Change in soil carbon storage in a heterogeneous,
ecologically-managed landscape compared to two
conventionally managed urban turfs
Zena Grecni, Elizabeth Gula, & Connor Lee
Oberlin College Environmental Studies
BACKGROUND AND GOALS
Human-induced changes in carbon flows are a major cause of global climate
change. Terrestrial ecosystems can be sinks for atmospheric carbon dioxide, so
increasing carbon storage in soil and woody biomass is a potential means to
counter carbon emissions1. Soil carbon pools are particularly significant, storing
roughly three times more carbon than plants2. While land use changes trend
strongly towards increased urbanization, the effects of this conversion on soil
carbon pools is not well understood. Between 1980 and 2000, urban land-use in
North American grew by 34%. Urbanization can increase or decrease soil
carbon storage depending on pre-urban soil structure and urban ecosystem
factors such as human disturbance, management and plant species 3.
The AJLC lawn and orchard will have more fallen and decomposed biomass
because of the larger number of trees and herbaceous species than South
and Science Center lawns. This will likely lead to a slightly higher, and more
spatially variable % SOM than in South and Science Center lawns. We also
predicted that the AJLC lawn will have accumulated SOM at a higher rate
relative to South lawn from 2000 to 2007 because older turf ecosystems, like
South turf, have been shown to accumulate SOM at a slower rate5.
SAMPLE SITES, MANAGEMENT HISTORY, AND
We sampled from the four sites sampled in 2001 and also from the Science
Center lawn, as it is similar in age to the AJLC. All locations were found and
recorded using a Trimble Global Positioning System (GPS) unit accurate to
within approximately 0.5 meters, matching previously sampled locations 4. We
collected 9 samples from 3x3 grids with points about 4 meters apart in all
landscapes except the wetland. We found the five sample locations in the
wetland using the GPS coordinates recorded in the 2001 study. All terrestrial
soil samples were collected to a 15 cm depth with a metal coring device (2.5
cm radius), while the wetland samples were to a 12cm depth with an 8cm
diameter PVC pipe and rubber stopper. We determined SOM in 50g
subsamples using the loss-on-ignition method6.
A thirty-year-old, conventionally-managed lawn. Well
established, naturalized turf grass mix. Fertilizer and
herbicide applications occur once a year. Grounds
crews leave all grass clippings and most leaf mulch on
Five-year-old, conventionally managed lawn in the
center of campus. Fertilizer and herbicide
applications occur once a year. All grass clippings
are left on site, and leaves are removed once in
Adam Joseph Lewis Center (AJLC)
Seven-year-old, spatially heterogeneous landscape composed of three distinct
ecosystems: a wetland planted with a variety of native trees and herbs, a grassy
orchard with two species of apple and two varieties of pear trees, and a lawn
planted with a mix of grass species and deciduous trees native to Ohio. The lawn
is managed without the application of synthetic fertilizers, pesticides, or
herbicides. All grass clippings and leaf mulch are left on site.
We predicted the AJLC lawn will be similar in % SOM to the orchard, as both
landscapes have grass-cover and the same organic management regime. We
expected that after six years the wetland will continue to have a high relative
%SOM because of the larger amount of above ground biomass and the
waterlogged sediments that inhibit decomposition4.
Photo credit: Oberlin College
We calculated standard deviation of % SOM in each of the three turfs sampled in
2007 and the two turfs sampled in 2001. Between 7 and 11 samples were taken
at each site. The graph demonstrates higher spatial variability in % SOM
among 2007 samples in the AJLC lawn, an ecologically-managed site.
Variability in the AJLC lawn increased at a higher rate than in the
conventionally-managed South turf. Relative to the AJLC lawn, SOM in South
lawn appears to be stable over time.
Average % SOM
Standard Deviation of % SOM
Our project, a follow-up to parallel studies in 2000 and 2001, quantifies change in
percent soil organic matter (SOM), a measure of organic soil carbon, in
conventionally and ecologically-managed landscapes at Oberlin College. We aim
to increase understanding of soil carbon storage potential at these various sites.
As a part of a long-term study, our data will inform Oberlin Colleges actions
towards reduced carbon emissions. Results regarding the effects of soil
development between management regimes can also influence grounds keeping
choices in any similar urban turfs.
Spatial Heterogeneity of % SOM
There was no significant difference in percent SOM among the five sample
locations. Because this is a long term study, we suggest that continued research
will reveal differences in SOM accumulation among the differently managed
Of the three turfs sampled, variability in % SOM was higher in the AJLC lawn
than in the Science Center and South lawns, which indicates that greater species
diversity may foster more spatially heterogeneous SOM accumulation. Spatial
patterns of soil carbon pools within a landscape may be related to the presence
of certain species or biological communities.
We found the average % SOM among conventionally managed and ecologically
managed sites in 2000, 2001, and 2007. Error bars show standard deviation of
% SOM from each location. Between 5 and 12 samples were taken at each site.
Differences in average % SOM among sites were not statistically
significant in any of the years examined. The fourth series (blue) represents
% SOM averaged over the three sample years in each landscape. The 2000
and 2001 studies did not sample from the Science Center.
Further studies on the relationship between soil carbon storage and biological
diversity could focus on specific species and ecological communities that
enhance SOM accumulation rates.
Estimating carbon sinks and boosting storage capacity in Oberlin Colleges
landscapes will help in achieving the Colleges pledge to become carbon neutral.
1 IPCC. 2007. Summary for Policymakers. In S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B.
Averyt, M.Tignor and H.L. Miller (eds). Climate Change 2007: The Physical Science Basis. Contribution
of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate
Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
We calculated the change in % SOM at each sample point over time and
averaged the change by location. We found the differences in average % SOM
between 2000, 2001, and 2007. Differences in average change in % SOM
among sites were not statistically significant in any of the years examined.
2 Schlesinger, WH, Andrews, JA. 2000. Soil respiration and the global carbon cycle. Biogeochemistry. 48, 720.
Percent SOM in all of the landscapes, except the wetland, demonstrates
an increase over time from 2000 to 2007. The oldest sample location, South
lawn has the highest % SOM, averaged over the three sample years (7.14%).
This is not consistent with our hypothesis that % SOM would be higher under
ecological management. It appears that turf age is the dominant factor in soil
carbon storage capacity5. The decrease in average SOM from 2000 to 2001 is
most likely the result of methodological variation between the two years.
5 Golubiewski, Nancy E. 2006. Urbanization increases grassland carbon pools: effects of landscaping in
Colorados front range. Ecological Applications. 16:(2) 555-571.
3 Pouyat, RV, Yesilonis, ID, Nowak, DJ. 2006. Carbon storage by urban soils in the United States. Journal
of Environmental Quality. 35, 1566-1575.
4 Turner C, Ramsden J, Newhouse B. 2001. Quantifying a one-year change in soil carbon content and
calculating total carbon stored in soil and sediments of the AJLC landscape. Unpublished.
6 Nelson, DW, and Sommers, LE. 1996. Total Carbon, Organic Carbon, and Organic Carbon. Pages 9611010 in J.M. Bartels, editor. Methods of Soil Analysis Part 3- Chemical Analysis. Soil Science Society of
America, Inc., American Society of Agronomy, Inc, Madison, Wisconsin, USA.
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