Hopane,sterane and n-alkane distributions in shallow sediments hosting high arsenic groundwaters in Cambodia

The presence of elevated As in ground waters exploited for drinking water and irrigation in South-East Asia is causing serious impacts on human health. A key mechanism that causes the mobilization of As in these waters is microbially mediated reductive transformation of As-bearing Fe(III) hydrated oxides and the role of degradable organic matter (OM) in this process is widely recognized. A number of different types of OM that drive As release in these aquifers have been suggested, including petroleum derived hydrocarbons naturally seeping into shallow sediments from deeper thermally mature source rocks. However, the amount of information on the characteristics of the OM in South-East Asian aquifers is limited. Here the organic geochemical analyses of the saturated hydrocarbon fractions and radiocarbon analysis, of two additional sites in SE Asia are reported. The results show that the OM in a given sedimentary horizon likely derives from multiple sources including naturally occurring petroleum. The importance of naturally occurring petroleum as one of the sources was clearly indicated by the n-alkane CPI of approximately 1, the presence of an unresolved complex mixture, and hopane (dominated by 17α(H),21β(H) hopanes) and sterane distribution patterns. The results also indicate that the OM in these aquifers varies tremendously in content, character and potential bioavailability. Furthermore, the presence of petroleum derived OM in sediments at both sites doubles the number of locations where their presence has been observed in association with As-rich, shallow aquifers, suggesting that the role of petroleum derived OM in microbially mediated As release might occur over a wider range of geographical locations than previously thought.     

Effective governance for competitive regions in Europe: the difficult case of the Randstad

Europe has come to recognize that its regions have a major role to play in achieving its cohesion and competitiveness objectives. EU policies and Structural Fund principles are therefore increasingly geared towards enhancing regional capacities. Regions across Europe are responding, with varying results so far. The Randstad, in the Netherlands, presents itself as a ‘far from best’ example. Despite continued and serious attempts to strengthen capacities and institutions, the region still lacks effective governance. This paper explores the question why it is next to impossible to establish a framework for effective governance in the Randstad and distils some lessons for other regions in Europe.     

Effect of channel deepening on tidal flow and sediment transport—part II: muddy channels

Natural tidal channels often need deepening for navigation purposes (larger vessels). The depth increase may lead to tidal amplification, salt intrusion over longer distances, and increasing sand and mud import. Increasing fine sediment import, in turn, may start a process in which the sediment concentration progressively increases until the river becomes hyper-turbid, which may lead to increased dredging volumes and to decreased ecological values. These effects can be modeled and studied using detailed 3D models. Reliable simplified models for a first quick engineering evaluation are however lacking. In this paper, we apply both simplified and detailed 3D models to analyze the effects of channel deepening in prismatic and weakly converging tidal channels with saturated mud flow. The objective is to gain quantitative understanding of the effects of channel deepening on mud transport. We developed a simplified tidal mud model describing most relevant processes and effects in saturated mud flows with only minor horizontal transport gradients (quasi uniform conditions). The simplified model is not valid for non-saturated mud flow conditions. This model can either be used in standalone mode or in post-processing mode with computed near-bed velocities from a 3D hydrodynamic model as an input. The standalone model has been compared to various field data sets. Mud transport processes in the mouth region of muddy tidal channels can be realistically represented by the simplified model, if sufficient salinity and sediment data are available for calibration. The simulation of tidal mud transport and the behavior of an estuarine turbidity maximum (ETM) in saturated and non-saturated mud flow conditions cannot be represented by the simplified model and requires the application of a detailed 3D model.     

Distributions of boulders ejected from lunar craters

We investigate the spatial distributions of boulders ejected from 18 lunar impact craters that are hundreds of meters in diameter. To accomplish this goal, we measured the diameters of 13,955 ejected boulders and the distance of each boulder from the crater center. Using the boulder distances, we calculated ejection velocities for the boulders. We compare these data with previously published data on larger craters and use this information to determine how boulder ejection velocity scales with crater diameter. We also measured regolith depths in the areas surrounding many of the craters, for comparison with the boulder distributions. These results contribute to understanding boulder ejection velocities, to determining whether there is a relationship between the quantity of ejected boulders and lunar regolith depths, and to understanding the distributions of secondary craters in the Solar System. Understanding distributions of blocky ejecta is an important consideration for landing site selection on both the Moon and Mars.     

Work sharing in Kerala's fisheries

Earlier studies suggest that once population growth and market integration reach a certain critical level, traditional practices of work sharing tend to degenerate or disappear altogether. Work sharing has, however, survived to date in small-scale fisheries in Kerala, India. Artisanal fishermen strongly favor the system, for ethical reasons as well as for their personal benefit. Besides, boat owners appear not to be hindered by the system. Contrary to observations in crop production, work sharing has not inhibited the introduction of modern technologies like motorization.     

Floods at the northern foothills of the Tatra Mountains — A Polish-Swiss research project

The present paper introduces the topical area of the Polish-Swiss research project FLORIST (Flood risk on the northern foothills of the Tatra Mountains), informs on its objectives, and reports on initial results. The Tatra Mountains are the area of the highest precipitation in Poland and largely contribute to flood generation. The project is focused around four competence clusters: observation-based climatology, model-based climate change projections and impact assessment, dendrogeomorphology, and impact of large wood debris on fluvial processes. The knowledge generated in the FLORIST project is likely to have impact on understanding and interpretation of flood risk on the northern foothills of the Tatra Mountains, in the past, present, and future. It can help solving important practical problems related to flood risk reduction strategies and flood preparedness.     

Assessing the effects of forest biomass reductions on forest health and streamflow

Forest biomass reductions in overgrown forests have the potential to provide hydrologic benefits in the form of improved forest health and increased streamflow production in water-limited systems. Biomass reductions may also alter evaporation. These changes are generated when water that previously would have been transpired or evaporated from the canopy of the removed vegetation is transferred to transpiration of the remaining vegetation, streamflow, and/or non-canopy evaporation. In this study, we combined a new vegetation-change water-balance approach with lumped hydrologic modelling outputs to examine the effects of forest biomass reductions on transpiration of the remaining vegetation and streamflow in California's Sierra Nevada. We found that on average, 102 mm and 263 mm (8.0% and 20.6% of mean annual precipitation [MAP]) of water were made available following 20% and 50% forest biomass-reduction scenarios, respectively. This water was then partitioned to both streamflow and transpiration of the remaining forest, but to varying degrees depending on post-biomass-reduction precipitation levels and forest biomass-reduction intensity. During dry periods, most of the water (approximately 200 mm [15.7% on MAP] for the 50% biomass-reduction scenario) was partitioned to transpiration of the remaining trees, while less than 50 mm (3.9% on MAP) was partitioned to streamflow. This increase in transpiration during dry periods would likely help trees maintain forest productivity and resistance to drought. During wet periods, the hydrologic benefits of forest biomass reductions shifted to streamflow (200 mm [15.7% on MAP]) and away from transpiration (less than 150 mm [11.8% on MAP]) as the remaining trees became less water stressed. We also found that streamflow benefits per unit of forest biomass reduction increased with biomass-reduction intensity, whereas transpiration benefits decreased. By accounting for changes in vegetation, the vegetation-change water balance developed in this study provided an improved assessment of watershed-scale forest health benefits associated with forest biomass reductions.     

Stabilizing greenhouse gas concentrations at low levels: an assessment of reduction strategies and costs

On the basis of the IPCC B2, A1b and B1 baseline scenarios, mitigation scenarios were developed that stabilize greenhouse gas concentrations at 650, 550 and 450 and – subject to specific assumptions – 400 ppm CO₂-eq. The analysis takes into account a large number of reduction options, such as reductions of non-CO₂ gases, carbon plantations and measures in the energy system. The study shows stabilization as low as 450 ppm CO₂-eq. to be technically feasible, even given relatively high baseline scenarios. To achieve these lower concentration levels, global emissions need to peak within the first two decades. The net present value of abatement costs for the B2 baseline scenario (a medium scenario) increases from 0.2% of cumulative GDP to 1.1% as the shift is made from 650 to 450 ppm. On the other hand, the probability of meeting a two-degree target increases from 0%–10% to 20%–70%. The mitigation scenarios lead to lower emissions of regional air pollutants but also to increased land use. The uncertainty in the cost estimates is at least in the order of 50%, with the most important uncertainties including land-use emissions, the potential for bio-energy and the contribution of energy efficiency. Furthermore, creating the right socio-economic and political conditions for mitigation is more important than any of the technical constraints.     

Evapotranspiration of deforested areas in central and southwestern Amazonia

Considering the high rates of evapotranspiration of Amazonian forests, understanding the impacts of deforestation on water loss rates is important for assessing those impacts on a regional and global scale. This paper quantifies evapotranspiration rates in two different pasture sites in Amazonia and evaluates the differences between the sites. In both places, measured evapotranspiration varies seasonally, decreasing during the dry season. The decrease is higher at the southwestern Amazonia site, while at the central Amazonia site, the decrease is less pronounced. During the dry season, average values of evapotranspiration are around 2.2?±?0.6?mm?day^?1 in central Amazonia and 2.4?±?0.6?mm?day^?1 in southwestern Amazonia, while during the wet season, those values are 2.1?±?0.6?mm?day^?1 in central Amazonia and 3.5?±?0.8?mm?day^?1 in southwestern Amazonia. On an annual basis, the pasture in southwestern Amazonia has higher evapotranspiration than in central Amazonia. We conclude that the main reason for this difference is the lower available energy in the wet season at the central Amazonian site, combined with a lower leaf area index at this site during the whole year. Still, the evapotranspiration is significantly controlled by the vegetation, which is well coupled with the local moisture conditions in the dry season.     

Modelling the sorption of Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Eu(III), Am(III), Sn(IV), Th(IV), Np(V) and U(VI) on montmorillonite: Linear free energy relationships and estimates of surface binding constants for some selected heavy metals and actinides

In solution thermodynamics, and more recently in surface chemistry, it is well established that relationships can be found between the free energies of formation of aqueous or surface metal complexes and thermodynamic properties of the metal ions or ligands. Such systematic dependencies are commonly termed linear free energy relationships (LFER). A 2 site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model has been used to model “in house” and literature sorption edge data for eleven elements: Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Eu(III), Am(III), Sn(IV), Th(IV), Np(V) and U(VI) to provide surface complexation constants for the strong sites on montmorillonite. Modelling a further 4 sets of sorption isotherms for Ni(II), Zn(II), Eu(III) and U(VI) provided complexation constants for the weak sites. The protolysis constants and site capacities derived for the 2SPNE SC/CE model in previous work were fixed in all of the calculations. Cation exchange was modelled simultaneously to provide selectivity coefficients. Good correlations between the logarithms of strong ^SK_x−1 and weak ^W1K_x−1 site binding constants on montmorillonite and the logarithm of the aqueous hydrolysis constants ^OHK_x were found which could be described by the following equations: Strong (≡S^SOH) sites:

SlogKX−1=8.1±0.3+(0.90±0.02)log^OHKX