Estimating water fluxes in the critical zone using water stable isotope approaches in the Groundnut and Ferlo basins of Senegal

• Published in: Hydrological processes Vol. 37; no. 1
• Main Authors: Diongue, Djim M. L., Stumpp, Christine, Roupsard, Olivier, Orange, Didier, Do, Frederic C., Faye, Serigne
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.01.2023; Wiley Subscription Services, Inc; Wiley
• Subjects: Agricultural practices; Agriculture; Annual precipitation; Aquifer recharge; Aquifers; Arid regions; Arid zones; Basins; Earth Sciences; Eddy covariance; Evaporation; evapotranspiration; Fluxes; Groundnuts; Groundwater; Groundwater recharge; Hydrology; Isotope composition; Microbalances; Modelling; Monsoons; One dimensional models; Pasture; recharge; Sciences of the Universe; semi‐arid; Soil water; Stable isotopes; Sustainability management; Transpiration; Vegetation; water balance; Water management; Wind; Senegal; stable isotopes; water balance; evapotranspiration; semi-arid; recharge
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.14787

Sustainable water management in semi‐arid agriculture practices requires quantitative knowledge of water fluxes within the soil‐vegetation‐atmosphere system. Therefore, we used stable‐isotope approaches to evaluate evaporation (Ea), transpiration (Ta), and groundwater recharge (R) at sites in Senegal's Groundnut basin and Ferlo Valley pasture region during the pre‐monsoon, monsoon, and post‐monsoon seasons of 2021. The approaches were based upon (i) the isothermal evaporation model (for quantifying Ea); (ii) water and isotope mass balances (to partition Ea and Ta for groundnut and pasture); and (iii) the piston displacement method (for estimating R). Ea losses derived from the isothermal evaporation model corresponded primarily to Stage II evaporation, and ranged from 0.02 to 0.09 mm d−1 in the Groundnut basin, versus 0.02–0.11 mm d−1 in Ferlo. At the groundnut site, Ea rates ranged from 0.01 to 0.69 mm d−1; Ta was in the range 0.55–2.29 mm d−1; and the Ta/ETa ratio was 74%–90%. At the pasture site, the ranges were 0.02–0.39 mm d−1 for Ea; 0.9–1.69 mm d−1 for Ta; and 62–90% for Ta/ETa. The ETa value derived for the groundnut site via the isotope approach was similar to those from eddy covariance measurements, and also to the results from the previous validated HYDRUS‐1D model. However, the HYDRUS‐1D model gave a lower Ta/ETa ratio (23.2%). The computed groundwater recharge for the groundnut site amounted to less than 2% of the local annual precipitation. Recommendations are made regarding protocols for preventing changes to isotopic compositions of water in samples that are collected in remote arid regions, but must be analysed days later. The article ends with suggestions for studies to follow up on evidence that local aquifers are being recharged via preferential pathways. Because crops at Site 1 are rainfed, the soil is bare during the dry season (February to June), and Ea (0.08 mm d−1) is the only component of ETa. Between June and August (first stage of crop development), and from August to December (crop maturity and harvesting), Ta (which ranges from 1.08 to 2.04 mm d−1) exceeds Ea (0.32 to 0.61 mm d−1). The estimated recharge rates are less than 2% of annual rainfall.