A simple non-linear model for the investigation of the effects of the gap closure at the abutment joints of short bridges

Closure of the gap at the abutment joints of bridges has been the source of extensive damage during the 1971 San Fernando and more recent earthquakes. In this paper a model for the investigation of the effects of this gap closure is presented and analysed. The focus of the model is the representation of the non-linear response of the bridge abutments, the foundation and the columns. The model is used for the investigation of the response of a short bridge located in California.     

Groundwater-dependent ecology of the shoreline of the subtropical Lake St Lucia estuary

The ecology of the St Lucia estuary in South Africa is of unique international importance. During droughts the estuary experiences high salinities, with values above that of seawater. Ion-poor groundwater flowing into the estuary from prominent sand aquifers along its eastern shoreline forms low-salinity habitats for salt-sensitive biota. During droughts, plants and animals can take refuge in the groundwater discharge zone until the condition in the estuary regains tolerable salinity. Simulations of the groundwater discharge indicate that the flow can persist during droughts over at least a decade, and be of great important for the resilience of the estuary. Anthropogenic activities have reduced the river inflow and made the St Lucia estuary more sensitive to droughts. The groundwater has thereby become increasingly important for the estuary’s ecology. Protection of the groundwater discharge along the shoreline itself and actions to increase the groundwater recharge are therefore important management tasks.     

Crustal architecture above the high-pressure belt of the Grenville Province in the Manicouagan area: new structural, petrologic and U–Pb age constraints

Recent U–Pb age determinations and P–T estimates allow us to characterize the different levels of a formerly thickened crust, and provide further constraints on the make up and tectono-thermal evolution of the Grenville Province in the Manicouagan area. An important tectonic element, the Manicouagan Imbricate zone (MIZ), consists of mainly 1.65, 1.48 and 1.17 Ga igneous rocks metamorphosed under 1400–1800 MPa and 800–900 °C at 1.05–1.03 Ga, during the Ottawan episode of the Grenvillian orogenic cycle, coevally with intrusion of gabbro dykes in shear zones. The MIZ has been interpreted as representing thermally weakened deep levels of thickened crust extruded towards the NW over a parautochthonous crustal-scale ramp. Mantle-derived melts are considered as in part responsible for the high metamorphic temperatures that were registered.New data show that mid-crustal levels structurally above the MIZ are represented by the Gabriel Complex of the Berthé terrane, that consists of migmatite with boudins of 1136±15 Ma gabbro and rafts of anatectic metapelite with an inherited monazite age at 1478±30 Ma. These rocks were metamorphosed at about the same time as the MIZ (metamorphic zircon in gabbro: 1046±2 Ma; single grains of monazite in anatectic metapelite: 1053±2 Ma) and under the same T range (800–900 °C) but at lower P conditions (1000–1100 MPa). They are mainly exposed in an antiformal culmination above a high-strain zone, which has tectonic lenses of high P–T rocks from the MIZ and is intruded by synmetamorphic gabbroic rocks. This zone is interpreted as part of the hangingwall of the MIZ during extrusion. A gap of 400 MPa in metamorphic pressures between the tectonic lenses and the country rocks, together with the broad similarity in metamorphic ages, are consistent with rapid tectonic transport of the high P–T rocks over a ramp prior to the incorporation of the mafic lenses in the hangingwall.Between the antiformal culmination of the Gabriel Complex and the MIZ 1.48 Ga old granulites of the Hart Jaune terrane are exposed. They are intruded by unmetamorphosed 1228±3 Ma gabbro sills and 1166±1 Ma anorthosite. Hart Jaune Terrane represents relatively high crustal levels that truncate the MIZ-Gabriel Complex contact and are preserved in a synformal structure.Farther south, the Gabriel Complex is overlain by the Banded Complex, a composite unit including 1403+32/−25 Ma granodiorite and 1238+16/−13−1202+40/−25 Ma granite. This unit has been metamorphosed under relatively low-P (800 MPa) granulite-facies conditions. Metamorphic U–Pb data, limited to zircon lower intercept ages (971±38 Ma and 996±27 Ma) and a titanite (990±5 Ma) age, are interpreted to postdate the metamorphic peak.The general configuration of units along the section is consistent with extrusion of the MIZ during shortening and, finally, normal displacement along discrete shear zones.     

Exploring the Solution Space of Semi-structured Geographical Problems Using Genetic Algorithms

Semi-structured geographical problems are often addressed by groups of decision-makers. Each group member is likely to have a specific set of objectives that they wish to address and a unique perspective on the way in which the problem should be solved. The solution to such problems often requires consensus building and compromise among decision-makers as they attempt to optimize their own criteria. The set of criteria adopted by a particular decision-maker constrains the set of solutions he/she will deem acceptable. Compromise among multiple decision-makers can occur at the intersection of these constrained solution sets. Knowledge about the criteria space, the solution space, and the relation between the two is often incomplete for semi-structured problems. New tools are needed to explore, analyze, and visualize the solution space of a problem with respect to multiple analytical models and criteria. In this research we explore the utility of genetic algorithms as an effective means to: (1) search the solution space of geographical problems; (2) visualize the spatial ramifications of alternative criteria spaces; and (3) identify compromise solutions.     

The international at-sea intercomparison of fCO2 systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean

The ‘International Intercomparison Exercise of fCO₂ Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO₂) systems, one discrete fCO₂ system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO₂ measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO₂, temperature measurements) and a common procedure for calculation of final fCO₂ were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO₂ in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO₂ measurements can be made in good agreement (±3 μatm) with underway fCO₂ data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO₂ system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO₂ results. Calculation of fCO₂ from high-quality total dissolved inorganic carbon (C_T) and total alkalinity (A_T) measurements does not yield results comparable in accuracy and precision to fCO₂ measurements.     

Modeling the response of primary production and sedimentation to variable nitrate loading in the Mississippi River plume

Increases in nitrate loading to the Mississippi River watershed during the last 50 years are considered responsible for the increase in hypoxic zone size in Louisiana-Texas shelf bottom waters. There is currently a national mandate to decrease the size of the hypoxic zone to 5000 km² by 2015, mostly by a 30% reduction in annual nitrogen discharge into the Gulf of Mexico. We developed an ecosystem model for the Mississippi River plume to investigate the response of organic matter production and sedimentation to variable nitrate loading. The nitrogen-based model consisted of nine compartments (nitrate, ammonium, labile dissolved organic nitrogen, bacteria, small phytoplankton, diatoms, micro- and mesozooplankton, and detritus), and was developed for the spring season, when sedimentation of organic matter from plume surface waters is considered important in the development of shelf hypoxia. The model was forced by physical parameters specified along the river-ocean salinity gradient, including residence time, light attenuation by dissolved and particulate matter, mixed layer depth, and dilution. The model was developed using measurements of biological biomasses and nutrient concentrations across the salinity gradient, and model validation was performed with an independent dataset of primary production measurements for different riverine NO₃ loads. Based on simulations over the range of observed springtime NO₃ loads, small phytoplankton contributed on average 80% to primary production for intermediate to high salinities (>15), and the main contributors to modeled sedimentation at these salinities were diatom sinking, microzooplankton egestion, and small phytoplankton mortality. We investigated the impact of limiting factors on the relationship between NO₃ loading and ecosystem rates. Model results showed that primary production was primarily limited by physical dilution of NO₃, followed by abiotic light attenuation, light attenuation due to mixing, and diatom sinking. Sedimentation was mainly limited by the first three of these factors. Neither zooplankton grazing or plume residence times acted as limiting factors of ecosystem rates. Regarding nutrient reductions to the watershed, simulations showed that about half of the percent decrease in NO₃ load was reflected in decreased plume sedimentation. For example, a 30% decrease in NO₃ load resulted in a 19% decrease in average plume primary production and a 14% decrease in sedimentation. Finally, our model results indicated that the fraction of primary production exported from surface waters is highly variable with salinity (7–87%), a finding which has important implications for predictive models of hypoxic zone size that assume a constant value for this ratio.     

Estimating restorable wetland water storage at landscape scales

Globally, hydrologic modifications such as ditching and subsurface drainage have significantly reduced wetland water storage capacity (i.e., volume of surface water a wetland can retain) and consequent wetland functions. While wetland area has been well documented across many landscapes and used to guide restoration efforts, few studies have directly quantified the associated wetland storage capacity. Here, we present a novel raster‐based approach to quantify both contemporary and potential (i.e., restorable) storage capacities of individual depressional basins across landscapes. We demonstrate the utility of this method by applying it to the Delmarva Peninsula, a region punctuated by both depressional wetlands and drainage ditches. Across the entire peninsula, we estimated that restoration (i.e., plugging ditches) could increase storage capacity by 80%. Focusing on an individual watershed, we found that over 59% of restorable storage capacity occurs within 20 m of the drainage network, and that 93% occurs within 1 m elevation of the drainage network. Our demonstration highlights widespread ditching in this landscape, spatial patterns of both contemporary and potential storage capacities, and clear opportunities for hydrologic restoration. In Delmarva and more broadly, our novel approach can inform targeted landscape‐scale conservation and restoration efforts to optimize hydrologically mediated wetland functions.     

Implementing marine reserve networks: A comparison of approaches in New South Wales (Australia) and New Zealand

Marine reserve networks are an essential and effective tool for conserving marine biodiversity. They also have an important role in the governance of oceans and the sustainable management of marine resources. The translation of marine reserve network theory into practice is a challenge for conservation practitioners. Barriers to implementing marine reserves include varying levels of political will and agency support and leadership, poorly coordinated marine conservation policy, inconsistencies with the use of legislation, polarised views and opposition from some stakeholders, and difficulties with defining and mapping conservation features. The future success of marine reserve network implementation will become increasingly dependent on: increasing political commitment and agency leadership; greater involvement and collaboration with stakeholders; and the provision of resources to define and map conservation features. Key elements of translating marine reserve theory into implementation of a network of marine reserves are discussed based on approaches used successfully in New Zealand and New South Wales (Australia).     

Global Sensitivity Analysis Techniques for Probabilistic Ground Water Modeling

Global sensitivity analysis techniques are better suited for analyzing input-output relationships over the full range of parameter variations and model outcomes, as opposed to local sensitivity analysis carried out around a reference point. This article describes three such techniques: (1) stepwise rank regression analysis for building input-output models to identify key contributors to output variance, (2) mutual information (entropy) analysis for determining the strength of nonmonotonic patterns of input-output association, and (3) classification tree analysis for determining what variables or combinations are responsible for driving model output into extreme categories. These techniques are best applied in conjunction with Monte Carlo simulation-based probabilistic analyses. Two examples are presented to demonstrate the applicability of these methods. The usefulness of global sensitivity techniques is examined vis-a-vis local sensitivity analysis methods, and recommendations are provided for their applications in ground water modeling practice.