3.a. human factors can disturb and enhance the natural processes, stores in water and carbon cycles

dynamic equilibrium with water and carbon cycles

dynamic in the sense that they have continuous inputs, throughputs, outputs and variable stores of energy and material. in short term inputs, outputs and stores of water and carbon will fluctuate from year to year

long term flows and stores maintain a balance= retain stability in system. negative feedback loops restore balance. in drainage basin unusually heavy rainfall will increase the amount of water stored in aquifers= raise water table, increase flow from springs until water table returns to normal. in carbon burning fossil fuels increases co2 but photosynthesis slightly counteracts. negative feedback response removes excess co2 from atmosphere and restore equilibrium

land use changes

urbanisation: woodland/farmland replaced by housing and infrastructure. vegetation= concrete brick tarmac. artificial surfaces are impermeable, no infiltration and provide minimal water storage capacity to buffer run off. drainage systems to remove surface water= high proportion of water flows quickly into streams and rivers= rise in water level. also encroaches on floodplains= natural storage areas for water= reduced= more flood risks

farming: clearance of forest= reduce carbon stored. soil carbon storage also reduced by ploughing and exposure of soil organic matter to oxidation. losses in harvesting of crops with only small amount of organic matter returned to soils. soil erosion accompanies arable farming. wind and water erosion more severe when crops lifted and soils have little protective cover. carbon effects are less apparent on pasture land where farming replaces natural grasslands. carbon exchanges through photosynthesis are generally lower than in natural ecosystems. lack of biodiversity in farm systems and growth cycle of crops often compressed into 4/5 months. interception= less, so is evaporation and transpiration. ploughing increases evaporation and soil moisture loss and furrows ploughed downslope act as drainage channels accelerating run off and soil erosion. infiltration due to ploughing is usually greater in farming systems, artificial underdrainage increases the rate of water transfer to streams draining farmland are generally higher than in natural ecosystems. 

forestry: management in plantations modifies the local water and carbon cycles. changes to water: higher rates of rainfall interception in plantation in natural forests. increased evaporation. reduced run off and stream discharge- streams draining plantations typically have relatively long la times, low peak flows and low total discharge= can reduce water yield for public supply. compared to farmland and moorland transpiration rates are increased. clear felling to harvest timbers creates sudden but temporary changes to the local water cycle increasing run off reducing evapotranspiration and increasing stream discharge. increases carbon stores when land is changed. typical carbon stores are 10x times higher than grassland. soil represent an even larger carbon pool. forest trees extract co2 from atmosphere and sequester it for 100s of years, most stored in wood of tree stem. only active carbon sink for first 100 years after planting.

water extracted

from surface and groundwater to meet public demand plus industrial and agricultural. water extraction on the River Kennet Catchment: southern england drains area of 1200 km2. groundwater contributes most of the flow. as a chalk stream supports a diverse range of habitats and wildlife. its water filtered through the chalk= exceptional clarity, high oxygen levels and is fast flowing. among the native fauna, salmon, brown trout, water voles. several urban areas rely on water from the kennet basin to meet public supply. water extraction from the kennet and its catchment has had a significant impact on regional water cycles: rates of groundwater extraction have exceeded rates of recharge and the falling water table has been reduced flows in the river is 10%. during the 2003 drought flows fell by 20% and in dry conditions o the early 1990s by up to 40%. lower flows have reduced flooding and temporary area of standing water and wetlands on the floodplain. lower groundwater levels have caused springs and seepages to dry up and reduced the incidence of saturated overland flow on the chalk

aquifers and artesian basins

permeable water bearing rocks. groundwater is abstracted for public use/supply from aquifers by wells and boreholes. emerging in springs and seepages, groundwater feeds rivers and makes a major contribution to their base flow. within an aquifer- upper surface= water table- height fluctuates seasonally, affected by periods of exceptional rainfall, drought and attraction. in normal years in southern england the water table falls between march and sept as rising temps increase evapotranspiration losses. recharge returns in the late autumn

fossil fuels and the carbon cycle

past 2 centuries fossil fuels have driven global industrialisation and urbanisation. despite the development of nuclear power and renewable energy, the global economy remains overwhelming dependent on fossil fuels. releases 10 bil tonnes of co2 to the atmosphere annually increasing atmospheric co2 conc to over 1ppm. estimated that since 1750 cumulative anthropogenic co2 emissions total 2000 GT. ¾ from burning fossil fuels. today levels are highest. despite efforts to limit human carbon emissions, 200-09 they grew faster than in any previous decade. without increased absorption of anthropogenic carbon by the oceans and biosphere conc would exceed 500ppm

feedback loops

positive feedback- snowball effect- when something is added to the system and disrupts the equilibrium negative feedback- controlling effect- when something is added to the system which brings the system back into equilibrium

pos (cycles back around): increased co2, increased temp, melts sea ice, reduces albedo, more heat absorbed by oceans, increased temps, further ice melting

increased co2, increased temp, permafrost melts, methane clathrate melts, methane released, increased temp, permafrost melts

neg(doesnt cycle back around): increased co2, increased photosynthesis, increased plant growth more photosynthesis, co2 removed