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How well can we predict permeability in sedimentary basins? Deriving and evaluating porosity-permeability equations for noncemented sand and clay mixtures
Full text linkThe permeability of sediments is a major control on groundwater flow and the associated redistribution of heat and solutes in sedimentary basins. While porosity-permeability relationships of pure clays and pure sands have been relatively well established at the laboratory scale, the permeability of natural sediments remains highly uncertain. Here we quantify how well existing and new porosity-permeability equations can explain the permeability of noncemented siliciclastic sediments. We have compiled grain size, clay mineralogy, porosity, and permeability data on pure sand and silt (n=126), pure clay (n=148), and natural mixtures of sand, silt and clay (n=92). The permeability of pure sand and clay can be predicted with high confidence (R(2)0.9) using the Kozeny-Carman equation and empirical power law equations, respectively. The permeability of natural sediments is much higher than predicted by experimental binary mixtures and ideal packing models. Permeability can be predicted with moderate confidence (R-2=0.26- 0.48) and a mean error of 0.6 orders of magnitude as either the geometric mean or arithmetic mean of the permeability of the pure clay and sand components, with the geometric mean providing the best measure of the variability of permeability. We test the new set of equations on detailed well-log and permeability data from deltaic sediments in the southern Netherlands, showing that permeability can be predicted with a mean error of 0.7 orders of magnitude using clay content and porosity derived from neutron and density logs
The limits of increasing food production with irrigation in India
No full textGrowing populations and dietary shifts to include higher proportions of meat are projected to double global food demand by 2050. Previous global studies have proposed and evaluated possible solutions by closing agricultural yield gaps, defined as the difference between current and potential crop yields. We compliment previous studies by developing a method for more accurately calculating potential changes in cereal grain production under different irrigation scenarios, explicitly incorporating yield differences associated with different sources of irrigation. Irrigating with groundwater often leads to higher crop yields than irrigating with surface water because of the greater facility to tailor both the volumes of water and the timing of application. Two possible scenarios for increasing production in India are examined, the first where all non-irrigated fields are irrigated proportionally to the State-specific distribution of irrigation sources, and the second where all non-irrigated fields are irrigated with groundwater: Rice production increases by 14 and 25 % in scenarios 1 and 2 respectively, but wheat production increases by only 3 % in both scenarios. Increased irrigation water consumption from irrigating fields that are currently non-irrigated is estimated at 31 % for rice and 3 % for wheat using the Global Crop Water Model. A third scenario estimates the potential loss in production without the use of irrigation: rice would be 75 % and wheat 51 % of current production. Our methodology and results can help policy makers estimate the current and potential contribution of irrigation sources to agricultural production and food security in India and can with facility be applied elsewhere
How well can we predict permeability in sedimentary basins? Deriving and evaluating porosity-permeability equations for noncemented sand and clay mixtures
No full textIs the permeability of crystalline rock in the shallow crust related to depth, lithology, or tectonic setting?
No full textIs the permeability of crystalline rock in the shallow crust related to depth, lithology or tectonic setting?
No full textThe permeability of crystalline rocks is generally assumed to decrease with depth due to increasing overburden stress. While experiments have confirmed the dependence of permeability on stress, field measurements of crystalline permeability have not previously yielded an unambiguous and universal relation between permeability and depth in the shallow crust (<2.5km). Large data sets from Sweden, Germany and Switzerland provide new opportunities to characterize the permeability of crystalline rocks in the shallow crust. Here we compile in situ permeability measurements (n=973) and quantitatively test potential relationships between permeability, depth (0-2.5km), lithology (intrusive and metamorphic) and tectonic setting (active and inactive). Higher permeabilities are more common at shallow depths (<1km), but trend analysis does not support a consistently applicable and generalizable relationship between permeability and depth in crystalline rock in the shallow crust. Results suggest lithology has a weak control on permeability-depth relations in the near surface (<0.1km), regardless of tectonic setting, but may be a more important control at depth. Tectonic setting appears to be a stronger control on permeability-depth relations in the near surface. Permeability values in the tectonically active Molasse basin are scattered with a very weak relationship between permeability and depth. While results indicate that there is no consistently applicable relationship between permeability and depth for crystalline rock in the shallow crust, some specific lithologies and tectonic settings display a statistically significant decrease of permeability with depth, with greater predictive power than a generalized relationship, that could be useful for hydrologic and earth system models
Fresh groundwater discharge insignificant for the world’s oceans but important for coastal ecosystems
No full textThe authors here present the global entry of nutrients into marine systems through fresh submarine groundwater discharge to be below 1%. However, they also identify hotspots and argue that about 25% of world’s estuaries are at danger of eutrophication
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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