鄱阳湖水位波动显著,降水、土壤水、地下水转化过程复杂,受限于复杂的湿地野外条件和传统的监测手段,湿地土壤水分运动及其与地下水转化关系的定量研究较为困难.本研究选择鄱阳湖湿地不同高程处典型植被群落,基于生长季水文监测和降水、湖水、地下水、0~80cm根区土壤水氢氧同位素测试,分析了不同植被群落根区土壤水同位素变化特征,阐释了不同水文时期湿地土壤水分运动过程,量化了地下水与土壤水的转化关系.结果显示,高位滩地茵陈蒿群落(Artemisia capillaris)的土壤水蒸发线斜率(5.91)明显低于当地大气降水线(LMWL,7.60),0~60cm土壤水lc-excess指数为负,说明土壤蒸发作用较强,最大影响深度为60cm.而中、低高程滩地处芦苇(Phragmites australis)和灰化薹草(Carex cinerascens)群落的土壤水蒸发线斜率(6.70和6.75)略低于LMWL,土壤水lc-excess值均接近于0,显示蒸发作用较小.在土壤水分运动方面,茵陈蒿群落土壤水剖面δ18O在春季(5月)、夏季(6~8月)随深度增加而富集,表明土壤水受降水补给,并以活塞流模式下渗;秋季(9~10月)土壤水δ18O明显富集,且随深度增加而贫化,指示主要受蒸发作用的影响.此外,茵陈蒿群落根区土壤水δ18O较地下水同位素显著富集,在地下水埋深最浅时(1.92m),土壤水中未发现地下水的贫化同位素信号及明显的水分补充,说明根区土壤水与地下水间的垂向水文连通受阻.芦苇和薹草群落土壤水运动受地下水波动影响明显.在地下水位上升期(4~5月),芦苇和薹草群落浅层(0~40cm)土壤水主要来源大气降水,深层土壤水(40~80cm)受毛细水上升补给,地下水对根区土壤水的补给贡献超50%;在地下水浅埋期(6、8月),芦苇群落土壤水和地下水转化频繁;在地下水位下降期(9~10月),芦苇和薹草群落表现出非均匀土壤水流过程,存在明显优先流.
Abstract
Poyang Lake is characterized by significant water level fluctuations, leading to complex transformation processes among precipitation, soil water, and groundwater. Due to the limitations of intricate wetland conditions and traditional monitoring methods, it is challenging to conduct quantitative studies on soil water movement and its interaction with groundwater. In this study, three vegetation communities at different elevations in Poyang Lake were investigated to analyze the isotopic composition of precipitation, lake water, groundwater, and soil water (0~80cm). The characteristics of wetland soil water movement were examined across various hydrological periods. The results showed that the slope of the soil evaporation line (SEL) in the Artemisia capillaris community (5.91) was significantly lower than that of the local meteoric water line (LMWL, 7.60). The lc-excess values of soil water in 0~60cm layer were negative, indicating strong evaporation, with a maximum impact depth of 60 cm. The slopes of the SEL in the Phragmites australis and Carex cinerascens communities (6.70 and 6.75, respectively) were slightly lower than the LMWL, and the lc-excess values of soil water were close to 0, indicating minimal evaporation. Regarding soil water movement, the δ18O values of soil water in the A. capillaris community increased with depth during spring (May) and summer (June to August), indicating piston-flow dominated transport. During autumn (September and October), soil water δ18O values became enriched and decreased with depth, indicating the dominant influence of evaporation. Furthermore, the soil water δ18O values in the A. capillaria community were significantly enriched compared to groundwater isotopes. No depleted isotope signals or evidence of groundwater supply were detected in the soil water, even when the groundwater table was at its shallowest (1.92m). These results suggest that vertical hydrological connectivity between root-zone soil water and groundwater was blocked. In contrast, soil water movement in the P. australis and C. cinerascens communities was significantly influenced by groundwater level fluctuations. During the groundwater level rise period (April and May), shallow soil water (0~40cm) in these two communities primarily originated from atmospheric precipitation, while deep soil water (40~80cm) was replenished by capillary rise of groundwater. Groundwater contributed more than 50% to the replenishment of root-zone soil water. During the shallow groundwater table period (June and August), frequent exchanges occurred between soil water and groundwater in the P. australis community. In the groundwater table decline period (September and October), the P. australis and C. cinerascens communities exhibited non-uniform soil water flow processes, characterized by noticeable preferential flow.
关键词
地下水补给 /
洪泛环境 /
鄱阳湖湿地 /
土壤水运动 /
稳定同位素 /
优先流
Key words
floodplain environment /
groundwater recharge /
Poyang Lake wetland /
preferential flow /
soil water movement /
stable isotope
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基金
国家自然科学基金项目 (41601031,42071036,42401049);江苏第二师范学院科研启动项目 (928201/030);江西省双千计划人才项目(jxsq2023101105);中国科学院青促会优秀会员项目(Y2023084);水灾害防御全国重点实验室 2023 年度“一带一路”水与可持续发展科技基金(2023490611)
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