Factors influencing organic carbon recycling and burial in Skagerrak sediments

Different factors influencing recycling and burial rates of organic carbon (OC) were investigated in the continental margin sediments of the Skagerrak (NE North Sea). Two different areas, one in the southern and one in the northeastern part of the Skagerrak were visited shortly after a spring bloom (March 1999) and in late summer (August 2000). Results suggested that: (1) Organic carbon oxidation rates (Cox) (2.2–18 mmol C m-2d-11) were generally larger than the O2 uptake rates (1.9 –25 mmol m-2d-1). Both rates were measured in situ using a benthic lander. A mean apparent respiration ratio (Cox:O2corr) of 1.3±0.5 was found, indicating some long-term burial of reduced inorganic substances in these sediments. Measured O2 fluxes increased linearly with increasing Cox rates during the late summer cruise but not on the early spring cruise, indicating a temporal uncoupling of anaerobic mineralization and reoxidation of reduced substances. (2) Dissolved organic carbon (DOC) fluxes (0.2–1.0 mmol C m-2d-1) constituted 3–10% of the Cox rates and were positively correlated with the latter, implying that net DOC production rates were proportional to the overall sediment OC remineralization rates. (3) Chlorophyll a (Chl-a) concentrations in the sediment were significantly higher in early spring compared to late summer. The measured Cox rates, but not O2 fluxes, showed a strong positive correlation with the Chl-a inventories in the top 3 cm of the sediment. (4) Although no relationship was found between the benthic fluxes and the macrofaunal biomass in the chambers, total in situ measured dissolved inorganic carbon (CT) fluxes were 1–5.4 times higher than diffusive mediated CT fluxes, indicating that macrofauna have a significant impact on benthic exchange rates of OC remineralization products in Skagerrak sediments. (5) OC burial fluxes were generally higher in northeastern Skagerrak than in the southern part. The same pattern was observed for burial efficiencies, with annual means of ~62% and ~43% for the two areas respectively. (6) On a basin-wide scale, there was a significant positive linear correlation between the burial efficiencies and sediment accumulation rates. (7) The calculated particulate organic carbon (POC) deposition, from benthic flux and burial measurements, was only 24 –78% of the sediment trap measured POC deposition, indicating a strong near-bottom lateral transport and resuspension of POC. (8) A larger fraction of the laterally advected material of lower quality seemed to settle in the northeastern Skagerrak rather than in the southern Skagerrak. (9) Skagerrak sediments, especially in the northeastern part, act as an efficient net sink for organic carbon, even in a global continental margin context

Benthic estuarine communities in Brazil: moving forward to long term studies to assess climate change impacts

Abstract Estuaries are unique coastal ecosystems that sustain and provide essential ecological services for mankind. Estuarine ecosystems include a variety of habitats with their own sediment-fauna dynamics, all of them globally undergoing alteration or threatened by human activities. Mangrove forests, saltmarshes, tidal flats and other confined estuarine systems are under increasing stress due to human activities leading to habitat and species loss. Combined changes in estuarine hydromorphology and in climate pose severe threats to estuarine ecosystems on a global scale. The ReBentos network is the first integrated attempt in Brazil to monitor estuarine changes in the long term to detect and assess the effects of global warming. This paper is an initial effort of ReBentos to review current knowledge on benthic estuarine ecology in Brazil. We herein present and synthesize all published work on Brazilian estuaries that has focused on the description of benthic communities and related ecological processes. We then use current data on Brazilian estuaries and present recommendations for future studies to address climate change effects, suggesting trends for possible future research and stressing the need for long-term datasets and international partnerships

Fatigue evaluation of surface coated railway rails using shakedown theory, finite element calculations, and lab and field trials

One solution to prevent surface fatigue of rails, investigated by the European project INFRA-STAR, is to coat the surfaces with a material which reduces or eliminates ratchetting. In this investigation, a systematic approach for fatigue design of surface coated rails (called two-material rails) against rolling contact fatigue is presented. It incorporates dynamic train-track interaction simulations, three-dimensional finite element (FE) calculations, shakedown theory, and lab and field trials. The approach was validated against two-dimensional twin-disc tests in laboratory, where surface coated disc specimens were used. Next, heavy haul traffic field trials were performed using two-material rails. Dynamic train-track interaction simulations, for train traffic situations at the test site, were performed. The results from these simulations were contact load data, which were used in the fatigue design approach to calculate railhead stresses with a three-dimensional FE model of a piece of rail; 26 load cases were identified as critical with respect to rolling contact fatigue. The stresses from the FE calculations were used to calculate shakedown diagrams for various wheel-rail contact situations at the test site. The shakedown diagrams and calculations are used to illustrate how the improvement in shakedown performance of coated rails varies with the coating thickness, traction coefficient, contact load position, the strength of the coating and substrate materials, and strain hardening of the materials. It is shown that the two-material rails with the correct rail profile can be used to prevent rolling contact fatigue and reduce wear for the current train traffic situation. The results are discussed in the light of observations at the test site

Prevention of RCF damage in curved track through development of the INFRA-STAR two-material rail

Results from the European 5th frame research project 'INFRA-STAR' are presented. The goal of the project is to prevent rolling contact fatigue (RCF) and to reduce squeal noise in curves by applying an additional surface layer material on the top of the railhead, resulting in a two-material rail. In INFRA-STAR, a dynamic train-track interaction model is used to provide the contact forces. Wheel-rail profiles, wheel-rail friction, vehicle data, track data and operating conditions are included to calculate the wheel-rail contact forces and spin moments, contact positions and load distributions in the contact patch. The contact pressure, friction coefficient, coating thickness, material properties of the coating and the rail material are used in finite element calculations and shakedown theory to calculate shakedown limits, which are then used to predict the RCF performance of the system. The paper details the work on theoretical modelling, twin disc testing, metallurgical research and field testing completed to date (August 2002, the project just passed midterm). The development of the surface layer application methods that are used, and the further objectives of the INFRA-STAR project, are discussed

Two-material rail development to prevent rolling contact fatigue and reduce noise levels in curved rail track

Results from the European 5th frame research project 'INFRA-STAR' are presented. The goal of the project is to prevent rolling contact fatigue (RCF) and to reduce squeal noise in curves by applying an additional surface layer material on the top of the railhead, resulting in a two-material rail. A dynamic train-track interaction model is used to provide the contact forces. Wheelrail profiles, wheel-rail friction, vehicle data, track data and operating conditions are included to calculate the wheel-rail contact forces and spin moments, contact positions and load distributions in the contact patch. The contact pressure, friction coefficient, coating thickness, material properties of the coating and the rail material are used to calculate the shakedown limit, which is then used to predict the rolling contact fatigue performance of the system. The presented paper will detail the above proposed work as well as the work on theoretical modelling, twin disc testing and metallurgical research completed to date. The development of the surface layer application methods that are used and the further objectives of the INFRA-STAR project will also be discussed. The presented paper will account for interesting and industrially relevant RCF- and noise related research work. We believe that it will be of great importance in the future development of reliable and durable rail infrastructure

Development of a two-material rail for RCF and noise control

Abstract not available