how has human activity caused changes in the water and carbon cycles

Question 1

human activity and changes in the water cycle:
irrigation and agriculture

Answer 1

the most significant impact on they water cycle is on rivers and aquifers
as populations grow and societies become more affluent there is increased deman for water for irrigation of crops, agriculture and public supply, especially in arid and semi arid environments

Question 2

human activity and changes in the water cycle:
irrigation and agriculture example
colorado basin SW USA

Answer 2

the basin covers an area of 246000 miles sq
supplies water to 30 million people
irrigated 4 million acres of crop land
has caused surface supplies to diminish as more water is abstracted from the rivers and huge amounts evaporate from reservoirs such as Lake Mead and Lake Powell due to the high temps
in other areas the quality of freshwater has declined

Question 3

human activity and changes in the water cycle:
irrigation and agriculture example
Bangladesh

Answer 3

in bangladesh the growth of the capital Dhaka has led to increased extraction of groundwater which has caused the level of groundwater to fall by 200 feet over the past 50 years
this over pumping of water especially in coastal areas has led to the incursion of salt water which has meant that the water is unfit for drinking or irrigation

Question 4

human activity and changes in the water cycle:
deforestation and urbanisation

Answer 4

they reduce evapotranspiration and therefore precipitation as there is less moisture returned to the atmosphere
there’s also an increase in surface run off as without trees there is no interception of precipitation and the urbanised impermeable surfaces prevent absorption of precipitation
in addition throughflow is decreased and the water table is lowered as there is less precipitation entering the soil

Question 5

human activity and changes in the water cycle:
deforestation and urbanisation
Amazon Rainforest

Answer 5

since 1970s 20% of the amazon has been deforestated
this means that water is no longer transferred to the atmosphere by evapotranspiration and so there is reduced precipitation, triggering a positive feedback mechanism in which the climate starts to dry out so that the forest is unable to regenerate

Question 6

human activity and changes in the carbon cycle:
fossil fuel combustion

Answer 6

the world still relies on fossil fuels for 87% of its primary energy consumption
the exploitation of coal oil and natural gas has removed billions of tonnes of carbon from the geological store
this process has increased rapidly in the past 30 years as economies such as China and India are growing and industrialising at a rapid rate
currently 8 billion tonnes of CO2 are transferred to the atmosphere each year by burning fossil fuels
deforestation transfers approx 1 billion tonnes of carbon annually to the atmosphere
this additional input of CO2 means that 2.5 million tonnes is absorbed by oceans, and similar amounts by the biosphere

Question 7

human activity and changes in the carbon cycle:
deforestation

Answer 7

massive deforestation has reduced the global forest cover by 50% since historic times which has meant that the amount of carbon stored in the biosphere and fixed by the photosynthesis has declined steeply
eg in a forest the absorption by photosynthesis is 30.4 tonnes of carbon/hectare/year whereas in an area 10 years after deforestation its 12.3 tonnes
it also means that soils are more vulnerable to erosion by wind and precipitation and so the soil carbon store is degraded by soil erosion
eg in an area of forest soil stores 226 tonnes of carbon/hectare whereas for an area 10 years after deforestation the store is 150 tonnes

Question 8

human activity and changes in the carbon cycle:
ocean acidification

Answer 8

phytoplankton play a significant role in the carbon cycle as they absorb more than 1/2 the CO2 emitted by burning fossil fuels which is significantly more than the amount absorbed by tropical forests
with increasing industrial activity there is more CO2 in the atmosphere a proportion of which is absorbed by the ocean causing an increase in the acidity of the ocean
this threatens the vital biological carbon store as well as adversely affecting the marine life of the ocean by harming the phytoplankton
these organisms are essential in the absorption of CO2 by photosynthesis and they’re important components of the ocean food chain