ISSN 1000-3665 CN 11-2202/P

    海南岛东北部东寨港滨海地下水排泄及其对红树林生境的影响

    Submarine groundwater discharge and its impact on mangrove habitats in Dongzhaigang Area, Northeastern Hainan Island

    • 摘要: 海底地下水排泄(Submarine Groundwater Discharge,SGD)是经常被忽视的重要海陆物质交换途径,驱动着陆源淡水与生源要素输入海洋,影响滨海湿地生态系统健康。合适的盐度和良好的环境质量是适宜的红树林湿地生境特征,从地下水视角开展SGD对东寨港红树林生境的影响研究较少,红树林生态保护修复是否需要关注地下水的作用仍需探索。为揭示海南东寨港SGD的特征及其对红树林生境的影响,本研究以红树林湿地水体中氡(222Rn)活度为研究对象,分析海水222Rn活度的时空变化及其影响因素,并基于222Rn质量平衡模型,估算了东寨港地区SGD和其携带营养盐的通量。结果表明,222Rn活度变化主要受雨枯水期循环、潮汐水位波动、断裂带构造、表层沉积物性质等因素影响。基于该区域222Rn质量平衡模型,估算得到丰水期、枯水期SGD通量分别为8.90×105,6.84×105 m3/d;结合地下水端元的溶质浓度,估算了SGD驱动的营养盐通量。其中,丰水期磷酸盐、亚硝酸盐及硝酸盐的通量分别为6440,53.44,1084kg/d;枯水期营养盐通量约为丰水期的2/3。东寨港红树林湿地SGD通量与当地河流排泄量为同一数量级,其携带的营养盐通量也非常可观;SGD通量热区和冷区分别对应红树林稀疏区与繁茂区,暗示SGD可能通过降低红树林湿地盐度或环境质量对东寨港红树林湿地生境产生负面影响。该成果可为东寨港红树林湿地生态保护修复提供理论支撑。

       

      Abstract: Submarine groundwater discharge (SGD) is a significant yet often overlooked pathway for material exchange between terrestrial and marine environments, delivering freshwater and nutrients to coastal ecosystems and influencing mangrove wetland health. Salinity balance and environmental quality are key factors in maintaining healthy mangrove habitats, yet the role of SGD in shaping these conditions in the Dongzhaigang Area, northeastern Hainan, remains poorly understood. Moreover, the importance of groundwater considerations in mangrove ecological protection and restoration requires further exploration. This study investigated SGD characteristics and its ecological impacts on mangrove wetlands in Dongzhaigang using radon isotope (²²²Rn) as a natural tracer. The spatial and temporal variations of seawater 222Rn activity and its influencing factors were analyzed. Based on the 222Rn mass-balance model, the fluxes of SGD and the associated nutrients in the Dongzhaigang Area were estimated. The findings indicate that the variation in 222Rn activity is predominantly influenced by the seasonal rainfall, tidal water level fluctuation, fracture zone structure, and the nature of surface sediments. Using the 222Rn mass balance model for the region, SGD fluxes were estimated to be 8.90×105 and 6.84×105 m3/d in the wet season and dry season, respectively; SGD-driven nutrient fluxes were estimated by combining the solute concentrations in groundwater . The fluxes of phosphate, nitrite, and nitrate were estimated to be 6440 kg/d, 53.44 kg/d, and 1084 kg/d, respectively, in the wet season—approximately two-thirds of these values in the dry season. The estimated SGD fluxes of the mangrove wetland in Dongzhaigang Area are comparable to the local river discharge, and the associated nutrient fluxes carried by the wetland were very significant; the hot and cold zones of SGD fluxes corresponded to the sparse and lush zones of the mangrove forests, respectively, suggesting that SGD may negatively affect mangrove wetland habitats in Dongzhaigang Area by reducing mangrove wetland salinity or environmental quality. This study provides a theoretical basis for the ecological protection and restoration of mangrove wetlands in the Dongzhaigang Area.

       

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