Sediment characteristics of tropical, karst lakes and their relationship with watershed topography, lake morphometry, and human activities

We analyzed multiple variables in recent sediments from 18 tropical, karst lakes in "Lagunas de Montebello" National Park, a Mexican Protected Natural Area and Ramsar site, to explore relationships between sediment characteristics and lake attributes: topography/location (mountain, surface-water-dominated vs. plateau, groundwater-dominated), morphometry (shallow vs. deep), and human activities (urbanization/agriculture). The study lakes fell into two groups: (1) pristine, oligotrophic, mostly located in the SE mountain terrain, and (2) impacted, eutrophic, in the NW plateau region. Sediment samples were collected from the central, deepest zone of each lake and analyzed for texture (grain size), carbonate content, and organic C and N. Water variables were measured in the water column overlying the sediment collection sites. Specific conductance, chlorophyll a, and total particulate carbon were higher in impacted, eutrophic plateau lakes than in pristine mountain lakes. Sediments, although composed mostly of silts, differed in grain size. Pristine, oligotrophic mountain lakes possessed coarser sediments, with a higher concentration of most likely recalcitrant organic carbon, than impacted, eutrophic plateau lakes. Topography/location is the primary factor that contributes to sediment differences, whereas eutrophication, caused by deforestation and agricultural runoff, is the second most important agent modifying sediment characteristics. The only pristine plateau lake, San Jose, had water quality similar to pristine mountain lakes, but finer sediments with lower organic C, N, and C/N. Comparison of San Jose sediments with those of impacted eutrophic plateau lakes indicated eutrophication has led to coarser sediments, as well as enrichment in CO3, organic C and N. Eutrophication-related sediment characteristics are valuable variables that can be used in paleolimnological studies to identify the onset of lake eutrophication in tropical karst water bodies.