DISSOLVED REACTIVE PHOSPHORUS IN LARGE RIVERS OF EAST ASIA

Abstract

Dissolved reactive phosphorus (DRP) concentrations in large pristine rivers of East Asia (370 samples) are reported and the relationship to lithology (phosphorites, igneous apatite-bearing deposits), relief, climate (precipitation, temperature), and population density are investigated. The DRP concentration and yield of 93% of our samples were distinctly low (<0.06-0.89 μM DRP and <0.0008-800 mol DRP/km2/year). The samples with relatively high DRP (~7% of our samples) were most likely from point sources of human sewage rather than P-rich lithology. The principal component analyses using DRP, dissolved major elements, pH, Sr, and 87Sr/86Sr found DRP best grouped with dissolved Si and K. However, the correlation between DRP and dissolved Si is still not strong enough to justify using Si as a proxy of DRP export by chemical weathering. The large rivers draining the eastern Tibetan Plateau-the headwaters of the Mekong, Yangtze, and Yellow-together supplied 3.0 × 107 mol DRP/year, 7%, 3%, and 17% of those at mouths, respectively, and were not dominant source regions of DRP. The mouth values of the East Siberian rivers were especially low and this was due to multiple factors, e.g., low precipitation and sparse population. Stepwise regression of various parameters like precipitation, temperature, runoff, population density and relief indicated that the concentrations were not affected by any single factor, but precipitation and secondarily population density explained up to 44% of the variability in the DRP yield of the East Asian rivers. © 2007 Springer Science+Business Media B.V.