Mountainous Floodplain Connectivity in Response to Hydrological Transitions - Archive ouverte HAL
Article Dans Une Revue Water Resources Research Année : 2024

Mountainous Floodplain Connectivity in Response to Hydrological Transitions

Résumé

In mountainous watersheds, floodplain sediments are typically characterized by gravel bed layers capped by an overlying soil unit that serves as a hotspot for biogeochemical reactivity. However, the influence of soil biogeochemistry on gravel bed underflow composition remains unclear, especially during hydrological transitions that alter the vertical connectivity between overlaying soils and the underlying gravel bed. This study investigates these dynamics by measuring hydraulic gradients and water compositions over three hydrological years in a typical mountainous, low-order stream floodplain in the Upper Colorado River Basin. Results indicate that the timing of hydrological conditions strongly influences the vertical exchanges that control water quality. Specifically, during flooding events such as beaver ponding, that induce downward flushing of the soil, anoxic conditions prevalent in the biogeochemically active soil are transferred downstream via gravel bed underflow. Conversely, snowmelt and drought conditions increase oxic conditions in the gravel bed due to diminished hydrological connectivity with the overlying soil. To compare water quality response to hydrological transitions across similar floodplain environments, we propose a conceptual model that quantifies the inundation-induced flushing of soil porewater to measure solute exchange efficiency with the gravel bed solute convergence efficiency (SCE). This model provides a framework for quantifying biogeochemical processes in hydrological underflow systems, which is critical for water and elemental budgets in these globally important mountainous ecosystems. Mountains are important sources of freshwater for humans and ecosystems. They are however increasingly impacted by climate change. In this paper, we investigate how changes in water availability (droughts, snowmelt, inundations) can cascade into changes in water quality (concentrations of dissolved chemical elements). We show that in mountain valleys, the zone of contact between the soil and the underlying gravel bed aquifer is important for water quality. Chemical elements from the soil can be flushed down into the gravel bed aquifer, then transported by groundwater to the stream. Chemical elements from the soil can also react with chemical elements present in the aquifer. Our research can be used to better predict the water and elemental budgets in these important mountainous systems. Soil / gravel bed connectivity in floodplains is important for water quality Snowmelt and drought both reduce soil / gravel bed connectivity Beaver ponding increases downward flushing to gravel bed unit
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Dates et versions

hal-04653801 , version 1 (19-07-2024)

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Tristan Babey, Zach Perzan, Sam Pierce, Brian Rogers, Lijing Wang, et al.. Mountainous Floodplain Connectivity in Response to Hydrological Transitions. Water Resources Research, 2024, 60 (7), pp.e2024WR037162. ⟨10.1029/2024WR037162⟩. ⟨hal-04653801⟩
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