Victoriano Martínez Alvarez

The Mar Menor is the second largest coastal lagoon in the Mediterranean Sea, with a surface area of about 136 km². It is restricted from the open sea by a sandy barrier system (La Manga) interrupted by three tidal inlets. As a result of high evaporation, it is hypersaline (42–47 ppt) in parts. This study examines the factors leading to the rise in sea surface temperature in the Mar Menor through an analysis of long-term sea surface temperature using HadSST1.1 data together with shorter-term Moderate-Resolution Imaging Radiometer and Optimum Interpolation Sea Surface Temperature data. A thermal box model has been constructed for the lagoon in an attempt to balance major heat sources and sinks. Additionally, a thermal probe was deployed in 0.3 m of water to evaluate the benthic flux of heat of the shelly fine sand that covers the lagoon seabed. The results show that the vertical thermal gradient in the seabed inverts between the day and night. Prior to circa 1977, there was no clear trend in SST, and variations were strongly associated with the Atlantic Mutidecadal Oscillation and the North Atlantic Oscillation. Post circa 1980, the maximum summertime sea surface temperature showed a steady increase of 0.34 °C/decade. The cross-correlation of SST in the Mar Menor with external drivers showed that it is dominated by the sea surface temperature of the Western Mediterranean, followed by local air temperature, with a minor contribution from the Indian Ocean Dipole. No other significant correlations were evident, suggesting that local temperature was dominated by local drivers. In addition, a Spearman rank order evaluation and principal component analysis showed that the general trends of the Mar Menor SST were also influenced by the Atlantic Multidecadal Oscillation, CO₂, and GDP.

The Mar Menor is the second largest coastal lagoon in the Mediterranean Sea with a surface area of about 136 km². It is restricted from the open sea by a sandy barrier system (La Manga) interrupted by three tidal inlets. As a result of high evaporation it is hypersaline (42-47 ppt) in parts. This study examines the factors leading to the rise in sea surface temperature in the Mar Menor through the analysis of long-term sea surface temperature using HadSST1.1 data together with shorter term MODIS and OISST data. A thermal box model has been constructed for the lagoon in an attempt to balance major heat sources and sinks. As well, a thermal probe was deployed in 0.3 m of water to evaluate the benthic flux of heat of the shelly fine sand that covers the lagoon seabed. Results show that the vertical thermal gradient in the seabed inverts between the day and night. Prior to 1980 there was no clear trend in SST and variations were strongly associated with the AMO and NAO. Post 1980, maximum summertime SST showed a steady increase of 0.34°C/decade. Cross-correlation of SST in the Mar Menor with external drivers showed that it is dominated by SST of the Western Mediterranean, followed by CO₂, AMO and IOD. There was a strong inverse relationship with sun spot activity and the Spanish national GDP. There were no significant links in trends between SST in the Mar Menor and PDO, NAO or ENSO3,4 in a Spearman Rank order evaluation and PCA analysis.

Agroecological ecosystems produce significant carbon dioxide fluxes; however, the equilibrium of their carbon sequestration, as well as emission rates, faces considerable uncertainties. Therefore, sustainable cropping practices represent a unique opportunity for carbon sequestration, compensating greenhouse gas emissions. In this research, we evaluated the short-term effect of different management practices in alleys (tillage, no tillage, alley cropping with Rosmarinus officinalis and Thymus hyemalis on soil properties, carbon sequestration, and CO₂ emissions in a grapefruit orchard under semiarid climate). For two years every four months, soil sampling campaigns were performed, soil CO₂ emissions were measured, and rhizosphere soils were sampled at the end of the experimental period. The results show that alley cropping with Thymus and Rosmarinus contributed to improve soil fertility, increasing soil organic carbon (SOC), total nitrogen, cation exchange capacity, and nutrients. The CO₂ emission rates followed the soil temperature/moisture pattern. Tillage did not contribute to higher overall CO₂ emissions, and there were no decreased SOC contents. In contrast, alley crops increased CO₂ emission rates, especially Rosmarinus; however, the bigger root system and biomass of Rosmarinus contributed to soil carbon sequestration at a greater rate than Thymus. Therefore, Rosmarinus is positioned as a better option than Thymus to be used as an alley crop, although long-term monitoring is required to evaluate if the reported short-term benefits are maintained over time.

Spain is the leading citrus producer in the European Union, with the Segura River Basin in southeastern Spain playing a crucial role in this industry. However, the impact of local agricultural production on water appropriation has been overlooked. This study assesses the water footprint (WF) of both conventional and organic citrus production using the Water Footprint Network approach, addressing beneficial practices aiming to reduce the water appropriation impact. Focusing on four citrus fields, the evaluation covers green, blue, and grey components of the WF, and secondary impacts from electricity and fossil fuel consumption, which are usually omitted from the WF assessments. The results indicate that the total WF for organic orange and lemon production is over 19% lower than for the conventional system. Notable differences are observed in the blue component, attributed to the use of vegetative mulches, and in the grey component due to the reduced impact of fertilizers in organic practices. The individual and total WF values are lower than those reported in other citrus studies, and are linked to efficient resource management in semi-arid regions that helps overcome water scarcity. Nevertheless, the sustainability analysis reveals major challenges for the citrus sector in the basin, highlighting the strain on resources given the limited water availability. The available water remaining (AWARE) indicator demonstrates extremely high potential water deprivation in the area. Overall, the study underscores the necessity of integrating WF analyses in agricultural planning to manage resource scarcity effectively. Future research should focus on developing precise methodologies and incorporating unconventional farming practices to enhance sustainability. This research provides valuable insights for stakeholders aiming to optimize water use in agriculture under scarce resource conditions.

La escasez de recursos hídricos para regadío en zonas áridas y semiáridas como el sureste español ha fomentado el uso de recursos hídricos no convencionales, entre los cuales el agua marina desalinizada (AMD) se ha convertido en el más prometedor para paliar la sobredemanda de agua. Sin embargo, las ventajas e inconvenientes de su uso complementario en el riego agrícola deben ser consideradas. Este estudio evaluó la respuesta agrofisiológica de un cultivo de pomelo al riego con AMD durante tres años consecutivos. Se observaron diferencias significativas al comparar la calidad del AMD con los recursos convencionales de agua dulce disponibles, mayoritariamente procedentes del Trasvase Tajo‐Segura. Además, el estudio determinó el posible riesgo de sodicidad del suelo, las diferencias no significativas en las relaciones hídricas foliares y la elevada acumulación de boro en las hojas derivado del riego con AMD, comparado con el uso de recursos hídricos superficiales convencionales. Finalmente, una evaluación económica permitió analizar la rentabilidad de implantar total o parcialmente este recurso en el riego, considerando el coste del agua y del fertilizante y los ingresos obtenidos por la venta de la fruta. Los resultados proporcionan orientación para el uso y la gestión del AMD en zonas con escasez de recursos hídricos.

El objeto de este estudio es analizar, desde una perspectiva agronómica, el impacto sobre los principales cultivos de la cuenca del Segura de la progresiva sustitución de los recursos hídricos que tradicionalmente se aplican en el regadío por agua marina desalinizada (AMD). Para ello, se han definido distintos escenarios representativos de la situación actual y de posibles situaciones futuras, así como indicadores específicos para la caracterización de los impactos agronómicos y económicos bajo estos escenarios. Los resultados ponen de manifiesto que, al margen de posibles efectos de fitotoxicidad por boro, el impacto agronómico es favorable, y más relevante cuanto mayor es la sensibilidad del cultivo a la salinidad del agua de riego. La progresiva sustitución de los recursos hídricos disponibles por AMD conlleva mejoras en la productividad de los cultivos y reducciones en las necesidades de riego, cuya valorización económica supera holgadamente a los sobrecostes en la fertilización por la baja mineralización del AMD. El impacto económico ofrece resultados heterogéneos entre los grupos de cultivos, ya que integra la valoración económica del impacto agronómico (positivo) junto al efecto de la incorporación de AMD en el coste del agua (negativo). Resulta claramente favorable para el caso de frutales no cítricos, y desfavorable para los hortícolas al aire libre, mientras que en cítricos y almendro los impactos son muy reducidos. Finalmente, se destaca que el escenario de uso conjunto (50%AMD) resulta más favorable que el de riego con AMD (100%AMD).

Climate change is affecting water resources in south-eastern Spain, and this mainly affects irrigated agriculture. In this context, seawater desalination is an adaptive strategy that has provided increasing water allotments to agriculture for the last decade, to replace decreasing conventional resources. Farmers are concerned about the agronomic effects of this substitution and its economic consequences. This study focuses on the potential agronomic impacts of the progressive replacement of the irrigation water from the Tagus–Segura transfer (TST) with desalinated seawater (DSW) on the main crops of south-eastern Spain. To that end, five main agronomic concerns were selected and analyzed under three water supply scenarios using increasing rates of DSW (0, 50, and 100%). The results indicated that, in addition to other economic or environmental considerations, sufficiently relevant agronomic aspects exist that need to be considered when replacing the TST supply with DSW. This study evidences the risks of phytotoxicity and soil alkalinization, due to the increase in boron concentration and the imbalance between monovalent and divalent cations in the DSW, respectively, and also a slight increase in the cost of fertilizers. In addition, the irrigation water salinity effect on production and total irrigation requirements was negligible, as both water sources present sufficiently low salinity. The detrimental effects were mitigated under a partial replacement scenario, so the blended use of DSW with conventional resources seems the most recommendable option for its agricultural management, rather than irrigating with DSW alone.

For centuries, desalination, in one way or another, has helped alleviate water scarcity. Over time, desalination has gone through an evolutionary process influenced largely by available contemporary technology. This improvement, for the most part, was reflected in the energy efficiency and, in turn, in terms of the cost-effectiveness of this practice. Thanks to such advancements, by the 1960s, the desalination industry experienced notable exponential growth, becoming a formidable option to supplement conventional water resources with a reliable non-conventional resource. That said, often, there are pressing associated issues, most notably environmental, socioeconomic, health, and relatively recently, agronomic concerns. Such reservations raise the question of whether desalination is indeed a sustainable solution to current water supply problems. This is exceptionally important to understand in light of the looming water and food crises. This paper, thus, tends to review these potential issues from the sustainability perspective. It is concluded that the aforementioned issues are indeed major concerns, but they can be mitigated by actions that consider the local context. These may be either prophylactic, proactive measures that require careful planning to tailor the situation to best fit a given region or reactive measures such as incorporating pre- (e.g., removing particles, debris, microorganisms, suspended solids, and silt from the intake water prior to the desalination process) and post-treatments (e.g., reintroducing calcium and magnesium ions to water to enhance its quality for irrigation purposes) to target specific shortcomings of desalination.

Desalinated seawater (DSW) can provide water resources for irrigation in coastal regions where freshwater is scarce. Reverse osmosis (RO) is the most common technique to obtain DSW worldwide. Nevertheless, using DSW for irrigation could pose an agronomic risk as RO permeates may have a boron concentration above the phytotoxicity thresholds of certain crops, such as woody crops (0.5 to 1.0 mg/L). In this study, an on-farm ion exchange resin system with an average flow of 1 m³/h, designed to reduce the boron concentration of DSW, was evaluated from a technical and economic perspective. The impact of variations in the feed water and operating temperatures on the boron reduction process was assessed. The results show that the system can provide an outflow with a boron concentration below the threshold of 0.5 mg/L over 92 h of operation, with boron rejections of up to 99% during the first 41 h. The estimated cost of boron removal with the on-farm system of the trial was EUR 0.992/m³. However, this cost is expected to decrease to EUR 0.226/m³ for a commercial ion exchange resin (IX) plant (20 m³/h), highlighting the importance of the scale factor. Our results provide novel guidance on the viability of using boron removal IX systems for farms irrigated with DSW, when it is provided by coastal plants with boron concentrations above the crop tolerance.

Seawater desalination can provide water for irrigation in coastal regions where freshwater resources are scarce. Reverse osmosis (RO) is the most common technique to obtain desalinated seawater (DSW) worldwide. However, using DSW for irrigation may pose an agronomic risk as RO permeates have a boron concentration above the phytotoxicity thresholds of some sensitive crops, such as woody crops (0.5 to 1.0 mg/L). In this study, an on-farm RO system designed to reduce the boron concentration of DSW was evaluated from a technical and economic perspective. The impact of variations in the operating parameters feed water temperature, pressure, and pH, on the boron reduction process was assessed. The results showed that boron rejections close to 99% can be obtained by increasing the feed water pH to 11 with an operating pressure of 10 bar. Looking at the affordability of the system, a total production cost of 1.076 EUR/m³ was estimated for the 1.1 m³/h on-farm system used in the trial. However, this cost is expected to decrease to 0.307 EUR/m³ for a commercial RO plant (42 m³/h), highlighting the importance of the scale factor. Our results provide novel guidance on the feasibility of implementing on-farm boron removal RO systems, when DSW is provided by coastal plants with boron concentrations above the crop tolerance.