Water and carbon cycle case studies

Amazon Rainforest: tropical rainforest case study

- overview of water and carbon cycles

- 7 million sq km of South America, equatorial region

- 30-50% global photosynthesis - produces 20% global O2

- deforestation occuring to clear space for cattle ranching, logging, mineral extraction

- 20% destroyed in last 50 years

Water cycle =

- high frequency convectional rainfall - 1500-3000 mm annually

- high interception (dense vegetation/canopies)

- high rates of evapotranspiration

- stem flow/drip flow -transfers water down to the forest floor

- little infiltration - complex root systems absorb temporary ground surface stores

Carbon cycle =

- warm wet weather aids plant growth - lots of biomass, key carbon sink - mitigate effects of global warming

- wood = 50% carbon

- respiration of animals releases CO2, photosynthesis sequest/stores CO2

- rapid carbon cycle of leaf litter - broken down by decomposers (bacteria/fungi which thrive in warm damp conditions)

Amazon Rainforest: tropical rainforest case study

- changes to water and carbon cycles (environmental + human)

Factors driving change =

Water cycle =

Deforestation= reduced tree canopy/forest cover - reduced evapotranspiration - less humidity - more dry/arid climate - areas downwind of a deforested area experience a 20% decline in regional rainfall

Agriculture = arable farming (palm oil plantation) less change, still interception/evapotranspiration - cover crop protects soils whereas pastoral farming (cattle ranching) more harmful - no alternative vegetation planted

- increased overland flow/runoff due to reduced interception/ soil compaction- increases flood risk + river discharge

- in a cleared area warmer air rises faster - localised low pressure - increased clouds/thunderstorm

Carbon cycle =

- global impact on atmospheric carbon levels due to a halt in photosynthesis

- reduced plant/animal respiration

- increase in soil carbon content from ash from burnt trees (washed over soils by rainwater)

- vegetation burning releases CO2

Amazon Rainforest - strategies to reduce the effects of climate change

alternate solutions to deforestation/ slash-burn cultivation to allow the land to be used for agriculture - allow economic development by preventing significant long term impacts to water/carbon cycles of the area : damage created is small scale and localised, forest easily recovers, prevents increase of atmospheric carbon dioxide at a global level

Amazon Rainforest - strategies to reduce the effects of climate change

- selective logging

- 2-4 trees cleared/acre - replanting occurs after

- maintains overall forest cover, balanced with economic development and resource use

- overall forest integrity/structure harmed however not as significantly as when complete felling occurs

- first 6-8 months CO2 is lost to atmosphere before equilibrium/balanced is restored

- long term sustainable - forest not depleted

Amazon Rainforest - strategies to reduce the effects of climate change

- ecotourism

- encourages sustainable tourism that generates jobs and local incomes whilst also inputting money into forest protection and conservation - prevents deforestation of fragile ecosystem

- long term sustainable - forest protected for future generations

- Yachana lodge, Ecuador - reserve of 1700 ha protected forest

- requires careful management to prevent pollution

- critical: time taken to establish businesses - short term loss of income compared to if deforestation just continued - not motivate local farmers to switch- but long term source once established

- promotes flying via aviation - 705M tonnes of CO2 in 2013 - other carbon cycle change driven

Amazon Rainforest - strategies to reduce the effects of climate change

- type of agriculture used

- pastoral vs arable

- not as effective as fully preventing forest clearing - but more sustainable if one type used over other

- sequestration of palm oil - helps balance local levels

- methane release of cattle - increase - no vegetation cover for photosynthesis

River Exe + Exmoor mires project: local river catchment

- characteristics of the River Exe

- drains an extensive drainage basin in South West England

source = Exmoor - 514m (highest part of drainage basin)

- high rainfall 1900mm

mouth = Exmouth Sea - 26m (low lying catchment area)

- lower rainfall 700mm

- analysis of flood hydrograph shows high flood risk - short lag time between peak rainfall and peak river discharge

- high flood risk due to high urbanisation - impermeable surfaces prevent infiltration - increases surface runoff- Exeter (50m above sea level)

River Exe + Exmoor mires project: local river catchment

- water balance

- peaty moorland soils (high carbon storage from decay plant matter)

- soils easily saturated - high run off and flood risk

- 65% water balance due to run off

- impermeable rocks with little infiltration/percolation

- 85% catchment impermeable rock base

River Exe + Exmoor mires project: local river catchment

- impact on the water cycle (Wimbleball)

- 150 hectares surface area

- formed by damming of River Haddeo

- regulates water flow, prevents significant seasonal peaks and troughs in water discharge - reduces flood risk

- successfully releases water into River Exe to supply Exeter + Devon with water

River Exe + Exmoor mires project: local river catchment

- maintaining a sustainable water supply/mitigation of flooding

why =

- drainage ditches dug in Exmoor peat bogs in 1970s - allows for agriculture/arable farming

- increases rate of surface runoff of water into River Exe, carries more silt - reduced water quality

- peat surface dries out, exposed peat bog oxidises and decomposes - methane and carbon dioxide stored is released

what =

- drainage ditches blocked with peatbog/moorland bales

- water is retained in soils- water content increased, saturated boggy ground conditions return

- carbon stored in soils retained - more effective carbon sink

- 2000 hectares restored to natural conditions

- improves water quality - slower throughflow - less silt

- more carbon storage - wetted peat sequesters CO2

- steady water supply all year round

success? =

by 2017 - 100km ditches blocked - local restoration