how do water and carbon cycles change? Flashcards
what is a dynamic equilibrium?
a system displaying unrepeated average state through time
how does urbanisation effect the flows of water?
natural surfaces are replaced by concrete and tarmac which is impermeable so there is no infiltration and provide minimal water storage increasing surface run off
drainage systems to remove surface water meaning a high proportion of water flows into rivers increasing the water level
built on floodplains, reducing water storage capacity in drainage basins, increasing river flow and flood risk
what is urbanisation?
the conversion of land use from rural to urban
how does farming effect carbon cycles?
clear forest for farming reducing carbon storage in the above and below ground biomass
soil carbon storage reduced due to ploughing which kills micro-organisms and exposes soil organic matter to oxidation
harvesting crops only returns small amounts of organic matter to woils
increased erosion by wind and water
how does farming effect water cycles?
modifies natural water cycle
crop irrigation diverts surface water from rivers and groundwater to cultivated land. Some of this water is extracted by crops from soil storage and released by transpiration but it is mostly lost to evaporation and soil drainage
limits interception and therefore evaporation and transpiration from leaf surfaces
ploughing increases soil moisture loss
furrows planted downstream act as drainage channels, accelerating run off and soil erosion
what are 5 forestry management schemes in plantations to modify the local water and carbon cycles?
higher rates of rainfall interception in plantations in natural forests. In eastern england, interception rates can be as high as 60% for sitka spruce, where temperatures are colder, it is only 30%
increased evaporation - a large proportion of intercepted rainfall is stored on leaf surfaces where it is evaporated directly into the atmosphere
reduce run-off and stream discharge - with high interception and evaporation rates and the absorption of water by tree roots, drainage basin hydrology is altered. streams draining the plantations typically have a long lag time, low peak flows and low discharge
compared to farmland and moorland, transpiration rates are increased.Typical transpiration rates for Sitka spruce in Pennines are around 350mm/year
clear felling to harvest timber creates sudden but temporary changes to the local water cycle, increasing run-off, reducing evapotranspiration and increasing stream discharge
how much carbon do mature forest trees hold in the UK?
170-200 tonnes c/ha
why are forest trees an effective carbon store?
sequester it for 100s of years
sequester 20x more than heathland
water extraction River Kennett catchment
rates of extraction have exceeded rates of recharge and the falling water table has reduced the flows in river kent by 19-14%
2003 drought flows fell by 20%
lower flows have reduced flooding and temporary areas of standing water and wetlands on the Kennet’s flooding
Lower groundwater levels have caused springs and seepages to dry up and reduced the incidence of saturated overland flow on the chalk
what is an aquifer?
permeable or porous water-bearing rocks such as chalk and New Red Sandstone
how do aquifers effect public water supply?
groundwater abstracted for public water supply
what makes the water table in an aquifer fluctuate?
rainfall, drought, abstraction
how are artesian aquifers formed?
sedimentary rocks form a syncline or basin-like structure and aquifer confined between impermeable rock layers may contain groundwater which is under artesian pressure
if the groundwater is trapped by a well or borehole, water will flow to the surface under its own pressure.
what is potentiometric surface?
the level to which the water will rise in an artesian aquifer?
what is the potentiometric surface determined by?
height of the water table in areas of recharge on the edges of the basin
