Environmental Problems, Their Causes, and Sustainability 1

Restoring a WetlandINDIVIDUALSMATTERHumans havedrained, filled in,or covered overswamps, marshes,and other wetlandsfor centuries.They have done this to create ricefields and other land to grow crops,create land for urban developmentand highways, reduce disease suchas malaria caused by mosquitoes,and extract minerals, oil, and naturalgas.Some people have begun toquestion such practices as we learnmore about the ecological and economicimportance of coastal and inlandwetlands. Can we turn backthe clock to restore or rehabilitatelost marshes?California rancher Jim Callenderdecided to try. In 1982, he bought 20hectares (50 acres) of a SacramentoValley rice field that had been amarsh until the early 1970s. To growrice, the previous owner had destroyedthe marsh by bulldozing,draining, leveling, uprooting thenative plants, and spraying withchemicals to kill the snails and otherfood of the waterfowl.Callender and his friends set outto restore the marshland. They hollowedout low areas, built up islands,replanted bulrushes andother plants that once were there,reintroduced smartweed and otherplants needed by birds, and plantedfast-growing Peking willows. Afteryears of care, hand planting, andannual seeding with a mixture ofwatergrass, smartweed, and rice,the marsh is once again a part of thePacific flyway used by migratorywaterfowl (Figure 12-15, p. 246).Jim Callender and others haveshown that at least part of the continent’sdegraded or destroyed wetlandscan be reclaimed with scientificknowledge and hard work.Such restoration is useful, but tomost ecologists the real challenge isto protect remaining wetlands fromharm in the first place.farmers, and resource extractors vigorously opposethese suggestions.Case Study: Restoring the Florida Everglades:Will It Work?The world’s largest ecological restoration project involvestrying to undo some of the damage inflictedon Florida’s Everglades by human activities.South Florida’s Everglades was once a 100-kilometerwide(60-mile-wide), knee-deep sheet of water flowingslowly south from Lake Okeechobee to Florida Bay(Figure 13-11). As this shallow body of water trickledsouth it created a vast network of wetlands with a varietyof wildlife habitats.But since 1948 much of the southward naturalflow of the Everglades has been diverted and disruptedby a system of canals, levees, spillways, andpumping stations. The most devastating blow came inthe 1960s, when the U.S. Army Corps of Engineerstransformed the meandering 103-mile-long KissimmeeRiver (Figure 13-11) into a straight 84-kilometer (56-mile) canal. The canal provided flood control byspeeding the flow of water but drained large wetlandsnorth of Lake Okeechobee, which farmers then turnedinto cow pastures.Below Lake Okeechobee, farmers planted and fertilizedvast agricultural fields of sugarcane and vegetables.Historically the Everglades has been a nutrient–poor aquatic system, with low phosphorus levels. Butrunoff of phosphorus from fertilizers has greatly increasedphosphorus levels. This large nutrient inputhas stimulated the growth of nonnative plants such ascattails, which have taken over and displaced sawgrass, choked waterways, and disrupted food webs ina vast area of the Everglades.Mostly as a result of these human alterations, thenatural Everglades has shrunk to half its original sizeand dried out, leaving large areas vulnerable to summerwildfires. Urbanization has also contributed to theloss of biodiversity in the Everglades by fragmentingmuch of its habitat.To help preserve the lower end of the system, in1947 the U.S. government established EvergladesNational Park, which contains about a fifth of the remainingEverglades. But this did not work—as conservationistshad predicted—because the massive plumbingand land development project to the north cut offmuch of the water flow needed to sustain the park’swildlife.As a result, 90% of the park’s wading birds havevanished, and populations of other vertebrates, fromdeer to turtles, are down 75–95%. Florida Bay, south ofthe Everglades is a shallow estuary with many tiny islandsor keys. Large volumes of fresh water that onceflowed through the park into Florida Bay have beendiverted for crops and cities, causing the bay to becomesaltier and warmer. This and increased nutrientinput from crop fields and cities have stimulated thegrowth of large algae blooms that sometimes cover40% of the bay. This has threatened the coral reefs andthe diving, fishing, and tourism industries of the bayand Florida Keys—another example of unintendedconsequences.By the 1970s, state and federal officials recognizedthat this huge plumbing project threatens wildlife—amajor source of tourism income for Florida—and thewater supply for the 6 million residents of south266 CHAPTER 13 Sustaining Aquatic Biodiversity