The Ecology of Tijuana Estuary, California: An Estuarine Profile

Closely associated with the research activities
at PERL are three ~rojects that will create artificial '
wetland habitat, provide nurseries for wetland
plants, and enhance an existing riparian/estuarine
channel (Figure 69). The State Resources Agency
(Environmental License Plate Fund) and the State
Coastal Conservancy are sponsoring these
activities. Fresh, brackish, and saline
impoundments of several sizes wiil be constructed
to provide alternative habitats for estuarine
species. As Boland's (1981) research on
shorebirds has shown, alternative wetland types
can subsidize the estuarine populations. In many
cases, these wetlands may provide essential
refuges during times of whole-ecosystem
perturbation.
6.2 MANAGEMENT NEEDS
Tijuana Estuary is an urban estuary subject to
the chronic and acute impacts of an enormous
human population. The city of Imperial Beach
surrounds the northern arm of the estuary.
Agricultural lands and a large system of levees for
flood control have modified the Tijuana River
floodplain. Just upstream, the city of Tijuana,
Mexico, includes over 2 million inhabitants, most of
whom do not even have access to a sewer system.
The watershed above Tijuana is scheduled for
rapid and extensive development. At the same
time, the downstream estuary is supposed to serve
as a sanctuary for research and education, a
refuge for endangered species, and a State park.
The nurseries will be used to propagate wetland
plants for transplantation to restoration projects
wlthin the region. One potential use will be the
development of a living collection of plant species
and gene pools from the region's wetlands, so that
b~oioglcal diversity can be maintained in the face of
continuing wetland disturbance The local
extinct~on of annual pickleweed and sea-blite
indlcate the need for such a collection When the
reglon's few whole ecosystems continue to be
subjected to catastrophic disturbances (both
natural and human), the need to take an active role
in preserving gene pools becomes urgent
Enhancement of a riparian/estuarfne channel
will serve a variety of wetland spectes The area
that once carried part of the Tijuana River flow
south along the bluffs (Figure 4) is now mostly dry
The riparian, or riverine, portion IS dry because the
river has been rerouted, the estuarine portion is
dry because sediments have reduced tidal action
Enhancement will cons~st of removing exotic
vegetation, planting native species, and removing
recent sediments Habitat for estuarine channel
organisms wrll be increased.
These activrl~es are management oriented, yet
each will ultimately enhance our understandrng of
Tijuana Estuary The artificial wetlands wiil attract
wildlrfe and help to determ~ne how sal~n~ty and
vegetation tnfluence animal usage The nurseries
will contribute ~nformat~on on what conditions
optimize growth of d~fferent plant specres Flnally,
the enhanced channel wrll prov~de a demonstration
of our ability to restore disturbed habitats As with
elmost at! of our studies at Tijuana Estuary.
research and management will go hand in hand
With understanding has come the abrlrty to rnod~fy
the system to achieve desired management goals,
a process that we call "ecatechnology." There is a
very real need for such actrve management at
Tijuana Estuary
Management of Tijuana Estuary is the
responsibility of several agencies that either own
property within the estuary or have legal
jurisdiction there. These include the U.S. Fish and
Wildlife Service, the U.S. Navy, the California
Department of Parks and Recreation, the California
Coastal Commission, the California State Coastal
Conservancy, the County of San Diego, and the
Cities of Imperial Beach and San Diego. All of
these agencies interact under the umbrella of the
Tijuana River National Estuarine Sanctuary
Management Authority. A recently adopted
management plan for the sanctuary (Dobbin
Associates 1985) details the roles of each
participating agency and outlines a wide range of
issues. Those that bear directly on estuarine
ecology are examined here.
Management problems are numerous, but four
stand out as having the greatest impact on
estuarine ecology: sedimentation of channels,
erosion of the beach and dunes, inputs of sewage,
and modification of streamflow. Each problem has
multiple causes. Increased sedimentation follows
disturbance of soil-stabilizing vegetation both
within the watershed and on the beach. The beach
and dunes erode when storms and high sea levels
coincide. Sewage spills are almost entirely
traceable to breaks in Mexican sewage lines.
although local leaks are not unknown. Streamflow
augmentation is associated with reservoir and
wastewater discharges: their effect is greatest
during summer, when the river might otherwise be
dry.
These many drsturbances are interrelated.
dune sands contribute sediment to channels, and
sewage spills alter streamflows The causes of
these problems must often be dealt wrth
separately, for exampie, dunes can be stabll~zed
with fencrng or vegetation to reslst slarm damage,
but nothing can control sea levels. Mitigation of
impacts, on the other hand, requires a