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<br />and other sea mammals and shellfish and bivalves used for human consumption absorb <br />and accumulate copper, chromium, cadmium, nickel, lead, and iron (American Oceans <br />Campaign 1997). When large amounts of nutrients from urban and agricultural <br />wastewater enter rivers, a rapid increase of plant and phytoplankton growth occurs. Algal <br />respiration and decomposition of dead algae and plankton lead to diminished levels of <br />dissolved oxygen (DO) available for all aquatic species, including fish. If there is not <br />enough dissolved oxygen available, fish and other aquatic species die from lack of <br />oxygen, a condition known as hypoxia. If fish populations are dying or non-existent due <br />to hypoxia, then fish-eating migratory waterfowl do not have a food source (American <br />Oceans Campaign 1997). Heavy metals and pesticides found in agricultural wastewater <br />discharged into the rivers weaken bird immune and reproductive systems. <br /> <br />Water Supply Costs and Infrastructure. When water quality degrades in local ground <br />and surface water reservoirs, water agencies must either treat contaminated water or find <br />alternative sources of water to replace the contaminated water supply. In any event, the <br />cost of water supply increases. If the city chooses to treat the contaminated water, then <br />the local government must pay to buy, install, operate, and maintain water treatment <br />technology. Another option is to import water from distant sources such as the Colorado <br />River. However, the economic burden of importing water is much greater than that of <br />preserving local water resources. For example, in San Diego it costs $65 to produce one <br />acre-foot of water from local groundwater resource. Water from the Colorado River costs <br />approximately $550 per acre-foot, a nine-fold increase of water costs (Michel 2000). <br />Water supply costs for Tijuana were not available, but the cost differentials are probably <br />similar in scale. Imported water is expensive because it requires building, operating, and <br />maintaining long distance water transport and storage facilities. Substantial energy costs <br />incur when water is pumped over the mountain ranges that separate Tijuana and San <br />Diego from the Colorado River. A third source of water supply, desalination, is expensive <br />and currently not as cost-effective as the strategy of protecting and recharging local water <br />resources (Dallman and Piechota 2000). Local surface and groundwater resources do not <br />require the economic burden of infrastructure and energy costs associated with water <br />imports and desalination. <br /> <br />Given the increased demands upon local water supplies for Tijuana's growing <br />economy and urban population, the city cannot afford to contaminate or lose a critical <br />economic asset-water resources supplied by local rivers. Local clean water resources <br />provide a healthy and cost-effective service to the city and local economy. This service, <br />or clean water, is a renewable source of natural capital. One efficient strategy to protect <br />the city's local water resources (water supply and water quality) is through watershed <br />management that includes restoration and protection of riparian vegetation corridors. <br /> <br />Recommendations <br /> <br />A watershed approach to integrated water management offers the best long-term <br />mechanism to conserve critical water resources for Tijuana. The first step prior to the <br />implementation of specific actions and activities is to conduct a thorough watershed- <br />based study of natural resources and land use in the Alamar River Valley. In terms of <br /> <br />18 <br /> <br />