Biogeochemistry of sedimentary phosphorus species in the world’s longest river on an Island, the Kapuas River (West Kalimantan, Indonesia)

Abstract

ABSTRACT In this study, surface sediments along the mainstream of the Kapuas River were determined for sedimentary phosphorus (P) species, which include exchangeable-P (Ex-P), iron-bound P (Fe-P), apatite P (Ca-P), detrital P (De-P), and organic P (OP). The objective of this study was to determine the dynamics of sedimentary P species in the world’s longest river on an island. The results showed that the composition of sedimentary P species of the river to total P (TP) was in this order: Ca-P (57% of TP) > Ex-P (21%) > Fe-P (11%) > OP (6%) > De-P (5%). As the bioavailable P (BAP), which includes Ex-P, Fe-P, and OP, represents around 38% of TP, this could indicate the river sediments’ potential to release P. The sedimentary BAP showed an overall decreasing trend from the upper river to downstream of the river. In contrast, Ca-P showed an increasing trend from the upper river to downstream of the river. All these indicate the dynamics of a localised P cycle along a river, as the BAP released to the overlying water could contribute to Ca-P formation.