Phosphate distribution and sources in the waters of Huangbai River, China: using oxygen isotope composition of phosphate as a tracer

We investigated the distributions of phosphate (PO4-P) and used the oxygen isotope composition of phosphate (delta O-18(P)) to quantify PO4-P sources in the waters of Huangbai River. According to the environmental characteristics of Huangbai River basin, the sampling stations in the Huangbai River were divided into three groups: sampling stations in the phosphate mining area, in the outcrop area of phosphate rock, and in the residential/agricultural area. The average PO4-P concentration was highest (2.34 +/- 1.00 mu mol/L) in the outcrop area of phosphate ore, intermediate in the residential/agricultural area (1.06 +/- 1.21 mu mol/L), and lowest in the phosphate mining area (0.58 +/- 0.31 mu mol/L). The delta O-18(P) measured in the Huangbai River waters ranged from 6.0 to 20.9 parts per thousand, with the highest average value in the outcrop area of phosphate rock (average: 14.6 parts per thousand +/- 3.1 parts per thousand). The majority of the measured delta O-18(P) values in the Huangbai River deviated greatly from the expected equilibrium values, indicating that delta O-18(P) in this area could be used to trace PO4-P sources. We used two end-member mixing models to quantify the contribution of PO4-P from different sources. In the phosphate mining area, the average fractions of PO4-P from phosphate ore and sewage were 49.5% +/- 23.8% and 50.5% +/- 23.8%, respectively. In the outcrop area of phosphate rock, the average fractions of PO4-P from phosphate ore and sewage were 60.1% +/- 21.7% and 39.9% +/- 21.7%, respectively. In the residential/agricultural area, the average fractions of PO4-P from fertilizer and sewage were 49.2% +/- 23.2% and 50.8% +/- 23.2%, respectively. These results indicate that phosphate mining activities was not an important source for PO4-P in the waters of Huangbai River. The natural weathering of phosphate rock, fertilization, and domestic sewage contributed more to the high PO4-P concentrations in the Huangbai River waters.