the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Crop salinization by intense pumping in regional discharge areas of an inland aquifer system (Cenozoic Duero basin aquifer, Spain)
Abstract. Salinization of crops irrigated with groundwaters in the Tordesillas area has been investigated to determine its cause. Hydrogeological, geophysical, and geochemical techniques reveal that regional saline groundwater flows through the Cenozoic aquifer system of the Duero Basin discharge into the Tordesillas area. Groundwater salinity increases below 150–200 depth. TDEM profiles indicate that salinity distribution is influenced by local and regional flow mixing, as well as by fault structures affecting the Cenozoic succession. Isotopic analyses (δ18O, δD, δ34S) suggest multiple sources of dissolved sulphate and evidence that regional groundwaters recharged at higher altitudes and/or lower temperatures.
Irrigation return flows do not noticeably contribute to salinization, as δ18O and δD data from boreholes in the Duero Floodplain do not show an evaporation trend. Instead, intensive groundwater pumping (from boreholes in the Duero River floodplain), particularly during the irrigation season, induces upwelling of saline groundwater. Piezometric records indicate that hydraulic potential at intermediate depths (about 100 m depth) decreases during pumping (summer), facilitating upwelling of deeper saline groundwaters. Salinity profiles confirm this process, demonstrating a shift from fresher to more saline conditions over time.
Groundwater management authorities must address this issue to prevent further salinization. These findings provide crucial insights for optimizing well design and identifying depths where groundwater is unsuitable for irrigation, ensuring sustainable water use in the region.
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Status: open (until 13 Nov 2025)
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RC1: 'Comment on egusphere-2025-2395', Anonymous Referee #1, 03 Jul 2025
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AC1: 'Reply on RC1', Pedro Huerta, 26 Jul 2025
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2395/egusphere-2025-2395-AC1-supplement.pdf
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AC1: 'Reply on RC1', Pedro Huerta, 26 Jul 2025
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RC2: 'Comment on egusphere-2025-2395', Anonymous Referee #2, 10 Oct 2025
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The manuscript focuses on the crop salinization event that occurred in the Tordesillas region. Based on hydraulic head observations, TDEM geophysical surveys, chemical analyses, and stable isotope data, the authors proposed that summer irrigation pumping induced the upwelling of deep saline water, leading to salinization as the main cause. The research topic has certain significance for regional water resources management. However, the current manuscript lacks sufficient evidence in several key aspects (especially the quantitative relationship between pumping volume and salinity variation, geochemical end-member identification, and validation between TDEM and well data) to support the conclusion proposed by the authors. The paper requires substantial additional work (including more data, quantitative modeling, and end-member analysis) and major rewriting. Therefore, my recommendation is Reject. The main issues and revision suggestions are listed below.
1. The authors mainly infer that pumping-induced upwelling occurs based on the temporal correlation between the observed seasonal decline in water level and the simultaneous increase of EC in the middle layer (100–150 m). However, no detailed extraction records—such as pumping volume, well location, and pumping schedule—are provided. In addition, no numerical hydrodynamic or solute transport modeling is conducted to quantify the relationship between upwelling intensity and salinity response, which weakens the persuasiveness of the key conclusion.
It is recommended to supplement and present detailed pumping records of the main irrigation wells (including well locations, pumping volumes, pumping time series, borehole structure, and screen intervals). A simple hydrodynamic and solute transport simulation, or a simplified 1D/2D model, should be performed to test whether the observed water-level decline and EC variations can be reproduced under the recorded pumping intensity, thereby quantifying the upwelling flow rate, salt flux, and EC variation timescale.
2.The authors use δ¹⁸O/δD, δ³⁴S, and δ¹⁸O(SO₄) data to discuss water and sulfate sources, but they have not adequately sampled or characterized the potential “end-members” (e.g., local Paleogene/Miocene gypsum, agricultural sulfate fertilizers, river water, or near-surface return flow) in terms of isotopic and chemical composition. The conclusion that “irrigation return flow is insignificant” is based merely on the absence of an evaporation line in δ¹⁸O/δD, which is not sufficient.
It is suggested to supplement the analysis of potential source contributions, perform end-member mixing analysis (EMMA, SIAR, or a simple mass-balance approach) to quantitatively estimate the contributions of different end-members, and assess the associated uncertainties.
3. The authors conducted TDEM surveys and presented several geoelectric units (GU-1 to GU-4), but the calibration between resistivity and salinity, the discussion of inversion uncertainty, and the evaluation of model non-uniqueness are insufficient. Moreover, no validation was carried out using borehole lithology, downhole resistivity, or in-well conductivity data. As a result, the geophysical (TDEM) interpretation lacks strong quantitative support.
4. The conclusion emphasizes that “pumping-induced upwelling leads to salinization,” but no salt flux estimation (such as upward salt flux, irrigation-area salt input/output, or accumulation rate) is provided. It is recommended to estimate salt fluxes and perform simplified salt mass-balance calculations based on observed water levels, salinity, and pumping data, and to model long-term salinity evolution under different pumping strategies. This would enable quantitative management recommendations (e.g., allowable extraction thresholds or well-screening depth strategies).
5. The Results and Discussion sections overlap considerably, and the current section division is fragmented, resembling a technical report rather than a scientific article. The Introduction lacks the background and research progress on issues such as crop salinization induced by intensive pumping, and does not sufficiently review recent literature. Most references are outdated. It is recommended to add recent studies from the past five years concerning groundwater-extraction-induced salinization in inland basins, TDEM interpretation, and isotopic tracing, to strengthen the arguments and improve the logical focus of the paper.
Citation: https://doi.org/10.5194/egusphere-2025-2395-RC2
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Unfortunately, this paper is not suitable for publication in an international journal such as HESS. It has no novel aspects and would not be of interest to the broader academic community. The conclusions are reasonable, but the main finding that groundwater pumping causes changes to aquifer salinities is not unexpected and not novel. In its present form it is more suited to a regional journal. Case studies are certainly acceptable in the international literature, but they need to add to our general understanding; so, indications of what new ideas come out of a study and what researchers working on similar projects elsewhere can take from it are needed.
The limited and parochial scope of the paper is evident in the Introduction, which is focused on the local issue of crop yields being impacted by salinization. Salinization of water resources is a major problem globally, but there is no effort here to review the global understanding or to put this study into a broader context. The Aims are also very specific to understanding the local hydrogeology and the Conclusions are just a restatement of the specific findings of the research with no indication of how or why this research is of general interest. Even within the local context, the end of the paper is underwhelming with a general suggestion that these data should help management (without specifying how).
There are several issues with the data and its interpretation.
I have not gone through the paper in more detail, as I cannot see that the data can be woven into a story that is of sufficient interest for this journal. It is never pleasant to receive negative reviews, but I would encourage the authors to see if they can bring more rigor to the study and consider how generally interesting / novel this work is, which will dictate where it should be submitted.