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The study of fluvial network rearrangement provides a key to understand past and future landscape evolution. Large perturbations of hydrographic basins such as the change from endorheism to exorheism have repercussions in the steady or disequilibrium state of the basins and their drainage divides. Such transitions from internal to external drainage imply a major lowering of the geomorphological base level causing a major retreating knickpoint wave that separates the upstream low-relief area (inherited from the endorheic period) from the downstream incised area. Subsequently, the water divide migrates to reach an equilibrium in which erosion rates at both sides of the divide are similar. Previous fluvial analyses suggest that both the Duero and Ebro drainage networks, the two largest catchments in Iberia, experienced a change from endorheism to exorheism sometime between the Late Miocene and the Pliocene. Fluvial capture evidence argues for a Pliocene westward migration of the Ebro-Duero divide implying an area decrease for the Duero fluvial network (victim) in favor of the Ebro (aggressor). We used river profiles, knickpoint distribution and Chi-map calculation to understand the different degree of erosion of the Duero and the Ebro catchments and the dynamics of their drainage network. The results show an equilibrated Ebro drainage network in contrast with a disequilibrium in the erosional state of the Duero drainage, which remains reorganizing and adapting to the newly-imposed Atlantic base level. We identified at least two knickpoint wave trains in the Duero drainage resulting from the onset of exorheism: a fast-propagating wave through the cover and a low-propagating wave affecting the bedrock. Field evidence and topographic analysis suggest a westward migration of the Ebro-Duero divide, resulting in an ongoing headward erosion of the Ebro against the Duero catchment. Chi analysis provides the degree of disequilibrium of the drainage network indicating a large-sc

In arid lands, irrigation is necessary for agriculture to be profitable. However, the nature of soils and parent materials is significant enough to trigger permanent management limitations and the loss of important investments, as happened in some areas of the Flumen irrigation district in the Central Ebro Basin, NE Spain. We studied the distinct soil characteristics of a salt-affected agricultural plot and its recurrent problems from the last 30 years. We describe and discuss the prominent features of this soil and their effects on plant life and agricultural management. The evidence of post-irrigation salt-related effects is documented together with the water and soil salinity monitoring records. The presence of varved Holocene sediments comprising alternating clays and carbonate-rich silt with high levels of salinity and sodicity, together with a shallow saline water table, were found to be the key unfavorable conditions. Despite a noticeable decrease in sodium adsorption ratio (SAR) from 1999 to 2015 and a reduction in soil salinity down to a steady state after rice paddy cultivation, SAR and alkalinity remained high enough to hamper irrigated agriculture. Only the native plant Puccinellia festuciformis thrives in the studied plot. The article presents and discusses chemical features―analytical data―and morphological features―pictures and descriptions―that are seldom reported and interpreted together in the scientific or technical literature about irrigation of sodic soils, often limited to chem data. The paddy field studied is deemed representative of the most unfavorable soils for agriculture in the irrigated districts of the Ebro valley.

River incision into bedrock resulting from the combined effects of tectonic uplift and climate governs long-term regional landscape evolution. We determined spatial and temporal patterns of post-orogenic stream incision from a sequence of well-preserved staircase terraces developed over the last 1 Ma in the Central Pyrenees and its southern foreland Ebro basin (NE Spain). Extensive remnants of ten vertically separated terraces (Qt1 to Qt10, from oldest to youngest) were mapped along 170 km of the Cinca River valley, transverse to the Pyrenean mountain belt. Multiple outcrops appear in the upper reach of the valley (Ainsa sector, 50 km from headwaters) as well as in the lower reach (Albalate sector, 125 km from headwaters). Fluvial incision into bedrock was calculated using (i) differentially corrected GPS measurements of the altitude of straths and (ii) numerical dating of alluvial sediments from the lower terraces (Qt5 to Qt9) by Optically Stimulated Luminescence, previously reported by Lewis et al. (2009), and supplemented with new dates for the upper terraces (Qt1, Qt2 and Qt3) based on paleomagnetism and supported by soil development. Considering altitude differences and the elapsed time between successive well preserved terrace couples (Qt3–Qt7, Qt7–Qt9 and Qt9-Active channel), mean bedrock incision rates ranged from 0.76 to 0.38 m ka− 1, at the upper reach of the valley (Ainsa section), and from 0.61 to 0.20 m ka− 1, at the lower reach (Albalate section). River incision along the valley produced vertically separated, near-parallel longitudinal terrace profiles evidencing a rapid near-uniform regional uplift as response to (i) the tectonic lithospheric thickening in NE Iberia and (ii) the erosional download rebound related to the Ebro basin exorheism. Moreover, a subtle upstream divergence of strath profiles may have been a consequence of an increase in uplift rate toward the head of the valley. Additionally, incision rates changed over time as indicate results

In this study, 50 pesticides were analyzed in the Ebro River basin in 2010 and 2011 to assess their impact in water, sediment and biota. A special emphasis was placed on the potential effects of both, individual pesticides and their mixtures, in three trophic levels (algae, daphnia and fish) using Risk Quotients (RQs) and Toxic Units (TUs) for water and sediments. Chlorpyrifos, diazinon and carbendazim were the most frequent in water (95, 95 and 70% of the samples, respectively). Imazalil (409.73 ng/L) and diuron (150 ng/L) were at the highest concentrations. Sediment and biota were less contaminated. Chlorpyrifos, diazinon and diclofenthion were the most frequent in sediments (82, 45 and 21% of the samples, respectively). The only pesticide detected in biota was chlorpyrifos (up to 840.2 ng g−1). Ecotoxicological risk assessment through RQs showed that organophosphorus and azol presented high risk for algae; organophosphorus, benzimidazoles, carbamates, juvenile hormone mimic and other pesticides for daphnia, and organophosphorus, azol and juvenile hormone mimics for fish. The sum TUsite for water and sediments showed values < 1 for the three bioassays. In both matrices, daphnia and fish were more sensitive to the mixture of pesticide residues present.

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula. Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.

In this study we analyzed the response of monthly runoff to precedent climatic conditions at temporal scales of 1–48 months in 88 catchments of the Ebro basin (northeast Spain). The standardized precipitation evapotranspiration index (SPEI) was used to summarize the climatic conditions at different time scales, and was correlated with the standardized streamflow index (SSI) calculated at the mouth of each catchment. The Ebro basin encompasses a gradient from Atlantic to Mediterranean climates, and has remarkable complexity in topography, geology and land cover. The basin is highly regulated by dams, which were built to produce hydropower and supply water for agriculture. These characteristics explain why sub-basins of the Ebro River basin respond in differing ways to precedent climatic conditions. Three main sub-basin groups were distinguished on the basis of the correlation of their streamflow responses to different time scales of the SPEI: (1) sub-basins correlated with short SPEI time scales (2–4 months), which generally corresponded to unregulated headwater areas; (2) sub-basins correlated with long SPEI time scales (10–20 months), where groundwater reserves play a major hydrological role; and (3) sub-basins correlated with medium SPEI time scales (6–10 months). The latter occur in the lower sectors of the Ebro basin and its tributaries, which receive river flows from the other two sub-basins, and where dam regulation has a significant influence on the hydrological characteristics. In addition to the three main sub-basin groups, other streamflow responses associated with seasonal factors were identified, particularly those related to snowpack and the various management strategies applied to reservoirs.

Among the major factors controlling soil erosion, as vegetation cover or soil erodibility, rainfall erosivity has a paramount importance since it is difficult to predict and control by humans. Accurate estimation of rainfall erosivity requires continuous rainfall data; however, such data rarely demonstrate good spatial and temporal coverage. Daily weather records are now commonly available, providing good coverage that better represents rainfall intensity behavior than do more aggregated rainfall data. In the present study annual rainfall erosivity was estimated from daily rainfall records, and compared to data obtained employing the RUSLE R factor procedure. A spatially-dense precipitation database of high temporal resolution (15 min) was used. Two methodologies were applied: (i) daily rainfall erosivity estimated using several parametric models, and, (ii) annual rainfall erosivity estimated by regression-based techniques employing several intensity precipitation indices and the modified Fournier index. To determine the accuracy of estimates, several goodness-of-fit and error statistics were computed in addition to a spatial distribution comparison. The daily rainfall erosivity models accurately predicted annual rainfall erosivity. Parametric models with few combined parameters and a periodic function simulating intra-annual rainfall behavior provided the best results. Where daily rainfall records were not available, good estimates of annual rainfall erosivity were also obtained using regression-based techniques based on 5-day maximum precipitation events, the maximum wet spell duration, and the ratio between the lengths of average wet and dry spells. Inherent limitations remain in the use of daily weather records for estimating rainfall erosivity. Future research should focus on incorporating measures of natural rainfall properties of the particular region, including kinetic energy and intensity, and their effects on the soil.

A Holocene alluvial morphostratigraphy, based on geomorphological mapping, sedimentological analysis, soil development and radiocarbon chronology is presented for the semiarid Blanca basin in the Bardenas Reales Natural Park (NE, Spain). Four morphopedosedimentary alluvial units (MU1, MU2, MU3 and MU4) were differentiated, which may correspond to two palaeogeographical stages. The first one includes the morphopedosedimentary unit MU1 and is the most extensive in the area. It is made up of a complex aggradation (fill up) sequence comprising a braided channel system, a sand–mud flat (9200–7900 cal BP) and a playa-lake environment related to a nearly closed depression. An intensive fluvial entrenchment period is recognized, leading the opening of the Blanca basin, before the second stage that includes the units MU2, MU3 and MU4. This set of units forms a sequence of cut-and-fill and nested fill terraces recording the alluvial activity in the Blanca basin during the last 6 ka. The MU2 unit, 5900–3300 cal BP in age, represents a period of high geomorphic instability with rapid alluvial sedimentation/channel incision oscillating changes. On the other hand, the MU3 unit has an age of 1050–500 cal BP and appears as a thin extensive alluvial cover overlying previous units. Finally, the MU4 unit comprises superposition of numerous flood depositional sequences, centimetric in scale, dated from 450–10 cal BP. The established soil chronosequence supports the numerical chronology of the four units. These accumulation periods (MU1, MU2, MU3, MU4) are associated with dry phases and/or high hydrological variability (floods and droughts) at a regional scale. Changes on the North Atlantic atmospheric circulation mode over Southern Europe may provide the key to explain the nature of alluvial activity during Holocene in Bardenas Reales.

The geographic range of the freshwater naiad Margaritifera auricularia has declined alarmingly since the beginning of the 20th century. The last records of live specimens date from 1933, and this species was thought to be extinct until 1996 when the authors found a population of about 2000 mussels in a channel of the Ebro River basin (Spain). The habitat, biology and host fish of the species are here described for the first time. The habitat is a well oxygenated, subsaline and oligo-mesotrophic water with high values of calcium (150 mg/l) where M. auricularia shows a patchy distribution in a substrate of pebbles, gravels and sand. In aquarium experiments all individuals released glochidia and developing embryos during 35 days (February-March), the former becoming attached to the gill filaments of the sturgeon (Accipenser baeri) 1 day after emission. One month later, at a temperature of 16-20oC, metamorphosed juveniles were obtained from induced infestations on the sturgeons. We review the current situation of this population and measures that should be urgently implemented to conserve this species through conservation of the habitat (Canal Imperial de Aragon) and long term programmes of artificial propagation.

The Quaternary evolution and the morpho-sedimentary features of some of the most important rivers in Spain (Ebro and Tagus rivers among others) have been controlled by subsidence due to alluvial karstification of the evaporitic bedrock. The subsidence mechanism may range from catastrophic collapse to slow sagging of the alluvium by passive bending. In the Ebro Basin, the mechanisms and processes involved in karstic subsidence were studied through the analysis of present-day closed depressions as well as through old subsidence depressions (palaeocollapses and solution-induced basins) and associated deformations recorded in the Quaternary alluvial sediments. The Gállego–Ebro river system is presented as a case study of channel adjustments and geomorphic and sedimentary evolution of fluvial systems in dissolution-induced subsidence areas. In this fluvial system, evaporite dissolution during particular Quaternary time intervals (namely early and middle Pleistocene) have lead to the development of a solution-induced basin, approximately 30 km-long by 8 km-wide, filled by Quaternary deposits with a total thickness in excess of 190 m. The main river response to balance the subsidence in the alluvial plain was aggradation in the central reach of the subsiding area, and degradation both in the upstream reach and in the valley sides where alluvial fans and covered pediments may prograde over the fluvial sediments. The main sinking areas are recognized in the sedimentary record by anomalous thickenings in the alluvial deposits and fine-grained sediments deposited in backswamp and ponded areas.

The stream terrace evolution of the Gállego river during the Quaternary was controlled by both climatic change and subsidence. Quaternary terrace deposits, overlying Tertiary clay and limestone, are between 2 and 5 m thick, whereas above evaporite formations the alluvial deposits may be as much as 110 m thick. Chronologically, the first period of alluvial thickening involved the stream terraces T2 (+ 105 m above the present thalweg), T3 (+ 95 m) and T4 (+ 85 m), which have been dated by paleomagnetic reversals as Matuyama (pre-780,000). The second subsidence period affected the deposits of the stream terrace T9 (+30), dated as Brunhes (post-780,000). In both thickening periods, the subsidence was due to solution of the underlying evaporite formations (halite and gypsum), presumably, during intervals of high water flow. In the proposed model, the valley subsidence was balanced by stream aggradation maintaining the river equilibrium profile. The subsidence recorded in the alluvial deposits shows a complex spatial and temporal evolutionary pattern and total subsidence was assumed to be equal to the alluvial thickening for each subsidence period, reaching up to 165 and 25 m, respectively.

Evidence coming from subsurface studies of Middle and Upper Jurassic in the Ebro Basin (easten Iberia) shows ageneral homogeneity and a good correlation with Iberian Chain on what concerns the distribution of facies and the main litho-stratigraphic units: (1) the thick, carbonate Chelva Formation (Middle Jurassic); (2) the sponge limestone, Yátova Formation (middle-upper Oxfordian), (3) The Sot de Chera formation (upper Oxfordian - lower Kimmeridginan) formed by a uniform marly interval; (4) the Loriguilla Formation (Kimmeridgian), formed by a homogeneous interbedding of shaley marls and limestones. The uppermost Jurassic unit, the oncolitic limestone Higueruelas Formation (Tithonian to Berriasian) has not been evidenced so far in the Ebro Basin due, most probably, to erosion. Correlation appears much less evident with other adjacent areas, such as the Catalan Coastal Range, farther East, or the Pyrenees, at the North, where lithological successions are distinct and facies are predominantly dolimitic. On the other hand, the Middle-Upper Jurassic successions appear much more complete at the southern part of the Ebro Basin than in the north, where they are progressively affected by pre-Cretaceous and pre-Tertiary erosion. © 1991.