Ra
Doxazosin Mesylate was measured using incubations of coarse-grain (n = 6, 0.0346 m2) and fine-grain (n = 2, 0.055 m2) sediment cores collected from the GP (intertidal, salinity 17) and CB (channel, salinity 22) sites, respectively (Bird et al., 1999 and Beck et al., 2007). Ra-free YRE water (salinity ~ 18, pre-extracted over two manganese fiber columns placed in line) was carefully added to the sediment cores to minimize sediment disturbance. Although salinity of the added water was slightly different from in situ salinity, this should not have artificially inflated fluxes due to desorption as changes in Ra sorption are small above a salinity of ~ 10 (Webster et al., 1995; Elsinger and Moore, 1980). The overlying water was gently bubbled with air to stir and oxygenate the water, preventing redox processes such as Mn-reduction that may affect Ra flux (e.g., Daniel, 2011). Water column oxygen depletion is occasionally observed in the YRE during late summer in the lower main channel, but average oxygen concentrations during these periods are not particularly low (4.1 mg L- 1; Reay, 2009). The sediment-water interface of the CB site cores were disturbed during transfer from the box core to sample box, and sediments were smoothed and allowed to sit for 72 hours to equilibrate with the Ra-free water. This disturbance did not appear to influence the
diffusion rate as additional (unpublished) diffusion experiments measured with fine sediments had similar diffusion rates. The increase in water column Ra was measured by draining the overlying water (4-5 L) at varying time intervals (1-600 h) and extracting 223Ra and 224Ra for analysis as described previously.
