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<p>Plateau lake ecosystems are highly susceptible to degradation and eutrophication, with sediment organic phosphorus (OP) playing a critical yet poorly understood role in internal phosphorus (P) cycling. This study investigated Lake Caohai, a representative degrading plateau karst lake in southwestern China, to characterize sediment P speciation, OP bioavailability, and its release potential, using complementary methods, including Psenner and Ivanoff sequential extractions, <sup>31</sup>P nuclear magnetic resonance (<sup>31</sup>P-NMR) spectroscopy, and enzymatic hydrolysis. Results demonstrated that NaOH-NRP (organic phosphorus associated with humic substances) dominated the total P pool, with humic-bound P (Hum-Po) being the most abundant fractions. Labile monoester P, readily hydrolyzed by alkaline phosphatase, was the primary bioavailable OP form, followed by diester P and phytate-like P; while a substantial amount of organic phosphorus remained resistant to enzymatic hydrolysis. Orthophosphate (Ortho-P) and phosphate monoesters (Mono-P) were identified as the dominant inorganic and organic P species, respectively, by <sup>31</sup>P-NMR. Within the Mono-P pool, myoinositol hexakisphosphate was the primary component, with glycerophosphates ranking second. Meanwhile, DNA-P, a diester P compound, contributed 14.76–24.04% of total P, suggesting significant microbial involvement in P cycling. Multiple P release risk indices, including bioavailable P (BAP), equilibrium P concentration (EPC<sub>0</sub>), P sorption index (PSI), degree of P saturation (DPS), and eutrophication risk index (ERI), indicated a moderate to high risk of internal P loading in Caohai, particularly in agriculturally impacted areas. Ortho-P, and Mono-P were identified as central nodes within the co-occurrence network of various P fractions. Hum-Po and Res-Po showed significant correlations with enzyme activities, and organic P fractions were significantly correlated with release risk indices. Seasonally, moderately labile OP and P release risk were higher in the dry season, while wet season conditions (agricultural runoff input, enhanced microbial activity, and hydrodynamic disturbance) led to increased concentrations of non-labile OP and Ortho-P. This study highlights the critical role of organic P in internal P loading and eutrophication processes.</p>

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Biogeochemical Characteristics and Bioavailability of Organic Phosphorus in Sediments of Degrading Plateau Lake Caohai: Implications for Internal Phosphorus Loading and Eutrophication Risk

  • 期刊论文

  • 发表日期：

    2025年11月20日

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  • Yunchuan Long,
  • Longyan Wang,
  • Jing Hu,
  • Juan Jiang

摘要

Plateau lake ecosystems are highly susceptible to degradation and eutrophication, with sediment organic phosphorus (OP) playing a critical yet poorly understood role in internal phosphorus (P) cycling. This study investigated Lake Caohai, a representative degrading plateau karst lake in southwestern China, to characterize sediment P speciation, OP bioavailability, and its release potential, using complementary methods, including Psenner and Ivanoff sequential extractions, 31P nuclear magnetic resonance (31P-NMR) spectroscopy, and enzymatic hydrolysis. Results demonstrated that NaOH-NRP (organic phosphorus associated with humic substances) dominated the total P pool, with humic-bound P (Hum-Po) being the most abundant fractions. Labile monoester P, readily hydrolyzed by alkaline phosphatase, was the primary bioavailable OP form, followed by diester P and phytate-like P; while a substantial amount of organic phosphorus remained resistant to enzymatic hydrolysis. Orthophosphate (Ortho-P) and phosphate monoesters (Mono-P) were identified as the dominant inorganic and organic P species, respectively, by 31P-NMR. Within the Mono-P pool, myoinositol hexakisphosphate was the primary component, with glycerophosphates ranking second. Meanwhile, DNA-P, a diester P compound, contributed 14.76–24.04% of total P, suggesting significant microbial involvement in P cycling. Multiple P release risk indices, including bioavailable P (BAP), equilibrium P concentration (EPC0), P sorption index (PSI), degree of P saturation (DPS), and eutrophication risk index (ERI), indicated a moderate to high risk of internal P loading in Caohai, particularly in agriculturally impacted areas. Ortho-P, and Mono-P were identified as central nodes within the co-occurrence network of various P fractions. Hum-Po and Res-Po showed significant correlations with enzyme activities, and organic P fractions were significantly correlated with release risk indices. Seasonally, moderately labile OP and P release risk were higher in the dry season, while wet season conditions (agricultural runoff input, enhanced microbial activity, and hydrodynamic disturbance) led to increased concentrations of non-labile OP and Ortho-P. This study highlights the critical role of organic P in internal P loading and eutrophication processes.