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Managing Wastewater in Coastal Urban Areas
hazardous materials, and introductions of nonindigenous species have all been associated with the degradation of coastal environments. Natural events such as hurricanes can cause major perturbations in the coastal zone. It is not only important, but imperative, that the entire range of factors that may have an impact on coastal environmental quality be considered when strategies for protection are developed.
WASTEWATER AND STORMWATER MANAGEMENT
Among the myriad of factors that affect coastal environmental quality, the management of wastewater and stormwater are perhaps the two most critical considerations. Without appropriate control measures, these activities have the potential to wreak serious harm on the coastal environment. As with any other activity that takes place in the environment, the potential for harm depends on the magnitude of the insult, where it occurs, and the characteristics of the stress.
Constituents and Impacts
Municipal wastewater comes from a variety of sources including households, schools, offices, hospitals, and commercial and industrial facilities. Stormwater runoff comes from streets, parking lots, roofs, lawns, commercial and industrial developments, construction sites, farmland, forests, and a number of other settings. While wastewater and stormwater contain a wide variety of constituents, these constituents generally can be described using several characterizations: solids; suspended and dissolved substances that exert a biochemical oxygen demand (BOD) in natural waters; nutrients; pathogens; organic chemicals; metals; oil and grease; and plastics and floatables. Some constituents may fall into more than one of these categories. For example, metals, organics, and pathogens in wastewater are often associated with suspended solids; and organics can be a component of BOD.
In general, each of these categories of constituents can have an adverse effect in the marine (as well as land and air) environment if present in sufficient concentrations. Table 1.1 provides an overview of these categories, examples of the types of constituents, and a summary of the possible impacts associated with the marine environment. The primary concern associated with BOD is, as the name implies, the depletion of oxygen as organic wastewater constituents degrade in the environment. Oxygen depletion associated with BOD can be a serious problem in lakes, rivers, estuaries, and other enclosed water bodies having limited exchange. In most open coastal areas, however, oxygen depletion due to BOD from wastewater is limited and not important. Oxygen depletion in these waters usually results from excess nutrient concentrations, which cause overgrowth of algae. This