We evaluate experimentally the effect of carbonate saturation state at the sediment-water interface (SWI) on survivorship of various size classes of the juvenile bivalve Mercenaria mercenaria. Populations of 0.2-mm, 0.3-mm, 1-mm, and 2-mm M. mercenaria were introduced to sediments realistically undersaturated (experimental, saturation state with respect to aragonite ϭ ⍀ aragonite ϭ IMP/K ϭ ϳ0.3) and saturated (control, ⍀ aragonite ϭ ϳ1.5) Ј sp with respect to aragonite in order to evaluate the impact of saturation state and dissolution on survivorship. Linear regression analysis was used to examine mortality within each treatment over time and show significant mortality for each size class in experimental-undersaturated treatments only (P Ͻ 0.05). Mortality rates in experimentalundersaturated sediments were Ϫ11.8, Ϫ4.8, Ϫ1.9, and Ϫ1.1% d Ϫ1 for the 0.2-, 0.3-, 1.0-, and 2.0-mm bivalves, respectively. Analysis of covariance (ANCOVA) was used to examine differences in mortality between treatments over time and show significantly different mortality rates for the 0.2-, 0.3-, and 1-mm individuals (P Ͻ 0.05).

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and U.S. Army Corps of Engineers (USACE). A comprehensive dataset of streamflow, stage, and tidal elevations for the Lower Columbia River basin was compiled. Data were compiled from gaging stations in Oregon and Washington along the Columbia River from Astoria to The Dalles and along the Willamette River from Salem to Portland. Tidal gages along the Washington, Oregon, and California coasts were also compiled. Seasonal maximum values were calculated for both streamflow and stage for the winter (November-March) and spring (April-July) flow seasons, as well as for the full water year when underlying data were available.