Seasonal Biotic Events in Two Colorado Alpine Tundra Ponds

Washboiler Pond and Dead Hat Pond are two small alpine tundra ponds located on the western slope of the Continental Divide in Summit County, Colorado, at an elevation of 3,582 meters (11,750 feet). Washboiler Pond is 2 by 6 meters and 0.56 m deep, and Dead Hat Pond is 4 by 9 meters with a maximum depth of 0.5 m. This study extended from July 18 to October 19, 1957, and this period represented the entire open season for that year. Visits were made at 5 to 11 day intervals. Routine physical and chemical determinations were conducted. It was found that both ponds are characterized by low temperatures, highly colored water, slightly acid pH, and low dissolved solids and organic content. Emergent growths of Carex aquatilus were the only rooted aquatic plants present in either pond. Quantitative and qualitative sampling was carried out in connection with the bottom fauna and zooplankton. Quantitative determinations revealed that Tendipes, Metriocnemus, and Pisidium casertanum were the dominant bottom organisms common in both ponds. Free-ranging Tendipes reached a seasonal maximum of 350 individuals per square meter in Washboiler Pond on August 31, tapering off thereafter and being replaced by an increasing number of Tendipes in cocoons toward the close of the open season. Both free-ranging and cocoon forms represented the same species of Tendipes. Metriocnemus had a bimodal population curve, with distinct peaks during July and September in both ponds. Tendipes produced one generation per year, while Metriocnemus produced two generations per year. Tubificidae were almost negligible in Dead Hat Pond, but populations varied from 70 to 490 individuals per square meter in Washboiler Pond. Pisidium casertanum was most abundant in Dead Hat Pond, attaining a seasonal maximum of 163 individuals per square meter on July 26. On the whole, Pisidium was the least abundant of all bottom organisms taken during the open season. Total mean open season standing crops were 388 pounds per acre wet weight in Washboiler Pond and 184 pounds per acre wet weight in Dead Hat Pond. The benthic productivities of both ponds are compared with those of certain North American lakes. Daphnia pulex was the dominant zooplankter in both ponds, reaching a seasonal maximum of 91 individuals per liter in Washboiler Pond on September 28, and only 16 individuals in Dead Hat Pond on October 5. Ephippial eggs were recovered as early as August 16 in Washboiler Pond. Chydorus sphaericus and the copepods, C