Resumen de Effects of reclaimed water irrigation in the soil-plant system of Madrid urban parks
- español
Una de las grandes crisis que debe afrontar la humanidad hoy en día es la escasez de agua que tiene lugar en muchas partes del mundo. El incremento del consumo, unido al descenso en la disponibilidad del recurso son los principales factores que determinan la escasez hídrica. Así pues, el riego con agua regenerada se ha convertido en una práctica habitual a lo largo del planeta, especialmente en aquellas zonas que sufren estrés hídrico, como es el caso de Madrid. Sin embargo, y a pesar de sus grandes ventajas, el riego con agua regenerada, más mineralizada que el agua potable, puede producir efectos adversos en suelos y plantas. Por lo tanto, el objetivo de esta tesis ha sido realizar una evaluación de los efectos que produce el riego con agua regenerada sobre las características del suelo y la vegetación en los parques urbanos de la ciudad de Madrid. Con ese fin se ha llevado a cabo este estudio durante seis años consecutivos (2012-2017), seleccionándose a tal efecto dos parques urbanos de Madrid regados con agua regenerada desde el año 2002 y 2012, respectivamente. Se seleccionaron dos parcelas experimentales en cada parque, una regada con agua regenerada y otra, a modo de control, en la que se mantuvo el riego con agua potable. En cada una de ellas se tomaron periódicamente muestras del agua de riego, del agua del suelo, del suelo y de cuatro especies representativas de vegetación. Los resultados obtenidos han mostrado que el agua regenerada de Madrid es adecuada para el riego conforme a los parámetros internacionales de calidad del agua de riego. Sin embargo, el uso de agua regenerada para el riego de parques urbanos puede conducir potencialmente a una modificación de las propiedades fisicoquímicas del suelo. Así, se ha observado una ligera salinización del suelo tras quince años de riego con agua regenerada en uno de los parques. También se ha producido un aumento constante del Cl¿, Na+, SAR y de la conductividad eléctrica de los suelos regados con agua regenerada durante cinco años, mientras que, en las parcelas regadas con agua potable, se han obtenido unos valores significativamente inferiores para estos mismos parámetros. Asimismo, se ha producido un incremento en la estabilidad de los microagregados en superficie, a la vez que la estabilidad de los macroagregados disminuyó en la capa más superficial y en la más profunda. La resistencia a la penetración del suelo ha resultado significativamente mayor y la tasa de infiltración menor en la parcela regada con agua regenerada. Por otra parte, los resultados relativos a la porosidad del suelo no han mostrado ninguna influencia del tipo de agua de riego utilizada. Tampoco se ha observado sodificación del suelo en las parcelas regadas con agua regenerada y la concentración de micronutrientes ha sido inferior que la descrita en otros estudios con este tipo de riego en parques urbanos.En cuanto a la vegetación, se han obtenido valores porcentuales significativamente superiores de Cl y Na en las hojas de algunas especies regadas con agua regenerada frente a las regadas con agua potable. En general, la concentración de sales y de micronutrientes en las hojas se ha situado en la mayoría de casos por debajo del umbral en el que las plantas empiezan a mostrar daños. El riego con agua regenerada ha producido un incremento de la biomasa herbácea y ha contribuido también al significativo aumento en la eliminación de nutrientes por parte de la cubierta herbácea.
- English
Water scarcity in many regions of the world is one of the greatest crises that mankind needs to address. The steady increase of water consumption and the decrease of available water resources are the main factors that determine it. This scenario leads to a paradigm shift: circular economy, where waste will become resources. Therefore, water reuse plays a fundamental role in circular economy.
Reclaimed water irrigation has become a long-standing practice over the world, especially among water deficit areas such as Spain. One of the first cities in Spain that started using reclaimed water to irrigate its urban parks was Madrid. Since the beginning of the 2000s, the City Council has developed a vast system of pipes and deposits to irrigate most of its parks with reclaimed water. Despite its great advantages, water reuse could involve some risks. Reclaimed water irrigation, more mineralized than drinking water, may produce adverse effects in soils and plants, including the presence of pathogens and chemical contaminants as well as salinization, impacts on soil structure and effects on vegetation. Therefore, the main objective of this Doctoral Dissertation was to assess the effects of reclaimed water irrigation in the soil-plant system of urban parks of Madrid (Spain). To that end, this research was carried out along six successive years (2012–2017) in two public urban parks of Madrid: Emperatriz María de Austria Park and Garrigues Walker Park. Both were irrigated with reclaimed water since 2002 and 2012, respectively. Furthermore, two plots from each park were irrigated with reclaimed water (RW) and two other plots with drinking water (DW). Samples of irrigation water, soil solution, soil and leaves of four plant species –cedar, grass, hackberry and Photinia– were taken for further analysis. Results achieved showed that reclaimed water of Madrid was adequate for irrigation according to international water quality standards. However, the use of reclaimed water to irrigate urban parks was potentially leading to a modification of some soil properties. The park which has been irrigated with reclaimed water for 15 years showed a slight soil salinization (EC > 2 dS m-1 ). Furthermore, there was a steady increase of Cl− (157%), Na+ (180%), SAR (127%) and EC (69%) in soils that were irrigated for 5 years with reclaimed water. Whereas in plots irrigated with drinking water significant lower values (p < 0.05) for these parameters were observed. Likewise, it caused an increase of microaggregate stability in the topsoil, while macroaggregate stability decreased after RW irrigation in the top and the deepest layer. Soil penetration resistance was significantly higher (p < 0.05) and infiltration rate was lower in the RW plot. On the other hand, soil porosity results showed that there was no influence of the kind of irrigation water used. Furthermore, there was no soil sodification in RW plots and lower values of micronutrient concentration in soils were obtained when compared with other studies on reclaimed water irrigation in urban parks. Regarding vegetation, Cl (%) leaf content was significantly higher (p < 0.05) in those hackberries and Photinias irrigated with RW in comparison with those irrigated with DW. However, for Na (%) leaf content, there were only significant differences for cedars irrigated with RW versus DW in PGW. In most of the cases salt concentration in leaves were below the threshold when plants start to show injuries. Thus, no major salt stress symptoms were observed. Likewise, foliar micronutrient content of cedar leaves was nearly always within the optimum parameters. The statistical analysis carried out showed no correlation between micronutrient concentration in irrigation water and cedar leaves, thus cedar decline cannot be attributed to the input of these micronutrients by reclaimed water. Moreover, irrigation with reclaimed water led to a grass biomass increase (on average of 66%), mainly due to the high proportion of nutrients received through the irrigation water, which acted as a fertilizer. Reclaimed water irrigation also contributed to a significant increase in nutrient removal by grass. In conclusion, prolonged reclaimed water irrigation may be altering the features of the soilplant system of urban parks. For that reason, and in order to avoid future problems, the use of reclaimed water in urban parks irrigation should be continuously monitored. One of the recommended measures proposed is to use an adequate leaching requirement (10%) in order to wash out the excessive salt accumulation in parks irrigated with reclaimed water.
Eventually, the transfer of these research results to municipal managers may contribute to a better management of reclaimed water irrigation in urban parks, with the aim to prevent the likely appearance of adverse symptoms on sensitive plants.
