WATER AND CARBON
CYCLES
Describe how water reaches a river channel within a drainage
basin [4 marks]
Water can reach a river channel in a drainage basin by channel fall where precipitation (e.g. rain.
sleet, hail or snow) directly enters the river channel. Another way is through groundwater flow
where water moves laterally at a very slow rate through the bed and banks however this can’t take
up to thousands of years. A quicker way is throughflow where water also moves laterally through
the soil to the river channel. Additionally, the water can also reach the ground by flowing down
trunks or stems or by dropping off leaves and then it can travel over an impermeable surface via
surface runoff
What is the water balance? [2 marks]
The water balance is an equation used to get a better understanding of the drainage basin system.
An important aspect of the equation is the total runoff (expressed as a percentage of precipitation).
This is a measure of the proportion of the total precipitation that makes its way into rivers and
streams.
P = O + E +/- S
P = precipitation
O = total runoff (streamflow)
E = evapotranspiration
S = storage (in soil and rock)
Assess the factors causing variations in runoff [4 marks]
One factor that can cause variations in runoff is the type and intensity of precipitation. if there is
intense rainfall, it's more likely to pass quickly into rivers, increasing the amount of runoff. Rain
droplets or drizzle will be held in the trees -interception and most of it will evaporate, so a high
vegetation cover or a heavily forested river basin leads to low runoff values. If the precipitation is
snow, then that can lead to high runoff values because the frozen soils can melt so infiltration no
longer occurs, so the water just stays on the surface. Also, runoff variation depends on the rock
type. If the surface is made of impermeable rock it will prevent percolation from occurring so
reducing infiltration rates because the soil will saturate quicker and it will become unable to absorb
excess water, thus leading to high runoff values. Additionally, during spring/summer runoff values
are low because higher temperature encourages higher rates of evapotranspiration and lower
interception rates, so the climate is a factor of runoff variations.
, Explain why only a small amount of water can be used by
humans on Earth [4 marks]
Only a small amount of water can be used by human on Earth because freshwater only makes up a
small percentage of the Earth's total water supply (2.5%) while saline water (which is not useful for
drinking water) makes up the majority of 97.4%, most of which is stored in the oceans. Furthermore
only 30% of our freshwater comes from groundwater while most of it is trapped in glaciers, ice caps
and ice sheets making it very hard to access by humans.
Suggest how a glacier store may change over time [4 marks]
Snow falling on glaciers and ice sheets becomes compressed and enters long term storage – forming
layers of glacial ice – scientists have drilled ice that is 400,000 years old. On a shorter timescale,
snow accumulated during the winter adds to the mass of a glacier or ice sheet. In the summer,
melting occurs and ice calves (breaks away). In recent decades (as the climate has warmed), the
equilibrium line has risen to higher altitudes – most glaciers in the world are now shrinking and
retreating. On a glacier, the equilibrium line marks the attitude where annual accumulation and
melting are equal.
Name 3 examples of water 'transfers' on the hillslope water
cycle [3 marks]
- Stemflow: water moving down the stems of plants or trunks of trees under gravity (following
interception).
- Surface runoff - water moving downslope on the surface of the ground.
- Stream flow: water moving downslope within a stream or river.
(other points - Throughflow: water moving downslope underground through soil.
- Groundwater flow: Water moving downslope underground on the surface of impermeable bedrock.
- Infiltration: water moving down from the surface into soil due to gravity.
- Percolation: water moving down from soil (or the surface) into permeable rock due to gravity.)
Explain the impact of deforestation on water stores in an area
[4 marks]
Removal of trees reduces interception, meaning a reduction in interception storage, therefore more
water reaches the ground in a short timescale. This can lead to the ground becoming overwhelmed if
infiltration cannot take place quick enough. Therefore, there is a reduction in infiltration and an
increase in surface runoff.
Surface runoff is quick, therefore there is a quick reduction in the amount of water being stored in
the immediate area. The reduction in infiltration will lead a to a reduction in the quantity of soil
moisture and groundwater storage. This would have an impact on the future growth of vegetation in
the area. On the other hand, the amount of infiltration, soil moisture and groundwater could
increase if infiltration can happen quickly enough and the land is relatively flat, due to the increased
amount of water reaching the ground from the lack of interception.
CYCLES
Describe how water reaches a river channel within a drainage
basin [4 marks]
Water can reach a river channel in a drainage basin by channel fall where precipitation (e.g. rain.
sleet, hail or snow) directly enters the river channel. Another way is through groundwater flow
where water moves laterally at a very slow rate through the bed and banks however this can’t take
up to thousands of years. A quicker way is throughflow where water also moves laterally through
the soil to the river channel. Additionally, the water can also reach the ground by flowing down
trunks or stems or by dropping off leaves and then it can travel over an impermeable surface via
surface runoff
What is the water balance? [2 marks]
The water balance is an equation used to get a better understanding of the drainage basin system.
An important aspect of the equation is the total runoff (expressed as a percentage of precipitation).
This is a measure of the proportion of the total precipitation that makes its way into rivers and
streams.
P = O + E +/- S
P = precipitation
O = total runoff (streamflow)
E = evapotranspiration
S = storage (in soil and rock)
Assess the factors causing variations in runoff [4 marks]
One factor that can cause variations in runoff is the type and intensity of precipitation. if there is
intense rainfall, it's more likely to pass quickly into rivers, increasing the amount of runoff. Rain
droplets or drizzle will be held in the trees -interception and most of it will evaporate, so a high
vegetation cover or a heavily forested river basin leads to low runoff values. If the precipitation is
snow, then that can lead to high runoff values because the frozen soils can melt so infiltration no
longer occurs, so the water just stays on the surface. Also, runoff variation depends on the rock
type. If the surface is made of impermeable rock it will prevent percolation from occurring so
reducing infiltration rates because the soil will saturate quicker and it will become unable to absorb
excess water, thus leading to high runoff values. Additionally, during spring/summer runoff values
are low because higher temperature encourages higher rates of evapotranspiration and lower
interception rates, so the climate is a factor of runoff variations.
, Explain why only a small amount of water can be used by
humans on Earth [4 marks]
Only a small amount of water can be used by human on Earth because freshwater only makes up a
small percentage of the Earth's total water supply (2.5%) while saline water (which is not useful for
drinking water) makes up the majority of 97.4%, most of which is stored in the oceans. Furthermore
only 30% of our freshwater comes from groundwater while most of it is trapped in glaciers, ice caps
and ice sheets making it very hard to access by humans.
Suggest how a glacier store may change over time [4 marks]
Snow falling on glaciers and ice sheets becomes compressed and enters long term storage – forming
layers of glacial ice – scientists have drilled ice that is 400,000 years old. On a shorter timescale,
snow accumulated during the winter adds to the mass of a glacier or ice sheet. In the summer,
melting occurs and ice calves (breaks away). In recent decades (as the climate has warmed), the
equilibrium line has risen to higher altitudes – most glaciers in the world are now shrinking and
retreating. On a glacier, the equilibrium line marks the attitude where annual accumulation and
melting are equal.
Name 3 examples of water 'transfers' on the hillslope water
cycle [3 marks]
- Stemflow: water moving down the stems of plants or trunks of trees under gravity (following
interception).
- Surface runoff - water moving downslope on the surface of the ground.
- Stream flow: water moving downslope within a stream or river.
(other points - Throughflow: water moving downslope underground through soil.
- Groundwater flow: Water moving downslope underground on the surface of impermeable bedrock.
- Infiltration: water moving down from the surface into soil due to gravity.
- Percolation: water moving down from soil (or the surface) into permeable rock due to gravity.)
Explain the impact of deforestation on water stores in an area
[4 marks]
Removal of trees reduces interception, meaning a reduction in interception storage, therefore more
water reaches the ground in a short timescale. This can lead to the ground becoming overwhelmed if
infiltration cannot take place quick enough. Therefore, there is a reduction in infiltration and an
increase in surface runoff.
Surface runoff is quick, therefore there is a quick reduction in the amount of water being stored in
the immediate area. The reduction in infiltration will lead a to a reduction in the quantity of soil
moisture and groundwater storage. This would have an impact on the future growth of vegetation in
the area. On the other hand, the amount of infiltration, soil moisture and groundwater could
increase if infiltration can happen quickly enough and the land is relatively flat, due to the increased
amount of water reaching the ground from the lack of interception.
