Seasonal variations of groundwater discharge and associated nutrient fluxes in Changhu Lake
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摘要: (目的)为揭示地下水对湖泊水量和营养盐平衡的贡献及季节性变化,(方法)本文以长江中游长湖为研究对象,通过丰、枯水期野外采样,结合电导率(EC)、稳定同位素(2H和18O)、水化学元素(Ca2+、Mg2+)和氡(222Rn)同位素对湖底地下水排泄(Lacustrine Groundwater Discharge,LGD)进行了多手段示踪,并基于222Rn质量平衡模型量化了不同季节的LGD及其携带营养盐通量。(结果和结论)结果显示:丰、枯水期LGD速率分别为64.52 mm/d和14.95 mm/d,丰水期显著大于枯水期;丰、枯水期地下水携带的总氮(TN)输入通量分别为25.68×106 g/d和5.58×106 g/d,总磷(TP)输入通量分别8.14×106 g/d和0.17×106 g/d。丰、枯水期LGD强度的差异导致了地下水携带TN、TP输入的差异,丰水期TP的输入量还受该时期农业活动的影响;丰水期较强的降水和蒸发驱动了更大的LGD强度及其携带TN、TP通量。本研究可为长湖区域水资源管理和水生态保护提供重要理论依据。Abstract: To reveal the contribution and seasonal variation of groundwater discharge to lake water and nutrients budgets, this study investigated Changhu Lake in the middle reaches of the Yangtze River. Field sampling was conducted during both wet and dry seasons using multiple tracing techniques, including electrical conductivity (EC), stable isotopes (2H and 18O), hydrochemical elements (Ca2+ and Mg2+), and 222Rn isotopes. The 222Rn mass balance model was employed to quantify LGD and associated nutrient fluxes in different seasons. Our results show that LGD rate during the wet and dry seasons was 64.52 mm/d and 14.95 mm/d respectively, with a significant difference between these seasons. Furthermore, during the wet and dry seasons, groundwater carried TN inputs of approximately 25.68×106 g/d and 5.58×106 g/d, respectively. While TP inputs were approximately 8.14×106 g/d and 0.17×106 g/d in wet and dry seasons, respectively. Differences in LGD rate between the wet and dry seasons elucidated the variation in TN and TP input flux carried by groundwater, and the input of TP during the wet season was also influenced by agricultural activities during this season. The greater precipitation and evaporation experienced during the wet season drove higher LGD intensity and increased TN and TP fluxes. Overall, our study provides important theoretical insights that can inform water resources management and aquatic ecosystem preservation efforts in the Changhu area.
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Key words:
- lake /
- groundwater discharge /
- radon mass balance model /
- nitrogen /
- phosphorus
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