River Exe and the Amazon Rainforest

Where is the River Exe, and how long is it?

82.7km

its source is from the hills of Exmoor, through Tiverton and Exeter, to the sea on the south coast of Devon.

Basic facts on the Amazon Basin:

• largest, one of most diverse rainforests

• stores 1/5 of all carbon in planet’s biomass

• covers 5.5 million km²

• was long considered to be world’s largest carbon sink

Impacts of environmental change in the Amazon:

• burning and clearing of forests has led to 60% of carbon within its soil being lost to the atmosphere

• carbon stored in trees lost to atmosphere

• altered conditions in rainforest affects species’ ability to grow and survive, as well as their ability to respire

• increased amount of droughts, disrupting vegetation respiration due to increased heat in atmosphere

What is the Exmoor Mires Project?

aims to restore 200ha of Exmoor to the natural boggy conditions it used to be in.

Mitigation in the Amazon Rainforest - for carbon and water

international agreements:

• Amazon Cooperation treaty organization to promote harmonious developments

creation of national parks and forest reserves: helps conserve amazon, helping it become a carbon sink rather than producer (e.g. Para rainforest reserve - 15 million hectares or the tumucumaque national park- 3.84 million hectares)

forest biofuel could compete with ethanol production from sugar cane by 2030 - natural fuel not requiring co2 emissions

reforestation: much of Brazil’s industrial timber comes from planned forests which make up 2% of the forest area.

Short overview of carbon in amazon:

• estimated to store 80-120 billion tons of carbon

• negative feedback: 0.3-0.5% increases in above ground biomass annually (caused by sequestering CO2 concentrations in the atmosphere → increase seems to offset rising atmospheric levels of CO2

• due to the increased forest fires, hotter temperatures and droughts mean that the rainforest(not the untouched forests) is emitting more CO2 than absorbing. 

• forms a carbon sink of 1-3GtC/year

What is 84.4% of the River Exe upper catchment is underlain by?

impermeable rocks, accounting for its extensive drainage network

predom. Devon sandstones

Physical characteristics of Exe upper catchment:

Hilly with steep sided valleys and maximum elevation of 514m to the north. The land is much flatter in the south – lowest elevation is 26m.

Land use characteristics in upper catchment of Exe:

most of the land is agricultural grassland (67%) with some woodland (15%) and arable farmland. On the high ground of Exmoor, there are moors and peat bogs (3%).

What are the key human activities in the Amazon rainforest causing damage?

Deforestation and Fires

WHat impact has deforestation had on the Amazon rainforest’s carbon cycle?

• Disrupting the carbon stores in the trees causing large amounts of CO2 to be released

• In 2021, the Amazon experienced a 15 year high in deforestation

• In 2022 the estimated annual rate deforestation in the Amazon was 11,568 km2

• Tropical rainforests are responsible for about 9% of human caused CO2 emissions

• Recent estimates suggest that 17% of the Amazon has already been cleared ; WWF estimates that 20% of Amazon Forest has already been lost; this will rise to 27% by 2030 if current rate of deforestation continues.

What impact has fires had on the Amazon rainforest’s carbon cycle?

• Many trees and plants are burned to clear space for farming practices like beef and soy production

• In 2022, the Brazilian Amazon was responsible for 72% of the major forest fires of which 71% were human caused

• In 2022, fires in the Amazon affected almost 1 million hectares of land

What is the water balance like for River Exe?

• high rainfall, mostly absorbed by peaty moorland soils → when saturated, rolls of hills rapidly

• runoff accounts for 65% of water balance →due to impermeable nature of bedrock which reduces percolation and baseflow; also drainage ditches on Exmoor reduce the amount of soil water storage

• Drainage ditches on exmoore reduce the amount of soil water storage

Flood hydrograph of River Exe:

Exe response relatively slowly to rainfall events

after flooding, discarge recedes slowly, reflecting the rural nature of the lower catchment - 82% of the land use is either woodland/grass.

Amazon’s water cycle:

15% of freshwater entering oceans daily is from the Amazon River into the Atlantic, 175,000 m^3/s,

average rainfall is 2,300 mm annually, half being intercepted by forest canopy and evaporated back into the atmosphere

What impact did deforestation have on the Amazon Rainforest’s water cycle?

Deforestation removes the canopy layer which decreases interception and leads to increased surface runoff- increasing the risk of flooding. Nutrients in the soil are also leached into the Amazon river which has caused eutrophication to occur. 

- When large areas of trees are removed, evapotranspiration is reduced, leading to changes in local precipitation patterns. 

• This means less water vapour reaches the atmosphere, fewer clouds are formed, and rainfall is reduced.  

• In turn the effects of deforestation has increased the vulnerability of the Amazon to droughts. Drier conditions can lead to water stress and in addition increase the risk of wildfires. 

What impact did urbanisation have on the Amazon Rainforest’s water cycle?

detrimental effects to the water cycle ,particularly the pollution of water systems. 

-The creation of infrastructure and impermeable surfaces, such as pavement and concrete, reduces the natural ability of the land to absorb water. This leads to increased surface runoff, which can contribute to higher rates of flooding and pollute water systems   

-An example of this is in Manaus, located in the centre of the Amazon rainforest, and has a population of over 2 million. The threat to the rainforest is severe, with communities such as Monte Horebe causing deforestation and enormous environmental degradation- at least 100 football pitch-sized patches of forest have been destroyed to make space for squatters to build homes.   

Carbon flows and transfers in the Amazon Rainforest:

dead amazonian trees, which account for 20% of above ground biomass, emit estimated 1.9 billion tons of carbon annually.

normal year,amazon rainforest absorbs about 2.2 billion tons of CO2

Carbon is also absorbed by animals when they eat plants -> carbon moves through the food chain, only released when the animal respires or when its body decays 

Amazon river itself also releases huge amounts of CO2, as woody plant matter in the river is digested by bacteria, releasing carbon dioxide down the river. 

How has the construction of Wimbleball Reservoir affected River Exe’s water cycle?

• In 1979 an upland tributary of the River Exe was dammed to create WImbleball Reservoir

• It supplies water to Exeter and East Devon and regulates water flow(supplies a steady flow regime) → prevents peaks and troughs of water discarge that make flooding/drought more life.

• This makes Wimbleball a “strategic supply area” minimising flood/drought in Devon

Peatland restoration on Exmoor(River Exe)-why

• Drainage ditches in the peatlands of Exmoor make the area suitable for farming, but this leads to carbon loss(peat stores)

• Peat is also burned as a biofuel which scars the landscape

• When the peat surface dries out, decomposition occurs and greenhouse gases are released

• The Exmoor Mires Project helps restore peat bogs by blocking drainage ditches with peat or moorland'; this increases water content, returning ground to the natural boggy onditions, which helps to retain carbon stored in the past.

The Exmoor Mires Project:

Aims to restore 2000ha of Exmoor to the boggy conditions that would be naturally present by blocking drainage ditches with peat blocks and moorland bales.

What has results of monitoring the River Exe indicated (after restoration) ?

• Water tables have started to rise, meaning that more moisture is being retained within the soil

• Storm flow and flood peaks have been reduced and baseflow has increased

Conclusion: Increases in the water tables reflects the increased storage of water in the peat mass due to restoration and these changes are inline with changes seen in other restored peatlands across the UK and Ireland

Amazon(carbon cycle) - Links to the water cycle- relationships/ feedback mechanisms

• Slash and burn techniques which remove forest and thereby increase the CO2 emissions to the atmosphere also reduce retention of humidity in soil top layer(affecting healthy plant growth) and facilitate evaporation of water previously in the canopy 

• Impacts of climate change(from increased CO2/greenhouse gas emissions) mean that there are increased droughts/temperature changes in the rainforest, which kill millions of trees, thereby increasing carbon dioxide emissions - positive feedback mechanism 

Mitigation in Amazon Rainforest - water cycle:

Reforestation e.g Conservation International’s initiative to replant 73 million trees in Brazilian Amazon using a unique seed planting technique of spreading a large variety of native seeds across targeted areas, to increase diversity.

Amazon Cooperation Treaty Organisation - In 2004 they created the Manaus Declaration, a treaty which protected 2.9 million square miles of rainforest.

International Agreements: The Latin American Technical Cooperation Network on Watershed Agreement

Benefits of the Exmoor Mires Project:

• more water storage in upper catchments - slowed water transfer, increasing storage capacity and ensuring a steady supply of water throughout the year

• improve water quality - slower throughflod means that less sediment is carried into the rivers; cleaner water, less expensive to treat and good for wildlife like salmon

• more carbon storage - peat is an important carbon store, but dry peat releases carbon dioxide through oxidation. by re-wetting peat, CO2 is naturally absorbed from atmosphere and stored.

What did the Exmoor Mires project achieve?

over 1000ha of peat moorland has been restored, and nearly 100km of of ditches blocked, raising the water table by 2.65cm

this has reduced the amount of water that drains from the monitoring area by two-thirds.

Impact of climate change on River Exe catchment:

• climate change is expected to have

  the greatest impact on flood risk.

• following future scenario for climate change was used in the CFMO:

  • 20% increase in peak flow in all watercourses, which will increase the probability of large-scale flood events

  • a total sea level rise of 950mm by the 2100; increase the probability of tidal flooding around the Exe estuary

• using river models, estiamted that by 2100, approx. 10,950 roperties in key settlements may be at risk from a 1% annual probability flood.

What has an increase in atmospheric CO2 led to in the Amazon?

• increased rate of growth of Amazon trees, but this has led to a faster life cycle

• trees live faster, die faster

• surge in rate of trees dying

the 2000-2007 period of deforestation:

• more forest lost than the size of Greece

• deforested at a rate of 19,368km.

What may changes in total precipitation, extreme rainfall events and seasonality lead to in the Amazon:

• lead to an overall reduction in river discharge

• cause an increase in silt washed into the rivers, which

  could disrupt river transport routes

• lead to flash flooding

• destroy freshwater ecosystems; this could remove a

  source of protein and income to local inhabitants

• destroy water supply which fulfils the needs of

  Amazonian peoples

What may warming water temperatures lead to in the Amazon?

• kill off temperature-dependent species

• change the biodiversity of the river system by

  introducing new species and killing others

• reduce water-dissolved oxygen concentrations, which

  could destroy eggs and larvae, which rely on dissolved oxygen for survival.

Soil changes in the Amazon:

Amazonian soils contain from 4-9 kg of carbon in the upper 50 cm of the soil layer, while pasturelands(what forest deforestation leads to) contain only about 1 kg/m2.

When forests are cleared + burned, 30–60% of carbon lost to atmosphere; unburned vegetation decays and is lost within ten years. The soil fungi and bacteria that used to recycle the dead vegetation die off.

When forest clearance first occurs, soils exposed to the heavy tropical rainfall → rapidly washes away the topsoil and attacks the deep weathered layer below. Most of the soil is washed into rivers before the forest clearance has caused a reduction in the rainfall.