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 emissions 1 . Soil carbon pools are particularly significant, storing roughly three times more carbon than plants 2 . 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 . 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 College’s 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.

SAMPLE SITES, MANAGEMENT HISTORY, AND HYPOTHESES HYPOTHESES

CONTINUED

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 rate 5 .

METHODS

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 method 6 . South Lawn 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 site. Science Center 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 the fall.

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.

RESULTS

2000 2001

Average % SOM

2007 Avg.

8 6 4 2

Science Center Lawn South Lawn AJLC Lawn AJLC Orchard AJLC Wetland

Orchard + 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 decomposition 4 .

Photo credit: Oberlin College

Lawn + Wetland 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.

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. 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 capacity 5 . The decrease in average SOM from 2000 to 2001 is most likely the result of methodological variation between the two years.

Spatial Heterogeneity of % SOM

Science Center Lawn

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.

CONCLUSIONS

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 landscapes.

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. 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 College’s landscapes will help in achieving the College’s pledge to become carbon neutral.

WORKS CITED

1

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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.

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Schlesinger, WH, Andrews, JA. 2000. Soil respiration and the global carbon cycle.

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3

Pouyat, RV, Yesilonis, ID, Nowak, DJ. 2006. Carbon storage by urban soils in the United States.

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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.

5

Golubiewski, Nancy E. 2006. Urbanization increases grassland carbon pools: effects of landscaping in Colorado’s front range. Ecological Applications. 16:(2) 555-571.

6

Nelson, DW, and Sommers, LE. 1996. Total Carbon, Organic Carbon, and Organic Carbon. Pages 961 1010

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.