A high marsh transfer function for sea-level reconstructions in the southern Bay of Biscay.

E. Leorri was supported by a postdoctoral grant from the Basque Government and by the Conseil Gà ©nà ©ral of the Vendà ©e (F). This work has been partially funded by the UNESCO06/08 and IT-332-07/GIU06-10 research contracts and it represents a contribution to IGCP project #495

Cambios recientes del nivel marino en el sur del Golfo de Vizcaya: reconstrucciones basadas en funciones de transferencia aplicadas en marismas en comparación con datos instrumentales

In order to assess the accuracy and regional significance of salt-marsh reconstructions of former sea level based on foraminiferal transfer functions, we compared the calibration of the foraminiferal assemblages of two salt-marsh cores from two estuaries using the regional transfer function constructed for the southern Bay of Biscay. The foraminifera-based reconstructions were placed into a temporal framework using 137Cs, heavy metal concentrations, and 210Pb-derived sediment accumulation rates. The resulting relative sea-level (RSL) curves were compared with the nearest tide-gauge data (Santander). The two RSL trends from core sediments show excellent agreement and are in very good agreement with instrumental data, providing a regional relative sea-level rise of 1.9 mm yr-1 for the 20th century.Con el fin de evaluar la precisión y el carácter regional de las reconstrucciones del nivel marino basadas en funciones de transferencia usando foraminíferos de marisma, hemos comparado la calibración de las asociaciones de foraminíferos de dos sondeos perforados en sendos estuarios, usando una función de transferencia de validez regional construida para el sur del Golfo de Vizcaya. Estas reconstrucciones basadas en las asociaciones de foraminíferos han sido situadas en un marco temporal utilizando 137Cs, concentraciones de metales pesados y los cocientes de acumulación sedimentaria basados en 210Pb. La curva del nivel marino resultante ha sido comparada con el mareógrafo más próximo al área de estudio (Santander). Las dos curvas obtenidas a partir de los sondeos presentan una excelente correlación entre sí y muy buena correlación con los datos procedentes del mareógrafo, proporcionando un ascenso relativo del nivel marino de 1.9 mm año-1 para el siglo XX, siendo este ascenso de carácter regional

El registro geológico de la transformación ambiental de la ría de Bilbao durante el Holoceno y el Antropoceno

The northeastern coast of Spain is characterized by Mesozoic-Cenozoic sedimentary rocks forming high cliffs interrupted by short, narrow estuaries that are separated from the open sea by sandbars, beaches and dune deposits. The morphology and extent of the different estuarine sedimentary environments are constantly altered by erosion and deposition of sediments, and they are sensitive to even small changes in sea level. The Holocene transgressive episode caused the deposition of large volumes of well preserved estuarine sediments that can be studied to understand environmental and sea-level changes during this interglacial. The Bilbao estuary was originally the most extensive estuarine area on the Cantabrian coast of northern Spain. The modern estuary is 15 km long, an average of 100 m wide, and its channel depth ranges from 2 m in the upper estuary to 9 m at the mouth. The estuary is formed by the tidal part of the Nervion river, although four other rivers (Kadagua, Asua, Galindo and Gobelas) discharge into the main course. The tidal channel discharges into a wide marine bay called El Abra (average 3.5 km wide; up to 30 m deep). Tides are semidiurnal, with ranges between 4.6 m (spring tides) to 1.2 m (neap tides). The first iron and steel industry was opened on the middle estuary over reclaimed marshes as early as 1854. Since then, the natural features of the Bilbao estuary have been dramatically modified by urban, industrial and port developments. The exploitation of abundant local iron ore led to the early industrial development of Bilbao in the mid-19th century. The original estuary was rapidly reduced in size through land reclamation to form a tidal channel. This was isolated by dyking from its original intertidal areas, to allow a navigable watercourse from the city to the open sea. Today the Bilbao estuary is a largely artificial system which bears little resemblance to the original estuary. It has been calculated that the total amount of the original estuarine surface lost through human activity is approximately 1,000 ha. During the last 150 years, the Bilbao estuary has received wastes from many sources (mineral sluicing, industrial wastes and urban effluents) which have significantly degraded the environmental quality of the estuary. At present, the Bilbao estuary is the most polluted coastal area of northern Spain. A significant decrease in the flux of organic matter and heavy metal contaminants has occurred over the last decades, however, due to the implementation of environmental protection policies, the improvement in waste-treatment systems and the closure of some major factories during recent periods of economic recession. Furthermore, estuarine regeneration is currently being undertaken as part of a Revitalization Strategic Plan. Despite these improvements, the unremoved contaminated sediments from the intertidal areas may act as a long-term source of heavy metals to the aquatic environment through sediment mechanical reworking (e.g. dredging, shipping) and oxidation of anoxic sediments. Thus, these pollutants may continue procedures have been implemented. To reconstruct the palaeoenvironmental evolution of the Bilbao estuary since its formation following the postglacial rise of sea level, it have been analyzed the foraminiferal assemblages contained in eleven boreholes taken in the reclaimed areas of the middle and lower parts of the estuary. Integration of these results with similar data from previously studied boreholes has allowed us to reconstruct the environmental development of the Bilbao estuary during the Holocene. This environmental development has been organized into different systems tracts following a sequence-stratigraphic interpretation. Radiocarbon dating and palynological studies helped to locate in time the different palaeoenvironments and depositional episodes identified in the boreholes. Sediments that compose the estuarine infill range from basal fluvial coarse materials (Lateglacial), almost barren of foraminifera, that are interpreted as the lowstand systems tract (LST). This system tract is followed upwards by lower and middle Holocene transgressive materials (TST; 8500-3000 years cal BP), with upper Holocene regressive sediments on top (HST; 3000 years cal BP-19th century). This general sedimentary sequence is best represented in the middle estuarine area, and its sedimentary and microfaunal features are variable depending on its palaeogeographic setting: increasing muddy sediments and absence of open-marine elements are characteristic of the upper estuary, whereas increasing sandy sediments and reworking of the basal fluviatile materials are typical of the lower estuary. Comparison of these data with other sedimentary sequences from different coastal areas in the Bay of Biscay allows to reconstruct a general picture of the Holocene sea-level changes and coastal evolution in this area for the last 8500 years. On the other side, six cores retrieved from the Bilbao estuary tidal flats have been studied in order to evaluate the historical impact of the long lasting record of anthropogenic inputs, which have led to the disappearance of the indigenous microfauna and to the significant pollution of the sediments. Three different zones can be identified in the recent sedimentary record, reflecting initially the preindustrial estuarine conditions with abundant and diverse foraminiferal assemblages and baseline levels of metals, followed by the industrial-period sedimentary record, when high concentrations of metals in the estuarine environment allowed the development of abundant foraminiferal assemblages during the older industrial zone (period 1850-1950) that disappeared during the younger industrial zone (period 1950-2000) due to complete defaunation of the Bilbao estuary caused by minimum oxygen levels during this period. Obtained data provide important information in planning the restoration of the Bilbao estuary, because sediments have proven to be an important storage reservoir for pollutants and microfossils. Finally, the distribution and abundance of benthic foraminifera (together with geochemical analysis of heavy metals) from surface sediment samples (1997- 2003) and sediment cores collected from the intertidal flats of the Bilbao estuary have been studied to determine recent environmental contitions of this estuary. Furthermore a foraminiferal sampling network has been created in order to evaluate the future progress of the current regeneration schemes on a seasonal and anual basis. Pb-210 and Cs-137 determinations have also been undertaken to provide a chronology for pollutant inputs and ecological changes in the Bilbao estuary

Rangos de ascenso marino relativo en el sur del Golfo de Vizcaya durante el Antropoceno frente al Holoceno

Con el fin de evaluar la aceleración en el ascenso relativo del nivel marino durante el Antropoceno, se han comparado los resultados previamente establecidos para el siglo XX con los resultados obtenidos a partir del estudio de 61 nuevos puntos indicadores del nivel marino durante el Holoceno en el sur del Golfo de Vizcaya. Estos resultados indican un ascenso rápido hasta los circa 7000 años cal BP que se puede estimar en 9-12 mm año-1. Desde entonces, el nivel del mar ha ascendido suavemente en concordancia con los datos proporcionados a nivel global, con una velocidad media de 0,7 mm año-1. Esta velocidad contrasta netamente con la tasa de ascenso registrada durante el siglo XX de 1,9 mm año-1, confirmando la aceleración detectada a nivel global como resultado de las actividades antropogénicas. Aunque los resultados obtenidos son altamente satisfactorios, los diferentes rangos de error proporcionados por ambos estudios hacen necesarios más estudios de este tipo para reducir los errores asociados a estas reconstruccione

Anthropocene versus Holocene relative sea-level rise rates in the southern Bay of Biscay

Rangos de ascenso marino relativo en el sur del Golfo de Vizcaya durante el Antropoceno frente al Holocen

Biological and synthetic approaches to inhibiting nitrification in non-tilled Mediterranean soils

Background: The increasing demand for food production has led to a tenfold increase in nitrogen (N) fertilizer use since the Green Revolution. Nowadays, agricultural soils have been turned into high-nitrifying environments that increase N pollution. To decrease N losses, synthetic nitrification inhibitors (SNIs) such as 3,4-dimethylpyrazole phosphate (DMPP) have been developed. However, SNIs are not widely adopted by farmers due to their biologically limited stability and soil mobility. On the other hand, allelopathic substances from root exudates from crops such as sorghum are known for their activity as biological nitrification inhibitors (BNIs). These substances are released directly into the rhizosphere. Nevertheless, BNI exudation could be modified or even suppressed if crop development is affected. In this work, we compare the performance of biological (sorghum crop) and synthetic (DMPP) nitrification inhibitors in field conditions. Results: Sorghum crop BNIs and DMPP prevented an increase in the abundance of ammonia-oxidizing bacteria (AOB) without affecting the total bacterial abundance. Both nitrification inhibitors maintained similar soil NH4+ content, but at 30 days post-fertilization (DPF), the sorghum BNIs resulted in higher soil NO3− content than DMPP. Even so, these inhibitors managed to reduce 64% and 96%, respectively, of the NO3−-N/NH4+-N ratio compared to the control treatment. Similar to soil mineral N, there were no differences in leaf δ15N values between the two nitrification inhibitors, yet at 30 DPF, δ15N values from sorghum BNI were more positive than those of DMPP. N2O emissions from DMPP-treated soil were low throughout the experiment. Nevertheless, while sorghum BNIs also maintained low N2O emissions, they were associated with a substantial N2O emission peak at 3 DPF that lasted until 7 DPF. Conclusions: Our results indicate that while sorghum root exudates can reduce nitrification in field soil, even at the same efficiency as DMPP for a certain amount of time, they are not able to prevent the N pollution derived from N fertilization as DMPP does during the entire experiment.This project was funded by the Spanish Government (RTI2018-094623-B-C22 MCIU/AEI/FEDER, UE) and by the Basque Government (IT-932-16). Adrián Bozal-Leorri holds a Grant from the Basque Government (PRE-2020-2-0142). Mario Corrochano-Monsalve holds a Grant from the Ministry of Economy and Business of the Spanish Government (BES-2016-076725)

Holocene salt-marsh sedimentary infilling and relative sea-level changes in West Brittany (France) using foraminifera-based transfer functions

International audienceIn order to reconstruct the former sea-levels and to better characterize the history of Holocene salt-marsh sedimentary infillings in West Brittany (western France), local foraminifera-based transfer functions were developed using Weighted-Average-Partial-Least-Squares (WA-PLS) regression, based on a modern dataset of 26 and 51 surface samples obtained from salt-marshes in both the bay of Tressseny and the bay of Brest. Fifty cores were retrieved from Tresseny, Porzguen, Troaon and Arun salt-marshes, which were litho- and biostratigraphicaly analyzed in order to reconstruct palaeoenvironmental changes. A total of 26 AMS 14C age determinations were performed within the sediment successions. The Holocene evolution of salt-marsh environments can be subdivided into four stages: (1) a development of brackish to freshwater marshes (from c. 6400 to 4500 cal. a BP); (2) salt-marsh formation behind gravel barriers in the bay of Brest (from 4500 to 2900 cal. a BP); (3) salt-marsh erosion and rapid changes of infilling dynamics due to the destruction of coastal barriers by storm events (c. 2900-2700 cal. a BP); (4) renewed salt-marsh deposition and small environmental changes (from 2700 cal. a BP to present). From the application of transfer functions to fossil assemblages, 14 new sea-level index points were obtained indicating a mean relative sea-level rise around 0.90±0.12 mm a-1 since 6300 cal. a BP

Biological and synthetic approaches to inhibiting nitrification in non‑tilled Mediterranean soils

[EN] Background: The increasing demand for food production has led to a tenfold increase in nitrogen (N) fertilizer use since the Green Revolution. Nowadays, agricultural soils have been turned into high-nitrifying environments that increase N pollution. To decrease N losses, synthetic nitrification inhibitors (SNIs) such as 3,4-dimethylpyrazole phosphate (DMPP) have been developed. However, SNIs are not widely adopted by farmers due to their biologically limited stability and soil mobility. On the other hand, allelopathic substances from root exudates from crops such as sorghum are known for their activity as biological nitrification inhibitors (BNIs). These substances are released directly into the rhizosphere. Nevertheless, BNI exudation could be modified or even suppressed if crop development is affected. In this work, we compare the performance of biological (sorghum crop) and synthetic (DMPP) nitrification inhibitors in field conditions. Results: Sorghum crop BNIs and DMPP prevented an increase in the abundance of ammonia-oxidizing bacteria (AOB) without affecting the total bacterial abundance. Both nitrification inhibitors maintained similar soil NH4+ content, but at 30 days post-fertilization (DPF), the sorghumBNIs resulted in higher soil NO3- content than DMPP. Even so, these inhibitors managed to reduce 64% and 96%, respectively, of the NO3--N/NH4+-N ratio compared to the control treatment. Similar to soil mineral N, there were no differences in leaf delta N-15 values between the two nitrification inhibitors, yet at 30 DPF, delta N-15 values from sorghum BNI were more positive than those of DMPP. N2O emissions from DMPP-treated soil were low throughout the experiment. Nevertheless, while sorghum BNIs also maintained low N2O emissions, they were associated with a substantial N2O emission peak at 3 DPF that lasted until 7 DPF. Conclusions: Our results indicate that while sorghum root exudates can reduce nitrification in field soil, even at the same efficiency as DMPP for a certain amount of time, they are not able to prevent the N pollution derived from N fertilization as DMPP does during the entire experiment. Graphic AbstractThis project was funded by the Spanish Government (RTI2018-094623-B-C22 MCIU/AEI/FEDER, UE) and by the Basque Government (IT-932-16). Adrian Bozal-Leorri holds a Grant from the Basque Government (PRE-2020-2-0142). Mario Corrochano-Monsalve holds a Grant from the Ministry of Economy and Business of the Spanish Government (BES-2016-076725)