Erosion and sedimentation on an abandoned terraced and gullied hillslope

Abandonment of agricultural terraces is one of the main drivers of erosion processes and land degradation in semiarid environments. Soil erosion is a complex process and it is difficult to capture erosion rates including the different phases of the erosion process, depending on the spatio-temporal scale of observation. In this work erosion processes were studied in a small abandoned cascade terraced system in SE Spain regarding its sedimentation rate. Here agriculture practices included plastic covers and the activities were abandoned 18 years before the field study. The objectives were to determine erosion and sedimentation rates in the system and explore the relationships between erosion vulnerability and soil physicochemical properties of the parent material. The methodological approach included the study of erosion features such as rilling, gullying, and piping. A budget per terrace was estimated, using dGPS surface height measurements, drone images and derived terrain modeling, detailed sampling, and GIS techniques; and the determination of material properties such as structural stability, slaking, bulk density, soil organic matter, pH, electrical conductivity, gypsum, carbonate content, and SAR. The results show that gullying and piping result in high detachment rates (5.5–38.9 ton Ha−1 ·yr−1), but deposition was found to be at least as important or larger than detachment for several terraces (31.7–130.4 ton Ha−1 yr−1). Even though not a full exploration of all components of the sediment budget could be done, the ‘on terrace’ sedimentation rates were high. This means that just mapping gullying or erosional features as indicators for degradation rates can be misleading. Additional information on temporary sedimentation is also crucial to get reliable erosion models, especially at finer spatial scales. Furthermore, this also demonstrates that leveling and abandonment of fields on dispersive substrates accelerates land degradation and that leaving the plastic on the fields also has negative environmental impacts concerning erosion

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

Finding common grounds for conflict resolution through value analysis of stakeholders around the socio-ecological crisis of the Mar Menor coastal lagoon (Spain)

Aligning with people’s values in landscape political decisions can help to minimise conflicts between stakeholders and support social acceptability of solutions for systemic transitions. This paper explores how shared and diverging values of the main stakeholders involved in socio-ecological crises, and the co-creation of solutions, can be key for finding common grounds for conflict resolution and sustainable socio-ecosystems management. These concepts were applied by a participatory process to identify and select solutions for the environmental and socio-economic crisis of the Mar Menor coastal lagoon and its watershed (SE Spain). With information from six sectorial workshops and one multisector workshop, a stakeholder analysis based on values and initiatives was performed. The results indicate that all the stakeholder groups prioritised transition to governance, economic and educational models that respect nature and cultural landscapes, with values aligning with the population’s identity and their livelihoods. The values and solutions linked with stakeholders ‘Farmers’, which representedCOASTAL 773782 (H2020 European Commission)AGRI_SER PID2020-119825RB-I00 (Spanish Ministry of Science and Innovation)AGROALNEXT (PRTR-C17.I1)THINKINAZUL (C17.I01) from the Spanish Ministry of Science and InnovationEuropean Union NextGenerationEUFundación S´eneca (Region of Murcia)María Zambrano postdoctoral grant by the Spanish Ministry of Universitie

Using soil organic matter fractions as indicators of soil physical quality

The objective of this study was to evaluate the use of chemical and physical fractions of soil organic matter (SOM), rather than SOM per se, as indicators of soil physical quality (SPQ) based on their effect on aggregate stability (AS). Chemically extracted humic and fulvic acids (HA and FA) were used as chemical fractions, and heavy and light fractions (HF and LF) obtained by density separation as physical fractions. The analyses were conducted on medium-textured soils from tropical and temperate regions under cropland and pasture. Results show that soil organic carbon (SOC), SOM fractions and AS appear to be affected by land use regardless of the origin of the soils. A general separation of structurally stable and unstable soils between samples of large and small SOC content, respectively, was observed. SOM fractions did not show a better relationship with AS than SOC per se. In both geographical regions, soils under cropland showed the smallest content of SOC, HA and carbon concentration in LF and HF, and the largest HF/LF ratio (proportion of the HF and LF in percent by mass of bulk soil). With significant associations between AS and SOC content (0.79**), FA/SOC (r = -0.83**), HA/FA (r = 0.58**), carbon concentration of LF (r = 0.69**) and HF (r = 0.70**) and HF/LF ratio (r = 0.80**), cropland showed lowest AS. These associations indicate that SOM fractions provide information about differences in SOM quality in relation to AS and SPQ of soils from tropical and temperate regions under cropland and pasture

Fluvial geomorphological dynamics and land use changes: impact on the organic carbon stocks of soil and sediment

The drainage basin of the Turrilla river (SE of Spain) went through important land cover changes since 1950s; from mainly an agrarian scenario in 1956 to other depopulated and forested in 2015. This study analyzes the effects of land use changes on fluvial dynamics and their relationship with the organic carbon (OC) stock in fluvial sedimentary deposits as well as in the soil of the basin. Methods included a fluvial geomorphological analysis and a land use change analysis in combination with OC databases of soil and sediment. Results showed that the fluvial channel experienced important morphological changes related to different erosion processes and stabilization of fluvial deposits, induced by land use changes in the drainage area. The active channel decreased 63% in the study period, while bank erosion and gully erosion increased (34% and 21 %, respectively). Alluvial fans and alluvial plain were also extended (21% and 7 %, respectively) and alluvial bars were colonized by vegetation. Sediment was impoverished in OC compared to catchment soils (0.24 enrichment ratio sediment/soil). However the increase of OC stock (Mg ha-1) was very similar between soil (25 %) and sediment (23 %). The total reservoir of OC (Mg) increased 27% in sediments and 25% in the catchment soils. Results show the large influence of geomorphological dynamics on the OC reservoir at the catchment scale. A very high potential of fluvial sediments to increase OC sinks was observed, particularly in scenarios where the active channel is narrowed and the fluvial channel is encroached with vegetation, facilitating the input of OC in sediment. The potential of sediment to sequester organic carbon could be very useful in planning and management of fluvial sedimentary zones in climate change mitigation policies. © 2019, Universidad Austral de Chile. All rights reserved.Este estudio ha recibido apoyo financiero del proyecto DISECO (CGL2014-55405-R) del Plan Nacional de Ciencia del Ministerio de Economía y Competitividad de España, del proyecto SOGLO (P7/24 IAP BELSPO) del gobierno de Bélgica. AHM recibió apoyo financiero para una estancia en la Universidad Nacional de Córdoba (Argentina) del Banco de Santander mediante el Convenio Becas de Intercambio Latinoamérica (Programa ILA). CBF recibió apoyo financiero para dos estancias en el extranjero del programa Salvador de Madariaga 2017 (Ministerio de Educación, Cultura y Deporte, Gobierno de España) y del programa Jiménez de la Espada 2017 (Fundación Séneca, Agencia de Ciencia y Tecnología de la Región de Murcia). MAB fue parcialmente financiada por un contrato Juan de la Cierva-Incorporación (Ref: IJCI-2015-23500). Todas estas estancias permitieron el trabajo continuado en la redacción de este artículo

Eco-geomorphological connectivity and coupling interactions at hillslope scale in drylands: Concepts and critical examples

The diagnosis of land degradation requires a deep understanding of ecosystem functioning and evolution. In dryland systems, in particular, research efforts must address the redistribution of scarce resources for vegetation, in a context of high spatial heterogeneity and non-linear response. This fact explains the prevalence of eco-hydrological perspectives interested in runoff processes and, the more recent, focused on connectivity as an indicator of system resource optimisation. From a geomorphological perspective and reviewing the concepts of eco-hydro-geomorphological interactions operating in ecosystems, this paper explores the effects of erosion on vegetation configuration through two case studies at different spatio-temporal scales. We focus on the structure-function linkage, specifically on how morphological traits relate with different stages in the erosional sequence, both in the abiotic and the biotic domain. Results suggest that vegetation dynamics are affected by structural boundary conditions at both scales, i.e. by surface armouring related with rock fragments at the patch scale, and by the degree of hillslope-channel coupling at the hillslope scale. Our preliminary results can serve as new working hypotheses about the structure-function interplay on hillslopes. All this, taking advantage of the recent technological achievements for acquiring very high-resolution geospatial data that offer new analytical possibilities in a range of scales

The combination of crop diversification and no tillage enhances key soil quality parameters related to soil functioning without compromising crop yields in a low-input rainfed almond orchard under semiarid Mediterranean conditions

Soils provide key ecosystem services and are crucial to combat climate change. Agriculture provides important ecosystem services but also causes negative environmental effects depending on agricultural management. In this regard, crop diversification is a promising sustainable land management strategy to combat soil erosion and degradation, mitigate climate change and ensure food security. Here, we assess the combined short-term effects of crop diversification and no tillage on several key soil physico-chemical parameters related to soil functioning as well as on crop yields in a rainfed almond (Prunus dulcis Mill.) orchard under semiarid Mediterranean conditions. Almond trees were inter-cropped with Capparis spinosa L. (caper) or Thymus hyemalis Lange (winter thyme) and compared with the almond monocrop system. The experimental design consisted of three plots in a randomized-block design, with three replicates for each crop management treatment (almond monocrop, almond inter-cropped with caper, and almond inter-cropped with winter thyme). Along with crop yields, the combined effects of crop diversification and no tillage on a range of soil quality and health indicators including soil physical (bulk density, aggregate stability, water retention and availability) and chemical (total and particulate organic carbon and nitrogen, ammonium and nitrate content, available macro- and micro-nutrients) properties were monitored in the topsoil and subsoil (at 0–10 and 10–30 cm depth, respectively) one and three years from establishment.EEA Delta del ParanáFil: Almagro, María. Consejo Superior de Investigaciones Científicas (CSIC). Centro de Edafología y Biología Aplicada del Segura; EspañaFil: Díaz-Pereira, Elvira. Consejo Superior de Investigaciones Científicas (CSIC). Centro de Edafología y Biología Aplicada del Segura; EspañaFil: Boix-Fayos, Carolina. Consejo Superior de Investigaciones Científicas (CSIC). Centro de Edafología y Biología Aplicada del Segura; EspañaFil: Zornoza, Raúl. Universidad Politécnica de Cartagena. Departamento de Ingeniería Agronómica; EspañaFil: Sánchez-Navarro, Virginia. Universidad Politécnica de Cartagena. Departamento de Ingeniería Agronómica; EspañaFil: Re, Paula. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Delta del Paraná; ArgentinaFil: Re, Paula. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Fernández, Cristina. Consejo Superior de Investigaciones Científicas (CSIC). Centro de Edafología y Biología Aplicada del Segura; EspañaFil: Martínez-Mena, María. Consejo Superior de Investigaciones Científicas (CSIC). Centro de Edafología y Biología Aplicada del Segura; Españ

Long-term effectiveness of sustainable land management practices to control runoff, soil erosion, and nutrient loss and the role of rainfall intensity in Mediterranean rainfed agroecosystems

Mediterranean environments are especially susceptible to soil erosion and to inappropriate soil management, leading to accelerated soil loss. Sustainable Land Management (SLM) practices (such as reduced tillage, no-tillage, cover crops, etc.,) have the potential to reduce soil, organic carbon (OC), and nutrient losses by erosion. However, the effectivity of these practices is site-dependent and varies under different rainfall conditions. The objective of this paper was to evaluate the effects of SLM practices in two rainfed systems (a wheat field and an almond orchard) representative of a large area of the driest Mediterranean regions - on runoff, soil erosion, particle size distribution, and OC and nutrient (N and P) contents in sediments. The influence of the rainfall characteristics on the effectiveness of the SLM practices was also evaluated. The SLM implemented were: reduced tillage (RT) in the wheat field and almond orchard and reduced tillage combined with green manure (RTG) in the almond orchard; these were compared to conventional tillage, the usual practice in the area. Open erosion plots were set up to monitor the effects of SLM on soil carbon and nutrients and on soil erosion after each rainfall event over six years (2010 2016). The results show that the SLM practices evaluated resulted in increased organic carbon (OC) and nutrients (N and P) contents in the soil, and reduced runoff, erosion, and mobilization of organic carbon and nutrients in sediments. Reductions in runoff of 30% and 65% and decreases in erosion of 65 and 85% were found in the wheat field and almond orchards, respectively. In addition, the total OC, N, and P losses in the wheat field were reduced by 56%, 45%, and 64%, respectively, while in the almond field the OC, N, and P losses were reduced by 90% under RT and by 85% under RTG. The beneficial effect of the SLM practices on soil erosion was observed within 18 months of their implementation and continued throughout the six years of the study. Furthermore, the effectiveness of tillage reduction with respect to erosion control and carbon and nutrients mobilization was highest during the most intense rainfall events, which are responsible for the highest erosion rates in Mediterranean areas. Our results support the key role of SLM practices under semiarid conditions as useful tools for climate change mitigation and adaptation, given the expected increase in high-intensity rainfall events in semiarid areas. © 2019 The AuthorsThis study site has been funded by several national (CYCIT AGL201125069//CICYT AGL2010-20941//CGL2013-42009-R//CGL2014-55-405-R), Regional (Séneca Foundation: 08757/PI/08//19350/PI/14), and European Commission H2020 (F6 DG RTD 037046 and Grant 728003, DIVERFARMING projects). Joris de Vente acknowledges support from a Ramón y Cajal research grant (RYC-2012-10375) and María Almagro was supported by the Juan de la Cierva Program (IJCI-2015-23500)

Movilización de carbono orgánico por distintos procesos erosivos en la conexión ladera-cauce

With the purpose of analysing the type (labile or stable) and quantity of organic carbon (OC) mobilized by different erosive processes identified at the slope-bed connection, the erosion deposits of gullies, sheet erosion, bank erosion and tillage erosion were studied in a small catchment (10 ha) and compared to the characteristics of the catchment soils. Selectivity upon soil detachment and transport was associated to different OC content and types in the erosion deposits. Enrichment ratios of organic carbon sediment/soil were low (~0,40 ± 0,26), even though a slight enrichment was described for fine particles (positively correlated to CO). These results were attributed to mineralization processes prevailing over OC burial in a very active channel where depositional sites are scarce.Con el fin de caracterizar la cantidad y tipo (lábil o recalcitrante) de carbono orgánico (CO) movilizado por distintos procesos erosivos identificados en las conexiones ladera-cauce, se estudiaron las características de los depósitos de erosión concentrada en cárcavas, erosión hídrica laminar, erosión lateral-gravitacional y erosión por laboreo en el contacto ladera-cauce de una cuenca de pequeño tamaño (10 ha) y se relacionaron con las características de los suelos-fuentes originales de donde procedían. La selectividad en el arranque y transporte de suelo de los distintos procesos se pudo asociar a diferentes contenidos y tipos de CO en los depósitos. Las razones de enriquecimiento de carbono orgánico sedimento/suelo fueron bajas (~0,40 ± 0,26), a pesar de haber un ligero enriquecimiento en partículas finas (correlacionadas positivamente con el CO) en los depósitos. Todo ello se atribuyó a los efectos de la mineralización en un cauce muy activo con pocas zonas de deposición y abundantes procesos de erosión no selectiva

Perennial alley cropping contributes to decrease soil CO2 and N2O emissions and increase soil carbon sequestration in a Mediterranean almond orchard

The implementation of alley cropping in orchards can be a sustainable strategy to increase farm productivity by crop diversification and contribute to climate change mitigation. In this research, we evaluated the short-term effect of alley cropping with reduced tillage on soil CO2 and N2O emissions and soil total organic carbon (TOC) in an almond orchard under Mediterranean rainfed conditions. We compared an almond monoculture with tillage in all plot surface (MC) with almond crop with reduced tillage and growth of Capparis spinosa (D1) and almond crop with reduced tillage and growth of Thymus hyemalis (D2). For two years, soil CO2 and N2O were measured, with soil sampling at the start and end of the experimental period. Results showed that CO2 emission rates followed the soil temperature pattern, while N2O emissions were not correlated with temperature nor moisture. Soil CO2 emissions were significantly higher in MC (87 mg m−2 h−1), with no significant differences between D1 and D2 (69 mg m−2 h−1). Some peaks in CO2 effluxes were observed after tillage operations during warm days. Soil N2O emission rates were not significantly different among treatments. Cumulative CO2 and CO2 equivalent (CO2e) emissions were significantly highest in MC. When CO2e emissions were expressed on a crop production basis, D2 showed the significantly lowest values (5080 g kg−1) compared to D1 (50,419 g kg−1) and MC (87,836 g kg−1), owing to the high thyme yield, additional to the almond yield. No production was obtained for C. spinosa, since at least two more years are required. TOC did not change with time in MC neither D1, but it significantly increased in D2 from 3.85 g kg−1 in 2019 to 4.62 g kg−1 in 2021. Thus, alley cropping can contribute to increase the agroecosystem productivity and reduce CO2 emissions. However, it is necessary to grow evergreen alley crops such as thyme to obtain short-term increases in soil organic matter. Thus, to estimate increases in TOC with alley cropping, the plantation density and the period required by the crop to cover most of the surface are essential factors at planning the cropping strategy.This work was supported by the European Commission Horizon 2020 project Diverfarming [grant agreement 728003]