Accuracy and precision of tidal wetland soil carbon mapping in the conterminous United States

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 9478, doi:10.1038/s41598-018-26948-7.Tidal wetlands produce long-term soil organic carbon (C) stocks. Thus for carbon accounting purposes, we need accurate and precise information on the magnitude and spatial distribution of those stocks. We assembled and analyzed an unprecedented soil core dataset, and tested three strategies for mapping carbon stocks: applying the average value from the synthesis to mapped tidal wetlands, applying models fit using empirical data and applied using soil, vegetation and salinity maps, and relying on independently generated soil carbon maps. Soil carbon stocks were far lower on average and varied less spatially and with depth than stocks calculated from available soils maps. Further, variation in carbon density was not well-predicted based on climate, salinity, vegetation, or soil classes. Instead, the assembled dataset showed that carbon density across the conterminous united states (CONUS) was normally distributed, with a predictable range of observations. We identified the simplest strategy, applying mean carbon density (27.0 kg C m−3), as the best performing strategy, and conservatively estimated that the top meter of CONUS tidal wetland soil contains 0.72 petagrams C. This strategy could provide standardization in CONUS tidal carbon accounting until such a time as modeling and mapping advancements can quantitatively improve accuracy and precision.Synthesis efforts were funded by NASA Carbon Monitoring System (CMS; NNH14AY67I), USGS LandCarbon and the Smithsonian Institution. J.R.H. was additionally supported by the NSF-funded Coastal Carbon Research Coordination Network while completing this manuscript (DEB-1655622). J.M.S. coring efforts were funded by NSF (EAR-1204079). B.P.H. coring efforts were funded by Earth Observatory (Publication Number 197)

A Simplified Treatise on the Effect of Wear in Cables

Cables and wire ropes are known to both elongate and reduce diametrically during their lifetime. The relationship between cable elongation and cable life has been observed for many years and includes three distinct stages. The first, the constructional stretch stage, occurs early in the cable’s use and is mostly the result of the core compressing and the cable elements fitting closely together. The second stage of the cable’s life is referred to as the normal life stretch stage and is a much more gradual occurrence in which wear is the most dominant mechanism. The third stage includes a rapid elongation and indicates impending failure. The current study offers a simplified explanation on the effect of wear in cables. This work utilizes the recently developed theory for wire ropes and cables in which the cable is considered to be a collection of thin helical wires and the equations of equilibrium for bending and twisting of thin rods are applied. A simple cable cross section is considered and the effects of wear on cable stiffness, diameter reduction and individual wire strains are evaluated. It is determined that cable stiffness can actually increase for small amounts of wire wear due to the disparity between the changes in the geometric and elastic stiffness components with wear.</jats:p