Soil properties and trace elements distribution along an altitudinal gradient on the southern slope of Mt. Everest, Nepal

The absence of significant local inputs of pollution makes remote mountain ecosystems suitable to assess the atmospheric deposition of contaminants, such as trace elements, which can derive from both natural and anthropogenic sources. The Himalayan range is a potential target for the atmospheric deposition of pollutants because of the regional monsoon climate and the presence of contaminant source regions in its vicinity (e.g. Kathmandu Valley). Studies of elevation gradients of trace elements in topsoils and soil profiles in the Himalaya are very limited. The main goal of this study was to determine the distribution of trace elements (Co, Cd, Cu, Zn, Cr, Pb, Ni, and Mn) in soils on the southern slope of Mt. Everest as a function of elevation, soil depth, and pedogenic properties. Trace elements were measured in 30 topsoils along an altitudinal gradient (3570-5320 m a.s.l.) and in 11 different soil profiles opened under different land uses and topographical settings. The contents of Co, Zn, Cr, and Ni in the topsoil were found positively correlated with the altitude, and on average reached a peak at 4900-5000 m a.s.l. The results showed a limited contamination, similar to the one measured in soils from other high mountain regions. Differently from the expectations, both soil depth and organic carbon, which significantly decreased with the altitude, were not found significant factors controlling the altitudinal distribution of trace elements. Pedogenic processes were associated with different depth trends of trace metals along the elevation gradient, with depletion in surface and accumulation in illuvial horizons where podzolization was active; at higher altitude, a weaker leaching resulted in higher surface concentrations.