Trends in River Flow Affecting the Northeastern Reach of the San Francisco Bay Estuary over the Past 7000 Years

Publisher Website
Google Scholar
Abstract
A variety of stratigraphic analyses (particle grain size, iron concentration, loss on ignition, and macrofossils) from sediments obtained from two marsh sites are used to reconstruct a middle to late Holocene record of stream flow into San Francisco Bay. Browns Island, a freshwater/brackish site, is located at the confluence of the Sacramento and San Joaquin rivers and is dominated by stands ofScirpus americanus.Peyton Hill is a brackish site located near Carquinez Straits and is dominated by stands ofScirpus robustus.Twenty-five AMS14C dates provide chronostratigraphic control. During the Holocene, discharge from the Sacramento and San Joaquin rivers was broadly comparable to modern flows; however, an extended period of higher flow began 3800 cal yr B.P. and continued for almost two millennia. At this time Browns Island supportedPhragmites communis,a freshwater species, and Peyton Hill supportedS. americanus.At least two floods, recognized by discrete increases in sand and silt, occurred at 3600 and 530 cal yr B.P.