Characteristics of organic phosphorus in sediments from lakes: Regeneration for eutrophication or a geological record in the Anthropocene?

Organic phosphorus (Po) plays a pivotal role in watershed biogeochemical cycling and lake eutrophication, but its potential as an indicator of Anthropocene stratigraphic change remains insufficiently understood. This study integrates carbon and nitrogen isotope analyses with 31P NMR spectroscopy of representative plants, soils, and sediment profiles to elucidate the compositional characteristics, depositional history, and anthropogenic linkages of Po in an alpine meadow lake (Yamdrok Lake, YH) and a temperate forest oligotrophic lake (Sihailongwan Lake, LW), and further compares these systems with Dianchi Lake (DC), a eutrophic lake in China. Sedimentary Po concentrations spanned 165.5-531.1 mg kg⁻¹ (LW) and 34.1-87.4 mg kg⁻¹ (YH), dominated by monoester phosphates (79.2 and 87.4 % of total Po, respectively). Terrestrial C3 vegetation drove Po accumulation in LW, particularly inositol phosphates, while authigenic and aquatic plant sources prevailed in YH. Oligotrophic sediments exhibited prolonged degradation half-lives of Po compounds (DNA phosphate: 88-170 yr; inositol phosphates: 130-179 yr), 4-5-fold longer than in hypereutrophic systems (e.g., DC), where algal-mediated internal phosphorus cycling sustains recurrent blooms. Critically, stratigraphic C/labile mono-P ratios emerged as a novel proxy, capturing century-scale anthropogenic perturbations (e.g., deforestation, urbanization) and aligning with Anthropocene demarcation criteria. These findings redefine sedimentary Po dynamics, highlighting its dual role as both a driver of eutrophication feedback and an archive of human-environment interactions in freshwater systems.