Presentation Title

Recent Sedimentation along the Mudflats Of an Urban Estuary

Start Date

November 2016

End Date

November 2016

Location

HUB 302-#101

Type of Presentation

Poster

Abstract

Southern California estuaries are often bounded by dense urban development making them vulnerable to sea level rise (SLR) if sedimentation cannot maintain elevation of critical habitats such as salt marshes and mudflats. This project investigated recent mudflat sedimentation in Upper Newport Bay in order to measure seasonal sediment fluxes to the mudflats, and assess the bay's vulnerability to SLR. Short sediment cores were collected in June and October 2016 from mudflats in three areas of the bay. The cores were analyzed for sedimentological characteristics, and short-lived radioisotopes (7Be, 234Th, 210Pb, and 137Cs). The results from June showed 7 cm and 3 cm of recent deposition at sites near the primary and secondary channels, respectively. While the 7Be data suggest centimeter-scale deposition over the previous winter and spring, decadal accumulation rates were only 2-4 mm/yr. These results suggest that wet-season (winter) deposition on the mudflats in the upper reaches of the estuary is nearly completely reworked and redistributed in subsequent seasons. This was confirmed with the October cores, as 7Be activity (recent deposition indicator) was only present at the surface. These results indicate that there was at least 3-4 cm of erosion from June to October. Although the decadal accumulation rate is lower than the seasonal deposition rate, it is equal to or greater than recent estimates of relative SLR for Newport Bay (2.2 mm/yr). We conclude that sedimentation throughout the estuary is dynamic on short time scales, but over time may be keeping up with/possibly even out-pacing relative SLR.

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Nov 12th, 4:00 PM Nov 12th, 5:00 PM

Recent Sedimentation along the Mudflats Of an Urban Estuary

HUB 302-#101

Southern California estuaries are often bounded by dense urban development making them vulnerable to sea level rise (SLR) if sedimentation cannot maintain elevation of critical habitats such as salt marshes and mudflats. This project investigated recent mudflat sedimentation in Upper Newport Bay in order to measure seasonal sediment fluxes to the mudflats, and assess the bay's vulnerability to SLR. Short sediment cores were collected in June and October 2016 from mudflats in three areas of the bay. The cores were analyzed for sedimentological characteristics, and short-lived radioisotopes (7Be, 234Th, 210Pb, and 137Cs). The results from June showed 7 cm and 3 cm of recent deposition at sites near the primary and secondary channels, respectively. While the 7Be data suggest centimeter-scale deposition over the previous winter and spring, decadal accumulation rates were only 2-4 mm/yr. These results suggest that wet-season (winter) deposition on the mudflats in the upper reaches of the estuary is nearly completely reworked and redistributed in subsequent seasons. This was confirmed with the October cores, as 7Be activity (recent deposition indicator) was only present at the surface. These results indicate that there was at least 3-4 cm of erosion from June to October. Although the decadal accumulation rate is lower than the seasonal deposition rate, it is equal to or greater than recent estimates of relative SLR for Newport Bay (2.2 mm/yr). We conclude that sedimentation throughout the estuary is dynamic on short time scales, but over time may be keeping up with/possibly even out-pacing relative SLR.