GIS for Assessing Land-Based Activities that Pollute Coastal Environments
According to Heathcote (1998), the development of workable management options (structural and non-structural actions) in a watershed requires the identification of all point and non-point sources of pollution. Discharge of effluents from industrial, urban and sewage treatment plants where a pipe or diffuser outfalls into a water body are called “point sources” of contamination. Another type of source, called a “non-point source” (NPS), is described as the diffuse drainage of rainwater from urban, industrial and agricultural lands that can introduce nutrients, pesticides, and metals to water bodies. Non-point sources are some of the more serious forms of pollution and the effects are often less obvious than those of point sources (Abel, 1998). Clapman et al. (1998) indicated that agricultural impacts on ground and surface water quality are more significant than other land use impacts because of their large aerial extent compared to other human land uses. Lack of information related to agricultural practices may lead to overuse of fertilizers and herbicides, and deforestation with serious impacts on soil erosion and water quality. The Yucatan Peninsula is blessed with large freshwater reserves, bays and coastal lagoons and an exclusive economic zone of 200,000 km2. However, the maintenance of the water quality seems to be an enormous challenge for the State and other interested groups considering the unfulfilled basic needs of a large part of the population, rates of population growth, immigration, and lack of an integrated approach to the management of the resources and coastal areas. In June 1996 a massive kill of 20,000 fish of the species Arius felis was reported in the Bay of Chetumal, State of Quintana Roo (SEMARNAP, 1996). Studies reported harm to their organs and accumulation of PCBs, organochlorine insecticides and polyaromatic hydrocarbon (Noreña-Barroso, 1998). Concerns exist that increasing loss of water quality may have adverse effects on mangroves and coral reefs in an area where the second most important barrier reef, the Mesoamerican reef, and the sanctuary of the manatee Trichechus manatus are drawing international attention.
Agricultural activities introduce diffuse pollution to watercourses, aquifers, lagoons and estuaries in the form of sediments, nutrients, pesticides, viruses, salt and other toxins which affect aquatic organisms. Pollution cause-and-effect relationships are complex and the need to find practical tools to generate useful information for decision-making may be addressed with models that introduce expert knowledge. Within this framework, this exercise attempts to rank the agricultural lands according to several factors that may contribute to water contamination on the Mexican side of the Rio Hondo watershed near the Othon P. Blanco municipality border with Belize.