Characterization of organic phosphorus in soils and sediments of a typical temperate forest reservoir basin: Implications for source and degradation

Reservoirs can intercept upstream inputs and greatly alter their migration and transformation processes at a basin scale. Taking a typical reservoir basin in the Xiaoxing'an Mountains of Northeast China as an example, the organic phosphorus (Po) and organic matter (OM) compositions in the upstream soil, river and reservoir sediments were characterized by 31P NMR, stable carbon (delta 13C) and nitrogen isotopes (delta 15N), and the migration and transformation processes of Po from soil to reservoir sediments were explored. The compositional data indicated that both the OM and Po in the reservoir were mainly imported by C3 plants from the upper reaches. Higher monoester phosphorus (P) components in the upstream soils than in the reservoir sediments, which indicated the migration and degradation process of Po from the upstream soils to the river and then to the reservoir sediments. The degradation rate of monoester P was higher, approximately 30.6% and the phosphonate fraction had the lowest degradation rate, about 0.4%. Specifically, the degradation of monoester P including inositol P was higher than that of organic carbon. Thus, at the basin scale, more forest-derived organic carbon was likely intercepted by reservoirs and precipitated to sediments, while Po might degrade to a greater extent. Aggregative results showed that reservoirs may play an important role in the differentiated migration and transformation process of forest-derived OM and Po. And then, the highly degradable Po including inositol P poses a greater risk of eutrophication in the typical temperate forest reservoirs and their downstream, even the ocean, and is accompanied by possible algal blooms in the future. Information derived from this study provides a more scientific basis for the assessment of the ecological and environmental effects of reservoir and dam construction projects.