In-depth notes explaining how human activity influences the water and carbon cycles, using the case studies of the Aral Sea and the River Kennet in South England. Also includes how land use change alters the flows and stores in the water and carbon cycles, as well as monitoring techniques for recor...
Earth’s Life Support Systems SG5
How Humans Can Disturb and Enhance the Natural Water and Carbon Cycles
Human Activity and Its Influence on the Water Cycle
Surface Extraction of Water
The two main sources of water are surface water (e.g. rivers, lakes and reservoirs) and groundwater
In some countries the surface water is more abundant compared to other arid areas where there is little so
groundwater has to be used:
Iceland – mainly use surface water, little groundwater used. Lots of rain, rarely hot enough for
evaporation.
Central Australia – groundwater is used as there is little surface water due to rapid evaporation and
little precipitation
In the UK:
80% of water is from surface water, 20% from groundwater stores
The west of the UK is wetter, so more surface water is used
The east of the UK is drier, so the percentage of groundwater used is more like 50% rather than 20%
Case Study: The Aral Sea
The northern part of the Aral Sea lies in Kazakhstan and the southern part in
Location of the Aral Sea
Uzbekistan. The whole of the Aral Sea Basin covers 1.8 million km 2
Main Rivers Which Feed The Syr Delta and the Amu Delta
into the Sea
The rivers flow from the mountains onto the plains
Regions These Rivers
The Syr Delta comes from the east, near the north of the sea
Originate From
The Amu Delta comes from the south
Why Was Water The Aral Sea was part of the Soviet Union, who wanted to grow cotton and rice
Extracted from the in the deserts of Kazakhstan and Uzbekistan. To do this they diverted water
1930s Onwards? from the rivers which fed the Aral Sea to irrigate the cotton and rice fields
1960-70 – Aral Sea’s level fell by 20cm per year, and grew to 80-90cm
per year
1960-98 – the surface area fell by 60% and volume by 80%
Changes to the Size of 1987 – split into the North Aral Sea and South Aral Sea
Sea Since the 1960s 2003 – South Aral Sea split into two, an eastern and western basin
2004 – the Aral’s surface area was only 17,160km 2 which was ¼ of its
original size
2007 – it had shrunk to 10% of its original size
Water has a high specific heat capacity, so it takes a long time to heat up in
summer but a long time to cool in winter, reducing seasonal variation in
Impacts on the Local
temperature. The shrinking of the Aral Sea exposed more land, which has a
Climate
lower heat capacity. This means more extreme temperatures – colder winters
and hotter summers
Loss of plants and animals due to the changing environment – animals
(e.g. wild horses) are unable to find food, so many animals die or
migrate to other areas
Other Changes Resulting
Declining health due to pollutants in the water, lots of dust and
from the Water
declining food. The dried out seabed contains many chemical residues
Extraction
from pesticides and fertilisers used in the cotton fields. These have
been whipped up into toxic dust storms by local winds, leading to high
rates of respiratory diseases
What Problems may the Global warming leads to more ablation of the glaciers at the source. If the
Aral Sea Region Suffer glaciers retreat, there will be even less flow in the two rivers making it
, due to Global Warming? impossible to irrigate the farmland
UK Case Study: The River Kennet, South England
Groundwater extraction led to a falling water table which has reduced the flow of the river by 10-
14%, particularly during drought conditions
During drought conditions, the river has been reduced to a few intermittent pools in the Marlborough
area
During 2003, flows fell by 20% and in the early 1990s flows fell by 40%
Lower groundwater levels have caused springs and seepages to dry up and reduced the incidence of
saturated overland flow on the chalk
Groundwater Extraction – Aquifers and Artesian Basins
Aquifer – a water bearing band of porous or permeable rock, an underground reservoir
Aquitard – non-porous rock which restricts the
flow of water from an aquifer
Water Table – the top of the saturated zone
Confined Aquifer – permeable rocks that hold
large amounts of groundwater that are capped
Unconfined
by impermeable rock
Unconfined Aquifer – permeable rocks that hold
large amounts of groundwater that is not
Confined
capped by impermeable rock
Artesian Well:
Artesian Well – water in the confined aquifer is under pressure causing the water to rise up a borehole and
flow out itself without need for pumping
Spring – where the water table reaches the surface
Recharge Area – where the aquifer is unconfined, and rainwater can
percolate
Artesian Basin – a confined aquifer which occupies a syncline. This
results in groundwater which will rise to the surface under its own
pressure without the need for pumping. The level which water will
rise to is determined by the height of the water table (potentiometric
surface)
Case Study: The London Basin
The London Basin is an artesian basin, located at the centre of a synclinal structure (dipping rocks that form a
bowl-like structure)
Overexploitation in 19th century caused a drastic
fall in the water table – 90m in London
In the past 50 years declining demand for water by
industry in London and reduced rates of
abstraction have allowed the WT to recover –
rising at a rate of 3m/year
Land Use Change Alters the Flows and Stores in the
Water and Carbon Cycle
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