Mitigation Between Regional Transportation Needs and Preservation of Eelgrass Beds--Appendices (Volume II)

The objectives of this study are to understand effects of ferry terminals and ferry operations on eelgrass (Zostera marina L.) meadows in Puget Sound and to design appropriate measures to avoid, minimize, and compensate for associated impacts.
Dramatic increases in population and ferry traffic in western Washington have resulted in the need to expand existing terminals. Our studies have shown that eelgrass meadows near ferry terminals are affected by light reduction and other initial and long-term disturbances associated with terminal construction and maintenance, propeller wash, and bioturbation by macroinvertebrates (i.e., sea stars and Dungeness crab). Experimental work on light showed that below about 3M m to the -2 power d to the -1 power photosynthetically active radiation (PAR) for one to two weeks resulted in death of the plants. Long-term growth and PAR monitoring, as well as short-term measurements in eelgrass meadows, corroborated this value. Technological measures to mitigate impacts showed that concrete blocks with clear plastic centers, reflective material placed under terminals, and artificial lighting could all enhance light under the terminals. Restoration of damaged meadows adjacent to the terminals is proposed as a viable alternative for mitigating impacts from terminal expansion.
Publication Date: 
Saturday, March 1, 1997
Publication Number: 
WA-RD 421.2
Last modified: 
10/12/2016 - 15:41
Charles A. Simenstad, Ronald M. Thorn, Annette M. Olson.
Washington State Transportation Center (TRAC)
Number of Pages: 
Aquatic life, Docks, Ecosystems, Environmental impacts, Ferries, Ferry service, Ferry terminals, Fishes, Habitat (Ecology), Plants, Sunlight, Traffic mitigation.