 160-180 ppm CaC0 3 , alkalinity 

 = 1 10-120 ppm CaCC^) (Marking and Dawson 1973) was used as the control solution in 

 sediment toxicity tests conducted in the first year. Standard reconstituted water was made as 

 needed. Filtered creek water was used to culture organisms used in the assays both years of the 

 study and as a control solution for the second year of work. Filtered creek water was obtained 

 by filtering Quiver Creek water (Havana, IL) through a sand filter. Dissolved oxygen, pH. 

 hardness, alkalinity, conductivity, and temperature of the control solution were measured and 

 recorded before testing. 

 2.2. Organisms 



2.2.1. Ceriodaphnia dubia 



Starter cultures of C. dubia were obtained from the Environmental Research Laboratory 



