Regresar

Assessment of a newly implemented irrigated area (Lerma Basin, Spain) over a 10-year period. II: Salts and nitrate exported

Abstract:

Irrigated agriculture impacts the quality of water bodies receiving irrigation return flows. The leaching of salts and nitrate from Lerma Basin (7.38km2), a newly-implemented pressurized irrigated area in the Ebro Basin (Spain), was assessed in this study for the hydrological years 2004-2013, covering years before (2004-2005), during (2006-2008) and after (2009-2013) the implementation of irrigation. The concentration of salts and nitrate were measured for all the components of the water balance and the amounts of these pollutants coming from the irrigated surface (352ha) were estimated. Besides, salt and nitrate contamination indices were computed. Under unirrigated conditions, the studied area exported 1.89Mgha-1year-1 and 11.4kgha-1year-1 of salts and nitrate-nitrogen, respectively. These amounts increased to 3.51Mgha-1year-1 for salts and 30.8kgha-1year-1 for nitrate-nitrogen after the implementation of irrigation. Salt and nitrate contamination indices (SCI and NCI, respectively) increased by a factor of three from unirrigated to irrigated conditions, reaching values of 0.96[Mgha-1year-1]/[dSm-1] and 0.12, respectively. Despite these values being well under the threshold considered for more sustainable irrigated areas (SCI<2.0[Mgha-1year-1]/[dSm-1] and NCI<0.2), it would be advisable to improve irrigation management to increase water use and decrease leaching. Complementary measures such as adjusting fertilization rates to temporal crop necessities or the use of catch crops may prove to be useful.