Predicting the resilience of transport infrastructure to a natural disaster using Cox’s proportional hazards regression model

Transport infrastructure is at significant risk of direct damage from extreme climate events such as flooding, where the cost implications of delayed recovery are generally significant. Previous research in this regard has focused on the technical and engineering aspects of infrastructure construction. The risk management of resilient transport infrastructure is poorly considered, and little has been done to quantify the capacity of transport infrastructure to recover from the impact of natural disasters under varying conditions. This paper applies Cox’s proportional hazards regression model to determine the rate of recovery and cumulative probability that recovery occurs for transport infrastructure across regional areas in New South Wales, Australia. Data for post-disaster reconstruction projects over the period 1992–2012 are used to analyze recovery rate against geographic region, natural disaster type and post-disaster transport infrastructure reconstruction cost. Results demonstrate that transport infrastructure recovered slowest when the failure is the result of a flood rather than bushfire or storm, and in regions with a riverine geography. To validate the accuracy of the model, a bootstrap resampling technique is used. The bootstrap result confirms that the model is robust and reasonable.

     

Biological reduction of chlorinated solvents: Batch-scale geochemical modeling

Simulation of biodegradation of chlorinated solvents in dense non-aqueous phase liquid (DNAPL) source zones requires a model that accounts for the complexity of processes involved and that is consistent with available laboratory studies. This paper describes such a comprehensive modeling framework that includes microbially mediated degradation processes, microbial population growth and decay, geochemical reactions, as well as interphase mass transfer processes such as DNAPL dissolution, gas formation and mineral precipitation/dissolution. All these processes can be in equilibrium or kinetically controlled. A batch modeling example was presented where the degradation of trichloroethene (TCE) and its byproducts and concomitant reactions (e.g., electron donor fermentation, sulfate reduction, pH buffering by calcite dissolution) were simulated. Local and global sensitivity analysis techniques were applied to delineate the dominant model parameters and processes. Sensitivity analysis indicated that accurate values for parameters related to dichloroethene (DCE) and vinyl chloride (VC) degradation (i.e., DCE and VC maximum utilization rates, yield due to DCE utilization, decay rate for DCE/VC dechlorinators) are important for prediction of the overall dechlorination time. These parameters influence the maximum growth rate of the DCE and VC dechlorinating microorganisms and, thus, the time required for a small initial population to reach a sufficient concentration to significantly affect the overall rate of dechlorination. Self-inhibition of chlorinated ethenes at high concentrations and natural buffering provided by the sediment were also shown to significantly influence the dechlorination time. Furthermore, the analysis indicated that the rates of the competing, nonchlorinated electron-accepting processes relative to the dechlorination kinetics also affect the overall dechlorination time. Results demonstrated that the model developed is a flexible research tool that is able to provide valuable insight into the fundamental processes and their complex interactions during bioremediation of chlorinated ethenes in DNAPL source zones.     

Using blood samples to estimate persistent organic pollutants and metals in green sea turtles (Chelonia mydas)

Persistent organic pollutants (POPs) and heavy metals have been reported in a number of green turtle (Chelonia mydas) populations worldwide. However, due to ethical considerations, these studies have generally been on tissues from deceased and stranded animals. The purpose of this study was to investigate the use of blood samples to estimate the tissue contamination of live C. mydas populations. This study analysed 125 POP compounds and eight heavy metals in the blood, liver, kidney and muscle of 16 C. mydas from the Sea World Sea Turtle Rehabilitation Program, Gold Coast, Australia. Strong correlations were observed between blood and tissue concentrations for a number of POPs and metals. Furthermore, these correlations were observed over large ranges of turtle size, sex and condition. These results indicate that blood samples are a reliable non-lethal method for predicting chemical contamination in C. mydas.     

Rangeland hydrology and erosion model (RHEM) enhancements for applications on disturbed rangelands

The rangeland hydrology and erosion model (RHEM) is a new process‐based model developed by the USDA Agricultural Research Service. RHEM was initially developed for functionally intact rangelands where concentrated flow erosion is minimal and most soil loss occurs by rain splash and sheet flow erosion processes. Disturbance such as fire or woody plant encroachment can amplify overland flow erosion by increasing the likelihood of concentrated flow formation. In this study, we enhanced RHEM applications on disturbed rangelands by using a new approach for the prediction and parameterization of concentrated flow erosion. The new approach was conceptualized based on observations and results of experimental studies on rangelands disturbed by fire and/or by tree encroachment. The sediment detachment rate for concentrated flow was calculated using soil erodibility and hydraulic (flow width and stream power) parameters. Concentrated flow width was calculated based on flow discharge and slope using an equation developed specifically for disturbed rangelands. Soil detachment was assumed to begin with concentrated flow initiation. A dynamic erodibility concept was applied where concentrated flow erodibility was set to decrease exponentially during a run‐off event because of declining sediment availability. Erodibility was estimated using an empirical parameterization equation as a function of vegetation cover and surface soil texture. A dynamic partial differential sediment continuity equation was used to model the total detachment rate of concentrated flow and rain splash and sheet flow. The enhanced version of the model was evaluated against rainfall simulation data for three different sites that exhibit some degree of disturbance by fire and/or by tree encroachment. The coefficient of determination (R²) and Nash–Sutcliffe efficiency were 0.78 and 0.71, respectively, which indicates the capability of the model using the new approach for predicting soil loss on disturbed rangeland. By using the new concentrated flow modelling approach, the model was enhanced to be a practical tool that utilizes readily available vegetation and soil data for quantifying erosion and assessing erosion risk following rangeland disturbance. Copyright © 2014 John Wiley & Sons, Ltd.     

A coupled hydrology–biogeochemistry model to simulate dissolved organic carbon exports from a permafrost‐influenced catchment

We outline the development of a simple, coupled hydrology–biogeochemistry model for simulating stream discharge and dissolved organic carbon (DOC) dynamics in data sparse, permafrost‐influenced catchments with large stores of soil organic carbon. The model incorporates the influence of active layer dynamics and slope aspect on hydrological flowpaths and resulting DOC mobilization. Calibration and evaluation of the model was undertaken using observations from Granger Basin within the Wolf Creek research basin, Yukon, northern Canada. Results show that the model was able to capture the dominant hydrological response and DOC dynamics of the catchment reasonably well. Simulated DOC was highly correlated with observed DOC (r² = 0.65) for the study period. During the snowmelt period, the model adequately captured the observed dynamics, with simulations generally reflecting the timing and magnitude of the observed DOC and stream discharge. The model was less successful over the later summer period although this partly reflected a lack of DOC observations for calibration. The developed model offers a valuable framework for investigating the interactions between hydrological and DOC processes in these highly dynamic systems, where data acquisition is often very difficult. © 2015 The Authors Hydrological Processes Published by John Wiley & Sons, Ltd.     

Detection of Pharmaceuticals and Personal Care Products in Agricultural Soils Receiving Biosolids Application

Increasing research has suggested that biosolids generated from municipal wastewater treatment can be a major sink for many pharmaceuticals and personal care products (PPCPs) and their land application potentially introduces these contaminants into the terrestrial and aquatic environments. In this study, methods were developed for the analysis of 14 PPCPs in biosolids and soils using pressurized liquid extraction, solid phase extraction and liquid chromatography‐tandem mass spectrometry. Recoveries were over 50% for all analytes except diphenhydramine (?30%) in soils. Soil properties or type of biosolids showed minor effects on method recoveries. Estimated method limits of quantification (LOQ) range from 0.1–15 ng g^–1 for soil and 0.3–27 ng g^–1 for biosolids. A field study utilizing the methods revealed that other than carbamazepine‐10,11‐epoxide, all targeted compounds were detected in biosolids. Diphenhydramine, fluoxetine, triclosan and triclocarban were detected up to the μg g^–1 range with the highest concentration of 23 μg g^–1 for triclocarban. Seven of the PCCPs found in biosolids were also detected in agricultural soils amended with these biosolids and several (carbamazepine, diphenhydramine, and triclocarban) appeared to be persistent in soils. Triclocarban was also found most abundant in soils with the highest average concentration of 0.2 μg g^–1 while the rest of compounds were in the lower ng g^–1 range. Generally, the concentrations found on the fields were 2–3 degrees of magnitude lower than in the biosolids, which is likely to be due to dilution, degradation and leaching processes.     

Identifying sources of organic matter in sediments of shallow lakes using multiple geochemical variables

We analyzed ²¹⁰Pb-dated sediment cores from four relatively shallow lakes (z_max < 10 m) in the Upper Ocklawaha River Basin, Florida, USA to compare primary producer community structure before and after anthropogenic impacts. We measured physical and chemical sediment variables including density, organic matter (OM), water-soluble phosphorus, polyphosphate (Poly-P), total P (TP), total carbon to total nitrogen mass ratios of OM (TC:TN), biogenic silica (diatoms, sponge spicules), total amorphous silica, and stable carbon and nitrogen isotope ratios of bulk OM. Principal component analysis showed that diatom biogenic silica, TC:TN, Poly-P and TP displayed discernible stratigraphic changes associated with the shift in the primary producer community. We applied k-means cluster analysis to these variables to identify macrophyte-derived, transitional, and phytoplankton-derived sediments. Our approach provides an objective method for identifying sediment sources that may be applied to shallow lakes in other regions. The four study lakes shifted from a macrophyte-dominated state to a transitional state before major anthropogenic disturbances, and became phytoplankton-dominated after ~1950.     

Collapse simulation of a four‐story steel moment frame by a distributed online hybrid test

The collapse of a one‐bay, four‐story steel moment frame is simulated in this study by the proposed peer‐to‐peer (P2P) Internet online hybrid test system. The typical beam hinging mechanism, which is ensured by a strong‐column, weak‐beam design, is reproduced. The plastic hinges at the column bases are taken as the experimental portions, while the superstructure is analyzed numerically by a general‐purpose finite element program. The implicit plastic rotations of the two column bases are treated as boundary displacements. In order to account for the complex behavior of the column bases, the P2P system is modified to use the secant stiffness during iterations, and the physical specimens are designed such that the plastic hinge behavior can be obtained. For this study, the three substructures are distributed to different locations. A large ground motion is repeatedly imposed until the column bases lose their capacity to sustain the gravity load. As a result, significant deterioration is observed at both column bases. The proposed P2P system is thus demonstrated to be able to accommodate multiple‐tested substructures involving unstable behavior. The results suggest that the P2P Internet online hybrid test system provides a reliable means of studying structures up to collapse. Copyright © 2008 John Wiley & Sons, Ltd.     

Medium timescale stability of tidal mudflats in Bridgwater Bay,Bristol Channel,UK: Influence of tides,waves and climate

This paper presents the results of an 11-year study into mudflat elevation changes within the intertidal zone at Stert Flats in Bridgwater Bay, Somerset. This site is located in the outer Severn Estuary/inner Bristol Channel which is a macro-hypertidal regime dominated by physical processes, characterized by strong tidal currents, high turbidity and a significant degree of exposure to wind generated waves. Two transects of stakes were installed perpendicular to the coast, extending seawards 300 m from the edge of the saltmarsh onto the mudflats, against which variations in accretion or erosion could be measured. The mudflats themselves consisted of an underlying consolidated clay of Holocene age and a surface veneer of fluid mud and/or mobile sand patches which varied both spatially and temporally. Mudflat development was recorded over both short-term (monthly/seasonal) and medium-term (inter-annual) timescales. The results display a significant degree of scatter over all timescales. Such variability in response may be expected in such a dynamic system where noise can be attributed to a combination of factors such as the mobility of surface fluid mud and sand patches and the migration of the underlying ridge–runnel drainage network. Despite this, the expected short-term variations related to neap–spring tidal conditions and seasonal influences were observed at a number of locations on the transects although these were weakly expressed. The over-riding feature of the profiles is a consistent long-term trend of erosion which appears to be masking shorter term trends within the dataset. Viewed over the 11-year period, the changes in mudflat elevation closely match the pattern of the index of the North Atlantic Oscillation (NAO) during the 1990s, suggesting a strong climatic control over mudflat development on a medium-term/decadal scale. Most profiles display a strong erosional trend during the early 1990s when the NAO index was positive. The erosional trend peaked in 1995 at a time during which the values for monthly winter mean significant wave height were notably high. Between 1996 and 2001 the profiles generally record accretion and the data display significant variability. This corresponds with a shift to a strongly negative and then weakly positive NAO index phase. The fact that such a general atmospheric factor correlates so closely with medium timescale elevation change is attributed to relative weakness of biological binding and burrowing at this site, and more-so to the overwhelming dominance of the physical regime, especially the tidal current and the wind–wave regime. Both the background erosional trend and the influence of the index of the NAO in controlling mudflat evolution have important implications relating to coastal management. These are discussed in relation to coastal defence measures, morphological response to major civil engineering projects (e.g. Severn Tidal Power Barrage) and the prospect of climate change, sea-level rise and a possible increase in strength of NAO conditions in the future.     

Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies

The North Pacific Oscillation (NPO) recently (re-)emerged in the literature as a key atmospheric mode in Northern Hemisphere climate variability, especially in the Pacific sector. Defined as a dipole of sea level pressure (SLP) between, roughly, Alaska and Hawaii, the NPO is connected with downstream weather conditions over North America, serves as the atmospheric forcing pattern of the North Pacific Gyre Oscillation (NPGO), and is a potential mechanism linking extratropical atmospheric variability to El Ni?o events in the tropical Pacific. This paper explores further the forcing dynamics of the NPO and, in particular, that of its individual poles. Using observational data and experiments with a simple atmospheric general circulation model (AGCM), we illustrate that the southern pole of the NPO (i.e., the one near Hawaii) contains significant power at low frequencies (7–10?years), while the northern pole (i.e., the one near Alaska) has no dominant frequencies. When examining the low-frequency content of the NPO and its poles separately, we discover that low-frequency variations (periods >7?years) of the NPO (particularly its subtropical node) are intimately tied to variability in central equatorial Pacific sea surface temperatures (SSTs) associated with the El Ni?o-Modoki/Central Pacific Warming (CPW) phenomenon. This result suggests that fluctuations in subtropical North Pacific SLP are important to monitor for Pacific low-frequency climate change. Using the simple AGCM, we also illustrate that variability in central tropical Pacific SSTs drives a significant fraction of variability of the southern node of the NPO. Taken together, the results highlight important links between secondary modes (i.e., CPW-NPO-NPGO) in Pacific decadal variability, akin to already established relationships between the primary modes of Pacific climate variability (i.e., canonical El Ni?o, the Aleutian Low, and the Pacific Decadal Oscillation).