南水北调中线干渠水体磷沉积关键过程研究 ^*

Key phosphorus deposition processes in the main canal in the Middle Route, South-to-North Water Diversion Project

摘要

南水北调中线干渠作为一项跨流域调水的重大工程，其水质安全至关重要. 本研究在中线干渠的14个淤积区采集了表层沉积物和水体样品，系统分析了水体的理化指标以及沉积物中营养盐含量和6种磷形态特征，评估了内源磷的释放潜能，并揭示了水体磷沉积的过程. 结果显示，藻类通过吸收水体中的磷并随其死亡沉降进入沉积物，与地球化学过程共同作用，驱动磷在沉积物中积累. 导致干渠水体处于磷限制状态（N与P物质的量比平均值为1 203.2），沉积物中总磷以有机磷和铁结合磷为主，生物有效磷占比高达65.8%，在空间分布上呈现中上游高、下游低的趋势. 单因子污染指数表明，多数点位处于清洁或正常水平，而生物有效磷指数则显示中上游多个点位处于中度至重度富集状态，表明沉积物中的磷具有较高的释放潜能. 建议从界面氧化还原调节和钙磷转化2个方面入手，以有效实现水质调控，支撑南水北调中线干渠的水质安全.

Abstract

As a major trans-basin water transfer project, water-quality safety of the Middle Route Main Canal in the South-to-North Water Diversion Project is of paramount importance. In this study surface sediment and water samples were collected from 14 siltation zones along the canal, to analyze water physicochemical parameters and sediment nutrient contents. Six phosphorus forms were characterized, release potential of endophytic phosphorus was evaluated, and the process of phosphorus deposition was examined. Algae were found to absorb phosphorus from water, to deposit it into sediments upon death, interacting with geochemical processes to drive phosphorus accumulation in sediments. This would result in a phosphorus-limited state in the canal water (average N/P molar ratio of 1 203.2), with total phosphorus in sediments predominantly consisting of organic phosphorus and iron-bound phosphorus, and bioavailable phosphorus accounting for 65.8%. Spatially, phosphorus levels showed a trend of higher concentrations in the middle and upper reaches and lower concentrations downstream. Single-factor pollution indices indicate that most monitoring points were at clean or normal levels, while the bioavailable phosphorus index revealed moderate to severe enrichment at multiple points in the middle and upper reaches, indicating high release potential of phosphorus in sediments. To implement water quality regulation, it is recommended to interface redox regulation and calcium-phosphorus transformation, to effectively ensure water quality safety at the Middle Route Main Canal of the South-to-North Water Diversion Project.

关键词

南水北调中线干渠 / 沉积物 / 磷赋存形态 / 空间分布 / 释放潜能

Key words

the main canal of the South-to-North Water Diversion Project central route / sediment / phosphorus speciation / space distribution / release potential

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基金资助

国家重点研发计划资助项目(2023YFC3205600)

国家自然科学基金面上资助项目(52270202)