Rocks and soils weathering in rivers constitutes an important feedback that can initiate shifts in atmospheric carbon dioxide concentrations.
In arid and semi-arid environments, floods can be characterized as relatively short-lived but high intensity events, during which large water volumes encounter exposed rocks that have remained dry for prolonged periods. Furthermore, In these environments water temperatures tend to be higher than in large perennial rivers potentially leading to enhanced weathering rates. Moreover, the rewetting of soils can trigger microbial respiration, releasing CO₂ into the atmosphere.
In Israel, flood-prone areas mostly consist of exposed carbonate rocks, whose weathering promotes CO₂ uptake due to the increase in water alkalinity.
Understanding the balance between mineral weathering and microbial respiration is essential for assessing the influence of flood events on the carbon cycle, yet their relative contributions remain poorly quantified.
In this study we examine the relationship between CO₂ emissions during soil wetting and CO₂ uptake resulting from mineral weathering. We sample floodwater from different ephemeral watercourses and measure the water chemistry, including sulfate, calcium, chloride, sodium, magnesium concentrations, and alkalinity.
We detect a relationship between the sampling location along the wadi riverbed and alkalinity, with downstream samples exhibiting higher alkalinity concentrations, as well as variations between drainage basins.
High Alkalinity levels indicate dissolution of carbonate minerals, whereas alkalinization of water leads to a CO₂ uptake effect from the atmosphere. Therefore, higher alkalinity corresponds to greater uptake of atmospheric CO₂ by floodwaters.
The results of this study indicate a relationship between the location of floodwater ponds along the wadi and the drainage basin characteristics, water chemistry and the solutes accumulated along the flow path.
These preliminary findings enable the estimation of relative weathering rates for different minerals during flood events, and an assessment of the amount of carbon dioxide absorbed during flooding events.