title: Detecting, sourcing, and age-dating dredged sediments on the open shelf, southern California, using dead mollusk shells.
abstract: Molluscan shell debris is an under-exploited means of detecting, sourcing, and age-dating dredged sediments in open-shelf settings. Backscatter features on the Southern California shelf are suggestive of dredged sediment hauled from San Diego Bay but deposited significantly inshore of the EPA-designated ocean disposal site. We find that 36% of all identifiable bivalve shells >2mm (44% of shells >4mm) in sediment samples from this 'short dump' area are from species known to live exclusively in the Bay; such shells are absent at reference sites of comparable water depth, indicating that their presence in the short-dump area signals non-compliant disposal rather than natural offshore transport or sea level rise. These sediments lack the shells of species that invaded California bays in the 1970s, suggesting that disposal preceded federal regulations. This inexpensive, low-tech method, with its protocol for rejecting alternative hypotheses, will be easy to adapt in other settings.
authors.affiliation: Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, United States.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Bizjack
authors.affiliation: Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, United States. Electronic address: skidwell@uchicago.edu.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Kidwell
authors.affiliation: Environmental Monitoring & Technical Services Division, Public Utilities Department, City of San Diego, 2392 Kincaid Avenue, San Diego, CA 92101, United States.
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Velarde
authors.affiliation: Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, United States.
authors.forename: Jill
authors.initials: J
authors.lastname: Leonard-Pingel
authors.affiliation: Geological Institute, Slovak Academy of Sciences, Dubravska cesta 9, 84005 Bratislava, Slovakia.
authors.forename: Adam
authors.initials: A
authors.lastname: Tomašových
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology; D000818:Animals; D061006:Bays; D049872:Bivalvia; D002140:California; D004784:Environmental Monitoring / Q000379:methods*; D019015:Geologic Sediments / Q000032:analysis*
keywords: Benthic response; Dead shell assemblages; Live-dead discordance; Mollusks; Ocean disposal; Paleoecology; Taphonomy