Ecohydrology_Lecture2_F11

Ecohydrology_Lecture2_F11 - Some Ecohydrology Examples to...

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Some Ecohydrology Examples to Animate
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Okavango Delta
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Okavango Watershed The Okavango river shared by Angola, Namibia and Botswana Endorheic system Delta 12,000 km2 wetland system in a semi-arid environment
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The Okavango Delta
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Water is NOT from Local Rainfall Rain falls in Angolan highlands Flows through semi- arid zone (losing stream) Water is critically limiting resource Namibia for supply and power Angola for irrigation
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G u m a r e f l t K n y T h k At the tail end of the East African Rift system
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Flood Characteristics Strictly seasonal rainfall over southern Africa – warm rainy summers, dry cool winters flood-pulsed wetland, with an annual flood event flooding asynchronous with rainy season
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Biodiversity
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High End…. To Shoot an Elephant or Lion: $75,000 for license, $50,000 for lodging, food and transport To shoot pictures: $500-1000 per person per
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Perennially flooded
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Seasonally inundated floodplains
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Drylands
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Sediment: ~1,700,000 tons/yr Dissolved Salts: ~500,000 tons/yr Dust deposition: ~250,000 tons/yr? Material inputs to the Delta
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Channel “avulsion” Example 1 - Ecological processes from sediment inputs Surface aggradation and isostatic adjustment
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Mechanism Distributary channels in the Okavango Delta Carry (and drop) sediment and distribute water Channels constrained by a dense mesh of macrophytes (papyrus) Rapid aggradation such that channels are higher than surrounding marsh Lower velocity/impoundment Increasing plant colonization further accelerates aggradation process Catastrophic bank failure and new channel initiation along pre- existing hippo trails McCarthy et al. (1992)
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Major Consequences Locally
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Feedback Diagram for Okavango – Sediment Aggradation and Channel Self-Organization Channel Confinemen t Channel Discharge - Sediment Delivery Downstrea m Sediment Deposition Discharge Competenc e + + + + Riparian Vegetation + - + Large Mammal Paths
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Example 2 – Maintaining Low Salinity 500,000 tons of salt delivered to Delta annually All water lost to ET in typical years Where’s all the salt?
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Where does the salt end up?
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Island building and density fingering Transpiration Induced Salt Translocation Mechanism Think about the nutrient budget implications as
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Salt Transport and Maintenance of Fresh Water Conditions in the Okavango Island Salt Conc. Tree Transpiration - Salt Advection Density Dependent Fingering + + + + Hydraulic Gradient Elephant Impacts - Ecological Processes March Salinity Ecological Processes - - - Island Accretion + - +
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Feedbacks How do anthropogenic impacts affect regional scale climate? Evidence that broad changes in irrigation
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This note was uploaded on 11/29/2011 for the course FOR 6934 taught by Professor Staff during the Fall '08 term at University of Florida.

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Ecohydrology_Lecture2_F11 - Some Ecohydrology Examples to...

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