Water and sediment chemistry of Lake Pumayum Co, South Tibet, China: implications for interpreting sediment carbonate

Abstract

A combination of water and sediment chemistry was used to investigate carbonate produc- tion and preservation in Lake Pumayum Co (altitude 5,030 m a.s.l.), south Tibet, China. We compared the chemical composition of lake water in various parts of the lake with that of input rivers and found that the loss of Ca 2? results from calcite sedimentation induced by evaporation and biogenic precipitation. This is sup- ported by evaporation data from the catchment and d 18 O measurements on water. Results suggest that CaCO3 is the predominant carbonate in this lake. There is a positive correlation in the sediments among concentrations of total inorganic carbon (TIC), Ca, total organic carbon (TOC), and total nitrogen, con- firming that most carbonates in sediment are endogenic. The Jiaqu River is the largest inflow to Lake Pumayum Co and has a strong influence on both lake water chemistry and sediment composition. The river and lake bathymetry influence carbonate sedi- mentation by affecting water flow velocity and grow- ing conditions for macrophytes. Different carbon contents and relationships between TIC and TOC in the two long cores from different depths in the lake reveal that hypolimnetic conditions also influence carbonate precipitation and preservation.