Recycling of Sedimentary Phosphorus Pools in Two Yunnan-Guizhou Plateau Lakes, Southwest China

Applying phosphate oxygen isotopes (δ¹⁸OP) to identify sediment phosphorus (P) sources and its recycling is still challenging due to poor understanding in δ¹⁸OP variations of sediment P pools and their driving mechanisms. Here, we analyzed the δ¹⁸OP in inorganic P (Pi) pools of sediment cores and varied P sources from Lake Dianchi and Lake Erhai in the Yunnan-Guizhou Plateau, Southwest China. The δ¹⁸OP values of sediment detrital Pi (Det-Pi, nonbioavailable P) were consistent with those of watershed soils (within ∼0.4-0.6‰), indicating that the δ¹⁸OP of sediment Det-Pi inherits the δ¹⁸OP of soil Det-Pi. The δ¹⁸OP values of aluminum-bound Pi (Al-Pi) and authigenic Pi (Auth-Pi) in sediment were close to or within the δ¹⁸OP equilibrium (δ¹⁸OP-eq) ranges, implying oxygen isotopic exchange equilibrium between phosphate and ambient water prior to the formation of sediment Al-Pi and Auth-Pi. However, the δ¹⁸OP of iron oxide-bound Pi (Fe-Pi) in sediment was lighter (∼3‰) than δ¹⁸OP-eq, retaining the negative isotopic signal of organic P (Po) remineralization. Furthermore, ³¹P NMR and metagenomic analysis indicated that microbial-mediated Po mineralization and Pi recycling are the driving factors for δ¹⁸OP changes in sediment Fe-Pi, Al-Pi, and Auth-Pi. These integrated insights deepen our understanding of the biogeochemical cycling for sedimentary P.