南四湖消落带底泥磷形态分布特征、影响因素及释放风险

南四湖是南水北调东线最大的调蓄湖泊，周期性水位涨落会形成大面积消落带，认知消落带底泥磷形态赋存特征、影响因素及释放潜能，对于保障东线调水水质具有重要的科学意义.本研究分析了南四湖消落带底泥磷形态分布特征，探讨了各形态磷与土地利用、母质类型及底泥理化因素之间的关系，评价了南四湖消落带底泥磷的污染程度并分析了其释放风险.结果发现，消落带底泥中总磷（TP）、无机磷（IP）、NaOH提取态磷（NaOH-P）、HCl提取态磷（HCl-P）和有机磷（OP）含量的平均值分别为745.37、510.51、50.42、460.09和234.86 mg/kg，以HCl-P为主的IP占比较高.南四湖消落带底泥各形态磷含量具有较高的空间异质性，TP、IP、OP、HCl-P和NaOH-P含量的变异系数分别为30.7%、36.9%、29.6%、37.6%和51.2%.自然湿地、乔木林地和水浇地等土地利用方式下的底泥NaOH-P、HCl-P、IP、OP和TP含量差异不显著.土壤类型对消落带底泥OP含量影响明显，但对TP、IP、NaOH-P和HCl-P含量则影响不大.NaOH-P含量与HCl-P含量具有显著正相关，与OP含量则具有极显著正相关.南四湖周边30多km²消落带底泥磷污染程度相对较高，轻度、中度和重度污染底泥分别占5.9%、76.5%和17.6%，部分区域底泥磷释放潜能较高.研究结果可为南四湖消落带内源磷释放控制以及水质保障提供科技支撑.

Distribution characteristics, influencing factors and releasing risk evaluation of phosphorus in the sediment of water-level-fluctuating zone in Lake Nansi

As an important storage hub of the Eastern line of the South-to-North Water Transfer Project, the periodic fluctuation of water level in Lake Nansi leads to the formation of a large-area water-level-fluctuating zone (WLFZ), which affects the water quality of Lake Nansi. Understanding the distribution characteristics, influencing factors and release potential of phosphorus in the sediment of the WLFZ of Lake Nansi is of great scientific significance to ensure the water quality of the Eastern line of South-to-North Water Transfer Project. In this work, the distribution characteristics, influencing factors and releasing risk evaluation of phosphorus in the sediment in the WLFZ of Lake Nansi were investigated. The results showed that the average contents of total phosphorus (TP), inorganic phosphorus (IP), NaOH-extractable phosphorus (NaOH-P), HCl-extractable phosphorus (HCl-P) and organic phosphorus (OP) in the sediment of the WLFZ of Lake Nansi were 745.37, 510.51, 50.42, 460.09 and 234.86 mg/kg, respectively. The percentages of IP to TP in the sediments of the WLFZ of Lake Nansi were higher than those of OP to TP. The contents of different P species in the sediments of the WLFZ of Lake Nansi had great spatial heterogeneity, with TP, IP, OP, HCl-P and NaOH-P at 30.7%, 36.9%, 29.6%, 37.6% and 51.2% respectively. There was no significant difference in the contents of NaOH-P, HCl-P, IP, OP and TP in the sediments of natural wetland, arbor forest land and irrigated land. The type of sediment parent material could affect the content of OP in the sediment, but it had a negligible effect on the contents of TP, IP, NaOH-P and HCl-P in the sediment. There was a significant positive correlation between NaOH-P content and HCl-P content, and a very significant positive correlation between NaOH-P content and OP content. The pollution evaluation results showed that 5.9% of the sediment samples were slightly contaminated with phosphorus, 76.5% were moderately contaminated with phosphorus, and 17.6% were heavily contaminated with phosphorus. On the whole, the phosphorus pollution in the sediments of the 30 km² WLFZ of Lake Nansi was relatively serious. The results can provide scientific and technical support for the control of phosphorus release from sediments and the protection of water quality in the WLFZ of Lake Nansi.