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World Resources 1996-97
(A joint publication by The World Resource Institute, The United
 Nations Environment Programme, The United Nations Development
 Programme, and the World Bank)
(Data edited by Dr. Róbinson Rojas)

3. Urban Impacts on Natural Resources


The true impacts of urban activities on natural resources cannot be captured with a media-specific approach--in other words, looking first at air pollution and then water. Natural resources are linked, so that the degradation of one resource affects not only the resource itself but also a wider resource base in and around the urban area (166). In Tetuoan, Morocco, for instance, peri-urban deforestation not only destroys local habitat but also increases soil erosion, which in turn leads to heavy siltation in downslope water reservoirs; 50 percent of the Nakhla Reservoir has already been lost. The construction of new dams to meet urban water demands has in turn reduced river flows, affecting riverine habitats and wildlife and reducing the capacity of the rivers to process sewage wastes (167).

As the Tetuoan example makes clear, strategies for environmental management need to consider the entire ecosystem and the range of insults it experiences. Integrated coastal zone management (ICZM) is one such strategy. Its premise is that a coastal ecosystem must be considered as a whole, even though it may be subject to an array of dissimilar threats and under the control of many separate governments. ICZM is also a participatory planning process that seeks to involve all the affected parties--from city residents, to industries, to the different levels of state and city governments-- so that the problems at hand and the possible options for addressing them are widely understood and the choices for action are broadly supported (168) (169) (170) (171).

This approach relies on scientific assessments to help define the scope of impacts, the natural tolerances of ecosystems to stress, and the benefits, costs, and trade-offs of control options. Even after a management choice is made--perhaps to treat sewage to remove some but not all nutrients--scientific monitoring is used to evaluate the impact of this action, which may then prompt further action in the next planning cycle. In this way, ICZM evolves as environmental conditions and the attitudes of the stakeholders change (172) (173).

The two profiles presented below provide a more comprehensive view of the variety of impacts that urban areas can have on coastal ecosystems, from land conversion, to land-based pollution, to urban use effects. The Chesapeake Bay profile illustrates how an integrated approach to environmental management has begun to pay off. The Hong Kong profile dramatically illustrates the range and severity of pressures on urban coastal waters and the difficulty of addressing them in the context of rapid industrial development.

Chesapeake Bay: Regional Mitigation Efforts Bearing Fruit

The effort to reverse the decline of the Chesapeake Bay, the largest estuary in the United States, represents both the promise and the difficulty of a regional approach to coastal zone management. In 1983, Maryland, Virginia, Pennsylvania, and the District of Columbia--all of which are part of the watershed of the Chesapeake Bay--entered into a formal partnership with the federal government to restore the Bay, which has suffered serious degradation from more than 300 years of heavy exploitation and pollution (174).

In the years since the Chesapeake Bay Agreement was signed, specific restoration goals have been wedded to a comprehensive set of actions designed to improve water quality, restore aquatic habitats, regulate development, restrict overexploitation of the Bay's resources, and develop a monitoring program to check the progress of these efforts. This Chesapeake Bay Program has resulted in measurable improvements in the Bay's health. The health of the Bay remains quite threatened, however, and aggressive action is required if the recovery is to continue (175).

The Chesapeake Bay is both extensive and ecologically complex. Stretching nearly 322 kilometers in length, with a shoreline of some 11,263 kilometers (176), the Bay is fed by 48 major rivers that drain a combined watershed of 165,760 square kilometers. This gives rise to a range of physical environments and salinity regimes as fresh water and saltwater mix, creating conditions that support more than 2,500 species of plants and animals. The traditional productivity of the Bay has meant employment to thousands of crabbers, oystermen, and fishers, and has been one of the main attractions for the Bay region's flourishing tourist industry (177).

The productivity of the Bay, however, has been badly compromised by overuse, pollution, and habitat conversion. The very size of its watershed makes the Chesapeake vulnerable to human activities over a vast area. By far the most serious threat to the health of the Chesapeake today is the tremendous influx of the nutrients nitrogen and phosphorus from both urban and agricultural sources throughout its watershed. Whereas forest previously covered 95 percent of the watershed, agriculture now accounts for about 30 percent of the land use and is the largest source of nutrient pollution. Urban development, which covers about 10 percent of the watershed, is close behind as a source of nutrient pollution and is growing quickly. The situation is worsened by suburban sprawl, which causes the loss of wetlands and riparian forest cover, both of which, in their natural states, provide important nutrient buffers (178).

Damage to the Bay from nutrient pollution became evident in the 1960s and 1970s and provides a classic example of progressive eutrophication. At first, extensive algal blooms appeared and the Bay's clarity declined. Eutrophication in turn led to a serious decline in sea grasses and other submerged vegetation, whose loss affected the numerous species that used the vegetation as habitat. Finally, a buildup of organic matter in the depths led to a progressive decrease in dissolved oxygen levels in extensive reaches of the Bay, leaving anoxic dead zones along much of the bottom and stressing many of the organisms in shallower areas (179) (180) (181).

In addition to nutrient enrichment, other pressures on the Bay include industrial effluents and urban runoff, which have left toxic contaminants such as heavy metals, pesticides, and chlorinated hydrocarbons in sediments. Overharvesting of fish and shellfish resources has contributed to the demise of important species such as striped bass, oysters, and shad and may currently be stressing the blue crab fishery--the last major commercial fishery in the Bay. Waterfowl populations have also diminished substantially as shallow water habitats and wetlands have declined (182) (183).

In the mid-1970s and 1980s, the U.S. government undertook an extensive research program to sort out the factors contributing to the Bay's decline. The research revealed the central role of nutrient pollution, providing an essential basis for developing a recovery plan. Later modeling studies indicated that nutrients would need to be cut some 40 percent from 1985 levels for the Bay to recover. In 1987, this 40 percent reduction goal was officially adopted as a centerpiece of the Chesapeake Bay Program (184) (185).

As it stands today, the Chesapeake Bay Program is the most ambitious attempt at integrated coastal zone management in the United States. The program grew out of extensive discussion and negotiation among all interested parties--including state and federal representatives, industries, local governments, environmental and sporting groups, and private citizens--and now has wide public and private support (186).

Achieving that consensus was impressive, considering that more than 1,600 separate communities in three states and the District of Columbia surround the Bay and its tributaries. A regional executive council coordinates the program, receiving oversight and direction from a citizen's advisory committee, a scientific and technical advisory committee, and a committee of local government representatives. State governments and the federal government have lent legal and financial support as well as enforcement powers and monitoring capabilities (187) (188).

Although goals for nutrient reduction and habitat restoration have been set for the Bay as a whole, more detailed goals have also been developed for each of the 10 major tributaries. The actual actions taken to achieve these goals vary widely depending on the location and the nature of the local threats. They include efforts to encourage better methods of farming and timber harvesting throughout the Chesapeake watershed, management of fish and shellfish harvests, stream revegetation and marshland restoration, regulation and monitoring of toxic releases from industry, and mitigation of the effects of shoreline development through such means as vegetative buffer zones, setback requirements, and other zoning restrictions (189) (190) (191) (192) (193).

The results to date have been impressive. Phosphorus levels declined 16 percent from 1985 to 1992 through the use of a combination of bans on phosphorus-containing detergents, upgrades in municipal sewage treatment plants, and soil erosion controls and nutrient management on agricultural land (194). Progress in controlling nitrogen levels has come more slowly, but it is still significant, despite the increasing population in the watershed (195). These gains in nutrient control have led to dramatic improvements in the abundance of submerged vegetation, which increased 75 percent from 1978 to 1993 (196). The striped bass population has rebounded, thanks in part to improved habitat and strict limits on fishing (197).

Even so, a significant effort will be required to meet the goals of a 40 percent reduction in nutrients and a significant improvement in habitat quality throughout the Bay--especially since the area's population is expected to grow nearly 20 percent over the next 25 years (198). So far, the Chesapeake Bay Program has proved to be a flexible mechanism for improving the quality of the Chesapeake Bay, and area leaders are hopeful that the gradual improvement in the Bay's condition will fire public enthusiasm for the difficult steps ahead (199) (200).

Hong Kong: A Study in Multiple Impacts

Pressures on Hong Kong waters are far greater than those on the Chesapeake, and reversing them promises to be even more difficult. Hong Kong is the most densely populated urban center in the world. The Hong Kong conurbation consists of several adjacent cities on the Kowloon Peninsula and nearby Hong Kong Island. It is home to 6.1 million people and more than 200,000 large and small industries whose byproducts flow into two major and several smaller marine embayments (201).

Located in the subtropical climes of the South China Sea, Hong Kong waters once boasted productive coral reefs and mangrove stands and yielded abundant catches of fish and shellfish. However, extensive reclamation projects along the Hong Kong shoreline, massive pollution of the harbor areas, and heavy fishing pressures both in nearby coastal waters and in the more distant waters of the South China Sea have exacted a major toll (202) (203).

Because much of the Hong Kong coast is rather steep, reclamation has played a major role in accommodating urban growth. Filled land now accounts for more than 25 percent of the urban land area, and seawalls armor much of the reclaimed shore. This has radically altered Hong Kong's shoreline ecology, eliminating most mangroves and reducing the diversity of shoreline habitat (204).

Aside from the direct destruction of intertidal, seabed, and coral communities, extensive reclamation around both Victoria and Tolo harbors--Hong Kong's two main harbors--has restricted tidal flushing in the harbor areas, exacerbating the already severe pollution problems there (205). Construction of new airport and port facilities has required some 500 million cubic meters of sand fill, most of which has been obtained by suction dredging from inshore waters. Dredging has stirred up clouds of silt that settle on nearby sea grass beds and coral communities, significantly reducing their original extent (206) (207).

Raw sewage from some 3.6 million people flows into Victoria Harbor, giving rise to severe effects from nutrient loading. Despite generally good water circulation in the harbor, water quality continues to decline. Fecal coliform levels from sewage contamination, for instance, are extremely high, and shellfish contaminated with human pathogens such as salmonellae, shigellas, and hepatitis viruses are common (208). In 1988, a hepatitis epidemic involving nearly 1,400 people was traced to the consumption of contaminated shellfish (209). Dissolved oxygen levels have steadily declined in harbor waters, and some areas where water circulation is poor suffer from permanent or intermittent anoxic conditions. In nearby Tolo Harbor, a smaller embayment with very restricted flow that receives the effluents of 1 million people, conditions are much worse and anoxic waters are much more extensive (210).

Further toxic insult to the harbor areas comes from industrial wastes--solvents, oils, acids, heavy metals, tannery wastes, and other compounds--most of which have been, until recently, discharged through the sewer system. Agricultural chemicals and animal wastes from nearby farms also find their way into the waters around Hong Kong. Shipping traffic is heavy in Victoria Harbor, bringing with it associated hydrocarbon pollution. As a result, the coastal waters are significantly contaminated with trace metals such as cadmium and organochlorines such as dichlorodiphenyltrichloroethane (DDT)(211) (212).

Marine life in Victoria and Tolo harbors has reacted predictably. Severe pollution has resulted in long-term changes in community structure, species abundance, and species diversity of the bottom- dwelling organisms, intertidal organisms, coral communities, and fish. Toxic algal blooms, products of the persistent eutrophication also known as red tides, are common in Tolo Harbor. In 1977, 2 such red tides occurred, but in the peak year of 1988, the number rose to 38. The incidence has declined somewhat with improvements in wastewater treatment (213) (214) (215) (216).

Hong Kong authorities are trying to mitigate these pollution problems in several ways. Already in place are a number of laws that restrict effluent discharges from industry and ships and that regulate the dumping of dredge spoils and sewage sludge at sea (217). Local authorities have constructed a chemical waste treatment plant, and efforts are being made to collect and process animal wastes as well (218).

To address the largest threat to its aquatic environment--sewage-- Hong Kong has launched a three-phase project. The first phase, now under way, involves reconstruction of urban sewer lines. The second phase will involve construction of a large sewage treatment facility on a former island in Victoria Harbor. The final phase will be construction of a marine outfall to transport treated wastes well beyond the harbor waters. Marine experts warn, however, that until the marine outfall is built--which is not scheduled for another decade or so--excessive nutrient loading from sewage will continue to degrade Hong Kong's urban waters (219).

To better meet the growing environmental challenges, the Hong Kong government is moving toward integrated coastal zone management. The planning department has issued maps that broadly identify regions where development should be concentrated and is now compiling a database on the physical and biological characteristics of the coastal zone for use in future planning efforts (220).

At the same time, however, continued expansion of the Hong Kong urban zone threatens to degrade coastal areas to the east of the urban core where environmental stresses have previously been light. In response, efforts are under way to establish several marine parks and reserves to afford some protection to these eastern waters, where coral reefs and other components of the marine community are still healthy (221) (222).

To the west, Hong Kong lies adjacent to one of the most rapidly developing areas of China. Chinese authorities have already commenced port construction, and proposals are in hand for construction of an automobile manufacturing plant and other heavy industrial facilities in nearby coastal areas. These potential threats give weight to the argument that regional coastal planning is urgently needed to avoid catastrophic declines in coastal ecosystems not just in Hong Kong but along the entire southern coast of China (223).

References and Notes

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