Limnological comparison of pristine and impacted lakes from a tropical, high-altitude karst region in southern Mexico

Abstract

Climatic conditions strongly influence tropical karst lake limnology, but more information is required to understand how human impacts can modify their ecological patterns. The “Lagunas de Montebello” lake district, a tropical, high-altitude karst landscape, contains 139 solution lakes surrounded by tropical rainforests. To investigate the limnological changes that have been taking place in the “Lagunas de Montebello” in the past 20 years, we selected fourteen lakes for a comparative study: four impacted and ten pristine. The impacted lakes are on the northwest (NW) plateau area fed by surface waters and underground, whereas the pristine ones are on the southeast (SE) intermontane zone fed underground. Impacted lakes receive nutrients and organic matter from agricultural and urban/domestic wastewater from point and nonpoint surface sources. Heavy tropical storms flood the plateau zone, interconnecting the lakes and facilitating pollutant dispersion among lakes. Pristine lakes remain isolated, and groundwater pollution is limited since most anthropogenic activities occur in the NW plateau zone. Most of the limnological variables measured differed between pristine and impacted lakes. Nutrients, chlorophyll-a, total suspended solids, and particulate organic carbon concentrations were higher in the impacted lakes. The hydraulic connection between the Montebello Lakes facilitates the rapid dispersion of pollutants from one lake to another, threatening lakes that are still pristine. Although aquatic karst environments promote phosphorus precipitation strongly P-limiting primary production, anthropogenic additions of N, P, and organic matter make this process impossible, stimulating ecosystem degradation and leading to eutrophication as evidenced in the “Lagunas de Montebello” lake district.