The Beartooth Mountains in southern Montana has abundant lakes formed by glacial activity 15,000 years ago. This high elevation area supports snowfields throughout the year, as shown by this September, 2010 photo. Because they lie above treeline, there is little vegetation and soil development, and hence the runoff to the lakes has little dissolved organic carbon (DOC, DOM). This allows ultraviolet light (UV) to penetrate deep into the water so that zooplankton must either develop protective pigments (sunscreen) or migrate to deeper strata during the bright days.
Limnology: The study of inland waters
Photo: September 2010