Geochemical modeling of systems affected by irrigation: The case of Lerma basin (Spain, 2004-2020).

Geologically "saline" zones with scarce pluviometry, which are already susceptible to the salinization of natural drainage, can experience the acceleration of the salinization of the receiving water systems with the implementation of irrigation. The main objective of this paper is to analyze the geochemical processes that control the variations of the hydrosaline balance due to the implementation of irrigation of the Lerma basin (Spain) from the beginning of its transformation into irrigation land (2004) until the consolidation of irrigation (2020). The results of this study evidence the dissolution of some mineral phases, such as halite, gypsum, and dolomite, and the precipitation of others, such as calcite. Additionally, the final composition of the irrigation return flows cannot be explained without consideration of the NaCa exchange. Part of the dissolved Ca2+ is deposited in the soil, which, in turn, contributes with Na+ to the solution. These natural processes are accelerated with irrigation but progressively slow down as the soil salts are washed with time. Although less evident, there is an additional negative agroenvironmental effect associated with the precipitation of calcite and the possible formation of petrocalcic horizons in the soil. The results obtained herein indicate that studies focusing on the salinity of irrigated zones should go a step further and include the geochemical processes in quantifying the global mass of exported salts.

Hydrosaline balance evolution of an irrigated zone: The case of Lerma basin (Spain, 2004-2020).

Geologically saline zones with scarce pluviometry are areas susceptible to salinization of their natural drainage. However, the salinization of the receiving water systems can be accelerated with the implementation of irrigation. This work aims to analyze the effects of irrigation on some zones transformed into irrigation land, from the beginning of the process until its complete consolidation. To this end, salt balances are evaluated as a whole and for each significant chemical element. The study zone is the irrigable area of the Lerma basin (Spain), where hydrosaline balances have been carried out since the hydrological year 2004 (before the implementation of irrigation) until 2020 (after the consolidation of irrigation). The implementation of irrigation in the area has doubled the mass of exported salts up to an average of 3177 kg/ha irrigable·year, for the entire study period. 55 % of that amount results from a global mineral dissolution, although this process seems to decrease with time as these minerals are being flushed from the soil. Before irrigation was implemented, the general global dissolution pattern produced more concentration of most ions (SO42-, Cl-, Mg2+, Na+, and K+) in the water outputs than in the water inputs. After the implementation of irrigation, there were more water inputs than outputs in the balance and that was shown by the decrease in the dissolved HCO3- and Ca2+.These results indicate that the consolidation of irrigation progressively decreases the induced salinization in the water systems that receive the irrigation return flows. Further studies are required to expand the general understanding of the process and its effects, quantify the different geochemical processes involved, and identify possible additional environmental issues induced by irrigation.

Geochemical processes controlling water salinization in an irrigated basin in Spain: identification of natural and anthropogenic influence.

Salinization of water bodies represents a significant risk in water systems. The salinization of waters in a small irrigated hydrological basin is studied herein through an integrated hydrogeochemical study including multivariate statistical analyses and geochemical modeling. The study zone has two well differentiated geologic materials: (i) Quaternary sediments of low salinity and high permeability and (ii) Tertiary sediments of high salinity and very low permeability. In this work, soil samples were collected and leaching experiments conducted on them in the laboratory. In addition, water samples were collected from precipitation, irrigation, groundwater, spring and surface waters. The waters show an increase in salinity from precipitation and irrigation water to ground- and, finally, surface water. The enrichment in salinity is related to the dissolution of soluble mineral present mainly in the Tertiary materials. Cation exchange, precipitation of calcite and, probably, incongruent dissolution of dolomite, have been inferred from the hydrochemical data set. Multivariate statistical analysis provided information about the structure of the data, differentiating the group of surface waters from the groundwaters and the salinization from the nitrate pollution processes. The available information was included in geochemical models in which hypothesis of consistency and thermodynamic feasibility were checked. The assessment of the collected information pointed to a natural control on salinization processes in the Lerma Basin with minimal influence of anthropogenic factors.

Irrigation efficiency and quality of irrigation return flows in the Ebro River Basin: an overview.

The review analysis of twenty two irrigation efficiency (IE) studies carried out in the Ebro River Basin shows that IE is low (average IE)(avg)(= 53%) in surface-irrigated areas with high-permeable and shallow soils inadequate for this irrigation system, high (IE)(avg)(= 79%) in surface-irrigated areas with appropriate soils for this system, and very high (IE)(avg)(= 94%) in modern, automated and well managed sprinkler-irrigated areas. The unitary salt (total dissolved solids) and nitrate loads exported in the irrigation return flows (IRF) of seven districts vary, depending on soil salinity and on irrigation and N fertilization management, between 3-16 Mg salt/ha x year and 23-195 kg NO)(3) (-)-N/ha x year, respectively. The lower nitrate loads exported from high IE districts show that a proper irrigation design and management is a key factor to reduce off-site nitrogen pollution. Although high IE's also reduce off-site salt pollution, the presence of salts in the soil or subsoil may induce relatively high salt loads (>or=14 Mg/ha x year) even in high IE districts. Two important constrains identified in our revision were the short duration of most surveys and the lack of standards for conducting irrigation efficiency and mass balance studies at the irrigation district level. These limitations {emphasize the need for the establishment of a permanent and standardized network of drainage monitoring stations for the appropriate off-site pollution diagnosis and control of irrigated agriculture.