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Tidal wetland restoration - lessons from San Francisco Bay
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Guidance: There are some clearly promising things about restoration,
which come from the work in San Francisco Bay:
- Restoration happens: Natural marsh restoration is readily
apparent by the mature state of many marshes in the Pacific north west
that have been restored without human intervention;
- Marsh-building processes persist: To a large degree, underlying
processes are still operative if often moderated - salinity regimes
remain, suspended material still provides minerals and organic matter
for accretion, and plant and animal recruitment is pervasive;
- Many functions respond rapidly: While some functions require
lengthy processes, the return of the tide often promotes rapid functionality,
as in an increased tidal prism contributing to floodwater storage and
to habitat and food web support for important resources such as salmon.
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The challenge is to have appropriate science and engineering to evaluate trade-offs,
and to know when, how, how long, and how much we must invest in intervention
and control. Do people have the patience, the will, and the knowledge to incorporate
science, rather than gardening, into tidal marsh restoration? What is the risk,
particularly for recovering tidal marsh-dependent species like certain Pacific
salmon stocks, of continuing to pursue our present ad hoc approach? Studies
of approximately 940ha of 15 sites restored to tidal flooding confirm the importance
of height of the substratum to vegetation development. A second key conclusion
is that higher pre-flooding levels (above approximately 0.3 m below mean higher
high water) restrict creek development (Williams
& Orr 2002).
Comment: Some very important points for more information contact
simenstd@u.washington.edu and see
http://www.abag.ca.gov/bayarea/sfep/sfep.html
for the National Estuary Programme web site.
References
Williams, P.B. & Orr, M.K.
2002.
Physical evolution of restored breached levee salt marshes in the San Francisco Bay Estuary.
Restoration Ecology, 10., 527-542.
Abstract...
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