| Wetlands are low-lying marshy
areas that connect inland waterways to the sea. Wetlands are saturated or covered by water
at least part of the year, and have hydric soils. Hydric soils are saturated with water.
Oxygen diffuses about four times more slowly in water than in air, so hydric soils have
very little or no oxygen.
Wetland soils are highly organic and commonly form a black muck. The underlying minerals are usually close to the surface. Sulfur compounds in the soil give some wetlands their characteristic smell. Wetlands can form where water collects in depressions in the land or where soil and organic matter collect in ponds, along rivers and other waterways, or in river mouths at the edge of the sea. As sedimentation occurs, the water becomes more shallow and plants suited to wetlands spread into the area. Some of the most common types of wetland areas include bogs, swamps, and prairies potholes. Temporary pools of water created by the spring thaw or spring rains (vernal pools) provide temporary habitat and are used by some wildlife for breeding. Wetlands are found in many places but are most common along coasts, estuaries, ponds, lakes, and rivers.
San Diego County wetlands Unlike East Coast wetlands, Southern California’s inland wetlands are generally dry in summer, and wet only when saturated by storms or local runoff. Most of San Diego’s coastal wetlands are open to the ocean’s tides, and experience an ever-changing mixture of salt water and fresh that supports a tremendous variety of wildlife. The most typical San Diego County wetlands are salt marsh, freshwater marsh, and riparian habitats. Though not a wetland, San Diego’s upland chaparral habitat surrounds and impacts the watershed. Much more rare but important to mention is the occasional vernal pool. Salt marshes are coastal wetlands that form where rivers empty into the sea. Because of the influx of fresh water into the system, the salinity in salt marshes changes seasonally as river flow increases in winter and decreases in summer. Salt marshes are affected by the rise and fall of the tides. As they recede, tides carry some of the living and dead matter from the marsh to the ocean where the matter becomes food for many ocean animals.
When the tide comes back in, it brings minerals and salts from the ocean. Minerals and salts fertilize the plant life in the marsh. Salt marshes are among the most productive habitats in the world. Many marine animals spend part or all of their lives in a salt marsh. By contrast, very few species of plants are able to live in such salty conditions. Those with this ability are called halophytes. Halophyte plants are classified as accumulators, excreters, and excluders. Accumulators are able to absorb salts, store them in their leaves, and drop the leaves with accumulated salt. Excreters are able to excrete salts from their tissues, while excluders have the ability to exclude salt from tissues entirely. Brackish and freshwater marshes are slightly inland from salt marshes. Brackish marshes are exposed to limited tidal action. Brackish marshes contain a mixture of both salt and fresh water. Freshwater marshes are found further upstream, beyond the reach of the tides. Cattails and bulrushes are two common plants found in both brackish and freshwater marshes.
Riparian streamsides. San Diego’s high tabletop mesas are split by rugged canyons and broad valleys that were carved out by eons of runoff water, creating a complex drainage system of rivers and creeks that flow into the sea. In the bottoms of these canyons and valleys we find the streamside or riparian (riverbank) community. Even where the streams are only seasonal, there is still enough water to support large, thirsty trees like sycamores, coast live oaks, and cottonwoods. All plants take in and eliminate water, and sycamores are particularly heavy drinkers. A single tree needs 300 gallons a day to survive—that’s six bathtubs-full! San Diego’s streamsides are some of its pleasantest locations. Besides the trees, there are tall leafy shrubs like arroyo (creek) willows and mulefat, and water-loving plants like wild roses, California fuchsia, and, less welcome, but undeniably pretty in autumn, poison oak. Foxes, bobcats, deer, raccoons, and many smaller animals and reptiles find these areas good places to live, with plenty of water, food, and shelter. In spring, resident hawks, owls, and woodpeckers share the trees with colorful migrants like orioles, flycatchers, and tanagers. Native peoples, too, found streamsides attractive. They liked to set up their camps near water, gather acorns from the live oaks, and use convenient granite boulders for acorn grinding. Centuries of patient pounding hollowed out bowl-like depressions in the granite, sure signs of Indian presence. Upland chaparral. Considerably inland from the coastal marshes, but still essential to their overall well-being, is the upland chaparral community. Chaparral takes its name from a Mexican word for scrub oak: chaparro, meaning “shorty.” Chaparral is the most common plant community in San Diego, as typical of the area as pine forests are of the mountains. Strictly speaking, however, chaparral is taller than sage scrub, with characteristic evergreen qualities.
While the chaparral may seem like nothing but a hot, dry, barren land, many species of plants, invertebrates, birds, reptiles, and mammals call it home. Chaparral plants are opportunistic, taking advantage of the slightest rainfall to bloom, drop their seeds, and carry on the species. They have to be tough to survive the long dry periods in Southern California. All year long, they hoard water in their small waxy leaves and deep roots. In summer, when there’s almost no water to be had, most of them lie dormant, just as some animals hibernate to survive the winter. During this time, they can catch fire easily—chaparral wildfires are common seasonal events. And while fires that occur too often may cause significant destruction to the chaparral community, periodic fires may actually stimulate its growth. Following a fire, the land may look dead and bare, but the plants are actually waiting for the chance to make their move. Plants are continually competing for space, and some plants inhibit the growth of others. Fire clears out areas, giving new plants a chance to grow. It also gets rid of dead wood and gives certain seeds the conditions they need for sprouting. Some seeds may wait in the ground for years until a fire cracks their tough outer coatings enough to make them susceptible to the next rainfall. The early natives of San Diego knew this, and sometimes set fire to an area they expected to return to later on, assuring themselves a good harvest.
Vernal Pools are an extremely scarce wetland habitat type occurring only where certain soil conditions exist. In late summer, fall and early winter, vernal pools appear as dry, dusty indentations mostly devoid of vegetation. Then, in late winter, a spectacular transformation occurs. As these depressions fill with rain water, high numbers of endangered, rare, and sensitive species of plants and animals appear in and around the pools, many of which can only be found in this system. Spadefoot toads lie dormant in the pool’s dusty crevices until the sound of rain signals breeding time. San Diego fairy shrimp lay their eggs in the pools, which then wait out the dry summer, hatching when the rains fill the pools once again. Delicately hued plants also grow during this wet phase. As the water begins to evaporate, blossoms of every color fill these seemingly insignificant indentations in the landscape. In summer, these temporary wetlands dry out completely until the cycle of life begins again with the onset of winter rains. Vernal pools in San Diego have survived for at least 125,000 years, and perhaps as long as 400,000 years. It was only in the 1940s and 50s that their numbers began to drastically decline. Today only 3% of the region’s vernal pools remain.
Why do we need wetlands? What’s so important about some mud and murky water? Wetlands are the most productive ecosystems in the world. Coastal wetlands support an enormous array of resident wildlife, as well as a fair amount of migrant species. Birds moving south from Alaska along the migratory route known as the Pacific Flyway, use Southern California coastal wetlands as rest stops where they can rest and refuel before continuing their journey. Wetlands are essential nursery and breeding grounds for fishes, shellfish, waterfowl, and other wildlife. About 35% of endangered and threatened animals and plants in the United States depend on wetlands in some way. Wetlands are also important in water purification. Waterways containing natural wastes and pollution are cleaned as they pass through forested swamps. Pollutants such as nitrogen and phosphorus are taken in by many wetland plants as nutrients. Nutrient cycling varies from one kind of wetland to another. Decomposition by organisms such as bacteria, worms, and aquatic insects, release mineral nutrients as well as soluble organic compounds back into the cycle. By absorbing large volumes of water following a heavy rainfall, wetlands protect surrounding areas from flood damage and erosion. Wetlands also have great economical significance. Seven of the ten most economically valuable fishes and shellfish require estuaries for breeding and/or for habitat: salmon, menhaden, flounder, shrimp, crabs, oysters, and clams. About 66% of the commercial fish taken along the Atlantic and Gulf Coasts of the United States depend on wetlands for survival. Many of the food products we depend on need wetland areas. Rice, mint, and cranberries are grown in wetlands.
Disappearing wetlands For all their usefulness, wetlands are little appreciated. Coastal wetlands are among the most endangered habitat types in the world, second only to tropical rain forests. It’s estimated that more than 50% of the wetlands in the continental United States have been irreversibly altered or destroyed. California has lost more wetland habitat than any other state in the U.S. Only about 450,000 acres remain of the state’s original 5 million acres. This is a loss of more than 90% in the last 200 years. And while coastal Southern California has just 8.6% of the state’s total land area, it has almost 50% of the state’s entire population. Growing human populations and rapid coastal development put impossible strains on these fragile habitats. San Diego County wetlands are probably the most threatened resource on the California coast. By 1900, all had been modified by human activities. Wetlands everywhere have been filled in for development of housing, industrial plants, and airports. They’ve been dredged for use as canals, waterways, and marinas. Major highways arc over the streamside canyons and cut right through coastal marshes, causing habitat fragmentation.
The natural processes of erosion and sedimentation are increased as much as 10,000 times by land development. The increased sedimentation clogs waterways and causes water flow to jump natural banks, resulting in flooding. Sediment can collect at the mouth of a river, gradually cutting off the wetland habitat from the ocean. When a lagoon or other wetland closes, without the continual feed of tidal flow, the resulting conditions can have deadly consequences. Too much fresh water can kill plants and animals that favor a higher salinity. Water that is stagnant rather than flowing can become too warm and low in nutrients, with an improper chemical balance. Coastal marshes are not the only wetlands affected by development. Riparian streamside communities are threatened by erosion from overwatering, and introduced exotic plants like pampas grass, acacia, and thistle, that spread quickly and threaten the survival of natives. Neighborhood cats and dogs prey on wildlife, threatening native species. Particularly threatening are feral animals. Feral animals are pets that have escaped and turned wild, and the offspring of these pets. Since these animals must forage for themselves, they can devastate native species populations.
Threat from a foreign invader. An alien green algae, Caulerpa taxifolia, recently discovered in Agua Hedionda lagoon, threatens to spread out of control and choke out native plant life in San Diego’s coastal wetlands. Caulerpa taxifolia is native to tropical waters. In the late 1970s this hardy and fast-growing species became popular with the saltwater aquarium trade. Caulerpa taxifolia has the ability to form a dense smothering blanket of growth on any surface. It is capable of rapid growth— up to one inch per day. A small fragment of this seaweed has the potential to start a new colony that can expand to more than 75 square feet in one year. It can grow in shallow coastal lagoons as well as in deeper waters, and has reportedly survived out of water for up to 10 days. Caulerpa taxifolia has already invaded the Mediterranean Sea, the result of a single plant released in 1984. The devastation has not only altered the habitat, but has harmed tourism, destroyed recreational diving, and had a costly impact on commercial fishing. The recent introduction in San Diego County is believed to have resulted from someone dumping their home saltwater aquarium. If this species is not controlled in Southern California, it could be disastrous for our kelp forests and coastal wetlands, and the many animals that depend on them.
Saving our Wetlands The preservation of our wetland communities is an awesome task. It is not enough to protect the coastal areas when the damage begins far upstream. In the 1970s and 80s state and federal agencies, together with many private conservation groups, spent millions of dollars to purchase San Diego County wetlands to establish wildlife preserves. As a result, most of the county’s wetlands are now publicly owned. This has largely stopped the filling, dredging, and other direct destruction of the wetlands. But they are still suffering from the erosion and sedimentation caused by upstream development. Restoration projects represent a hopeful trend for coastal wetlands. Some recent successful projects include removing sediment and man-made structures, restoring tidal or freshwater flows, and recreating particular habitats. In most cases a wetland cannot be restored to its original state, but restoration can greatly enhance remaining wetland habitat for wildlife. Several restoration projects have already occurred. The Coastal Conservancy has administered projects in the San Dieguito and Batiquitos lagoons, and the Tijuana River Estuary. The City of San Diego has recently restored seven acres of salt marsh on the north end of Mission Bay, which expands the wetlands of Mission Bay Northern Wildlife Preserve. The lessons learned will be used for other projects in Mission Bay. The Southern California Wetlands Recovery Project aims to acquire more than 1,500 acres, and to restore or enhance more than 500. In San Diego County the Project includes 20 acres of restored salt marsh in the Tijuana River Estuary with an aim to restore a 500-acre portion, plans to redesign the Famosa Slough culvert to increase tidal circulation and enhance 26 acres of wetlands, and resources to provide for the ongoing removal of sand and cobble from the mouth of the San Elijo Lagoon to restore tidal action to 415 acres of degraded salt marsh. These projects are only the beginning of what still must be accomplished.The effects of watershed disturbance may go unseen for decades, until an exceptionally wet winter brings it all crashing down around us. If we don’t prevent damage now, we could end up spending millions to repair it, or lose our remaining wetlands altogether.
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