EVSC30006 Lecture Notes - Lecture 4: Carbon Sequestration, Emission Intensity, Carbon Sink
1 Jun 2018
School
Department
Course
Professor
LECTURE 4: URBAN BIOGEOCHEMISTRY
• Cities are interesting to study due to climatic issues & because of management & cultural differences
Urban Nitrogen Cycle
• In constant flux
• Main output is into atmosphere as a gas – often exceeds inputs
o Leave through waterways, exported in food
• Inputs: hotspots in large urban areas & populated areas
o Accumulated in city by humans eating, gardens – fertiliser input
• Uninvited nitrogen enrichment – changes productivity and competition
URBAN CO2 EMISSIONS
• Sources: transport (fossil fuels), energy to light, heat & cool buildings, cement
from the construction industry & plant/soil respiration (night time)
o Fossil fuels provide 80% of global energy source
• Different fuels have different carbon intensities
o Measured by carbon released per unity of energy production
o Coal has highest carbon intensity, followed by oil, then gas
o Technology slowly decreasing carbon intensities over time, yet fuel being burned in developing countries
• Cities: depends on how different fuel is sourced for diff activities in diff cities
o Low densities suburbs use more energy & more GHG’s per person than high density suburbs
Urban CO2 Mitigation
• Urban green infrastructure: green walls & roofs, urban green space, street trees, urban agriculture
o Provide direct carbon sequestration benefits
o Indirect energy saving benefits due to provision of shade & mitigation of UHI
Measuring Urban Carbon sink & sources
Inventory Method
Integration Methods
• Bottom-up approach of counting & surveying
• Relies on forestry techniques
• Need to establish the allometric relationships between stem area, biomass
and leaf area for tree species
• Hard in cities as many different species without allometrics
• Top-down approach
• Collection of sections of air
and chemically analyse
them
• Costly, timely
Urban CO2 Exchange in Melbourne
• Summer: spike in the morning due to peak traffic, less peak in the evening as commuters coming home at different
times
• Winter: greater emissions than summer – due to less photosynthesis (deciduous trees)
o Peaks in both morning and evening
• Trees partially offset carbon in the suburbs
• Daily CO2 patterns greatly influenced by traffic
Mitigation through Vegetation
Biogeochemistry: the study of the cycling of matter, energy and chemical elements in space & time
Global Carbon Pools
• Stocks of carbon: forests, tropical savannas, soil (higher sinks than actual trees)
o Carbon sequestration by planting trees
• Sources & sinks: oceans (extremely high amount), soil, atmosphere
• Fluxes: photosynthesis, respiration and soil respiration – subtle changes lead to accumulation of CO2 in atmosphere
Document Summary
Biogeochemistry: the study of the cycling of matter, energy and chemical elements in space & time: cities are interesting to study due to climatic issues & because of management & cultural differences. Urban nitrogen cycle: main output is into atmosphere as a gas often exceeds inputs. Inputs: hotspots in large urban areas & populated areas: accumulated in city by humans eating, gardens fertiliser input, uninvited nitrogen enrichment changes productivity and competition. Sources: transport (fossil fuels), energy to light, heat & cool buildings, cement from the construction industry & plant/soil respiration (night time) Fossil fuels provide 80% of global energy source: different fuels have different carbon intensities, measured by carbon released per unity of energy production, coal has highest carbon intensity, followed by oil, then gas. Technology slowly decreasing carbon intensities over time, yet fuel being burned in developing countries: cities: depends on how different fuel is sourced for diff activities in diff cities.
