Greenhouse Gas Research: Summer Results

With (more than) “seven weeks of serious summer fun” coming to a close, it’s time to reveal what you’ve all been waiting for…. results!

After spending the beginning of the summer building flux chambers, testing out sampling protocols, and learning how to use a finicky greenhouse gas analyzer,  I finally turned my focus towards obtaining summer flux data from two bodies of water on campus: the Grim Dell and the Crim Dell.  While the Crim Dell is a well-known campus icon, the Grim Dell is a smaller stormwater pond hidden at the intersection of the “trails” that connect new and old campus.  Both bodies of water were built to store runoff during rainfall events, and while they fluctuate in depth, both maintain water year round.

Sampling from a canoe in the Grim Dell

Sampling from a canoe in the Grim Dell.  Photo credit: Professor Chambers

Since the Crim Dell is large with two distinct arms and a lot of variation in depth, I sampled the Crim Dell in four different sections to get a more accurate estimate of the total flux.  Since the Grim Dell is smaller, rounder, and more homogeneous in depth, I sampled from near the center of the pond and used this data for the average flux.

The Crim Dell: divided into four sampling sections

The Crim Dell: divided into four sampling sections

These four different areas of the Crim Dell showed variation in fluxes of the three greenhouse gases measured.  The back inlet of the Crim Dell, which is regularly flushed with nitrogen-rich runoff from old campus, was a clear standout in all three greenhouse gas emissions.  See the graphs below for flux comparisons between these four sampling locations.

CrimDellGraphs2To get a perfect number for greenhouse gas fluxes from campus ponds, someone would need to be sampling every inch of each body of water for every minute of every day.  Since I am only one person with only four flux chambers and can’t sample twenty-four hours a day, the data I’ve calculated is far from perfect. Factors like temperature, rainfall, and time of day cause the flux to vary, so my samples only represent a single place and point in time that might not necessarily be representative of the whole body of water during the whole summer.  So the data below are just estimates of the flux and hopefully give an idea of the order of magnitude of emissions the Crim Dell and Grim Dell are giving off in the summer.

 

Grim Dell Flux Data


  CH4 CO2 N2O  Total 
moles/day 47.23447526 103.362853 0.005392024
CO2eq*  moles/day 1322.565307 103.362853 1.428886351 1427.357047

 

Crim Dell Flux Data


CH4 CO2 N2O  Total 
moles/day 149.042938 483.1172324 0.03775619
CO2eq* moles/day 4173.202256 483.1172324 10.00539035 4666.324879

*based on 2014 IPCC Annual Report 5 global warming potential values

To put these numbers in perspective, the data I gathered indicate that the emissions coming from the Grim Dell during the summer are roughly equivalent to burning 7.1 gallons of gasoline per day (based on 19.6 lbs of CO2 released per gallon).  In terms of electricity, this is about equivalent to 113.3 kWh (based on 1.22 lbs of CO2 per kWh), or roughly the electricity used to power 3 average homes per day.

For the Crim Dell, summer emissions are roughly equivalent to burning 23.1 gallons of gas each day.  If driving a car that gets 30 miles per gallon, a similar amount of emissions would be released by driving from Williamsburg to Philadelphia and back every day.   Or in terms of electricity, the Crim Dell is producing roughly the same emissions as using 370 kWh per day, enough to power 11 homes.

Since each greenhouse gas measured has a different degree of warming potential, its easier to compare them in terms of CO2 equivalents (see my previous blog post to learn more about CO2 equivalents!)  The bulk of the total CO2e calculated is coming from methane, a gas with a warming potential 28 times higher than CO2.  Methane is produced by microbes under anaerobic conditions (meaning an absence of oxygen) and is often released from the bottom of lakes and ponds when the decomposition process uses up dissolved oxygen in the water.  While this is a natural process that has been occurring in lakes and ponds for ages, the number of anaerobic bodies of water has increased dramatically in recent centuries as humans dig out and dam flowing, oxygen-rich rivers and streams to create stagnant, oxygen-depleted reservoirs, stormwater ponds, and man-made lakes.  Nutrient pollution from agriculture, lawn fertilizer, and sewage have also led to an increase in anaerobic conditions by causing eutrophication,  which leads to algal growth and decomposition.   Since the Crim Dell and Grim Dell were built by humans to control human-sourced stormwater runoff and fed with human-sourced nutrient pollution, the methane emissions from these ponds can be considered largely anthropogenic.

So while the Crim Dell and Grim Dell are not single-handedly destabilizing the global climate, they are contributing to anthropogenic emissions, and maybe more than our campus community realizes.  And with over 200 stormwater ponds like these in James City County alone, these emissions likely add up.  While I’ve finished off the summer with a few answers, I’m leaving with even more questions than I started with.  How does rain affect greenhouse gas emissions?  What will happen in the winter?  If I sampled all day and all night, when would emissions peak and when would they reach a low?  How much is Lake Matoaka releasing?  Maybe most importantly, what should we do about it?

I plan to keep pursuing (at least some of) these questions during the next school year.  Since the data I’ve taken over the summer is likely not representative of emissions throughout the year, my goal is to get an idea of the seasonal flux in these two ponds in order to calculate year-round emissions.  Also, since the Grim Dell is getting drained and “dredged” (getting the bottom mud scooped out) in the fall, this will provide an opportunity to study how dredging affects greenhouse gas emissions, a practice that has the potential to be an emission-reducing management option.  I look forward to getting more data throughout the year and trying to learn more about the climate impact of our campus stormwater ponds.

Thanks to Professor Chambers and Research Assistant Adrianna for being my project advisors throughout the summer, and thanks to my readers for your comments and questions!

 

 

 

Comments

  1. cccopeland says:

    What a cool project! Methane emissions from the Stormwater Retention Ponds increase as the body of water undergoes eutrophication in anaerobic conditions — is there anyway to reverse this? Crim Dell is pumped with oxygen to the point where it’s saturation is pretty high. Is pumping oxygen into the system the only way of reversing eutrophication? Also, what steps can/should be taken to reduce the methane impact of stormwater ponds around the world? Great research always leads to more questions I guess!

  2. Hi Carolina,

    This is a super interesting project. What do you think the best way to mitigate the excess emissions is? Reducing runoff? Using less nitrogen fertilizer?

    Do you think that this occurs in nature, or is it just a product of our engineering and chemistry?

    – Alec

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