Fine-scale Evaluation on Phosphorus Dynamics in Sediments of Hongjian Nur, the Largest Desert Lake in China

Very few reports on the fine-scale behavior of phosphorus (P) in desert lakes largely restricts our comprehensive comprehension of their eutrophication processes and the evolution of effective lake management strategies. This study presented the novel application of two advanced high-resolution imaging technologies, i.e., diffusive gradients in thin films (DGT) and planar optode (PO), to investigate the micro-distribution and kinetic mobility of P in sediments of a typical desert lake (Hongjian Nur) for the first time. The obtained high-resolution profiles of labile P and microenvironments (e.g., pH, DO, sulfide (S^2-), iron (Fe²⁺)) in all sediments underscored the intricate biogeochemical complexity and pronounced heterogeneity inherent in the sediments. Specifically, labile P concentrations ranged from 0.10 to 0.61 mg/L with an average value of 0.33 ± 0.16 mg/L. It is noteworthy that the mosaic distribution of labile P hotspots was observed predominantly at depths between -100 mm and -130 mm, which was probably corresponding to the active layer of labile P under the sediment-water interface (SWI). Moreover, the co-distributions of labile S and P in most sediments revealed significant correlations (p < 0.01), thereby highlighting that P mobility is intrinsically linked to the S cycle. Sediment adsorption simulation experiments revealed a gradually increasing risk of P release from Hongjian Nur sediments as the desert lake’s progressive salinization accelerates under a warming, drying climate. Collectively, these findings firstly offer valuable insights into distribution and mobility mechanisms of P in desert lakes at a fine-scale, which are essential to understand the complex biogeochemical processes that regulate nutrient cycling in these fragile ecosystems.