三峡库区支流消落带土-水界面磷素迁移过程与通量

Water level fluctuation zone (WLFZ) in the Three Gorges Reservoir (TGR) is a giant and unstable land-water ecotone which has been developed recently. There are flourishing nutrient exchanges via land-water interface due to intense soil erosion and inversive dry-wet season alteration. This may result in eutrophication in the branch water and bring to great pressure to water environment of TGR. However, processes and mechanisms of phosphorus transfer and release through the soil-water interface of WLFZ are very complicate and have been unclear up to now. In particular, mechanisms of “source-sink” transformation under inundation and drawdown year after year have not been revealed. Thus, comprehensive researches involved in multi-scale monitoring of hillslopes, small catchments and river transactions combined with isotopic tracing techniques, phosphorus fractionation and P-31 nuclear magnetic resonance spectroscopy (NMR) method are planned to conduct to study mechanisms and processes of phosphorus transference and transformation via soil-water interface of WLFZ in some typical braches of TGR so as to find out key driving mechanisms of processes of phosphorus movement from the hillslope and through sediment-water interface. Meanwhile, scientific understandings of transformation of phosphorus fractions especially organic phosphorus fractions will be explored. Then, mechanism of “source-sink” transformation and scientific laws on processes of phosphorus transference via soil-water interface of WLFZ will be revealed and clarified. Based on above scientific findings, calculating and modeling methods of transfer fluxes of phosphorus via soil-water interface will have been constructed for estimating phosphorus loading fluxes through land-water interface in some typical branches, thus providing for scientific knowledge and guidance for phosphorus loading reduction and further water environment protection of TGR.

三峡水库消落带是特大型、不稳定新生水陆交错带，严重的水土流失和频繁的反季节干湿交替导致消落带水陆界面物质交换极为活跃，可能加剧支流水体富营养化。但消落带土-水界面过程复杂，磷素迁移、释放过程与机理不清楚，特别是反复淹没-出露交替作用下磷源汇转换机制尚未查明。针对上述问题，通过坡面、小流域与水域多尺度、多断面同步监测，结合自然或残留同位素示踪技术、磷形态分级和P-31核磁共振分析方法，系统研究典型支流消落带土-水界面磷素迁移、转化与释放的过程、机理，查明消落带土壤（泥沙）磷素坡面迁移和泥沙-水界面磷交换过程及其关键驱动机制，揭示干湿交替作用下消落带土壤（泥沙）磷形态尤其有机磷形态转化机理，阐明消落带土-水界面磷素迁移、转化的过程规律及源汇转换机制，建立土-水界面磷素迁移通量的计算方法与模型，估算典型支流消落带水陆界面磷素迁移通量，为入库磷素负荷削减和水环境保护提供科学依据。

三峡水库消落带是特大型、不稳定新生水陆交错带，严重的水土流失和频繁的反季节干湿交替导致消落带水陆界面物质交换极为活跃，可能加剧水库水体富营养化。但消落带土-水界面过程复杂，磷素释放过程与机理不清楚，特别是反复淹没-出露交替作用下磷源-汇转换机制未查明。针对上述问题，项目选取典型支流消落带为研究对象，通过坡面、支沟、小流域与水域多尺度、多断面同步监测，结合同位素示踪技术、磷形态分级和液体31P核磁共振等技术，系统研究三峡支流消落带土壤（泥沙）-水界面磷素迁移过程与机理。主要取得以下研究结果与结论：（1）支流输沙与干流顶托沉沙是支流消落带泥沙和外源磷的主要来源，其中干流顶托输入支流消落带磷约占22-35%，支流上游输入占33-51%，而消落带坡面侵蚀输入磷约占14-38%。（2）薄层岩性土（紫色土、黄壤）特有的岩-土二元结构及频繁淹没-出露导致的干湿交替造成的大孔隙与土壤裂缝发育，壤中流与裂缝优先流成为消落带坡面磷素迁移的重要机制，加剧了溶解态、胶体态磷养分快速流失。（3）正磷酸盐是支流消落带土壤（泥沙）最主要的生物可利用磷，活性单酯磷是消落带土壤中最主要的可酶解有机磷，潜在生物活性较高；淹没消落带泥沙间隙水的磷释放以铁结合态磷的还原释放为主，而涨水期土-水界面磷交换通量为72.3 ng/cm2/d，其它淹水时期在-3.3~17.1 ng/cm2/d之间，消落带泥沙大部分时期表现为重要磷源。（4）消落带落干期土壤磷含量呈增加趋势，而优势植物落干期作为磷养分的重要“汇”，平均富集25.7±4.5 kg P/hm2；然而，淹水浸泡后消落带植被将向水体释放22.8±3.2 kg P/hm2，三峡消落带土壤（泥沙）-植物系统总体表现为水体磷素养分的重要“源”，且源强远高于其他陆地面源的污染负荷，消落带土壤-植物系统的“源”-“汇”转换可能成为驱动支流库湾水体富营养化的重要机制。项目成果为三峡库区磷素负荷管理与水环境保护提供了科学依据。该项目发表论文50篇，其中SCI论文29篇，第一标注19篇，EI论文7篇；培养博士、硕士研究生13名。