Sediment accumulation in a manipulated bay of Puget Sound, Bellingham, WA.
Benson, Mary Alice
MetadataShow full item record
Mud Bay, located in Bellingham, Washington at the north end of Chuckanut Bay, is filling with sediment at a rate greater than projected sea-level rise. This is worrisome as the bay is an important habitat for eelgrass meadows, shellfish beds, and birds. Also, Chuckanut Creek, the primary fluvial input into the bay, has historically been a salmon-spawning ground. In 2013 the City of Bellingham identified this bay and pocket estuary as a top-ranked 10-year restoration priority due to degradation of wildlife habitat from sediment accumulation. Anthropogenic stressors that could increase sediment accumulation include logging, mining and quarrying in proximal areas during the late 1800s to early 1900s. In the 1920s a rip-rap railroad causeway was constructed across the mouth of the bay, limiting tidal and storm wave energy. During the construction of Interstate 5 in the early 1960s, additional sediment could have been transported to the bay by Chuckanut Creek. To determine if the bay is filling, I collected cores from 4 sites in the intertidal zone of the study area, near where Chuckanut Creek enters the bay. Using 210Pb, I calculated the accumulation rates to range from 0.20 to 1.07 cm yr-1, with spatial variations attributed to differences in tidal and fluvial energy at each coring location. This accumulation rate was corroborated using 137 Cs at one coring site, and depth-of-penetration values for both radiochemical analyses agree. All 210Pb profiles indicated constant accumulation rates, and a link between increased accumulation and construction of the causeway was not found. Grain size analyses and X-radiography images were used to interpret sedimentation patterns in the bay. Grain-size distributions indicate that the east side of the bay is finer grained. There is potentially a sediment signature that can be linked to the construction of Interstate 5. Sea level has risen by 0.12 cm yr-1 since 1934 and relative sea-level projections range from ~0.38 to 0.71 cm yr-1 by 2100 so accommodation space has, and continues to, fill faster than sea-level rise in the bay.