Unusual Monomixis in Two Saline Arizona Ponds

Red Pond and Green Pond are shallow, saline pools in Apache County, Arizona, that stratify chemically during winter and circulate in midsummer. Stability is brought about by addition of dilute runoff and seep water to the surfaces; circulation occurs because evaporation increases the salinity of the upper waters and lowers the pond surfaces. Isothermy, dichothermy, mesothermy, and poikilothermy occur during the year. Winter stabilities are in excess of 200 g-cm/cm2in spite of anomalous temperature profiles and the shallow nature of the ponds. The waters are chloro-carbonates derived by concentration from dilute waters relatively high in sulfate and carbonate. At the overturn, Red Pond and Green Pond have salinities of 22% and 11%. Phosphate concentrations are remarkably high-up to 500 mg/liter in Red Pond. Ctenocladus circinnatus is present in both ponds; this may be the fourth North American record for this green alga.