Human impacts on carbon and water cycles (3a)

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- Geography (Water and carbon cycle) Flashcards on Human impacts on carbon and water cycles (3a), created by Emily H on 03/17/2020.
Emily H
Flashcards by Emily H, updated more than 1 year ago
Emily H
Created by Emily H over 4 years ago
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Resource summary

Question Answer
Dynamic equilibrium in the short term inputs, outputs and stores will fluctuate but in the long term flows and stores maintain a balance due to negative feedback loops restoring the balance
~ water cycle heavy rain increases amount of water stored in aquifers raises water table increases flow from springs until water table reverts back to normal
~ carbon cycle burning fossil fuels increases CO2 increases photosynthesis removes excess CO2 helps restore equilibrium
*LAND USE CHANGES* urbanisation forestry farming
URBANISATION -
Water cycle: -
Impermeable artificial surfaces e.g. tarmac, concrete, brick replacing farmland and woodland little/ no infiltration minimal water storage to buffer runoff - aquifers removed as storage as water can't infiltrate through surfaces to reach it, few lakes etc
Drainage systems e.g. pitched roofs, guttering, sewerage systems designed to remove surface water rapidly > high proportion of water from precipitation flows quickly into streams and rivers > rapid rise in water level
Encroaching on floodplains reduces water storage capacity in drainage basins > increased river flow and flood risk
Carbon cycle: -
Increased anthropogenic emissions (from building, travel, industry) > more carbon in atmosphere
Removal of vegetation reduces carbon in biosphere and reduces photosynthesis
FARMING -
Water cycle: -
Crop irrigation diverts water from rivers and groundwater to cultivated land > some extracted by crops from soil storage but most lost to evaporation/ soil drainage
Less ... than forest/ grassland interception evaporation and transpiration from leaf surfaces
Ploughing increases evaporation and soil moisture loss furrows ploughed downslope act as drainage channels > accelerate run-off and soil erosion greater infiltration
Artificial underdrainage increased rate of water transfer to streams and rivers
Heavy machinery compacts soils increases surface run-off
Carbon cycle: -
Clearance of forest for agriculture reduces carbon storage in above- and below-ground biomass
Ploughing and exposure of soil organic matter to oxidation reduced soil carbon storage
Harvesting of crops further losses - only small amounts of organic matter returned to soils soil erosion by wind and water worse as soils have little protective cover
Lack of biodiversity and short growth cycle lower carbon exchanges through photosynthesis
(Changes less apparent when replacing grassland) North America NPP of wheat on the Great Plains exceeds original Prairie grasslands
FORESTRY -
Water cycle: -
Higher rates of rainfall interception in plantations in natural forests in eastern England interception rates fro Sitka spruce as high as 60% in upland britain about half of this - temps and evaporation lower UK preferred plantation species conifers - high rates of interception: needle-like strcuture evergreen high planting density
Increased evaporation intercepted and stored on leaf surface then evaporated
Reduced run-off and stream discharge due to high interceotion, evaporation and absorption by tree roots > streams draining plantations long lag times, low peak flows, low discharge
Transpiration rates increased compared to farmland/ moorland transpiration rates for Sikta spruce in Pennines around 350 mm/year
Clear felling to harvest timber increased run-off, reduced evapotranspiration, increased stream discharge
Carbon cycle: -
Changing land use from farmland/ moorland to forestry increased carbon stores mature trees in uk plantation contain 170-200 tonnes C/ha = 10x higher than grassland, 20x higher than heathland forest soils 500 tonnes C/ha
Forest trees extract CO2 from atmosphere and sequester it for hundreds of years most stored in the wood of the tree stem
~ forest trees only a carbon sink for 100 years after planting respiration, soil decomposers > plantations rotation period 80-100 years
*WATER EXTRACTION* water extracted from surface and groundwater to meet public, industrial and agricultural need
RIVER KENNET CATCHMENT -
Location southern england drains area of 1200km2 in Wiltshire and Berkshire
Main rock type chalk = permeable
The rock type encourages ... groundwater flow percolation stored in aquifers
Urban areas relying on water supply from the area largest Swindon with population of 200,000 marlborough, newbury
Thames Water abstracts groundwater from boreholes from upper catchment none returned to river as waste water
Why water good for diverse habitat and use by humans chalk acts as filter > good clarity and high oxygen levels and fast-flowing
~ native fauna Atlantic salmon, brown trout, water voles, otters, white-clawed crayfish
Impact on regional water cycle: -
- rates of groundwater extraction exceeded rates of recharge falling water table reduced flows in River Kennet by 10-14%
- drop in river flow due to dry conditions drought 2003 20% 1990s 40%
- lower discharge reduced flooding also reduced areas of standing water and wetlands on floodplain
- lower groundwater levels springs and seepages dried up reduced saturated overland flow on chalk
Aquifers = permeable/ porous water-bearing rocks e.g. chalk and New Red Sandstone
~ groundwater abstracted for public supply from aquifers by wells and boreholes groundwater emerges in springs and seepages it feeds rivers and makes big contribution to their base flow
~ water table upper surface of saturation within aquifer height fluctuates seasonally affected by periods of heavy rainfall, drought and abstraction
~~ southern England water table falls between march and september (rising temps increase evapotranspiration losses) recharge in late autumn (precipitation greater than evaporation)
Artesian basin = where sedimentary rock forms a basin (=syncline ), groundwater is confined between impermeable rock layers under artesian pressure
~ artesian pressure = hydrostatic pressure exerted on groundwater in a confined aquifer sufficient to lift to level higher than ground
~ artesian aquifer groundwater tapped by well or borehole and water will rise up by artesian pressure
~ potentiometric surface level to which water will rise determined by height of water table in areas of recharge on edge of basin
~ London located at centre of synclinal structure which forms artesian basin
~~ London groundwater groundwater in chalk aquifer trapped between impermeable London clay and Gault clay
~~ overexploitation 19thC and first half 20thC drastic fall in water table - central london by 90m water table recovered in recent years as reduced demand fro water from industry by early 1990s rising 3m/year threatening buildings and tunnels >> Thames Water abstraction license since 1992 to slow rise
*FOSSIL FUELS AND THE CARBON CYCLE* -
Fossil fuels driven global industrialisation and urbanisation 2013 87% of global energy consumption
Increases CO2 concentration over 1ppm per year
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