A note on the effects of an individual large rainfall event on saline Lake Alchichica, Mexico

The present study reports on perturbations of the water column by large rainfall at Lake Alchichica, a saline lake in Central Mexico. Alchichica is located in the “Llanos de San Juan,” a high-altitude plateau with a minimum elevation of 2,300 m above sea level. The climate is arid with annual precipitation less than 400 mm and annual evaporation of 500–600 mm. A single day large rainfall event delivered 1,810,000 m³ of water to the basin, raising the lake’s water level by about 1 m. Temperature and salinity profiles showed an atypical temperature inversion up to 1°C in the upper layer accompanied by salinity decrease up to 0.5 g l⁻¹. Transparency and pH were slightly altered, but dissolved oxygen, nutrients and chlorophyll a concentrations were not changed. In spite of the heavy rainfall and associated wind, the effects of the event were limited to the upper half of the epilimnion. After 2 days, the lake water level returned to its original level. The rapid leakage of the runoff minimized any long-term effects of the large rainfall.