River Mouths, Brakish and Estuarine Coastal Wetlands
III. Elkhorn Slough

Elkhorn Slough is the extreme example of the remarkable reduction of freshwater and the intrusion of salt water along the MBNMS coast. Just 150 years ago the Slough was a shallow arm of the Salinas River; it was dominated by long periods of freshwater flow and shocked by brackish water at the mouth and along the main channel (ABA Consultants 1989, Gordon 1996, MacGinitie 1935, Silberstein and Campbell 1989). The mouth of the river was about a mile north of the present entrance to Moss Landing Harbor and Elkhorn Slough. Here the entire watershed of the Salinas River emptied into the sea, and comingled with Elkhorn and Moro Cojo Slough waters; the Pajaro River used the same mouth (Schwartz et al. 1986). The low back dune region was a large estuarine lagoon, dominated by large and long periods of freshwater flow (Hornberger 1992). Peat marshes, produced in fresh water several thousand years ago, flanked the main slough channel from the mouth to the head of the system (ibid).

Human activity converted the slough into a deep, marine lagoon with strong daily tidal currents, extensive intertidal mudflats, the highest rates of marsh erosion along the coast, and radically reduced inputs of fresh water (Smith 1973, ABA Consultants 1989, Silberstein and Campbell 1989, Schwartz et al. 1986, Gordon 1996, Kvitek et al. in review). Fresh water peat marshes are now covered by salt water. The related changes in ecological communities and processes have been dramatic (MacGinitie 1935, Nybakken et al. 1977, Kvitek et al. 1988, Silberstein and Campbell 1989, ABA Consultants 1989, Gordon 1996).