Browsing by Subject "Water"

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    Dissolving differences: Law and water's role in legitimizing global hierarchies
    (2008) Krohn, David; Gibson, John
    We live under the false illusion that there is an infinite supply of water on earth. In reality, quantities of available freshwater have remained constant for at least 2000 years while the global population has increased 33 fold during this same period. Rainfall remains the only form of renewable water resource and recycles around 45000 km3 of water per year, yet the world's population rises by around 85 million people per annum. Worryingly, World Bank estimates postulate a 56% increase in demand by 2025. As a result, the available quantity of water per capita is steadily decreasing and more than five million people, most of them children die every year from illnesses caused by drinking poor quality water. While at least one billion lack any access to clean water, North Americans use about 5,000 litres of water per person per day.
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    The distribution of tree and grass roots in savannas in relation to soil nitrogen and water
    (2010) February, Edmund C; Higgins, S I
    Here we describe the fine root distribution of trees and grasses relative to soil nitrogen and water profiles. The primary objective is to improve our understanding of edaphic processes influencing the relative abundance of trees and grasses in savanna systems. We do this at both a mesic (737 mm MAP) site on sandy-loam soils and at an arid (547 mm MAP) site on clay rich soils in the Kruger National Park in South Africa. The proportion of tree and grass fine roots at each soil depth were estimated using the δ13C values of fine roots and the δ13C end members of the fine roots of the dominant trees and grasses at our study sites. Changes in soil nitrogen concentrations with depth were indexed using total soil nitrogen concentrations and soil δ15N values. Soil water content was measured at different depths using capacitance probes. We show that most tree and grass roots are located in the upper layers of the soil and that both tree and grass roots are present at the bottom of the profile. We demonstrate that root density is positively related to the distribution of soil nitrogen and negatively related to soil moisture. We attribute the negative correlation with soil moisture to evaporation from the soil surface and uptake by roots. Our data is a snapshot of a dynamic process, here the picture it provides is potentially misleading. To understand whether roots in this system are primarily foraging for water or for nitrogen future studies need to include a dynamic component.