Carbon redistribution by erosion processes in an intensively disturbed catchment

29 Pags.- 6 Tabls.- 6 Figs. This article belongs to a special issue of Catena titled "Geoecology in Mediterranean mountain areas. Tribute to Professor José María García Ruiz". The definitive version is available at: http://www.sciencedirect.com/science/journal/03418162Understanding how organic carbon (OC) moves with sediments along the fluvial system is crucial to determining catchment scale carbon budgets and helps the proper management of fragile ecosystems. Especially challenging is the analysis of OC dynamics during fluvial transport in heterogeneous, fragile, and disturbed environments with ephemeral and intense hydrological pulses, typical of Mediterranean conditions. This paper explores the catchment scale OC redistribution by lateral flows in extreme Mediterranean environmental conditions, from a geomorphological perspective. The study area is a catchment (Cárcavo) in SE Spain with a semiarid climate, erodible lithologies, and shallow soils, which is highly disturbed by agricultural terraces, land levelling, reforestation, and construction of check-dams. To increase our understanding of catchment scale OC redistribution induced by erosion, we studied in detail the subcatchments of eight check-dams distributed along the catchments main channel. We determined 137Cs, physicochemical characteristics, and the OC pools of the catchment soils and sediments deposited behind each check-dam, performed spatial analysis of catchment properties and buffer areas around the check-dams, and carried out geomorphological analysis of the slope-channel connections. The soils showed very low total organic carbon (TOC) values, oscillating between 15.2 and 4.4 g kg− 1 for forest and agricultural soils, respectively. Sediments mobilized by erosion were poor in TOC (6.6 ± 0.7 g kg– 1) compared to the eroded (forest) soils, and the redistribution of OC through the catchment, especially of the mineral associated organic carbon (MAC) pool, showed the same pattern as clay particles and 137Cs. The TOC erosion rates estimated for the Cárcavo watershed are relatively low (0.031 ± 0.03 Mg ha− 1 y− 1) but similar to those reported for subhumid Mediterranean catchments that are less fragile and more conducive to plant growth. The TOC erosion/total erosion ratio was lower (0.06%) than other estimates, although the average OC concentration of the sediments was higher than that of the agricultural soils of the catchment, underlining the problem of maintaining sustainable soil OC contents. The OC in deposited sediments came not only from surface erosion processes, but also from deeper soil or sediment layers mobilized by concentrated erosion processes. Sediment richer in OC came from the surface soil of vegetated (reforested) areas close and well connected to the channels. Subcatchments dominated by laminar erosion processes showed a TOC erosion/total erosion ratio that was two times higher than that of subcatchments dominated by concentrated flow erosion processes. The lithology, soils, and geomorphology exert a more important control on OC redistribution than land use and vegetation cover in this geomorphologically very active catchment.This work was financially supported by the projects ADAPT (CGL2013-42009-R) and DISECO (CGL2014-55-405-R) from the Spanish Government, National Plan of Science; the project CAMBIO (18933/JLI/13) of the Seneca Foundation, Regional Government of Murcia (Spain); and the project SOGLO (P7/24 IAP BELSPO) from the Belgian Government. Joris de Vente was supported by a ‘Ramón y Cajal’ grant (RYC-2012-10375).Peer reviewe

Effects of irrigation on water salinization in semi-arid environments. A case study in Las Bardenas, Spain

[ES] Se estudia la exportación de sales y sedimentos en una cuenca de regadío de ambiente semiárido en Bardenas (Zaragoza). Los resultados muestran un incremento de sedimentos en el agua de salida de cuenca respecto a la de entrada, correspondiendo mayoritariamente a sales disueltas y muy poco a material en suspensión. Durante el periodo riego la concentración de sales es más baja que en los días sin riego, debido a una mayor dilución, si bien las pérdidas totales son superiores en fase de riego en relación con un caudal de retorno mucho más elevado.[EN] In this work, we analyse the salt and sediment load from an irrigation area located in a semi-arid environment in the Ebro Valley (Bardenas, Zaragoza). The results show higher solute and sediment load in the waters exiting the irrigation area compared to the inputs waters. Changes in the suspended load are very small, and most of the mercase corresponds to soluble salts. During the period of irrigation, solute concentration is lower than during the non-irrigation periods because of higher dilution. However, the total load output during the irrigation periods is greater because the irrigation flows and returns are also higher.This study has been supported by: Water resources management in a changing envirornnent: the impact of sediment on sustainabilitv” (WARMICE, ENV 4-CT98-0789), (Comisión Europea, Dirección General XII) La identificación de fuentes de sedimento y áreas generadoras de escorrentía en relación con los cambios de uso del suelo” CICYT (REN2000-1709-C04-O1/GLO). La recuperación del espacio agrícola como estrategia de gestión integrada del territorio en áreas de montaña: El ejemplo de los Altos Valles del Aragón y del Gállego” DGA(P049/2000). Los retornos salinos del sistema de riego Bardenas 1 y su contribución a la salirilzación de las aguas superficiales” CICYT (Nat 90-1077 - C02-02). “Impacto ambiental del regadío de Bardenas 1. Fuentes de contaminación y transporte de nutrientes en los efluentes de riego CICYT (HID. 96-1306).Peer reviewe

Variabilidad espacial de la pérdida de solutos en un polígono de regadio de Bardenas durante una campaña de riego

[ES] Se estudia la concentración de solutos en un polígono de regadío de Bardenas durante el verano de 1999. Se señala que el balance de sedimentos es 8,4 veces mayor en el agua de salida de la cuenca que en el de entrada, correspondiendo mayoritariamente a sales disueltas. La distribución espacial de la concentración de solutos muestra dos áreas diferenciadas: En una dominan los iones SO4-2, Ca2+ y Mg2+, mientras que en la otra las concentraciones más altas corresponden a Na+- HCO3 y Cl-. Se discute sobre el papel de los cultivos y de la gestión del riego como fuentes de solutos.[EN] Solute concentration from an irrigated area has been studied during the summer of 1999. Total sediment outputs are 8.4 times greater than inputs, largely corresponding to dissolved salts. The spatial distribution of solute concentration shows two dfferent areas: In the flrst one SO4-2, Ca2+ y Mg2+ ions prevail, while in the second one the highest concentrations correspond to Na+- HCO3 y Cl-. Tbe role of crops and irrigation management is discussed as solute sources.Este trabajo se ha realizado con apoyo del proyecto de investigación: Impacto ambiental del regadío de Bardenas I: Fuentes de contaminación agrícola y transporte de nutrientes en los efluentes de riego, financiado por la CICYT (Proyecto H1D96- 1306).Peer reviewe