Coastal Wetland Restoration:
Several wetland-dependent species have become endangered with extinction due to habitat losses of 75% or more of Southern California natural coastal
wetlands. While there are many plans to restore degraded wetlands and enhance
disturbed estuaries, recent PERL research at (funded by Calif.
Sea Grant) has shown that constructed salt marshes do not match the functioning
of natural wetlands--even 10 years after construction.
- In a major new research effort, the National Biological Survey and the Earth
Island Institute are providing funding to improve restoration of coastal
wetlands in southern California. Studies of the wetland fish food web are
underway, a salinity model is being developed for Tijuana Estuary, and
experiments to control exotic plant invasions are in progress.
- To follow the progress of salt marsh restoration, CalTrans and NOAA's
Coastal Ocean Program fund comparisons of constructed and natural wetlands. In
a field experiment using organic and inorganic soil amendments, we showed that
nitrogen was limiting. A subsequent experiment showed the greatest growth with
nitrogen addition continued through summer. The need to add nitrogen beyond
the first year is currently being evaluated at San Diego Bay.
- "A Manual for Assessing Restored and Natural Coastal Wetlands" (105 pages)is available for $10 and "The Ecology of Tijuana Estuary" (151 pages) is available for $4. "Tidal Wetland Restoration--A Scientific Perspective and Southern California Focus" (129 pages) is available for $10
- Remote sensing tools are being developed to track the progress of wetland restoration and construction sites. Pixel sizes of <1m2 allow the resolution needed to characterize plant establishment in small sites.
- A detailed study of efforts to reintroduce an endangered plant, salt marsh bird's beak, to Sweetwater Marsh, San Diego Bay, was funded by the NBS and Caltrans. The transplanted population increased in size for several years, with a peak in 1995.
- The California Department of Parks and Recreation funded dune plant
restoration at Border Field State Park, within the Tijuana River NERR.
Techniques of propagating and establishing native dune plants were developed.
Restoration involves fencing, seeding, transplanting, and irrigating the dune,
with a diverse on-site garden planted with dune-stabilizing native shrubs.
Impacts of non-point source inflows:
Raw sewage entered Tijuana Estuary daily through 1991 and
intermittently thereafter. Treatment facilities at the US-Mexico border will
be built in 1995. To characterize the water quality at the Tijuana Estuary,
NOAA's Marine and Estuarine Management Division funds our long-term studies of
- Salt marsh vegetation and soil salinities have been censused annually since
- Fishes and invertebrates have been studied since 1986.
- Water quality has been monitored since 1989.
In a region where most of the water supply comes from distant watersheds, irrigation runoff and wastewater spills often enter coastal wetlands, making the normally marine waters brackish. Recent research has sought to determine 1) how much salinity dilution the sensitive estuarine animals can tolerate, 2) how exotic plant invasions respond to lowered marsh soil salinity, and 3) how wastewater wetlands might be used to reduce the problem.
- The City of San Diego's Clean Water Program funded tests of the amount and duration of salinity reduction that California halibut, arrow gobies, and other native fishes and invertebrates can tolerate. These species are sensitive to brackish water, and their population have been reduced where major sewage spills have occurred. Invertebrates were especially sensitive to lowered water salinity.
- The Environmental Protection Agency, NOAA's Sanctuaries and Reserves Division, and California Sea Grant are funding greenhouse experiments that show how lowered soil salinity favors the invasion of exotic weeds. Field trials show that such invasions can be controlled by adding salt to restore the natural hypersaline conditions.
- The California Sea Grant Program funded innovative work with wastewater wetlands that had variable hydroperiods and pulsed discharges (and reduced freshwater influence in downstream coastal water bodies). Pulsing significantly improved nutrient and metal removal.