Dept. Catchment Hydrology, Helmholtz Centre for Environmental Research - UFZ, Halle (Saale) 06120, Germany; Dept. River Ecology, Helmholtz Centre for Environmental Research - UFZ, Magdeburg 39114, Germany.
Dept. River Ecology, Helmholtz Centre for Environmental Research - UFZ, Magdeburg 39114, Germany.
Sci Total Environ. 2024 Nov 15;951:175617. doi: 10.1016/j.scitotenv.2024.175617. Epub 2024 Aug 17.
Groundwater inflow can be a significant source of nutrients for riverine ecosystems, which can affect eutrophication i.e., the elevated primary production and the corresponding accumulation of algal biomass. Experimental and modelling work has shown that benthic algae (autotrophic biofilms) in particular benefit, as they have direct access to the inflowing groundwater-borne nutrients. Primarily the supply of phosphorus (P) enhances pelagic algal biomass, as it is the limiting nutrient for primary production in most freshwater systems. In this study, we estimate the effect of groundwater inflow on overall eutrophication of a large, European lowland river and tested its seasonal effect on biofilms in particular. We calculated the effects on overall eutrophication during summer according to the estimated input of groundwater-borne P and the C:P stoichiometry of planktonic algae in the Elbe River. Our model indicated that these diffuse P inputs have the potential to significantly increase eutrophication. Groundwater-P can contribute up to 1.5 t/d PO4 over the investigated 450 km stretch of the Elbe River under low flow conditions. This would result in an additional planktonic load of about 46 t/d of particulate organic carbon, thereby contributing to eutrophication at the regional scale in this river. In contrast, at the local scale, biofilms were collected seasonally from artificial substrata exposed in the river either in hydrogeologically active areas with groundwater inflow, or in areas of varying hydraulic connectivity. Analyses of biofilm macronutrients, structural components and biofilm community composition show distinct effects of season, hydrogeology and groundwater inflow. The dominant predictors were season and the interaction between hydrogeology and groundwater. Benthic eutrophication is most likely to occur in autumn in areas of loose rock with high groundwater inflow. The strong interaction of environmental factors in determining benthic eutrophication highlights the need to assess these factors in combination rather than in isolation.
地下水的流入可为河流生态系统提供大量养分，从而影响富营养化，即初级生产力的提高和藻类生物量的相应积累。实验和模型研究表明，特别是底栖藻类（自养生物膜）会受益，因为它们可以直接获得流入的地下水携带的养分。主要是磷（P）的供应增强了浮游藻类生物量，因为它是大多数淡水系统初级生产的限制营养物质。在这项研究中，我们估算了地下水流入对大型欧洲低地河流整体富营养化的影响，并测试了其对生物膜的季节性影响。我们根据地下水中携带的 P 的估计输入以及易北河浮游藻类的 C:P 化学计量来计算夏季整体富营养化的影响。我们的模型表明，这些扩散的 P 输入有可能显著增加富营养化。在低流量条件下，通过调查的易北河 450 公里河段，地下水-P 每年可贡献高达 1.5 吨/天的 PO4。这将导致额外的 46 吨/天的颗粒有机碳浮游负荷，从而对该河流的区域尺度富营养化产生影响。相比之下，在局部尺度上，从易北河中暴露的人工基质中季节性采集生物膜，这些基质要么位于有地下水流入的水文地质活跃区，要么位于水力连通性不同的区域。生物膜宏量营养素、结构成分和生物膜群落组成的分析表明，季节、水文地质和地下水流入对生物膜有明显影响。主要预测因子是季节和水文地质与地下水之间的相互作用。在有大量地下水流入的松散岩石区，底栖富营养化最有可能发生在秋季。环境因素在确定底栖富营养化方面的强烈相互作用突出表明，需要综合评估这些因素，而不是孤立地评估。
