Valuing the effects of changes in land cover on water quality and public health in central Veracruz, Mexico

Background/Question/Methods : The conservation and restoration of the hydrological services provided by forest ecosystems is considered a matter of national security in Mexico. The Mexican Forest Fund has become one of the largest programs paying landowners for such services worldwide. Nevertheless its coarse-scale implementation and exclusive focus on water provisioning services may be limiting the program’s effectiveness. Particularly problematic is the lack of guidance on where forests should be conserved within priority watersheds to maximize the services provided. To address this concern we explored the relationship between changes in land cover, water quality and public health in 10 microwatersheds in central Veracruz state. Spatial statistics characterized microwatersheds as having areas of exceptionally high or low prevalence of cholera (n = 5 watersheds for each condition), insured that these trends were independent of population density, and identified areas for water quality sampling. Landsat derived maps helped evaluate land use patterns at different scales within the drainage area of each sampling point (50, 100, and 250 m riparian buffers; the entire catchment). A health production function evaluated the relationship between water quality (monthly E. coli concentrations) and prevalence of gastrointestinal infections. Finally, we evaluated the public health costs associated with this contamination and calculated the per hectare value of forest cover in mitigating such costs.

Results/Conclusions : Our results revealed high levels of E.coli contamination in all rivers sampled. Prevalence of cholera infections was significantly associated with E.coli concentrations in water samples. There were strong relationships between land use and water quality, particularly within riparian buffers extending 50-100 m from streams. These findings suggest that 80% or more forest cover within 100 m of streams would help maintain E.coli concentrations below 600 CFU/100 ml and would translate into a 1.49% reduction in cholera prevalence rates saving at least $189,351 USD/year in public health costs in the microwatersheds studied. Our data support a payment for the hydrological service of maintenance of water quality of $90 USD/ha within 100 m riparian buffers and $20 USD within the rest of the catchment and suggest that current calculations based on opportunity costs alone considerably underestimate the value of such services. Our research provides additional support for the conservation and restoration of riparian corridors and highlights the need for a catchment-scale approach to hydrological service payments and the need to consider both water quality and quantity in such programs.