SPATIAL AND TEMPORAL TRENDS IN FECAL COLIFORM CONCENTRATIONS AND OTHER WATER QUALITY PARAMETERS IN WEST-CENTRAL COSTA RICA

The west coast of Costa Rica has undergone significant shifts in land use with the rapid development of tourism in the past decade. We have attempted to assess the impact of tourism development using the Water Quality Index (WQI) as a metric. The WQI weights the results of nine water quality parameters, including fecal coliform. Our hypothesis is that land uses associated with tourism development, including clear cutting of jungle, commercial and residential construction, and infrastructure development, will decrease overall WQI scores in areas where these changes are concentrated. In the work presented here, we are focusing on the spatial and temporal patterns of fecal coliform concentration in the Rio Baru and Rio Uvita watersheds.

Fecal coliform are non-pathogenic bacteria present in the intestinal tract of all warm-blooded animals. When large amounts of fecal coliform are detected in a water source, it can indicate contamination by fecal matter. Other water-borne pathogenic organisms are usually highly correlated with the presence of high levels of coliform bacteria. Although, fecal coliform is innocuous, the ease with which it is detected makes it an ideal proxy for the presence of the pathogenic bacteria with which it associates. Research has shown that there are several factors which may influence the levels of coliform present in a water body. Key among these are population density around the water body and land use. The change in land use from rural to urban can have a profound effect on the levels of coliform bacteria as well as overall water quality.

We have investigated water quality using the WQI in the Rio Baru and Rio Uvita watersheds in west-central Costa Rica. Both these rivers flow through developing towns on the coast where tourism is very popular. The rivers and their tributaries were sampled in 2006, 2007, and 2009. The concentration of fecal coliform was determined along with an overall WQI score. The data were analyzed both spatially and temporally. We observed significant differences in the WQI fecal coliform Q-value across sub-watershed regions (p-value = 0.0003) and also through time (p-value = 0.0340). The fecal coliform Q-value was also compared to several other WQI parameters and a relationship between fecal coliform and those parameters was observed.