Origin of salinity in soil and water based on hydrogeochemistry and environmental isotopes in the Santa María Volcanic Field

doi:10.21203/rs.3.rs-4283788/v1

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Origin of salinity in soil and water based on hydrogeochemistry and environmental isotopes in the Santa María Volcanic Field

https://doi.org/10.21203/rs.3.rs-4283788/v1

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Salinization of soils and groundwater can be of natural or anthropogenic origin throughout the world. This process is found in arid or desert soils and influences the loss of nutrients in the soil, resulting in the decline of vegetation.

Salinization of soils and groundwater in the Tierra Nueva aquifer can be influenced by natural or anthropogenic activities. The aquifer is located in the Santa María Volcanic Field (SMVF). The SMVF is mainly made up of igneous rocks of andesitic and rhyolitic composition. In this work, an exhaustive study has been carried out to discover the origin of salinity through petrography, mineralogy, stable isotopes (δ2H and δ18O) and hydrogeochemistry. Applying hydrogeochemical techniques, the water families and the main routes of the evolutionary processes of water (dissolution and precipitation and ion exchange) were identified. With a textural analysis, the soil types derived from the alteration of dominant rocks in the region were classified.

The isotopic results revealed the evaporation and mixing processes, as well as the possible elevations of the recharge and influence of the surface water body on the aquifer.

The results indicate that salinization is of natural origin and is increased by anthropogenic activities in the region. Based on the results, three dominant groups were identified, such as (i) where the water-rock interaction process predominates, (ii) the mixing with urban water influences, and (iii) it is affected by the return of irrigation and evaporation, which subsequently intensifies the salinity of the water and soil in the Tierra Nueva region.

salinization

stable isotopes

rhyolites

ground water

Tierra Nueva

Salinization is one of the essential causes of desertification and soil degradation due to the increase in temperature and decrease in rainfall recorded in recent years (Soca, 2015). The salinization problem is one of the planet's most severe and widespread soil degradation processes (Van Lynden et al., 2004; Machado & Serralheiro, 2017). This phenomenon is associated with arid climatic conditions, original materials rich in sodium (rhyolitic rocks), and poor-quality water in agricultural soils (Singh, 2020). Salinization and sodicity are the main phenomena responsible for soil deterioration (Pulido et al., 2010). The origin of sodicity is due to the alteration of plagioclase (Bowen, 1928) when the minerals crystallize during the cooling of the magma. As the rocks are exposed to the climate, the minerals in the volcanic rocks are weathered by the presence of water, temperature, or the activity of organisms (Hasenmueller et al., 2017). Weathering can be classified into six types (GSL, 1995): type I, fresh rock; type II, slightly altered; type III, moderately altered; type IV highly altered; type V, completely altered; and type VI, residual soil. As the minerals that main component of rocks were formed at high pressure and temperature inside the magmatic chamber, which is different from environmental conditions and favors their instability (Colman and Pierce, 1981; Adnan et al., 2022). In addition, the minerals that form at high temperatures and pressure are unstable under ambient conditions whereas the minerals that form at lower temperatures and pressures are more stable (Goldich, 1938). This behavior is similar to the pattern of Bowen's series of reactions, where minerals that are the first to crystallize at high temperatures are also likely to chemically weather first (Goldich, 1938). This implies that the primary minerals (feldspars and plagioclase) are easily weatherable.

Weathering generates clay minerals and iron oxides that subsequently accumulate in fine material (e.g., muscovite, and montmorillonite), which increases when the interaction of plants is more significant (Sedov, 2019). The weathering of Haloclasty, which is derived from the growth of salt crystals immersed in its pores, and water (moisture, rain, dew, evaporation, etc.), play an important role because they hydrate the rock and therefore it increases in volume. Consequently, the soils are salinized and the environment where they develop is the main factor in arid, semi-arid, or semi-desert areas.

Mafic and ultramafic rocks with high ferromagnesian minerals and calcium content are precarious and alter faster than silica-rich felsic rocks where alkaline minerals have a more incredible difficulty to be changed (Kaneva et al., 2021). The alterability of minerals is essential for the formation of soils. In such a way, the soil is abundant in rocks with ferromagnesian whereas scarce in felsic rocks. Therefore, the objective of this study is to determine the origin of soil salinization due to the alteration of silicate minerals during the water-rock interaction.

The study area located in the Tierra Nueva in southeast city of San Luis Potosí (Fig. 1), having an area of 540.61 km², consists of Cretaceous to Quaternary rocks. It´s elevation ranges from 1,610 meters above sea level (masl), having hills, and medium to gentle slopes such as Cerro La Silva at 2,100 masl; likewise, moderately abrupt plateaus that reach a maximum altitude of 2,160 masl (Mesa de Salsipuedes). The average annual precipitation is 444.6 mm and the annual potential evaporation is 1740.92 mm (Koppen, 1936, Inafap, 2005). In the study area, the approximate irrigated surface is 162 hectares, and its main activity is the cultivation of Alfalfa (Medicago sativa) and maize (Zea mays).

2.1 Geology

The Cretaceous unit mainly composed of shales and clayey limestones and known as oldest unit of the Soyatal Formation. In addition, the Cretaceous unit is covered by volcanic rocks of rhyolitic composition interspersed with few agglomerates, and discordantly covered by lava spills with dacitic porphyry texture that intercalated with dacitic tuff (Labarthe & Tristán, 1980). These volcanic rocks are cross-cut by a series of intrusive rocks in the form of granitic composition of the Late Oligocene (Labarthe & Tristán, 1980). The Quaternary rocks are integrated by the alluvium deposited on the margins of the channels and streams and are composed of gravel of dacite, rhyolite, granite, sands, and silts. The geomorphology of the study area is governed mainly by weathering, denudation, and erosion; this is also influenced by climatic conditions that have acted since the Oligocene (30 Ma) to the present (Labarthe et al., 1984).

2.2 Hydrogeology

The hydrogeological characteristics of the geological units are low to slightly permeable; this is associated with the andesitic and rhyolitic volcanic rocks with a small degree of alteration and highly compacted with a basement of intrusive rocks of granitic composition (Padilla, 2014). Due to these conditions, wells, dug wells, and infiltration gallery are located near the bed of the Jofre river. A narrow filling of conglomerates and unconsolidated silt sands forms the Jofre River valley. The thickness of these sediments can reach 20 m in the central part of the Jofre Valley.

The primary source of recharge of the aquifer is the La Muñeca Dam. Downstream of the dam, there is an uplift pressure effect below the dam, evidenced by small runoffs. The shallow aquifer is affected by the return of irrigation, given the intense irrigation carried out with water from the La Muñeca dam.

The main objective of the study is to determine the origin of salinisation or sodicity in the study area by means of different methodologies involving petrographic, hydrogeochemical and isotopic studies with the aim of offering a response to this problem, be it natural or anthropogenic through land use change affecting soils and water, with low cost and short response times.

The methodology consists of petrography, mineralogy, and chemical analysis of water and soil. Nineteen groundwater, dam, well, and river samples were collected following standard methods (APHA, 1998). Physicochemical parameters pH, electrical conductivity (EC) and temperature (T), dissolved oxygen (DO), alkalinity, and oxidation reduction potentialwere measured in situ at each point, using a multiparameter model HI 98194 (pH/EC/DO Multiparameter). The chemical analysis of the cations Ca²⁺, Mg²⁺, Na⁺, K⁺, and B³⁺ were carried out by Emission Spectrometry with Inductively Coupled Plasma and Cl⁻, SO₄²⁻, PO₄³⁻, F⁻ and NO₃⁻ anions by colorimetry.

The mineralogical composition was determined by petrography with a Nikon Eclipse LV100 POL petrographic microscope (natural light/polarized light). To examine by counting points (100), determining the presence of principal components and X-ray diffraction (XRD) Smartlab Rigaku Smartlab Rigaku (Cu Ka X-ray tube; 40 kV 44 mA) was used to quantify the abundance of feldspars, plagioclase, and quartz in the analysis of diffractograms. The analytical procedures, accuracy, and precision were given by Verma et al., (2021).

In addition, 11 samples of soil (1 kilogram) were taken from the agricultural areas at the depth reached by the roots of the Alfalfa plant; each soil sample was determined by the texture touch method (Thien 1979), as well as conductivity and pH, with a depth of 0 to 30 cm, in silt, clay, and sand.

Stable isotope (δ²H and δ¹⁸O) compositions were determined by a stable isotope ratio mass spectrometer (Picarro L1102-i water isotope analyzer, PICARRO, INC) and the results are reported in ‰ with respect to the Vienna Standard Mean Ocean Water 2 and Standard Light Ant-arctic Precipitation 2 (VSMOW2/SLAP2). The analytical accuracy is of ± 0.1‰ for δ¹⁸O and ± 0.6‰ for δ²H. Additionally, the GISP (International Atomic Energy Agency) was used as control samples for the quality checks.

4.1 Petrography

The microscopic analysis shows a microcrystalline matrix with minor plagioclase (Fig. 2), and a bay edge structure of the quartz is observed (MacKenzie et al. 1984). Figure 4 confirms the sodification and content of isolated spherulites, an abundance of plagioclase to a lesser extent with feldspars, and a hypoalitic texture of the rock as described by MacKenzie (1984).

The degree of alteration indicates an increasing order from the primary relict to the secondary type since the hydrothermal fluid seeps more quickly than in the porphyritic class (Betsi & Lentz, 2010). Therefore, most of the primary minerals are altered to secondary minerals. Recrystallized quartz often shows an edge reaction of mafic minerals, indicating a bay edge (Fig. 2a). These quartz minerals are probably formed by a hydrothermal pseudomorphic replacement of early quartz and calcite minerals (Betsi & Lentz, 2010). Calcium plagioclase phenocrysts are sometimes replaced by sodium feldspar; some plagioclase may be albitized (these are in their natural form). Figure 2a shows a well-defined mineral surrounded by other minerals where it can be interpreted with a type II degree of weathering.

Figure 2b shows a feldspar crystal surrounded by a clayey matrix and is classified as a type III degree of weathering. Figure 2c defines plagioclase with an incipient alteration surrounded by a clayey matrix and is also classified as weathering grade III to IV.

The petrographic analysis of the samples is taken in this study contains rhyolite feldspar alkaline-dacite rocks (Fig. 3). The mineralogical composition of these volcanic rocks are fragments of glass or glassy matrix, clasts of feldspars, plagioclase, quartz and some other minerals such as albite (Fig. 2).

4.2 Diffractometry (XRD)

In the XRD diffractograms of rhyolitic rocks (Figs. 4a and 4b), the abundance percentages of sodium-albite-silica-albite are shown 52.7%, quartz oxide-silicate 45.6%, and potassium-alumino-silica 1.7%, 4a) the presence of Silica oxide is minimal or not perceptible in percent reflected (Fig. 4a). In 4b, the minerals present in rhyolitic rocks are identified.

In Fig. 5, a comparison of three diffractograms of the Rhyolite samples (TN-1) and Dacite sample (TN-2) is made with chemical changes that alter the minerals reflected in the soils, these minerals explained in the Bowen series (1928), which goes from the discontinuous series of ferromagnesian to the second being continuous with plagioclase, feldspars (potassium) and quartz. The rhyolite diffractogram shows the primary minerals such as Quartz (SiO₂), orthoclase KAlSi₃O₈, Enstatite (MgSiO₃), Sanidine (K,Na)(Si,Al)₄O₈, and Albite NaAlSi₃O₈, these give rise to weathering when clayey soils with high Na⁺ contents, due to its chemical composition (Figs. 5a, b and c).

4.3 Soil

The study area is made up of volcanic rocks of the rhyolitic composition. The soil is scarce in rhyolitic rocks particularly in this region. Only sandy textures are found, and clayey soil is more abundant in the downstream areas (Valley). Generally, various type of soil present in the Valley. Most of the valley is covered by lithosol, in some areas, there are Xerophiles, Regosol, and Luvisol, and in a smaller percentage, there is Fluvisol. Depending of their texture, soils vary from sandy-loam, loam, sandy-clay-loam, and clay-loam (Fig. 6).

In Fig. 6, on the right side, the different types of soils in the valley and a high resolution with the scanning electron microscope are shown. In Fig. 6a, minerals with weathering grade III-IV are observed. Figure 6b shows feldspar minerals with weathering grade III. In Fig. 6c, feldspar minerals with a degree of weathering of III can be observed.

4.4 Water chemistry or water-rock interaction

The wells in this study have depths ranging from 10 to 30 m. The results of the chemical analysis of these samples were represented in the trilinear Piper diagram (Piper, et al., 1953). The chart is dominated by Na-HCO₃ water families, with some mixed Na-Ca-HCO₃ type facies (Fig. 7), and some wells have Ca-HCO₃ hydrochemical facies (Fig. 7).

The Ca-HCO₃ hydrochemical facies are related to the interaction of water with carbonate rocks (limestones of the Soyatal Formation). The Na-HCO₃ water types are likely the result of weathering of underlying rocks that are predominantly Na-rich rhyolitic in composition; as well as ionic exchange reactions. Whereas the Na-Ca-HCO₃ types of water may be due to a mixture with Ca-HCO₃ hydrochemical facies water and ion exchange.

5.1. Water-rock interaction

Hydrolysis is the process where the breakdown of minerals from the silicate group (pyroxenes, feldspars, micas, hornblendes) occurs, which are the most vulnerable to chemical alteration (Earle, 2015). These reactions can develop in the hydrothermal environment or as exogenous processes (under atmospheric conditions) in the study area; the intense agricultural activity contributes to humid conditions for altering minerals.

The hydrolysis reaction of silicate minerals in an aqueous solution, where H⁺ and OH^- ions are selectively consumed, and K⁺, Na⁺, Ca²⁺ ions, and other cations are transferred from minerals to groundwater (Rose & Burt, 1979). In the mineral alteration process, the ions are released into the soil and groundwater to leave their hydrogeochemical signature so that Na-HCO₃-type waters predominate in the Jofre River aquifer.

The factors that directly influence the alteration are humidity and temperature; for example, in conditions of humidity and high temperature, the hydrolysis of clay, such as kaolinite, will form a gibbsite. Whereas in arid climates, the predominant clay will be of the illite-smectite type (Appelo & Postma, 1993).

KAlSi₃O₈ + H₂O == hydrolysis ==> HAlSi₃O₈ + K⁺ + OH^- 2HAlSi₃O₈ + 11H₂O == hydrolysis ==> Al₂O₃ + 6H₄SiO₄

Table 1. Set of hydrogeochemical phases that were considered in water-rock interaction and bibliographic references.

Phase	Reaction	Ref
Albite	NaAlSi₃O₈ + 8H₂O = Na⁺ + Al(OH)^-₄ + 3H₄SiO₄	1
Ortosa	2 KAlSi₃O₈ + 9H₂O + 2H⁺ → Al₂Si₂O₅(OH)₄ + 4Si(OH)₄ + 2K⁺	2
SiO₂(a) Quartz	SiO₂ + 2H₂O = H₄SiO₄	1
Kaolinite	Al₂Si₂O₅(OH)₄ + 6H⁺ = H₂O + 2H₄SiO₄ + 2Al³⁺	1
Feldespar	2KAlSi₃O₈ + 2H⁺ + 9H₂O = Al₂Si₂O₅(OH)₄ + 2K⁺ + 4H₄SiO	1
Plagioclase	Na_0.62Ca_0.38Al_1.38Si_2.62O₈ + 5.52 H⁺ + 2.48H₂O = 0.62Na⁺ + 0.38Ca⁺² + 1.38Al⁺³ + 2.62H₄SiO₄	1
Sanidine	(K,Na)(Si,Al)₄O₈ (Na_0:56K_0:40Ca_0:01 )_∑=_0:97 (Al _0:97Fe ³⁺ _0:03 )_∑=_1:00 Si _3:01O₈	1
Microcline	0.013K(AlSi₃O₈) + 0.013CO₂ + 0.0195H₂O = 0.065Al₂ Si₂O₅(OH)₄+0.013K⁺ + 0.013HCO^-3 +0.026SiO₂	1
Enstatite	MgSiO₃ - FeSiO₃ (Mg_1:77Fe ²⁺ _0:11Al_0:04Ca_0:02Na_0:02Fe ³⁺ _0:02 )_∑=_1:98Si_2:00O_6.	1

Parkhurst & Appelo (1999)
Heath (2007).

These minerals were identified in petrographic and XRD analysis, where their hydrolysis reactions are as follows (Table 1). In the albite hydrolysis reaction, Na⁺ is incorporated into groundwater, and clays such as kaolinite, montmorillonite, gibbsite are formed (Parkhurst &Appelo 1999). In the biotite hydrolysis, K⁺ and Mg²⁺ are released. While in the hydrolysis of the magnetite, the Fe⁺² passes to Fe³⁺ by oxidation-reduction reactions when interacting with the groundwater; as evidence of this process in the study area, the red porphyry is presented (pigeon blood) that is used as an ornamental material in houses.

Figure 8a shows evolutionary pathways for SiO₂ and HCO₃/Na behavior. In route I, there are samples 22, 21, 20, 18, 7, and 6; the behavior of SiO₂ concerning HCO₃/Na has an inversely proportional behavior; that is, as silica decreases, the HCO₃/Na ratio increases at a ratio of -0.17, these samples are related to the underground flow that goes from the dam to the groundwater discharge zone. Route II is formed by samples 19, 17, 13, 12, 5, 4, and 3; in this group, it also shows behavior inversely proportional to a ratio of -0.8; it also goes in the direction of the flow. Route III is formed by samples 1, 2, 8, 9, 10, 1, 11, 14, 15, and 16. This group is directly proportional; that is, as the silica increases, the HCO₃/Na ratio rises at a ratio of 1. In this group, the flow converges towards sample 15, located in the discharge zone.

Figure 8b shows the albite hydrolysis reaction, which is the SiO₂ ratio concerning Na/(Ca+Na), the evolutionary path I, with samples 22, 21, 20, 18, 13, 12, 10, 9, 7, 5, 4, and 3, has a relationship that is directly proportional to a ratio of 2.28; that is, the silica increases much faster than the Na/(Ca+Na) ratio. Route II, with 16, 15, 14, 11, 9, 8, 2, and 1, shows behavior inversely proportional to a percentage of -0.62; that is, as silica decreases, the Na/(Ca+Na) ratio increases. Route III, 6, and 19 have a relationship directly proportional to a ratio of 1.2; that is, the silica increases much faster than the Na/(Ca+Na) ratio.

In Figure 8c, the SiO₂ relationship concerning Ca²⁺ is shown; route I, with samples 22, 21, 20, 18, 7, and 4, has a relationship that is directly proportional to a ratio of 0.4; that is, Ca²⁺ increases much faster than silica. Route II, with samples 16, 15, 14, 11, 10, 9, 8, 2, and 1, shows behavior directly proportional to a ratio of 0.12; that is, Ca²⁺ increases much faster than silica. Route III, samples 3, 5, 6, 12, 13, 17, and 19 have a relationship directly proportional to a ratio of -0.4; that is, Ca²⁺ increases much faster than when silica decreases.

Figure 9a shows the relationship of F^- vs. Na⁺, in which the evolutionary pathways of groundwater are observed (F₁, F₂, and F₃). The evolution begins with sample 22 (La Muñeca Dam) with a directly proportional behavior up to 2 mg/L and 150 mg/L of Na (F₁) coordinates. From this point on, water has two paths of evolution, in one, there is no increase in F^-, and only Na⁺ increases, possibly due to the water-rock interaction (rhyolitic) with a high Na⁺ (F₂) content. The other evolutionary route has a significant increase in F and little growth in Na, possible interaction with irrigation return water. This area is characterized by using apatite (PO₄)₃Ca₅(F,Cl,OH) in samples 13 and 14 are an old gallery and a pond located in the lower part of probably cumulative irrigation areas (F₃).

In Figure 9b, Cl versus NO₂ two evolutionary routes are observed; in the first, with respect to Cl, there is a considerable increase in Cl^-, which places this group of samples (6, 4, 3, 20, and 15) as a more evolved water by water-rock interaction. In the second evolutionary route, it is subdivided according to its origin with respect to NO₂ that goes from samples 22, 21, 1, 19, 14, 18, 2, 5, and 17 linearly through the town of Tierra Nueva with a possible contribution of residual water urban, which explains the increase in NO₂. The second group identified in this route is found with a low Cl^-content, and an increase in NO₂ attributed to its location in irrigation areas to the use of fertilizers and irrigation returns; samples 10, 11, and 12 have the maximum concentration of NO₂, possibly due to contamination from discharges from a poultry farm.

5.2. Stable isotopes

Some researchers use the environmental isotope ratio for the interpretation of water-rock interaction (Barth, 2000; Jung et al., 2020; Sankoh et al., 2022). Figure 9c shows the relationship δ¹⁸O vs. Cl^-; in this figure. Based on result, two groups of water are identified. The first group corresponds to samples 3, 6, 20, 15, and 4, originating from the water-rock interaction, being the group with the most significant evolution. The second evolutionary path begins in the sample located in La Muñeca Dam (22) with a value of δ¹⁸O -4.33 ^o/_oo, indicating maximum evaporation, which is consistent with a surface water body exposed to temperature changes; sample 9 also has evaporation effects due to its proximity to the dam. The rest of the group tends to increase evaporation due to the possible return of irrigation and mixing with urban water.

Figure 10a is the isotopic relationship between δ¹⁸O and δ²H, for δ¹⁸O the minimum was -9.58 (Sample 3), the maximum was -4.33 (sample 22 from La Muñeca dam), and the average was -7.18, with a standard deviation of 1.37. While for δ²H, the minimum was -41.14 (sample 22 from Presa la Muñeca), the maximum was -73.94 (sample 3), and the mean was -54.34, with a standard deviation of 7.8. Two evolutionary routes are identified; the first one is related to the water-rock interaction with a low δ²H and δ¹⁸O, which is consistent with the type of exploitation (wells 3, 2, 6, and 5). The second evolutionary route shows greater evaporation from its origin shows 22, which is interpreted that the Dam influences the aquifer up to its lowest part. Group 14, 12, 17, 11, and 16 is identified as the mixing zone where their values are related to the World Meteoric Line.

In relation to the global meteoric line (GWWL) defined by Craig (1961) δ²H= 8*δ¹⁸O+10, the evaporation line of the Tierra Nueva aquifer (δ²H= 3.27* δ¹⁸O-28.9), shows a deviation of 22° concerning the line world meteorology, this deviated line represents the evaporation line of the Tierra Nueva aquifer. The evaporation line intersects the meteoric world line at -8.5 at δ¹⁸O and -63 at δ²H. Close to these coordinates are samples 17, 16, 14, 13, and 12. Some examples (3, 2, 6, and 5) do not fit this trend and have a horizontal displacement (green line) concerning the GWWL (Craig, 1961); this behavior is related to the water-rock interaction. It is worth mentioning that the red arrow direction indicates groundwater's evolution from La Muñeca Dam. This behavior can also be interpreted as a mixing effect between the water from the dam and the groundwater from the Tierra Nueva aquifer, in which the flow from below the dam mixes with the groundwater (Jung et al., 2020).

Figure 10b shows the relationship d-excess vs. δ¹⁸O, with a trend that is inversely proportional to d-excess concerning δ¹⁸O (d-excess=-4.9*¹⁸O-30.3); as d-excess decreases, δ¹⁸O increases, such that the highest value of d-excess is in sample 14, consistent with being influenced by irrigation return water, and the lowest value corresponds to sample 22 from La Muñeca Dam. On the other hand, samples 3, 2, 6, and 5 do not fit this pattern and intersect the line d-excess=-4.9*¹⁸O-30.3 at -6.5 of δ¹⁸O, which we identify as the evolutionary path of water interaction -rock, where d-excess has slight variation, and δ¹⁸O has a more significant variation (Sankoh et al., 2022).

Figure 10c shows the relationship between d-excess versus altitude. In figure 10c, the dug wells are found mainly at elevations from 1,725 to 1,750 masl. Three samples were obtained at an elevation of 1785 masl, while sample 22 (Muñeca Dam) was collected at 1845 masl. One sample of water was taken from the Muñeca Dam; however, it present elevations (1880 masl) that correspond to the heights of the catchment area of the Muñeca Dam.

The volcanic rocks that predominate in the study area are of rhyolitic composition. The minerals that form rhyolitic rocks are predominantly alkali feldspars. The chemical alteration of the alkali feldspars during hydrolysis releases Na ions, which are incorporated into the groundwater. The materials indicate III and IV degree of weathering. In the groundwater, the Na-HCO₃ water families predominate, with some mixed facies of the Na-Ca-HCO₃ type and, to a lesser extent, the hydrochemical Ca-HCO₃ facies. Due to the presence of clay minerals in the aquifer, the ionic exchange is possible. The hydrochemical analyses indicate three predominant evolutionary pathways (I, II, and III) where silica and the HCO₃/Na ratio decrease, and Ca²⁺ increases naturally. The intense agricultural activity, and the high temperatures, added to the presence of clayey horizons, facilitate the process of capillarity in the upper part of the terrain and its eminent evaporation so that the precipitation of salts in the soil gives rise to its salinity in an anthropogenic way.

The isotopic ratio of δ¹⁸O/δ²H and d-excess/δ¹⁸O mark the recharge effect of the La Muñeca Dam towards the aquifer, as well as the impact of water-rock interaction and the mixture with water that does not come from the La Muñeca dam.

The d-excess/altitude ratio indicates the catchment elevations of the dam and the recharge zone of the Tierra Nueva aquifer.

Acknowledgements

EML is thankful to the National Council of Science and Technology (CONACYT), Mexico for her Doctoral´s fellowship (grant # 519116), whose doctoral thesis is undergoing the supervision of Janete Morán-Ramírez and José Alfredo Ramos-Leal. Also thank CONACYT for the URR project "Consolidation of stable isotope laboratory for studies and teaching on the effects of global environmental change on ecosystem services".

Author contribution: Conceptualization, Erika Loyola Martínez , Janete Morán Ramírez and José Alfredo Ramos-Leal ; investigation, Erika Loyola Martínez , Janete Morán Ramírez and José Alfredo Ramos-Leal ; methodology,Erika Loyola Martínez , Janete Morán Ramírez and José Alfredo Ramos-Leal; resources, Erika Loyola Martínez , José Alfredo Ramos-Leal , Sanjeet Kumar Verma and Ulises Rodriguez Robles; supervision, Sanjeet Kumar Verma and Ulises Rodriguez Robles; writing—original draft, Erika Loyola Martínez, Janete Morán Ramírez and José Alfredo Ramos-Leal ; writing: review and editing, Erika Loyola Martínez, Janete Morán Ramírez and José Alfredo Ramos-Leal and Sanjeet Kumar Verma and. All authors have read and accepted the published version of the manuscript.

Data availability: No data sets were generated or analyzed during the current study.

Ethics approval and consent to participate Not applicable.

Consent for publication Not applicable

Conflicts of interest: The authors declare no conflict of interest

Funding Statement in the manuscript. If there was no financing

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Origin of salinity in soil and water based on hydrogeochemistry and environmental isotopes in the Santa María Volcanic Field

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Abstract

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1. Introduction

2. Study area

2.1 Geology

2.2 Hydrogeology

3. Methods and materials

4. Results

4.1 Petrography

4.2 Diffractometry (XRD)

4.3 Soil

4.4 Water chemistry or water-rock interaction

5. Discussion

6. Conclusions

Declarations

References

Additional Declarations

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