As Figure 11 shows, the relative vulnerability of individual basins varies significantly. Not only do we need to understand which river basins are most vulnerable, we must also understand the implications of specific land uses and human activities on those basins. With 75 to 100 percent of the surface paved over, however, these proportions shift dramatically. Runoff increases to 55 percent, while shallow and deep infiltration fall to 10 and 5 percent, respectively, and evapotranspiration drops to 30 percent. As a result, beneficial water uses are lost for example, aquifer storage diminishes significantly and evapotranspiration, which is essential to maintaining Florida s cyclical summer rains, is reduced by a fourth.
Vulnerability also varies depending on one s location in a river basin.
For instance, from the viewpoint of a homeowner who uses a septic tank to treat sewage, the tank fails only when sewage from the system actually backs up in the home. Yet those living downstream who are affected by septic tank pollution or whose wells become polluted with nitrate have a different perspective on system failure. Yet we need to control all sources, including septic tanks, for once nitrate pollution enters ground water, it is difficult to clean up and often travels great distances to public and private wells or natural springs. Once surface water and ground water vulnerabilities are understood, that knowledge can be used to plan the long-term development of our communities and make better land use decisions for example, designating protection zones or buffers around lakes, rivers, and sinkholes or using other means to protect the most vulnerable areas in each river basin. The information can also be used to restore water bodies that have been injured in the course of development.