CASE STUDY - TROPICAL RAINFOREST

Question 1

the water cycle in the amazon rainforest

Answer 1

• high rainfall (2000mm) evenly distributed - high-intensity and convectional
• high evapotranspiration bc dense veg and heat. 50-60% rainfall is recycled bc evapotranspiration
• rapid run off bc intense rainfall and steep slopes. low-lands - floodplains store water for months
• 25% rainfall intercepted - mainly from canopy trees

Question 2

the carbon cycle in the amazon rainforest

Answer 2

• high NPP (net primary productivity) of 2500g/m2/yr
• the dense biomass stores larger carbon: above ground 180 tonnes // below ground (roots) 40 tonnes
• stores 80-120 bill tonnes of carbon and sequesters 2.4bill tonnes/yr
• rapid decomposition due to heat and humidity releases carbon to soil and atmosphere
• soils thin and nutrient poor

Question 3

Physical factors affecting the flows and stores in the water cycle

Answer 3

1. TEMP
   - high all year round –> high evapotranspiration –> high humidity –> intense precipitation –> drives cloud formation and convection
2. RELIEF
   - most of amazon = flat lowlands –> slow run-off
   - western areas = steeper slopes –> faster run-off and flooding
3. GEOLOGY
   - ancient permeable shield rock –> limited percolation –> rapid surface run off.
   - some western areas made of limestone –> allow infiltration

Question 4

Physical factors affecting the flows and stores in the carbon cycle

Answer 4

1. TEMP
   - high temps –> fast decomposition and high NPP.
   - warm wet climate boosts co2 uptake and organic matter breakdown
2. VEG
   - trees intercept rain and return water to atmo via transpiration.
   - large biomass = key carbon store above and below ground
3. SOIL
   - thin and leached
   rapid nutrient cycling
   - decomposition = fast carbon release + nutrients recycling
4. GEOLOGY
   - lack of carbonate rocks = low geological carbon store
   - mainly igneous rocks in basin

Question 5

CHANGES to flows and stores in the WATER cycle - Madeira river basin - largest tributary of amazon - HUMAN factors

Answer 5

• deforestation –> reduced interception + transpiration –> less recycled rainfall
• increased surface run-off –> higher floor risk (eg Porto Velho flood 2014)
• less evapotranspiration –> less could formation –> less rainfall –> drying feedback loop
• deforestation reduces soil water storage and increases peak flow + shorter lag times
• previous floods during 2000-2012 mean Bolivian rainforest lost - more runoff - more floods

Question 6

CHANGES to flows and stores in the water cycle - Madeira river WATER - largest tributary of amazon - NATURAL factors

Answer 6

• seasonal rainfall variations –> affect river discharge (dry vs wet season)
• Andes slopes naturally produce high run-off rates

Question 7

Impact of human activity (deforestation, farming) on carbon flows, soil, and nutrient stores

Answer 7

DEFORESTATION
- reduces carbon absorption by 50-60% in degraded forest
- emissions rise due to burning
- above-ground carbon store drops 180 → 43 tC/ha, below-ground 64 → 12 tC/ha.
- Soil carbon falls due to erosion and reduced organic input
- loss of decomposer activity - reduces nutrients cycling

AGRICULTURE
- crops and pasture store less carbon
- burning and erosion degrade the soil carbon even more

Question 8

Strategies to manage the tropical rainforest – positive effects on water and carbon cycles

Answer 8

SCHEMES
- legislation to preserve primary forest (Amazon Regional Protected Areas)
- afforestation - Parica project (planting 20 million tropical hardwoods)
- agroforestry - ppl trained to crop rotate
- dark soils - enriched with charcoal + waste - improves fertility –> 5X more productive

IMPACTS
- reduces flooding, run off and loss of nutrients
- Sequesters CO2 in trees and soil
- restores water cycle - interception, transpiration etc