River Exe case study water and carbon cycle:

Question 1

Where is the River Exe:

Answer 1

• Source is in the hills of Exmoor.
• Flows for 82.7km, through Tiverton and Exeter to the sea at Exmouth.
• Has extensive network of tributaries and a high drainage density.

Question 2

Characteristics of the Exe upper catchment:

Answer 2

Physical - Area of upper catchment is 601km squared. Maximum elevation is 514m and lowest elevation is 26m.

Land use: areas surrounding the drainage basin.
67% = agricultural grassland.
15% = woodland
15% = arable farmland
3% = peat bogs.

Geology:
- estimated 84.4% of the catchment is underlain by impermeable rock (devonian sandstone), which accounts for the extensive drainage network.

Question 3

Water balance of the River Exe:

Answer 3

Precipitation = 1295mm
Rainfall is high over EXMOOR. Most absorbed by peaty moorland soils.

Run-off accounts for 65% of the water balance, which is high in comparison to other UK rivers.

2 reasons for this: impermeable bedrock, reduces percolation and base flow. Drainage ditches over Exmoor reduce the amount of Soil water storage.

Question 4

How have recent developments affected the water cycle and balance of the River EXE:

Answer 4

Wimbleball reservoir.
Peatland restoration of Exmoor.
Exmoor mires project.

Question 5

Wimbleball reservoir:

Answer 5

• surface area of 150 hectares.
• Supplies water to Exeter and parts of East Devon.
• regulates water flow, ensuring a steady flow regime throughout the year to avoid peaks and troughs of water discharge.

Question 6

Peatland restoration of Exmoor:

Answer 6

Drainage ditches have been dug up at Exmoor for decades for farming.

• This increases water speed to the Exe but reduces the water quality.

As peat has dried out decomposition has occurred releasing carbon from the lithosphere in the form of carbon dioxide and methane.

Question 7

Exmoor Mires project:

Answer 7

• Aims to restore 2000 ha of boggy conditions to Exmoor that would naturally be present by blocking drainage ditches.

Benefits:
- Improved water quality as slower through flow means less sediment is carried into rivers so water is cleaner and cheaper to treat.

• More carbon storage: dry peat releases carbon through oxidation, but by encouraging active peat growth carbon is naturally absorbed from the atmosphere.

More water storage in upper catchments: Increasing storage capacity and ensuring a steady supply of water throughout the year.

Improved water supply for animals.

Question 8

Results of the Exmoor Mires project:

Answer 8

• water table has started to rise meaning that more moisture is being retained in the soil.
• Flood peaks have been reduced and baseflow has increased.