Wednesday, April 10, 2013

Virtual Geography Convention 2013: Urban grass might be greener, but that doesn't mean it's 'greener'

Welcome to the Virtual Geography Convention 2013!  If you have a presentation or blog post you wished published please contact me at catholicgauze [at] gmail [dot] com!
Dr. Amy Townsend-Small of the University of Cincinnati is presenting "Carbon Sequestration and Greenhouse Gas Emissions in Urban Ecosystems" at the Association of American Geographers 2013 annual conference.
Townsend-Small's presentation is not available online.  However, Science Codex blog has an article on Townsend-Small's research analysis.  A key discovery was

"Townsend-Small found that while having a well-cared-for lawn will improve its carbon-quelling capacity, intensive lawn care isn't worth the atmospheric side effects. For example, in California's arid environment, the management required and fossil fuel energy expended to keep lawns looking lush consumes so much energy that it counteracts the soil's natural carbon sequestration abilities. But if you head nearly 2,500 miles east to Cincinnati, rainfall is more plentiful. This means more lawns don't require irrigation, helping reduce the carbon cost of lawn maintenance and preserve the carbon sequestration benefits."
Her abstract is below:

Urban areas may have high carbon densities in both above-ground and below-ground fractions, leading to questions about whether urban green spaces can serve as sinks for carbon dioxide emissions. We measured organic carbon stocks in soils along a chronosequence of two types of urban turfgrass ecosystems: ornamental lawns and athletic fields. We also measured nitrous oxide (N2O; 298 times the global warming potential of CO2) emission rates from each type of lawn for one year, and estimated indirect CO2 emissions from fossil fuel consumption for lawn maintenance, fertilizer production, and irrigation. We found that ornamental lawns could sequester C at a rate of approximately 140 g C m-2 yr-1, but that athletic fields did not sequester C due to frequent surface restoration. Nitrous oxide emissions were approximately 0.2 g N m-2 yr-1 from both types of lawns, similar to agricultural N2O emission rates from the same region. In terms of total global warming potential, direct N2O emissions were between 9 and 28% of carbon uptake observed in ornamental lawns. Conservatively managed ornamental lawns may be able to act as a positive sink for CO2, but intensive management practices such as frequent application of fertilizers, irrigation, and fuel consumption from mowing and leaf blowing all decrease the likelihood that urban turfgrass can mitigate greenhouse gas emissions in cities. Current work is focused on whether unirrigated and unfertilized urban soils can absorb CO2 at rates similar to managed lawns without large indirect emissions of CO2 and direct emissions of N2O and methane.

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