Dynamic equilibrium and the water and carbon cycle

Land use changes

Urbanisation

Farming

Forestry (forest management)

Water extraction (RIVER KENNET CATCHMENT)

Aquifers and artesian basins

Fossil fuels and the carbon cycle

Sequestration of waste carbon

Positive and negative feedback loops in the water and carbon cycles

Water

Carbon

WATER cycle

Artificial surfaces are impermeable and so allow little/no infiltration and provide minimal water storage capacity to buffer run-off speeds

Urban areas are designed to have drainage systems and remove water rapidly which leads to a high proportion of water flowing quickly into rivers and streams, leading to a rise in water level

CARBON cycle

Removal of vegetation leads to reduced amounts of organic carbon. And the development of factories increases release of carbon dioxide through burning of fossil fuels.

Urbanisation also encroaches on floodplains which further reduces water storage capacity and increases the risk of river overflow

Clearance of forests reduces carbon storage in biomass.

Soil carbon storage is reduced by ploughing and the exposure of soil organic matter to oxidation.

Rates of photosynthesis are generally lower due to the monocultures

Soil erosion occurs when plants have been lifted and soils have little protective cover and so harvesting of crops sees only small amounts of organic matter returned to soils

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 most is lost to evaporation and soil drainage.

Interception rates are less and so too is evaporation and transpiration from leaf surfaces. Ploughing increases evaporation and soil moisture loss

Furrows ploughed downslope act as drainage channels, accelerating run-off and soil erosion

Surface run-off increases where heavy machinery compacts soils. Peak flows on streams draining farmland are generally higher than in natural ecosystems.

Higher rates of rainfall interception

Increased rates of evaporation

Reduced run-off and stream discharge. Streams draining plantations often have long lag times, low peak flows and low total discharge and so the effect of a conifer plantation is to reduce water yield for public supply

Transpiration rates increased compared to farmland

Clear felling to harvest timber will increase run-off, reduce evapotranspiration and increase stream discharge

Typical UK forest plantation contains 200 tonnes C/ha, which is 10x higher than grassland and 20x higher than heathland.

Forest trees extract CO2 from atmosphere and sequester it for years and years

Forest trees only become active carbon sinks for the first 100 years and thereafter, the amount of carbon captured levels off

Rates of groundwater extraction have exceeded rates of recharge

During the 2003 drought, flows fell by 20%

Lower flows have reduced flooding and temporary areas of standing water and wetlands on the Kennet's floodplain

Lower groundwater levels have caused springs and seepages to dry up and reduced the incidence of saturated overland flow

Permeable/porous water-bearing rocks like chalk or sandstone

Groundwater is abstracted for public supply from aquifers by wells

Groundwater feeds rivers and makes major contributions to their base flow.

click to edit

Possible solution to the influx of atmospheric CO2 that negatively affects the environment is carbon capture and storage (CCS).

Where it is is injected into porous rocks after being compressed and transported by pipeline

CCS has the potential to reduce emissions by 80/90% in the USA

Drax project, North Yorkshire, designed to capture 2 million tonnes of CO2 per year, commencing in 2019

Negative feedback: more atmospheric vapour=greater cloud cover=reflects more radiation back into space=global temperatures fall

Positive feedback: Rising temperatures=evaporation increase=greater vapour (a greenhouse gas) in atmosphere=greater cloud cover=more precipitation

This means that the absorption of long wave radiation increases

Negative feedback: Neutralise rising levels of atmospheric CO2 by stimulating photosynthesis in a process called carbon fertilisation. Eventually more carbon would dissolve into soils and be locked there for many years, allowing systems to return to an equilibrium

Positive feedback: global warming=intensification of the carbon cycle=speeds up decomposition=release more CO2=amplifying greenhouse effect

Arctic Tundra: global warming occuring faster than in any other region=Arctic sea and ice exposed=more sunlight absorbed=warming tundra and melting permafrost