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
how does fossil fuels impact the carbon cycle?
87% of global energy
atmospheric CO2 concentration increases by 1 ppm annually
anthropogenic emissions are 2000 GT
how does the sequestration of waste carbon effect carbon cycles and what are the stages of the process?
new technology of carbon capture and storage
limits anthropogenic carbon from the atmosphere
1) CO2 separated from power station emission
2) compressed and transported by pipeline to storage areas
3) injected into porous rocks deep underground where it is stored permanently
what are the appeals of CCS technology?
has potential to reduce emissions by 80-90%
Drax project, Yorkshire designed to capture 2 million tonnes of CO2
what are the problems with CCS technology?
expensive - each project £1 billion
use large amounts of energy
requires storage reservoirs with specific geological conditions
what is positive feedback in the water cycle?
rising global temps effect cycle at the global scale meaning evaporation increases and atmosphere holds more vapour = greater cloud cover and more precipitation
positive feedback effect
water vapour = greenhouse gas
more vapour in the atmosphere increases absorption of long wave radiation from Earth causing further rises in temperature
what is negative feedback in the water cycle?
more vapour creates greater cloud cover which reflects more solar radiation back into space
smaller amounts of radiation absorbed by atmosphere, oceans and land meaning temperatures fall
feedback in a drainage basin
long term, inputs and outputs are in equilibrium
input-precipitation, is balanced by outputs of evapotranspiration and run-off
varies from year to year
system responds to above average precipitation by increasing river flow and evaporation
excess water recharges aquifers, increasing water storage in permeable rocks
feedback in a tree
when they don’t get enough water from soil they shed leaves
negative feedback global carbon cycle
currently in disequilibrium due to human activity
neutralise levels of rising CO2 = carbon fertilisation
excess CO2 extracted from atmosphere and stored in the biosphere
eventually would be stored in long-term stores
conditional on requirements for photosynthesis
positive feedback carbon cycle
could tip into greater disequilibrium
globan warming will increase rates of decomposition amplifying the greenhouse effect
Arctic tundra= ice and sea cover shrinks, more sunlight is absorbed, warming tundra and melting the permafrost
will release 1600 GT of carbon
diurnal changes
changes that occur over a 24h period
lower temps at night reduce evaporation and transpiration
covectional precipitation dependent on direct heating of the ground surface only happens at day time
seasonal changes
seasons controlled by intensity of solar radiation
peaks mid-june in UK
evapotraspiration highest in summer
summer output = 800 W/m2
winter output - 150 W/m2
river flows at lowest in summer
month to month changes in Net primary productivity of vegetation
in middle and high latitudes, photoperiod and temperature drives changes in NPP
oceans, phytoplankton stimulated into photosynthetic activity by rising water temperatures
long term changes climate
over the last 400,000 years there has been glacial and warmer inter-glacial periods
20,000 years ago, temps 5 degrees cooler than today
inter glacial period temperatures simalar
long term changes water cycle
net transfer of water between ice to oceans and reservoir
in glacial periods the sea level falls by over 100m
glaciers destroy vegetation= water stored in biosphere shrinks
lower rates of evapotranspiration reduce movement of water between atmosphere, oceans, biosphere and soil
long term changes carbon cycle
glacial periods = significant reduction in atmospheric CO2
100 ppm higher in inter glacial periods
excess CO2 goes to ocean and is stored in phytonplankton
CO2 soluble in deep ocean temps
land covered in ice, carbon cant be exchanged between soils and atmospheric
carbon sequestered in permafrost
less vegetation = less carbon trapped in photosynthesis
