Two‐dimensional physically based finite element runoff model for small agricultural watersheds: I. Model development

Soil erosion by water is the root cause of ecological degradation in the Shiwalik foothills of Northern India. Simulation of runoff and its component processes is a pre‐requisite to develop the management strategies to tackle the problem, successfully. A two‐dimensional physically based distributed numerical model, ROMO2D has been developed to simulate runoff from small agricultural watersheds on an event basis. The model employs the 2‐D Richards equation with sink term to simulate infiltration and soil moisture dynamics in the vadoze zone under variable rainfall conditions, and 2‐D Saint‐Venant equations under the kinematic wave approximation along with Manning's equation as the stage‐discharge equation for runoff routing. The various flow‐governing equations have been solved numerically by employing a Galerkin finite element method for spatial discretization using quadrilateral elements and finite difference techniques for temporal solutions. The ROMO2D computer program has been developed as a class‐based program, coded in C + + in such a way that with minor modifications, the model can be used to simulate runoff on a continuous basis. The model writes output for a runoff hydrograph of each storm. Model development is described in this paper and the results of model testing and field application are to be presented in a subsequent paper. Copyright © 2008 John Wiley & Sons, Ltd.     

Macroalgal survival in ballast water tanks

Despite a large amount of research into invasive species and their introductions, there have been no studies focused on macroalgal transport in ballast water. To address this, we collected replicate samples of ballast water from 12 ships in two Mediterranean harbours (Naples and Salerno). Filtered samples were kept in culture for a month at Mediterranean mean conditions (18 degrees C, 12:12h LD, 60micromol photons m(-2)s(-1)). Fifteen macroalgal taxa were cultured and differed according to the geographic origin of the ballast water. Most of the cultured algae were widely distributed species (e.g. Ulva spp. and Acinetospora-phase). However, Ulva ohnoi Hiraoka and Shimada, described from Japan, was hitherto unknown in the Mediterranean Sea. We show for the first time that ballast water can be an important vector for the transport of microscopic stages of macroalgae and that this can be a vector for the introduction of alien species.     

The pattern of Ni and Co abundances in lunar olivines

Near liquidus experiments on peridotite and other olivine normative compositions from 1.7 to 6 GPa confirm the applicability of exchange-based empirical models of Ni and Co partitioning between olivine and silicate liquids with compositions close to the liquidus of peridotite. Given that most estimates of lunar bulk composition are peridotitic, the partitioning models thus lend themselves to calculation of olivine compositions produced during the early stages of magma ocean crystallization. Calculation of olivine compositions produced by fractional crystallization of a model lunar magma ocean, initially 700 km deep, reveals a prominent maximum in Ni concentration versus fraction crystallized or Mg’ (molar MgO/(MgO + FeO)), but a pattern of monotonically increasing Co concentration. These patterns qualitatively match the puzzling patterns of Ni and Co concentrations observed in lunar rocks in which forsteritic olivines in magnesian suite cumulates have lower Ni and Co abundances than do less magnesian olivines from low-Ti mare basalts, and olivines from the ferroan anorthosite suite (FAS) have lower Ni, but similar Co to mare basalt olivines.The Ni and Co abundances in olivines from the magnesian suite cumulates can be reconciled in terms of fractional crystallization of a deep magma ocean which initially produces a basal dunite comprised of the hottest and most magnesian olivine overlain by an olivine-orthopyroxene (harzburgite) layer that is in turn overlain by an upper zone of plagioclase-bearing cumulates. The ultramafic portion of the cumulate pile overturns sending the denser harzburgite layer, which later becomes a portion of the green glass source region, to the bottom of the cumulate pile with Ni- and Co-rich olivine. Meanwhile, the less dense, but hottest, most magnesian olivines with much lower Ni and Co abundances are transported upward to the base of the plagioclase-bearing cumulates where subsequent heat transfer leads to melting of mixtures of primary dunite, norite, and gabbronorite with KREEP (a K-REE-P enriched component widely believed to be derived from the very latest stage magma ocean liquid). These hybrid melts have Al₂O₃, Ni, and Co abundances and Mg’ appropriate for parent magmas of the magnesian suite. Ni and Co abundances in the FAS are consistent with either direct crystallization from the magma ocean or crystallization of melts of primary dunite-norite mixtures without KREEP.     

Sulfur cycling at the Mid-Atlantic Ridge: A multiple sulfur isotope approach

The role of sulfur in two hydrothermal vent systems, the Logatchev hydrothermal field at 14°45′N/44°58′W and several different vent sites along the southern Mid-Atlantic Ridge (SMAR) between 4°48′S and 9°33′S and between 12°22′W and 13°12′W, is examined by utilizing multiple sulfur isotope and sulfur concentration data. Isotope compositions for sulfide minerals and vent H₂S from different SMAR sites range from + 1.5 to + 8.9‰ in δ³⁴S and from + 0.001 to + 0.051‰ in Δ³³S. These data indicate mixing of mantle sulfur with sulfur from seawater sulfate. Combined δ³⁴S and Δ³³S systematics reveal that vent sulfide from SMAR is characterized by a sulfur contribution from seawater sulfate between 25 and 33%. This higher contribution, compared with EPR sulfide, indicates increased seawater sulfate reduction at MAR, because of a deeper seated magma chamber and longer fluid upflow path length, and points to fundamental differences with respect to subsurface structures and fluid evolution at slow and fast spreading mid-ocean ridges.Additionally, isotope data uncover non-equilibrium isotopic exchange between dissolved sulfide and sulfate in an anhydrite bearing zone below the vent systems at fluid temperatures between 335 and 400 °C. δ³⁴S values between + 0.2 to + 8.8‰ for dissolved and precipitated sulfide from Logatchev point to the same mixing process between mantle sulfur and sulfur from seawater sulfate as at SMAR. δ³⁴S values between ? 24.5 and + 6.5‰ and Δ³³S values between + 0.001 and + 0.125‰ for sulfide-bearing sediments and mafic/ultramafic host rocks from drill cores taken in the region of Logatchev indicate a clear contribution of biogenic sulfides formed via bacterial sulfate reduction. Basalts and basaltic glass from SMAR sites with Δ³³S = ? 0.008‰ reveal lower Δ³³S lower values than suggested on the basis of previously published isotopic measurements of terrestrial materials.We conclude that the combined use of both δ³⁴S and Δ³³S provides a more detailed picture of the sulfur cycling in hydrothermal systems at the Mid-Atlantic Ridge and uncovers systematic differences to hydrothermal sites at different mid-ocean ridge sites. Multiple sulfur isotope measurements allow identification of incomplete isotope exchange in addition to isotope mixing as a second important factor influencing the isotopic composition of dissolved sulfide during fluid upflow. Furthermore, based on Δ³³S we are able to clearly distinguish biogenic from hydrothermal sulfides in sediments even when δ³⁴S were identical.     

Establishing constraints on groundwater ages with Cl,C, H,and noble gases: A case study in the eastern Paris basin,France

Groundwaters from the Tithonian/Kimmeridgian, Oxfordian and Upper Dogger aquifers, within the eastern part of the Paris basin (France), were characterised using ³H, ¹⁴C and ³⁶Cl, and noble gases tracers, to evaluate their residence times and determine their recharge period. This information is an important prerequisite to evaluating the confinement properties of the Callovo-Oxfordian clay formation sandwiched between the Oxfordian aquifer and the Dogger aquifer, currently being investigated by the French nuclear waste management agency (Andra) for radioactive waste disposal. Data presented in this paper are used to test 4 hypotheses.     

A georeferenced agent-based model to analyze the climate change impacts on ski tourism at a regional scale

One main argument for modeling socio-ecological systems is to advance the understanding of dynamic correlations between various human and environmental factors, including impacts and responses to environmental change. We explore the shift in skier distribution among ski resorts taking into account the behavioral adaptation of individuals due to the impact of climate change on snow conditions. This analysis is performed at a regional scale by means of a coupled gravity and georeferenced agent-based model. Four different scenarios are considered. Two scenarios assume an increase of winter mean temperature of +2°C and +4°C, respectively, taking into account only natural snow conditions. Two additional scenarios add the effect of snowmaking to enhance the natural snow depth and extend the skiing season in the +2°C and +4°C base scenarios. Results show differing vulnerability levels, allowing the classification of ski resorts into three distinct groups: (1) highly vulnerable ski resorts with a strong reduction in visitors attendance for all climate change scenarios, characterized by unfavorable geographical and attractiveness conditions, making it difficult to ensure snow availability in the future; (2) low vulnerability ski resorts, with moderate reduction in season length during a high climate change scenario but no reduction (or even an increase) in a low one, characterized by ski resorts with a medium capacity and attractiveness to ensure enough snow conditions and capture skiers from other ski resorts; and (3) resilient ski resorts, with good conditions to ensure future snow-reliable seasons and outstanding attractiveness, allowing them to offer longer ski seasons than their competitors and potentially attracting skiers from other closed or marginal resorts. Ski resorts included in this last group increase their skier attendance in all climate change scenarios. Although similar studies in the literature foretell a significant reduction of the ski market in the near future, another probable effect outlined in this study is a redefinition of this market due to a redistribution of skiers, from vulnerable ski resorts to more resilient ones.     

Utilization of a multicriteria least cost path model in an aquatic environment

A critical component of maintaining biodiversity in fragmented habitats is maintaining connectivity among the usable fragments. Least cost path (LCP) analysis is a tool that can be used for predicting the ability of an organism to move from one habitat patch to another, based on geographical features of the landscape and life history traits of the organism. While this analysis has been utilized for terrestrial habitats, it is rarely applied to aquatic environments. Aquatic hypoxic conditions occur when dissolved oxygen falls below 2 mg/L. These conditions can create barriers in the water column that can either force fish to leave a habitat, or avoid that habitat altogether. Using the lower St. Johns River (LSJR) estuary in Florida, USA, as a study system, the ability of an adult silver perch, Bairdiella chrysoura, to escape a large-scale hypoxic event was modeled using a multicriteria LCP approach. Criteria-specific cost grids were constructed based upon current speed, risk of predation, and whether oxygen levels in the habitat area were normoxic (>5.5 mg/L), or hypoxic (<2.0–1.5 mg/L) as a function of water depth for the LSJR. The criteria cost grids were combined using relative weighting to produce the multicriteria cost grid used to implement the LCP analysis. Three origin and destination point locations within the LSJR study area were selected for modeling whether or not a silver perch would be able to escape a hypoxic zone. Since the LCP model will always determine a LCP from the specified origin point location, ecologically relevant swimming capacities for silver perch under normoxic and hypoxic conditions were then applied to assess the model, and to determine whether the fish would be able to reach areas unimpacted by hypoxia. The LCP model and the swimming capacity results for this study predict that under normoxic conditions, fish movement was unimpeded. During the rapidly developing hypoxic event that was modeled, the results from the LCP model indicate that the fish could move outside the hypoxic zone, but when swimming capacities were applied to the model, the silver perch could not escape. Ecologically, the results of this study suggest that silver perch would experience high mortality under a rapidly developing hypoxic event. Additionally, the results of this study indicate that a LCP model can be applied to an aquatic habitat, as long as the cost grids incorporate relevant abiotic and biotic factors.