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

Applying phosphate oxygen isotopes (δ 18 O P ) to identify sediment phosphorus (P) sources and its recycling is still challenging due to poor understanding in δ 18 O P variations of sediment P pools and their driving mechanisms. Here, we analyzed the δ 18 O P in inorganic P (P i ) pools of sediment cores and varied P sources from Lake Dianchi and Lake Erhai in the Yunnan-Guizhou Plateau, Southwest China. The δ 18 O P values of sediment detrital P i (Det-P i, nonbioavailable P) were consistent with those of watershed soils (within ∼0.4–0.6‰), indicating that the δ 18 O P of sediment Det-P i inherits the δ 18 O P of soil Det-P i . The δ 18 O P values of aluminum-bound P i (Al-P i ) and authigenic P i (Auth-P i ) in sediment were close to or within the δ 18 O P equilibrium (δ 18 O P-eq ) ranges, implying oxygen isotopic exchange equilibrium between phosphate and ambient water prior to the formation of sediment Al-P i and Auth-P i . However, the δ 18 O P of iron oxide-bound P i (Fe-P i ) in sediment was lighter (∼3‰) than δ 18 O P-eq, retaining the negative isotopic signal of organic P (P o ) remineralization. Furthermore, 31 P NMR and metagenomic analysis indicated that microbial-mediated P o mineralization and P i recycling are the driving factors for δ 18 O P changes in sediment Fe-P i, Al-P i, and Auth-P i . These integrated insights deepen our understanding of the biogeochemical cycling for sedimentary P.