Trophic categorization and eutrophication trend of a tropical karst lake district: "Lagunas de Montebello," México

Hydrological changes, land-use shifts, and nutrient enrichment threaten tropical karst lakes. Despite this vulnerability, long-term research on their trophic dynamics remains scarce. Located in southern Mexico, the "Lagunas de Montebello" National Park contains a complex mosaic of more than 130 karst lakes that vary in size, groundwater connectivity, and the degree of disturbance in their catchment areas. This study presents the first district-wide trophic classification, develops adaptive thresholds, and examines eutrophication trends over ten years (2014-2024). We measured Secchi disk depth, nutrient concentrations (total nitrogen and total phosphorus), chlorophyll-a, and physicochemical profiles in 18 representative lakes, then applied hierarchical clustering to the principal components. Our classification was compared with indices designed for temperate regions (Carlson and OECD), and we tracked temporal trajectories. Multivariate analyses revealed a bimodal trophic distribution, with no mesotrophic conditions. Lakes fed by groundwater and surrounded by intact forests remained ultraoligotrophic and oligotrophic, whereas lakes affected by human activities exhibited elevated nutrient levels, reduced transparency, and eutrophic to hypertrophic conditions. Mann-Kendall trend analyses revealed no significant temporal trends in eutrophic and hypertrophic lakes, but oligo- and ultra-olitrophic lakes showed significant increases in total nitrogen. Compared with temperate-derived indices, our trophic classification indicated that these indices overestimate trophic status in this tropical karst system when based on total phosphorus. This research establishes a baseline for adaptive management and highlights the critical need for integrated catchment protection. The district-scale framework provides a transferable methodology for evaluating eutrophication risk in tropical karst regions worldwide.