First investigation of ultraoligotrophic alpine Lake Puma Yumco in the pre-Himalayas, China

Abstract

Lake Puma Yumco is a typical alpine lake (altitude 5030 m) located in the pre-Himalayas of Tibet, China, and this study was the first limnological investigation ever conducted on it. Lake Puma Yumco (28°34″N, 90°24″E) has the following morphometric properties: maximum length 31 km, maximum width 14 km, mean width 9 km, shoreline 90 km, surface area 280 km², and shoreline development 1.5. Transparency was approximately 10 m, even in the thawing season. The extinction coefficient of the lake water was calculated as 0.15 m⁻¹. Annual maximum transparency was estimated from the depth of the Chara zone to be 30 m. Dissolved oxygen was 7 mg O₂ l⁻¹ and showed saturated values, and salinity was 360 mg l⁻¹. The chemical type of the lake water was Mg-Ca-HCO₃-SO₄, and it was slightly alkaline in character. Total nitrogenous nutrients (sum of ammonia, nitrite, nitrate, and urea nitrogen), phosphate, and silicate were extremely low at 1, 0.02, and 9 µM, respectively. Dissolved organic carbon, nitrogen, and phosphorus concentrations were 160, 11, and 0.08 µM and the molar ratio was calculated as 2100 : 140 : 1. Chlorophyll a concentration was 0.2 mg m⁻³. Phytoplankton and zooplankton were dominated by Aphanocapsa sp. and Diaptomidae. Both nitrogen and phosphorus appear to be the limiting parameters for phytoplankton growth. Organic carbon and nitrogen contents in lake sediments were low and the sediments contained a large amount of CaCO₃. The grain size of sediment was that of silt-sand in most cases. The present results indicate that the pre-Himalayan alpine freshwater Lake Puma Yumco is an ultraoligotrophic lake.