The value of carbon sequestration and storage in coastal habitats

Coastal margin habitats are globally significant in terms of their capacity to sequester and store carbon, but their continuing decline, due to environmental change and human land use decisions, is reducing their capacity to provide this ecosystem service. In this paper the UK is used as a case study area to develop methodologies to quantify and value the ecosystem service of blue carbon sequestration and storage in coastal margin habitats. Changes in UK coastal habitat area between 1900 and 2060 are documented, the long term stocks of carbon stored by these habitats are calculated, and the capacity of these habitats to sequester CO2 is detailed. Changes in value of the carbon sequestration service of coastal habitats are then projected for 2000–2060 under two scenarios, the maintenance of the current state of the habitat and the continuation of current trends of habitat loss. If coastal habitats are maintained at their current extent, their sequestration capacity over the period 2000–2060 is valued to be in the region of £1 billion UK sterling (3.5% discount rate). However, if current trends of habitat loss continue, the capacity of the coastal habitats both to sequester and store CO2 will be significantly reduced, with a reduction in value of around £0.25 billion UK sterling (2000–2060; 3.5% discount rate). If loss-trends due to sea level rise or land reclamation worsen, this loss in value will be greater. This case study provides valuable site specific information, but also highlights global issues regarding the quantification and valuation of carbon sequestration and storage. Whilst our ability to value ecosystem services is improving, considerable uncertainty remains. If such ecosystem valuations are to be incorporated with confidence into national and global policy and legislative frameworks, it is necessary to address this uncertainty. Recommendations to achieve this are outlined

Salerno's model of DNA reanalysed: could solitons have biological significance?

We investigate the sequence-dependent behaviour of localised excitations in a toy, nonlinear model of DNA base-pair opening originally proposed by Salerno. Specifically we ask whether ``breather'' solitons could play a role in the facilitated location of promoters by RNA polymerase. In an effective potential formalism, we find excellent correlation between potential minima and {\em Escherichia coli} promoter recognition sites in the T7 bacteriophage genome. Evidence for a similar relationship between phage promoters and downstream coding regions is found and alternative reasons for links between AT richness and transcriptionally-significant sites are discussed. Consideration of the soliton energy of translocation provides a novel dynamical picture of sliding: steep potential gradients correspond to deterministic motion, while ``flat'' regions, corresponding to homogeneous AT or GC content, are governed by random, thermal motion. Finally we demonstrate an interesting equivalence between planar, breather solitons and the helical motion of a sliding protein ``particle'' about a bent DNA axis.Comment: Latex file 20 pages, 5 figures. Manuscript of paper to appear in J. Biol. Phys., accepted 02/09/0

Observations of open-ocean deep convection in the northwestern Mediterranean Sea: Seasonal and interannual variability of mixing and deep water masses for the 2007-2013 Period

We present here a unique oceanographic and meteorological data set focus on the deep convection processes. Our results are essentially based on in situ data (mooring, research vessel, glider, and profiling float) collected from a multiplatform and integrated monitoring system (MOOSE: Mediterranean Ocean Observing System on Environment), which monitored continuously the northwestern Mediterranean Sea since 2007, and in particular high‐frequency potential temperature, salinity, and current measurements from the mooring LION located within the convection region. From 2009 to 2013, the mixed layer depth reaches the seabed, at a depth of 2330m, in February. Then, the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly formed deep water. Each deep convection winter formed a new warmer and saltier “vintage” of deep water. These sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity (3.3 ± 0.2 × 10−3/yr) and potential temperature (3.2 ± 0.5 × 10−3 C/yr) observed from 2009 to 2013 for the 600–2300 m layer. For the first time, the overlapping of the three “phases” of deep convection can be observed, with secondary vertical mixing events (2–4 days) after the beginning of the restratification phase, and the restratification/spreading phase still active at the beginning of the following deep convection event

Multi-scale Assessment of Hydrodynamic Properties in a Karst Aquifer (Lez, France)

International audienceThe present study focuses on the hydrodynamic characterization of the Lez karst aquifer (Southern France) on the basis of hydraulic field tests performed at different scales of space and under distinct hydrological conditions. Depending on the water level conditions, the organization of the flow paths linked to the geological structure of the reservoir changes and a compartmentalization of the system due the hierarchization of hydraulic connections to the main flow paths was assessed. For the same parameter characterized at borehole scale and at regional scale, a difference of 10\textendash105 has been quantified. This quantification of hydrodynamic parameters provides important constraints on multiscale modeling and the characterization of main flow paths in such a karst system

Flow-bearing structures of fractured rocks: Insights from hydraulic property scalings revealed by a pumping test

International audienceA long duration pumping test conducted over 151 days in a fractured sandstone and shale formation displays a nonstandard drawdown response and anomalous pressure diffusion, which cannot be properly interpreted using existing frameworks (e.g., homogeneous, double porosity, boundary conditions, and fractal models). An alternative framework with simple geometry and more complex hydraulic properties is thus proposed to interpret such kind of drawdown responses. The analytical development allows first to demonstrate all scaling relations in this interpretation framework. Then, and most importantly, the multi-scale hydraulic test provides consistent scalings of transmissivity, T, to storativity, S, over distances ranging from 83 to 383 m in a faulted area. Drawdown analysis in several monitoring wells shows persistent decrease of transmissivity in highly channelized fracture flow structures. In one structure, the cubic dependency of transmissivity to storativity identifies a well-defined fault and also demonstrates the validity of Poiseuille flow at a scale rarely investigated. In the other structure, the linear dependency of transmissivity to storativity indicates that the flow-bearing structure is the surrounding fracture network. Well-designed pumping tests combined with scaling analysis driven by geological evidence thus provide essential information on flow-bearing structures for site characterization and modeling tasks. At least for moderate to low permeable fractured rocks, the scaling of transmissivity to storativity appears to be more informative than any separate interpretation of hydraulic property scaling exponents

Variability of nutrient and particulate matter fluxes between the sea and a polder after partial tidal

This paper aims to investigate the patterns of exchanges of nutrients and suspended sediments between the sea and a polder, after partial tidal restoration, and to assess if these are comparable to those observed in natural salt marshes. The study site, situated in the Bay of Veys, in Northwestern France, was embanked in the 1870s and accidentally reconnected to the sea in 1990. Water now flows in and out of the polder by a single communication point with the sea, which facilitated water sampling and flux calculation for dissolved and particulate elements. The study was carried out for two years, from May 2002 to April 2004. Results showed that for all the months studied the water flowing out of the polder had lower concentrations of nitrates and suspended sediments, which lead to a retention of these elements throughout the year. Nitrates uptakes in the polder were much higher in winter (up to 473.9 g N ha(-1) tide(-1)) than in summer where they were close to zero. The retention of suspended sediment could be over 80% of the import and was mainly composed of organic matter. Finally, the concentrations of dissolved organic carbon were higher in outflow than inflow water, but due to unbalanced water budgets this lead to low quantities imported in summer and higher amounts exported for all other seasons. No interpretable pattern was observed for ammonium. The nature of these fluxes, according to literature, is close to those observed in immature salt marshes, so as far as restoration is concerned, it has been shown that partial tidal restoration can allow the restitution of the salt marsh exchange functions that were studied. (c) 2005 Elsevier Ltd. All rights reserved

Apport de nouveaux traçages et forages à la connaissance hydrogéologique de l’aquifère karstique du Lez

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Scale-dependence of hydraulic properties observed in fractured sedimentary rocks through large scale pumping test

International audiencePredicting flow in fractured reservoirs remains challenging as it highly depends on hydraulic connectivity of fractures which can vary from point to point. Classical pumping experiments conducted in fractured reservoirs often display fractional flow and anomalous slow diffusion due to bottlenecks or dead zones, characteristic of heterogeneity. In order to investigate reservoir properties at a contaminated site in the Simi Hills (South California, USA), composed by sandstones (dominant calcite cement) inter-bedded with fine-grained formations (shales, siltstones and mudstones), a large scale pumping test was performed in a major fault over 151 days. Deconvolution was applied first to remove the effect of variable flow rates and obtain constant-rate responses of the reservoir. Next, pressure-transients were analyzed both in time and space to get flow dimension, n, through the pressure derivative and extract the anomalous diffusion exponent, dw, as well as the fractal dimension, df. Analysis revealed at least two kinds of responses characterized by flow dimensions of 0.08 and 0.39 and anomalous diffusion exponents of 2.16 and 2.93, respectively. These properties, which can be related to major geological structures (i.e. major faults and surrounding fractures network), shows decreasing hydraulic properties (transmissivity, T, and storativity, S), and consequently, decreasing hydraulic connectivity, with increasing scale of investigation. In particular, the major fault (n = 0.39 ; dw = 2.93) shows a relationship of about T~S3 with T~r-1.36 and S~r-0.43, consistent with flow within a fracture, while the surrounding fractures network (n = 0.08 ; dw = 2.16) displays a relationship which follow T~S with T~r-1.07 and S~r-0.91. This scale-dependence of hydraulic properties may help improve groundwater flow prediction in such fractured reservoirs and could be taken into account for long-term transport of contaminants at this site