ETM: The Estuarine Turbidity Maximum

1. ETM: The Estuarine Turbidity Maximum PSO 2009

2. St. Lawrence R. Elbe River Hudson R. Chesapeake Bay Gironde River Columbia R. San Francisco Bay Estuarine Turbidity Maximum (ETM) Depth River Ocean

3. 5 10 May 2,1998 15 5 10 May 17,1999 15 10 20 30 40 50 60 70 Stratification, turbidity, salt front location influenced by freshwater flow 200 May 1998 (above average freshwater flow) 0 Depth (m) May 1999 (below average freshwater flow) NTU 50 0 Kilometers from River Mouth Sanford et al. 2001, North and Houde 2001

4. Observations about particle trapping in ETMs • Particle trapping in ETMs occurs by asymmetrical tidal transport of a pool of resuspendible particles with a limited range of settling velocities • Fine sediments in estuarine environments almost always exist in aggregated (flocculated) form. Aggregation and disaggregation can be active processes, depending on concentration, stickiness, and small scale shear. • Settling velocities of fine sediments trapped in ETMs are determined by the aggregate properties (size and specific density), not the individual particle properties

5. ETM particles are packed with organics 20 to 63 um 10 to 20 um > 63 um < 10 um Close-up DAPI stained Columbia River Crump & Baross, 2000