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| 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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