BIO220H1 Lecture 20: Lecture 20 Hydrological Cycles

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19 Apr 2012
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BIO220H1 Full Course Notes
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This ratio: determines forest-grassland boundary, influences where aquifers (underground layer of water-bearing permeable rock) are recharging. Human diverting surface waters, tapping underground aquifers with wells. Long-term pattern occasional reversible drought, vary lengths. Direct, human: overcultivization, overgrazing, cutting trees, improper irrigation, diversion of water to other places. Natural: climate change (including human effects) Egypt depends on annual flooding cycle: provides water, sily nutrition, predictable, inconsistent build aswan dam. Biggest irrigators: demand (population), big mountains feeding big rivers traversing dry areas. Lower colorado river basin (in mexico); dried up. Lake chad provides water to people in sahel; almost dried up (over-irrigation, climate change) Agricultural irrigation using well water from underground aquifers, pivot irrigation. Downsides of irrigation: deplete fossil water, accumulate surface sale (from not using enough water) Tillage and grazing promote erosion into streams, especially at spring thaw. Soil is nutrient rich, fertilizer increases richness. Rivers transport to estuaries (phytoplankton growth is nutrient limited)

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