Recent human-induced ecological changes in a Neotropical karst lake of southern Mexico

• Anthropogenic eutrophication of currently ultraoligotrophic Lake Montebello started around 1950–1960. • Primary production increased between 1960 to 2010, leading to a dense periphytic vegetation cover. • Current condition dates only to ~2010, after an episode of increased turbidity and reduced light penetration. • Diatom community shifted from periphytic to pelagic and smaller taxa, better suited to nutrient-limited, warmer conditions. Lake eutrophication causes aquatic ecosystem changes that can be difficult to trace without a long-term perspective on water quality variables. This paper presents a study of a sediment core collected from Lake Montebello, which yielded such a long-term perspective of trophic state changes. We assumed that microfossil assemblages in the sediment had remained stable over time, as this lake is considered “pristine”. However, three distinctive lake periods over the last century were identified, with rapid environmental changes occurring ∼1960 and 2007–2010. Initially the lake was ultraoligotrophic (period A, 1930–1960), but it transitioned to oligo − mesotrophic conditions (period B, 1960 – 2010) and developed a dense bottom vegetation cover as erosion increased. Fire events during the 1998 “El Niño” and deforestation occurring between 2007 and 2010 increased lake turbidity and reduced light penetration, causing a decline in bottom vegetation cover and promoting diatom and testate amoebae species turnover. The landscape stabilized after ∼2010 and lake productivity declined, but the diatom community shifted from periphytic to pelagic dominance and from larger to smaller taxa, better suited to nutrient-limited, warmer conditions (period C). During the last century, changes in sediment and nutrient loadings altered the trophic status and functional diversity of this lake, and its limnological history is far from “pristine”. Climate warming likely contributed to reduced ecosystem resilience and favored species replacement.