The winter cover of a high‐mountain Mediterranean lake (Estany Redó, Pyrenees)

Deep lakes freeze late in the Pyrenees, and time for black ice growth is short because snow falls abundantly. More than 70% of the winter cover water equivalent comes from the lake, mainly in the form of flooding water. The quantity of flooding water is proportional to the accumulated precipitation. Silicate, bicarbonate, calcium, and inorganic nitrogen are the compounds more effectively excluded when ice forms. Fresh snow shows a high variability in its chemistry, especially in nitrogen compounds and chloride. The destructive metamorphism of the snow is accentuated during high radiation periods, promoting an enrichment of the slush layers with some ions by preferential elution. Nevertheless, the flooding process is the principal factor controlling the chemical composition of the cover and causes the cover composition to approach the lake water composition. The important role of the flooding water has implications in the evaluation of water resources and chemical budgets of the lake.