Ebro Basin Research Articles

Structure of an intraplate fold-and-thrust belt: The Iberian Chain. A synthesis

The Iberian Chain is a complex intraplate fold-and-thrust belt resulting from the convergence between the Eurasian, Iberian and African plates during the late Eocene to the Miocene. The main trend of its contractionalstructures is NW-SE, but E-W, NE-SW and N-S-trending structures are also present. The boundaries of the chain with its surrounding foreland basins are always thrusts. The North-Iberian Thrust separates thechain from the Ebro Basin to the North, while the Serrania de Cuenca Thrust makes the SE boundary of the chain, separating it from the Tajo Basin and La Mancha foreland areas. Between these thrusts, thecontractional structure is basement-involved, while South of the Serrania de Cuenca Thrust only Mesozoic and Cenozoic rocks are involved in the thrust-system, detached in the evaporitic Triassic materials. Twoparts can be differentiated considering the major structure of the chain. The western and central areas hold two major anticlinoriums separated by the Almazan Synclinorium. East of the Teruel Depression, E-WstrikingN-verging thrusts in the North, and NW-SE-striking S-verging thrusts in the center and South are the dominant structures.The crust thickened during the Cenozoic contraction generating a mean crustal thickening of about 5km. The horizontal shortening obtained from cross-sections is 32km, and from a density-gravity section of 57.5km.These two values may be considered end values.The relief of the Iberian Chain has a strong areal coincidence with the contractional structures and the thickened crust, indicating that they are genetically related.

Regiones y transferencias en el camino del Neolítico ibérico: el caso de las armaduras líticas

La extensión de las formas de vida neolíticas es un fenómeno universal, plasmado sobre geografías y cronologías diversas: su comprensión debe atender al proceso global y a las realidades regionales sobre las que se asienta. Renueva las directrices económicas, la estructura social, los inventarios materiales en sus aspectos formales y tecnológicos, la ideología incluyendo conceptos como la territorialidad, el arte, los rituales funerarios, los símbolos…. Nuestro interés recae sobre el desarrollo de un elemento específico que es una herramienta de primer orden como marcador del proceso neolitizador y de su estructura geográfica: los segmentos en doble bisel. Neolítico. Observamos: a) significan la culminación del desarrollo del geometrismo; b) su extensión geográfica cubre una amplia área de Iberia y de Francia; c) otras regiones se decantan por elementos materiales afines; d) se rescatan en yacimientos de funcionalidades diversas; e) que se asocian a otros elementos significativos de la cultura material.

Do users benefit from additional information in support of operational drought management decisions in the Ebro basin?

Abstract. We follow a user-based approach to examine how information supports operational drought management decisions in the Ebro basin and how these can benefit from additional information such as from remote sensing data. First we consulted decision-makers at basin, irrigation district and farmer scale to investigate the drought-related decisions they make and the information they use to support their decisions. This allowed us to identify the courses of action available to the farmers and water managers, and to analyse their choices as a function of the information they have available to them. Based on the findings of the consultation, a decision model representing the interrelated decisions of the irrigation association and the farmers was built. The purpose of the model is to quantify the effect of additional information on the decisions made. The modelled decisions, which consider the allocation of water, are determined by the expected availability of water during the irrigation season. This is currently informed primarily by observed reservoir level data. The decision model was then extended to include additional information on snow cover from remote sensing. The additional information was found to contribute to better decisions in the simulation and ultimately higher benefits for the farmers. However, the ratio between the cost of planting and the market value of the crop proved to be a critical aspect in determining the best course of action to be taken and the value of the (additional) information. Risk-averse farmers were found to benefit least from the additional information, while less risk-averse farmers stand to benefit most as the additional information helps them take better informed decisions when weighing their options.

Movements and dispersal of brown trout (Salmo trutta Linnaeus, 1758) in Mediterranean streams: influence of habitat and biotic factors.

Dispersal is a critical determinant of animal distribution and population dynamics, and is essential information for management planning. We studied the movement patterns and the influence of habitat and biotic factors on Mediterranean brown trout (Salmo trutta) by mark-recapture methods in three headwater streams of the Ebro Basin (NE Iberian Peninsula). Fish were sampled by electrofishing on five occasions over 18–24 months and movements of over 3,000 individually tagged trout (age 1+ onwards) were recorded. Most of the tagged fish exhibited limited movement and were recaptured within 100 m from the initial capture section. Small seasonal differences in the movement pattern were observed, but in two of the streams, displacement distances increased prior the spawning period in autumn. The frequency distributions of dispersal distances were highly leptokurtic and skewed to the right and fitted well to a two-group exponential model, thus trout populations were composed of mobile and stationary individuals, the latter being the predominant component in the populations (71.1–87.5% of individuals). The mean dispersal distances, for fish captured at least in three sampling events, ranged 20.7–45.4 m for the stationary group and 229.4–540.5 m for the mobile group. Moving brown trout were larger than non-moving individuals and exhibited higher growth rates in two of the streams. Habitat features were not consistently linked to movement rates, but there were some interaction effects between stream and habitat characteristics such as depth, cover and water velocity.

Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain)

We studied the fire record and its environmental consequences during the Holocene in the Central Ebro Basin. This region is very sensitive to environmental changes due to its semiarid conditions, lithological features and a continuous human presence during the past 6000 years. The study area is a 6 m buried sequence of polycyclic soils developed approximately 9500 years ago that is exceptionally well preserved and encompasses four sedimentary units. The content and size distribution of macroscopic charcoal fragments were determined throughout the soil sequence and the analysis of the composition of charcoal, litter and sediments via analytical pyrolysis (Py-GC/MS). The high amount of charcoal fragments recovered in most horizons highlights the fire frequencies since the beginning of the Neolithic, most of which were probably of anthropogenic origin. In some soil horizons where charcoal was not found, we detected a distribution pattern of lipid compounds that could be related to biomass burning. On the other hand, the low number of pyrolysates in the charcoal could be attributed to high-intensity fires. No clear pattern was found in the composition of pyrolysates related to the age of sediments or vegetation type. The most ancient soil (Unit 1) was the richest in charcoal content and contains a higher proportion of larger fragments (>4 mm), which is consistent with the burning of a relatively dense vegetation cover. This buried soil has been preserved in situ, probably due to the accumulation of sedimentary materials because of a high-intensity fire. In addition, the pyrogenic C in this soil has some plant markers that could indicate a low degree of transformation. In Units 2–4, both the amount of charcoals and the proportions of macrofragments >4 mm are lower than those in Unit 1, which coincides with a more open forest and the presence of shrubs and herbs. The preservation of this site is key to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change.

The role of short-term weather conditions in temporal dynamics of fire regime features in mainland Spain

In this paper we investigate spatial-temporal associations of fire weather danger and fire regime features from 1979 to 2013. We analyze monthly time series of fire activity (number of fires and burned area) and fire weather danger rating indices (Fire Weather Index, Burning Index and Forest Fire Danger Index) at two spatial scales: (i) regionally, splitting the Spanish mainland into Northwest, Hinterland and Mediterranean regions; and (ii) locally, using the EMCWF grid. All analyses are based on decomposing time series to retrieve differential indicators of seasonal cycles, temporal evolution and anomalies. At regional scale we apply lagged cross-correlation analysis (4 lags or months before fire) to explore seasonal associations; and trend detection tests on the temporal evolution component. At the local scale, we calculate Pearson correlation coefficients between each individual index and the 18 possible fire-activity subsets according to fire size (all sizes, >1 ha and >100 ha) and source of ignition (natural, unintended and arson); this analysis is applied to both cycles, temporal and anomalies series.Results suggest that weather controls seasonal fire activity although it has limited influence on temporal evolution, i.e. trends. Stronger associations are detected in the number of fires in the Northwest and Hinterland regions compared to the Mediterranean, which has desynchronized from weather since 1994. Cross-correlation analysis revealed significant fire-weather associations in the Hinterland and Mediterranean, extending up to two months prior fire ignition. On the other hand, the association between temporal trends and weather is weaker, being negative along the Mediterranean and even significant in the case of burned area. The spatial disaggregation into grid cells reveals different spatial patterns across fire-activity subsets. Again, the connection at seasonal level is noticeable, especially in natural-caused fires. In turn, human-related wildfires are occasionally found independent from weather in some areas along the northern coast or the Ebro basin. In any case, this effect diminishes as the size of the fire increases. Our work suggests that for some regions of mainland Spain, these fire danger indices could provide useful information about upcoming fire activity up to two months ahead of time and this information could be used to better inform wildland fire prevention and suppression activities.

The turtles from the upper Eocene, Osona County (Ebro Basin, Catalonia, Spain): new material and its faunistic and environmental context

Abstract. Eochelone voltregana n. sp. is a new marine cryptodiran cheloniid found at the Priabonian levels (latest Eocene) of the Vespella marls member of the Vic–Manlleu marls formation. It is the second cheloniid from Santa Cecília de Voltregà (Osona County, Spain), the first one being Osonachelus decorata from the same formation. Shell parameters indicate that the new species belongs to a branch of sea turtles including the Eocene Anglo–Franco–Belgian forms Argillochelys, Puppigerus and Eochelone (the shell of the latter was studied here for the first time) as well as Glarichelys from the Oligocene of Switzerland, all of them predating the worldwide living Miocene genera. The description of two other more littoral–continental Eocene species is given: Trionyx sp., from an older layer of the same formation; and the podocnemidid erymnochelyine, Cordichelys from a more basal layer of a middle Eocene (Lutetian) formation. The last one is identified as the only evidence of the Shweboemys subgroup in the European record, being distinct from the other known Osona County pleurodire Eocenochelus farresi, which is a member of the Erymnochelys group (same subfamily), from the younger Priabonian Sant Martí Xic layer. Thus, an update on the marine turtle fauna of the eastern Ebro Basin that variably opened in the east during Eocene times is provided. The turtles of Osona County belong to two suborders and five genera with three new species and extend the known distribution of their families (LSID urn:lsid:zoobank.org:act:48CE8676-7B82-4EF2-8165-27BEE90129F2).

A New Method for Environmental Flow Assessment Based on Basin Geology: Application to the Ebro Basin.

The determination of environmental flows is one of the commonest practical actions implemented on European rivers to promote their good ecological status. In Mediterranean rivers, groundwater inflows are a decisive factor in streamflow maintenance. This work examines the relationship between the lithological composition of the Ebro basin (Spain) and dry-season flows, in order to establish a model that can assist in the calculation of environmental flow rates. The explanatory variable used in the proposed model is easy to calculate and is sufficiently powerful to take into account all the required characteristics. The model has a high coefficient of determination, indicating that it is accurate for the intended purpose. The advantage of this method is that it requires very little data and provides a simple estimate of environmental flow. The results of this research also contribute to knowledge of the variables that influence low-flow periods on rivers in the Ebro basin.

Multiple movements recorded in a crustal weakness zone in NE Iberia: The Vallès-Penedès Fault revisited

Structural analysis and Anisotropy of Magnetic Susceptibility are here applied to the fault zone (several hundreds of meters thick) associated with an E-W striking, 20 km-long segment of the Vallès-Penedès Fault (Catalan Coastal Ranges). The results obtained indicate a complex structure, mainly resulting from the imprint of Paleogene compressional events on a fabric inherited from the Variscan orogeny, and its Late-Variscan and Mesozoic extensional history. The prevailing foliation on the fault gouge and microbreccia is oblique (striking NW-SE) to the main E-W trace of the fault. S-C structures affecting the foliation show both sinistral and dextral shear components on NE-SW and NW-SE planes, respectively, consistent with horizontal striations on quartz rods and planar bodies. Pure reverse and normal dip-slip shear components are also inferred from S-C structures at the meso- and micro-scale, indicating a NW to N (reverse), and S-SSE (normal) transport directions. The magnetic foliation averages the orientation of the observed foliation at the outcrop scale and the magnetic lineation shows two maxima. The first maximum has an overall horizontal plunge, parallel to the strike-slip transport direction inferred from S-C structures. The second maximum is parallel to the dip direction of foliation planes and also parallelizes the reverse transport direction and occasionally the intersection lineation between S and C planes, thus revealing the strong heterogeneity and partitioning of deformation. Cataclasis and pressure-solution are the main deformation mechanisms, in agreement with clay composition and low paleotemperatures determined for the Paleogene. The presented results are consistent with Paleogene transpression occurred through strain partitioning between the main thrust separating the Catalan Coastal Range from the Ebro basin (reverse slip) and the Vallès-Penedès fault zone (sinistral strike-slip), with an important influence of dextral shear associated to the secondary, WNW-ESE, segment of the fault (either an oblique ramp or resulting from the re-activation of the Llobregat Fault). A subsequent, Neogene extensional imprint slightly modified the compressional fabrics in the fault zone.

The extreme floods in the Ebro River basin since 1600 CE

Reliable and complete knowledge of the historical floods is necessary for understanding the extreme hydrological dynamics of the rivers, their natural variability and anthropic changes. In this work we reconstruct the most important floods of the Ebro basin during the last 400 years in different areas of the basin. The analysis is based on four different areas: the Ebro River at Zaragoza, the Cinca River at Fraga, the Segre River at Lleida, and the Ebro River near its mouth at Tortosa.Based on a documentary research, we have first obtained relevant information about the initial conditions (rainfall duration and distribution, snow cover influence) and the maximum flood heights that allow to reconstruct the maximum peak flows by using hydraulic models and to calculate the subbasins contributions.The results show four main types of extreme floods: a) those affecting simultaneously all the subbasins with the highest peak discharges (Ebro at Tortosa in 1787: 0.15 m3 s−1 km−2); b) those originated at the western basin, upstream from Zaragoza, with an Atlantic origin, presenting moderate maximum peak flows, caused by persistent winter rainfall and where snowmelt significantly contributes to the flood; c) those originating at the central Pyrenean subbasins, with Mediterranean origin, occurring, with high peak discharges. These mainly occur during autumn as a consequence of rainfalls of different duration (between 3 days and 1 month), and without significant snow thawing and d) finally, less frequent but very intense flash floods events centered in the Lower Ebro area with low peak flows.In terms of frequency, two different periods can be distinguished: from 1600 until 1850, the frequency of events is low; since 1850 the frequency of events is clearly higher, due to an increase of the climatic variability during last stages of the Little Ice Age. From the 1960's reservoirs construction modifies discharges regime.

Neogene-Quaternary onshore record in the lower Ebro river incised palaeovalley (Ebro margin, Catalan Coastal Range, NE Iberia)

The lower Ebro is a bedrock-alluvial mixed incised valley with a persistent degradational stacking architecture developed from latest Serravallian(?) to Holocene. This degradational pattern was probably controlled by isostatic rebound in NE Iberia and punctuated by major relative sea level changes that temporally accentuated or attenuated the palaeovalley entrenchment and sediment retention. Six allostratigraphic units in the palaeovalley constitute the onshore record of its evolution and the opening and connection of the Ebro Basin with the Mediterranean. This paper deals with the analysis and reinterpretation of these units in order to precise the sequence of events that took place on the onshore part of the Catalan continental margin during the Ebro River drainage entrenchment. Plausible chronology and palaeogeographic evolution of the Neogene-Quaternary drainage incision in the lower Ebro are also proposed. The early evolutionary stages of the incised palaeovalley (Latest Serravallian?-Tortonian-Early Messinian, from 11.63–9? to near 5.6Ma) were dominated by entrenchment and intense sediment transfer from the onshore to the offshore zones (erosion surface S2). These processes were only punctuated by the sedimentation of the alluvial palaeovalley unit M2 (late Messinian). The polygenetic onshore erosion surfaces S2 and S3 are linked here with the onshore erosive processes that fed the sedimentation of the terrigenous shelf-slope system of the offshore Castellon group and considered coeval with the offshore Messinian erosion surfaces (reflectors M and m). During a further evolutionary stage (Pliocene to Early Pleistocene from 5.3 to approximately 2Ma) the Early Pliocene major Mediterranean reflooding caused some sediment retention in the incised palaeovalley (sedimentation of unit P) but sediment transfer into the offshore remained very effective. In the last evolutionary stage (Early Pleistocene-Holocene, from 2Ma to present) the palaeovalley became again mainly degradational (generation of erosion surfaces S4 to S6 and sedimentation of stepped alluvial terraces Q1-2 to Q4). The onshore stratigraphic record, including the allostratigraphic units P and Q1-2 to Q4 and the related bounding surfaces S3 to S6, is correlated with the sedimentation of the terrigenous shelf-slope system of the offshore Ebro group.

Fish‐bearing deposits from the Upper Eocene Terminal Complex of the Plana de Vic (Catalonia, NE Spain): Sedimentary context and taphonomy

The Upper Eocene fish‐bearing deposits of the Terminal Complex of the Plana de Vic (Ebro Basin, Catalonia, NE Spain) and its fish assemblage are analysed in detail from a stratigraphic and sedimentological point of view. Moreover, the taphonomic features and taxonomy of the fishes are studied for the first time. Fishes belonging to the families Clupeidae, Synodontidae, and an indeterminate percomorph have been identified, including a new lizardfish taxon, Ausonasynodus almerai gen. et sp. nov. The fish specimens are preserved in finely laminated limestones, resulting from the development of microbial mats on the seafloor. The presence of these microbially induced biolaminations favoured the good preservation of the fossil material. The combination of the stratigraphic and sedimentological context of the studied deposits, together with the taphonomic and paleobiological information obtained from the fishes, suggest that they were likely deposited in a shallow marine setting, probably in restricted or protected areas, under arid climatic conditions.

El Paleolítico Superior de la península ibérica

Este artículo intenta ofrecer una síntesis relativamente completa de lo que se conoce en la actualidad sobre la transición del Paleolítico medio al superior y el desarrollo de las adaptaciones humanas y de las culturas durante el último periodo en la Península Ibérica (España y Portugal, así como Andorra y Gibraltar). Los énfasis del trabajo, que es inevitablemente selectivo y se basa principalmente en la bibliografía disponible más reciente, son las condiciones ambientales, el asentamiento humano, las tecnologías, la subsistencia y la expresión artística, desde una perspectiva que subraya en que medida la naturaleza y extensión de las redes sociales han cambiado durante todo el desarrollo del Estadio Isotópico Marino 3 tardío y todo el Estadio 2. El objetivo es abarcar todas las regiones de la península, pese a sus diferentes historias de la investigación y sus desiguales densidades de yacimientos. Una conclusión general es que a pesar de las fluctuaciones climáticas del Tardiglaciar, uno puede escribir diferentes histoires de la longue durée sobre importantes unidades geográficas como la región cantábrica (atlántica septentrional) de España, la cuenca del Ebro, la España levantina (mediterránea), Andalucía, las mesetas interiores de España y las cuencas del Duero y el Tajo, y las regiones meridional y central-septentrional de Portugal. Además, en diferentes grados a través del tiempo, hubo tanto una unidad cultural peninsular, creada por redes sociales entre esas regiones, como contactos con bandas de cazadores-recolectores al norte de los Pirineos.

Deterioration caused by dimensional change in stone (EBD pathology): the role of the organic matter — pore network — salt combination

Abstract We have studied a pathology produced by dimensional changes in Miocene lacustrine limestones of the Ebro basin with very low clay content (Briviesca and Tudela stone). The samples studied come from stone blocks of the Cathedrals of Burgos and Tudela and their respective original quarries. Three additional rocks that present a pattern of similar deterioration are also characterised. The pathology, known as “Expansion by Drying (EBD)”, looks like a mechanical fracture and is produced by important dimensional changes of the material. We have carried out a detailed study of the rocks with Mercury Intrusion Porosimetry (MIP) and establish four different porous systems in the materials studied. A relationship is found between the type of porous system and the presence of the pathology. In order to develop, EBD pathology needs a porosimetry like the one defined for group IV. On the other hand, oxidation of the organic matter present in the rock (proven by aging the rock with ozone) changes the porosimetry of group IV rocks, converting them into a porous network of group III. These facts explain why EBD pathology develops in oxidized rocks of historical buildings and not in fresh quarry rocks. In addition, we characterise dimensional changes of the rock by the intrusion of liquid water (conventional hydric expansion) and water vapour adsorption. These data have been relevant to understand the mechanisms of the dimensional change in the rocks studied.

Mapping the Basement of the Ebro Basin in Spain With Seismic Ambient Noise Autocorrelations

AbstractSingle‐station autocorrelations of seismic ambient noise allow to obtain the shallow subsurface reflection response without the need of any active source or earthquake. Recently, crustal‐scale studies successfully applied this method to map the crust‐mantle boundary. These studies employed different processing methodologies to stabilize and identify the weak‐amplitude reflections. Here we also analyze noise autocorrelations but use higher‐frequency bands to map the basement of the Ebro Basin in Spain. This basin has a nonuniform basement structure due to its complex evolution. We tested two autocorrelation methods (the classical and phase cross correlation) to retrieve the P wave reflection response for seismic broadband stations located in the basin. The phase correlation approach is amplitude unbiased since based on the instantaneous phase coherence of analytic signals. It is insensitive to the background seismicity from the Pyrenees and other noise and proved to be the more efficient approach to retrieve P wave reflections from the Paleozoic basement. The detected signals per station are quite stable and show only a small time variability. We also show that sidelobes caused by the convolution of a delta pulse at zero time lag with the effective noise source time function do not affect our measurements and compare the measured noise autocorrelations with synthetic data for lithological profiles from neighboring wells. The a priori information from well data was essential to identify the signals and to finally map the discontinuity in between and beyond the well positions. Our final result is a comprehensive map of the Paleozoic basement in the Ebro Basin.

Drainage reorganization and divide migration induced by the excavation of the Ebro basin (NE Spain)

Abstract. Intracontinental endorheic basins are key elements of source-to-sink systems as they preserve sediments eroded from the surrounding catchments. Drainage reorganization in such a basin in response to changing boundary conditions has strong implications on the sediment routing system and on landscape evolution. The Ebro and Duero basins represent two foreland basins, which developed in response to the growth of surrounding compressional orogens, the Pyrenees and the Cantabrian mountains to the north, the Iberian Ranges to the south, and the Catalan Coastal Range to the east. They were once connected as endorheic basins in the early Oligocene. By the end of the Miocene, new post-orogenic conditions led to the current setting in which the Ebro and Duero basins are flowing in opposite directions, towards the Mediterranean Sea and the Atlantic Ocean. Although these two hydrographic basins recorded a similar history, they are characterized by very different morphologic features. The Ebro basin is highly excavated, whereas relicts of the endorheic stage are very well preserved in the Duero basin. The contrasting morphological preservation of the endorheic stage represents an ideal natural laboratory to study the drivers (internal and/or external) of post-orogenic drainage divide mobility, drainage network, and landscape evolution. To that aim, we use field and map observations and we apply the χ analysis of river profiles along the divide between the Ebro and Duero drainage basins. We show here that the contrasting excavation of the Ebro and Duero basins drives a reorganization of their drainage network through a series of captures, which resulted in the southwestward migration of their main drainage divide. Fluvial captures have a strong impact on drainage areas, fluxes, and their respective incision capacity. We conclude that drainage reorganization driven by the capture of the Duero basin rivers by the Ebro drainage system explains the first-order preservation of endorheic stage remnants in the Duero basin, due to drainage area loss, independently from tectonics and climate.

Some evolutionary patterns of palaeokarst developed in Pleistocene deposits (Ebro Basin, NE Spain): Improving geohazard awareness in present‐day karst

Pleistocene detrital deposits in the central Ebro Basin frequently show deformation features due mainly to karstification in the underlying Neogene evaporites. In 123 cases, estimation of parameters of shape and minimum volume of materials involved was accomplished. Six of them were analysed in more detail to establish the main processes involved in their genesis and the succession of events. All the deformation features in the selected sites are synsedimentary. To achieve the objectives, intense fieldwork was made applying methods of sedimentology and structural geology. Usually, a complex evolutionary pattern was observed, with evidences of dissolution, sagging, collapse, gravity flow, suffosion, and plastic flow. In a schematic way, three main situations, independent of the age of the analysed deposits, can be distinguished: (a) slow subsidence, (b) collapse, and (c) temporal overlapping of both processes. In the first 2 scenarios, basins with smooth or abrupt borders, respectively, were generated on the land surface. In the third one, slow subsidence was followed by a collapse, located in the area of maximum flexure. These patterns are also observed in present‐day dolines. Comparison of direct and indirect parameters between paleodolines and present‐day dolines indicates a bigger size of the latter, probably caused by the different conditions of observation. This study helps to know the possibilities in the evolution of mantled karst features, to estimate the volume of material affected by karstification and to improve the knowledge of present‐day dolines behaviour. Consequently, study of paleodolines must be considered to achieve a better urban planning in active karstic areas.

Serpulids on living Eocene larger foraminifer Discocyclina

I report the first observation of the symbiotic relationship between a serpulid polychaete and a larger foraminifer, Discocyclina, from the Eocene of the Ebro Basin (NE Spain). Discocyclina tests are the larger and most abundant element of the fossil assemblage in a limestone bed within a fan delta series, and seems to be a preferred substrate by the serpulid larvae to settle. The bioimmuration of the serpulid tube within the foraminiferal test shows that the polychaetes attached and grew on living foraminifers, which continued growing after the serpulid’s death. The foraminifer could benefit from the filtering activity of the serpulid, although in some cases the serpulid attachment caused an anomalous growth of the foraminiferal test. Some foraminifer individuals survived to two, possibly three successive episodes of serpulid attachment, which suggests a life span of 1–3 years for this Discocyclina species, similar to that of recent hyaline larger foraminifers such as Amphistegina or Paleonummulites. This sheds new light on the paleobiology of this type of larger foraminifers without recent counterparts that thrieved during Late Cretaceous and Paleogene times.

Transport of sediment borne contaminants in a Mediterranean river during a high flow event

Pollutants' dynamics in rivers flowing through industrial areas is linked to the entrainment and transport of contaminants attached to solid particles. The transport of sediment is mainly associated to high discharges and flood episodes, and these events constitute one of the main factors causing fluxes of buried pollutants in rivers. We performed a field study in the lower River Cinca (Ebro basin, Northeast Spain) to quantify the mobilization and transfer of several contaminants present in the river bed sediments. We focused on contaminants previously identified (PCBs, DDXs, PBDEs, HBCDs and PFRs) to occur in the river. River bed sediment samples were collected during low flows and a subsequent sampling campaign was used to capture sediment borne contaminants during a flood event. Water samples were taken at the same locations as the static sediment samples and used to determine the suspended sediment concentrations and the contaminants content (i.e. mass of contaminant per sediment mass unit) during the event. We estimated mass fluxes for both sediment and pollutants, and determined that sediment transport followed a clockwise hysteresis. This is typically observed in high flow events after dry summer periods. With sediments there was a large mobilization of PFRs (36 kg in 48 h in one of the main tributaries) and PCBs not previously observed in the static sediment. Observed contaminant load ranges during the two-day sampling campaign were: PCB (34–152 g), DDT (12–213 g), PBDE (50–1740 g), HBCD (0–2.2 g) and PFR (2410–35,895 g). An environmental risk assessment was carried out by comparing the pollutant concentrations found in the sediments with the Canadian quality guidelines (ISQC), showing a significant noncompliance for PCBs in dynamic sediments. Our results point out to the need of a regular assessment of the downstream transfer of the sediment-borne pollutants in drainage basins historically affected by intense industrial activities and associated contamination.

Effects of Didymosphenia geminata massive growth on stream communities: Smaller organisms and simplified food web structure.

This study aims to contribute to the understanding of the impact of Didymosphenia geminata massive growths upon river ecosystem communities’ composition and functioning. This is the first study to jointly consider the taxonomic composition and functional structure of diatom and macroinvertebrate assemblages in order to determine changes in community structure, and the food web alterations associated with this invasive alga. This study was carried out in the Lumbreras River (Ebro Basin, La Rioja, Northern Spain), which has been affected by a considerable massive growth of D. geminata since 2011. The study shows a profound alteration in both the river community composition and in the food web structure at the sites affected by the massive growth, which is primarily due to the alteration of the environmental conditions, thus demonstrating that D. geminata has an important role as an ecosystem engineer in the river. Thick filamentous mats impede the movement of large invertebrates—especially those that move and feed up on it—and favor small, opportunistic, herbivorous organisms, mainly chironomids, that are capable of moving between filaments and are aided by the absence of large trophic competitors and predators -prey release effect-. Only small predators, such as hydra, are capable of surviving in the new environment, as they are favored by the increase in chironomids, a source of food, and by the reduction in both their own predators and other midge predators -mesopredator release-. This change in the top-down control affects the diatom community, since chironomids may feed on large diatoms, increasing the proportion of small diatoms in the substrate. The survival of small and fast-growing pioneer diatoms is also favored by the mesh of filaments, which offers them a new habitat for colonization. Simultaneously, D. geminata causes a significant reduction in the number of diatoms with similar ecological requirements (those attached to the substrate). Overall, D. geminata creates a community dominated by small organisms that is clearly different from the existing communities in the same stream where there is an absence of massive growths.