Search

Abstract Dissolved solids (DS) and suspended sediment (SS) loads are considered relevant environmental problems. They are related to a wide range of on-site and off-site impacts, such as soil erosion or salinization of water bodies. In this study, the dynamics of DS and SS concentrations and loads were assessed in five small watersheds covering representative agricultural land uses in Navarre (Spain). To this end, discharge, DS and SS concentration data were collected during ten hydrological years at each watershed outlet, and loads were computed from discharge and concentration values. DS concentration followed a seasonal pattern imposed by the availability of water, with higher concentrations recorded in low-flow periods and lower concentration in the high-flow period. SS concentration was extremely variable, with a range of 2–4 orders of magnitude in concentration for any specific discharge. Temporal variations (both intra- and inter-annual) in DS loads were explained by differences in runoff, whereas those of SS were not, being the SS loads associated mainly with specific high flow events. These temporal patterns were observed for both agricultural (this study) and non-agricultural (literature) watersheds. From the data in the Navarrese watersheds and those available in the literature, we inferred that agricultural land use, in general, tends to increase the concentration of both DS and SS. Regarding DS and SS yields, the effects of agricultural land use on DS yields are controlled by the changes in runoff rather than the (small) changes in DS concentration. In this sense, land uses changes expected to increase runoff (i.e., a shift from forested to arable or from rainfed to irrigated agriculture) would increase DS yields. On the other hand, agricultural land use tends to increase SS yields, although the effect is highly variable depending on site-specific factors, both natural (e.g., watershed shape) and anthropogenic (e.g., degree of soil conservation practices). In the Navarrese watersheds, DS yields ranged from 1.1 to 2.2 Mg ha−1 year−1 whereas SS yields ranged from 0.3 to 4.3 Mg ha−1 year−1. DS yields seem to dominate under non-agricultural conditions and in most agricultural land uses at the small watershed scale. On the other hand, SS yields dominate in watersheds with increased soil erosion as a consequence of arable land use over erosion-prone watersheds. Highlights • Dissolved solids concentration follows a seasonal pattern. • Suspended sediment concentration was extremely variable. • Dissolved loads behave conservatively with water. • The dissolved load dominated the exportation in most of the cases. • Agricultural land use increases suspended sediment concentration and loads. [ABSTRACT FROM AUTHOR]

Implementation of irrigated agriculture is common in semi-arid areas around the world. An assessment of irrigation performance is presented herein for a hydrological basin with an area of 7.38 km 2 , representative of pressurized irrigated areas within the Ebro Basin (Spain). The study covers ten hydrological years, comprehending periods before (2004–2005), during (2006–2008) and after (2009–2013) transformation to irrigated land. Water balances were carried out for each of the 55 agricultural plots and for the totality of irrigable area. Once the water balance for the basin is validated, indicators of irrigation performance were obtained from the soil water balances for the vegetative cycle of the crops in each plot. Water balances presented good results, with balance errors below 10.0% for most of the studied years and an error of 1.2% across the entire study period. After implementation of irrigation, irrigation became the main water input to the basin (approximately 60%) whereas actual evapotranspiration accounted for the major output (approximately 70%). Irrigation efficiency reached 76.1%, while the losses of efficiency were due to evaporation and wind drift of sprinkler irrigation (13.5%) and drainage fraction (10.4%). A water deficit of 17.8% was estimated. The irrigation efficiency increased (1.05% year −1 ), while the irrigation drainage fraction decreased (0.95% year −1 ). However, improvements in irrigation performance were not guaranteed as water deficits also increased (0.95% year −1 ). Optimal water use could be achieved through adequate design of irrigation schedules, i.e., irrigation rates adjusted to the requirements of crops and minimization of evaporation and wind drift losses. [ABSTRACT FROM AUTHOR]

Irrigation practice has increased considerably recently and will continue to increase to feed a growing population and provide better life standards worldwide. Numerous studies deal with the hydrological impacts of irrigation, but little is known about the temporal evolution of the affected variables. This work assesses the effects on a gully after irrigation was implemented in its hydrological basin (7.38 km2). Flow, electrical conductivity, nitrate concentration and exported loads of salts and nitrates were recorded in Lerma gully (Zaragoza, Spain) for eight hydrological years (2004–2011), covering the periods before, during and after implementation of irrigation. Non-parametric statistical analysis was applied to understand relationships and trends. The results showed the correlation of irrigation with flow and the load of salts and nitrates exported, although no significant relationship with precipitation was detected. The implementation of irrigation introduced annual trends in flow (3.2 L s-1, +23%), salinity (–0.38 mS cm-1, –9%), and nitrate concentration (5.4 mg L-1, +8%) in the gully. In addition, the annual loads of contaminants exported increased (salts and nitrates, 27.3 Mg km-2year-1, +19%, and 263 kg NO3–-N km-2year-1, +27%, respectively). The trends presented a strong seasonal pattern, with higher and more significant trends for the irrigation season. The changes observed were different from those of larger irrigation districts or regional basins, due to the differences in land use and irrigation management. It is important to understand these changes in order to achieve an adequate management of the environment and water resources. EditorZ.W. Kundzewicz CitationMerchán, D., Causapé, J., and Abrahão, R., 2013. Impact of irrigation implementation on hydrology and water quality in a small agricultural basin in Spain.Hydrological Sciences Journal, 58 (7), 1400–1413. [ABSTRACT FROM AUTHOR]

Copyright of Cuadernos de Investigación Geográfica is the property of Universidad de la Rioja, Servicio de Publicaciones and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)