Impacts of global change on two tropical, high mountain lakes in Central Mexico

High mountain lakes and their catchments are remote ecosystems in areas with low anthropogenic disturbance. High mountain lakes integrate changes in the atmosphere and catchment areas (e.g., acid rain, airborne pollutants, climate change). The present research analyses long-term datasets of meteorological and limnological variables representing two tropical high mountain lakes, El Sol and La Luna, in Central Mexico to identify the impacts of anthropogenic disturbance (i.e., sentinels of global/climate change). The 54-year meteorological analysis showed marked interannual variability with no statistically significant air temperature or rainfall trends. However, from 2000 to 2018, the air temperature increased by 0.5 °C. Accordingly, the lake water temperature increased (Lake El Sol: 0.8 °C, Lake La Luna: 0.6 °C). Although the rainfall displayed no change, the water level decreased in both lakes (1.5 m), most likely associated with increased evapotranspiration. Unexpectedly, the dissolved inorganic nitrogen (DIN) concentration in the lakes decreased. The initial acid pH rose to close neutrality in Lake La Luna and to alkaline values in Lake El Sol. The latter may be a consequence of the lowered SOx and NOx emissions from governmental regulations promulgated to control atmospheric pollution beginning in 2000 and probably resulting in less acidic deposition. An additional explanation for the lakes' deacidification is the increased deposition of alkaline ions derived from activities at the volcano slopes. Since the atmospheric supply is the primary nitrogen source to high mountain lakes, the DIN concentration decline could reflect the reduction in atmospheric HNO