The capacity of roadside vegetated filter strips and swales to sequester carbon

Ecological Engineering 54 (2013) 227–232

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The capacity of roadside vegetated filter strips and swales to sequester carbon Natalie R. Bouchard a,1 , Deanna L. Osmond b , Ryan J. Winston a , William F. Hunt a,∗ a b

Department of Biological and Agricultural Engineering, North Carolina State University, P.O. Box 7625, Raleigh, NC 27695-7625, United States Department of Soil Science, North Carolina State University, P.O. Box 7619, Raleigh, NC 27695-7625, United States

a r t i c l e

i n f o

Article history: Received 29 September 2012 Received in revised form 4 January 2013 Accepted 16 January 2013 Available online 1 March 2013 Keywords: Carbon sequestration Vegetated filter strip Swale Highway Ecosystem service Stormwater control measure Right-of-way Transportation Wetland

a b s t r a c t Carbon capture and storage within vegetation and soil is impacted by changing land uses, which results in either a net source or sink of greenhouse gases (GHGs) to the atmosphere. Transportation corridors are present world-wide, and the vegetated filter strip and vegetated swale (VFS/VS), a common stormwater control measure, often constitutes the right-of-way (ROW) adjacent to roadways. The roadway environment, specifically carbon pools in North Carolina highway ROWs, were studied for carbon sequestration potential, an important ecosystem service. The study was conducted in two North Carolina physiographic regions: the Piedmont (characterized by clay-influenced soils) and the Coastal Plain (predominantly sandy soils). Approximately 700 soil samples were collected in VFS/VSs and wetland swales alongside major highways and analyzed for percent total soil C (% total C) and bulk density to obtain the C density. Mean soil C densities (per unit area) were 2.55 ± 0.13 kg C m−2 (mean ± standard error, n = 160, 0.2 m sample depth) in the Piedmont and 4.14 ± 0.15 kg C m−2 (n = 160, 0.2 m depth) in Coastal Plain highway VFS/VSs. Previous studies on grasslands had similar C density values to those observed in this study; thus, grasslands could be a surrogate land use for highway VFS/VSs. A thirty-seven year soil chronosequence characterized C accumulation in Piedmont VFS/VSs. Carbon density increases showed an association with age in Piedmont VFS/VSs only, which were calculated to reach maximum C density of 3.34 kg C m−2 , at age = 21.5 years. Previous studies on grasslands show similar C density and accumulation values to those observed in this study; thus, again grasslands could be a surrogate land use for highway VFS/VSs. Carbon density did not differ between dry or wetland swales, although % total C was significantly greater in wetland swales. The mean VS C density was 3.05 ± 0.13 kg C m−2 (n = 40, 0.2 m depth), while that for wetland swales was 5.04 ± 0.73 kg C m−2 (n = 44, 0.2 m depth). To promote C sequestration in the vegetated ROW, wetland swales appear preferable to dry swales. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Climate change and land use changes are two of the largest and interconnected environmental issues facing society today. While fossil fuel combustion is the largest anthropogenic greenhouse gas (GHG) source, land use conversion, either implicitly or through additional agricultural emissions, is the second leading contributor (IPCC, 2007). Land use conversion, or the conversion of native or long standing vegetation to cultivated or mixed use urban land, produces a carbon (C) source to the atmosphere (IPCC, 2007). Leaders and policymakers recognize the need to mitigate climate change through better land use management (Litynski et al., 2006; Murray

∗ Corresponding author. Tel.: +1 919 515 6751; fax: +1 919 515 6772. E-mail addresses: [email protected] (N.R. Bouchard), Deanna [email protected] (D.L. Osmond), [email protected] (R.J. Winston), [email protected] (W.F. Hunt). 1 Present address: 231 Haywood Street, Asheville, NC 28801, United States. Tel.: +1 734 771 7744. 0925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2013.01.018

et al., 2007; Post et al., 2009). Carbon storage within biomass and soil is becoming an increasingly valuable ecosystem service (Davies et al., 2011). In the terrestrial system, the majority of C is usually held below ground (soil) rather than in above ground vegetation (IPCC, 2001; Golubiewski, 2006; Post and Kwon, 2000). Land use conversion, which exposes otherwise protected soil to oxygen and microorganisms, oxidizes soil C to CO2 and reduces soil C (Post and Kwon, 2000; IPCC, 2007). The decrease in soil C from agricultural cultivation and silviculture has been studied (Lal, 2004; Johnson et al., 2002), but the effects of urban land use development, like roadway construction, on soil C have been largely undocumented (Golubiewski, 2006; Grimm et al., 2008). Globally, urban landuse is expected to increase; by 2050 2.3 billion new inhabitants will be living in urban areas (United Nations, 2010). Therefore, it is important to understand what effect new urban land uses will have on soil C and the global C budget. Vegetated filter strips, VSs, and wetland swales, all popular stormwater control measures (SCMs), have been used along roadways to trap sediment and pollutants as they drain from the road

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of annual normal). Precipitation in both regions is relatively well distributed across the year. Because soil type and structure affect carbon accumulation (Post and Kwon, 2000; Jastrow et al., 2007), the sampling regions were further narrowed by soil system type. Sites in the Piedmont were selected from the felsic crystalline and mixed felsic and crystalline soils, while in the Coastal Plain the lower Coastal Plain (Wicomico Talbot) soil system was used (Fig. 2). Utilizing a soil chronosequence, roadside VFS/VS systems of different ages were sampled to evaluate C accumulation within the soil. Using ArcGIS, each site was identified prior to sampling and systematically sampled from May to July 2011. Vegetated filter strip, ‘dry’ swale, and wetland swale sites were grouped into four age classes: 1 (0–5 years), 2 (6–15 years), 3 (16–25 years), and 4 (≥26 years). Within each age group five VFS/VS sites were selected for a total of 20 VFS/VS sites in each region (Fig. 2 and Bouchard, 2012). An additional 22 wetland swales were sampled in the Coastal Plain region (Fig. 2 and Bouchard, 2012). Fig. 1. Representative photograph of VFS and VS bordering NC highway. Site sampling regime, where positions 1, 2, and 3, constitute the VFS and position 4 constitutes the VS or wetland swale. At each position two soil cores were taken at 0–0.1 m and 0.1–0.2 m depths. Site sampling regime depicted is not to scale.

(Line and Hunt, 2009; Wu et al., 1998) (Fig. 1). Vegetated filter strips are engineered grass filter strips, which facilitate sheet flow and trap sediment and pollutants (Deletic and Fletcher, 2006; Winston et al., 2012); VSs are broad open channels that receive sheet flow from the VFS and convey stormwater to a water body (Deletic and Fletcher, 2006; Winston et al., 2012). The VS may exhibit wetland characteristics – hydrophytic vegetation and hydric soils – due to the presence of a near-surface water table. These linear wetlands have the potential to regulate discharge of nutrients associated with runoff (Moore et al., 2011), a current driver for their use. While these practices have been extensively studied for runoff mitigation and pollutant control, other ecosystem services, such as C sequestration, remain relatively unknown. In the U.S., the Federal Highway Administration (FHWA) estimates the National Highway System is 262,000 km long with approximately 2 million ha of right-of-way (ROW) alongside (USDOT-FHWA, 2010). The FHWA estimates 45% of ROWs, or 900,000 ha, is grassed area, effectively serving as a VFS and VS combination (VFS/VS) (USDOT-FHWA, 2010). The capacity for VFS/VSs to accumulate C is undocumented. The purpose of this study is to establish average and maximum C density values of roadside VFS/VSs and wetland swales within North Carolina. 2. Materials and methods 2.1. Study area Highway VFS/VS and wetland swales that border four lane highways in central and eastern NC were the focus of this study. The Piedmont and Middle Atlantic Coastal Plain (hereafter referred to as Coastal Plain) physiographic regions were examined during this study (Griffith et al., 2002). In the Coastal Plain a high water table and abundant rainfall facilitate wetland swale formation in what would otherwise be a ‘dry’ VS. Thus, wetland swales were specifically compared to ‘dry’ VSs in the Coastal Plain. The annual temperature normal for the Piedmont and Coastal Plain are 15.7 ◦ C and 16.2 ◦ C, respectively (NCDC, 2012; 1981–2010 dataset of annual normals). Seasons are rather pronounced with the average temperatures in December–February (winter) and June–August (summer) of 3.8 ◦ C and 25.6 ◦ C, respectively. The Coastal Plain receives more rainfall (1348 mm yr−1 ) than the Piedmont (1175 mm yr−1 ) (NCDC, 2012; 1981–2010 dataset

2.2. Experimental design Each site was comprised of a VFS and a VS, except in the case of wetland swales which were sampled separately. The length of the VFS from the edge of pavement (EOP) was recorded and transects were staked with flags before sampling. Two transects, 1 m apart, were established at each VFS/VS site. The first sample position was 0.5–1 m from the EOP. After position 1 was established, the remaining sample points were spaced equidistantly to the swale invert. Positions 1 through 3 were in the VFS, while position 4, taken at the swale invert, represented the swale (Fig. 1). At each sample location, individual soil cores were taken at 0–0.1 m and 0.1–0.2 m depths. Each VFS/VS site consisted of n = 16 soil cores; each wetland swale was the equivalent of position 4, and had n = 4 soil cores. Therefore, a total of 640 VFS/VS and 88 wetland swale soil cores could be obtained. However, due to compaction of roadside soils, 32 soil cores at the 0.1–0.2 m depth were not extractable in VFSs. Thus, the complete data set consisted of 696 of a possible 728 soil cores. 2.3. Sample collection and analysis The initial layer of vegetation and thatch was removed, and an AMS hammer corer (ring diameter of 5 cm; AMS American Falls, Idaho, USA) was used to capture an intact soil core (Qian et al., 2010). Samples were taken at depth 1 (0–0.1 m) and then a pit (approximately 0.30 m × 0.30 m) was dug approximately 0.1 m below soil surface and soil cores were taken at depth 2 (0.1–0.2 m). All analyses were performed on individual cores, except for soil texture, where matching positions of each transect at matching depth (e.g. the two position 1 samples at 0–0.1 m depth) were composited at each site. Each core was independently analyzed, and then all VSF results (6 per site) were pooled for each sampling location as were VS samples (4 per site). For bulk density measurements, the cores were oven-dried at 105 ◦ C over a 24-h period and weighed (Blake and Hartge, 1986). Fine bulk density (FBD), or the mass of fine fraction (<2 mm) per volume (Golubiewski, 2006), was also determined. Because C is actively accumulating in the soil, not the rock or gravel fragments found within roadside soils, the FBD, rather than the bulk density, was used to quantify the C density of these soils. A subsample was taken from the 2 mm fine fraction, and further ground to less than 250 ␮m and analyzed for % total C (g C g−1 dry soil), which was measured at the NC State University Environmental and Agricultural Testing Services lab in Raleigh, NC, USA, through dry combustion at 550 ◦ C with a Perkin-Elmer 2400 CHN

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Fig. 2. Soil sampling locations. The black squares are VFS/VS sites in the piedmont; the red circles are VFS/VS sites in the Coastal Plain; theblue triangles are wetland swale sites in the Coastal Plain. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

Elemental Analyzer (Golubiewski, 2006). The addition of 4.0 N HCl (a strong acid) to a subset of samples produced no result, therefore the percentage of total C was assumed equal to organic carbon (Conant et al., 2001). Additionally, each transect at each depth was composited for particle size analysis via the hydrometer method, and then assigned to a texture class based upon USDA classification (Gee and Bauder, 1986). The increase in soil C density is a better basis by which to evaluate C sequestration rather than simply the mass of C or the % total C in the soil, as it accounts for potential changes due to soil erosion or compaction. The C density (kg C m−2 ) of soil was determined by the following equation (Pouyat et al., 2009): Cden = FBD × d × %C

(1)

where Cden is the C density (kg C m−2 ), FBD is the fine bulk density (kg soil m−3 ), d is the sample depth (m) (10 cm for both sample depths 1 and 2), and %C is the percentage total carbon (kg carbon kg−1 soil).

Segmented non-linear regression, splits the independent variable in multiple intervals where separate segments are fit to each interval. In this analysis the x variable was site age and C density was the y variable; thus the breakpoint identifies the site age where C density no longer followed the same trend, or slope, of earlier data. The breakpoint and plateau parameters are solved iteratively in SAS using convergence criteria, where R, the relative offset measure of Bates and Watts is less than 10−5 . The segmented regression equations are as follows: CDen1 = CDen0 + CSeq1 × Age1

(2)

CDen2 = Plateau

(3)

where CDen1 is the C density (kg C m−2 ) when site age < breakpoint age, CDen0 is the baseline C density (kg C m−2 ) at site age = 0, CSeq1 is the C sequestration rate (kg C m−2 yr−1 ) when site age < breakpoint age, Age1 is the site age (yr) < breakpoint age, CDen2 is the C density (kg C m−2 ) when site age ≥ breakpoint age, and Plateau is the maximum C density (kg C m−2 ). 3. Results

2.4. Statistical analyses 3.1. Average soil characteristics SAS 9.2© statistical software was used to test the effects of age class on the response variable, C density. Due to physiographic, soil, and climate differences between the two regions, the statistical analyses were performed on the Piedmont and Coastal Plain independently. Due to evidence of homogeneity of residual errors, the data were log transformed to stabilize variance (Shapiro–Wilk pvalues > 0.05 for residuals of all datasets). Using SAS 9.2©, the PROC MIXED type III model was used to fit the data and make statistical inferences; significance was established at ˛ = 0.05. Estimates of C sequestration rates and maximum C densities were made using segmented univariate non-linear regression (PROC NLIN SAS 9.2©) where each site was regressed with actual site age (not age class). Carbon sequestration rate generally decreases over time (Post and Kwon, 2000), thus a segmented model that quantified an initially high C sequestration rate associated with vegetation establishment and a more gradual rate associated with the older sites was employed.

Table 1 describes the mean values and standard errors of site and soil chemical conditions. As expected, sandier and more acidic soils were found in the Coastal Plain. Mean site age was 17 years for all sites examined. 3.2. Carbon density The mean areal C density for the soil profile sampled of VFS/VSs were 2.55 ± 0.13 kg C m−2 and 4.14 ± 0.15 kg C m−2 within the Piedmont and the Coastal Plain, respectively (Fig. 3). Wetland swales had a mean C density of 5.04 ± 0.73 kg C m−2 ; VSs without wetland characteristics had a mean C density of 3.05 ± 0.13 kg C m−2 (Fig. 3). The mean C density of Piedmont VFS/VSs and VSs is similar to that reported for grasslands (Table 2). The mean C density of Coastal Plain VFS/VSs is comparable to grasslands, and the higher C density

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Table 1 Mean ± standard error of general site characteristics. Region

SCM

Site age (years)

Piedmont Coastal Plain Coastal Plain Coastal Plain

VFS VFS VSa Wetland swale

17 17 17 17

a

± ± ± ±

12.07 11.03 1.68 1.76

Texture (USDA)

Bulk density (g cm−3 )

Sandy loam Loamy sand Loamy sand Sandy loam

1.65 1.77 1.66 1.34

± ± ± ±

0.19 0.18 0.04 0.03

Fine bulk density (g cm−3 ) 1.43 1.59 1.52 1.28

± ± ± ±

0.20 0.18 0.04 0.03

CEC (mequiv. 100 cc−1 )

pH 6.41 5.92 5.36 4.92

± ± ± ±

1.05 1.09 0.14 0.09

12.25 10.25 8.81 7.68

± ± ± ±

13.88 7.30 1.00 0.60

Coastal Plain VFS/VS and Coastal Plain VS are presented separately because Coastal Plain VS values were specifically compared to those of wetland swales in later analyses.

Table 2 Literature values of carbon density and sequestration. Reference

Land use

Depth sampled (m)

Carbon density (kg C m−2 )

Sequestration rate (kg C m−2 yr−1 )

Pouyat et al. (2009) Golubiewski (2006) Kaye et al. (2005) Conant et al. (2001) Unger (2009) Kaye et al. (2005) Moore and Hunt (2012)

Residential turf Residential turf Residential turf Meta-data of global grasslands Grassland (Conservation Reserve Program) Grassland Constructed stormwater wetland

0–0.2 0–0.2 0–0.15 0–0.32 0–0.2 0–0.15 0–0.1

2.0–6.0 3.2–6.7 4.4–5.0 N/A 3.5 2.56–3.14 1.0–2.2

0.09 0.072 N/A 0.054 N/A N/A 0.081–0.084

N/A, not available.

to managed turf land use (Table 2). The mean C density of wetland swales is comparable to that of turf, but interestingly higher than that of constructed wetlands in North Carolina (Table 2). 3.3. Maximum C density Each SCM in each region was tested independently to determine if site age affected C density. Per the ANOVA results, age class was significant in the Piedmont VFS/VSs only (p > 0.01). No statistical relationship was found for the Coastal Plain sites: Coastal Plain VFS (p > 0.9), dry VS (p > 0.2), and wetland swale (p > 0.8). Therefore, only the Piedmont VFS/VSs were investigated for C accumulation potential. Carbon density values were modeled with segmented regression (PROC NLIN) (Fig. 4). The segmented regression model predicted a maximum C density of 3.34 kg C m−2 (95% confidence interval of 2.51–4.16 kg C m−2 ) at age ≥ 21.5 years. This “saturation age” range was somewhat similar to literature values; West et al., 2004 found land converted to grassland accumulated C at a higher rate (0.074 kg C m−2 yr−1 ) within the initial 15 years, as compared to slower rates (0.065 and 0.054 kg C m−2 yr−1 ) at 15–30 and 30–45 years, respectively. Fig. 4 illustrates the individual mean Piedmont

Fig. 3. Boxplot of C density of upper 0.2 m soil depth within Piedmont and Coastal Plain VFS/VS, wetland swales, and swales.

VFS/VS site C densities, as well as the segmented regression prediction. Barring abrupt physical, climatological, or anthropogenic disturbances, terrestrial systems are expected to accumulate C more rapidly following initial vegetation establishment, and decrease sequestration rates with time (West et al., 2004; Neill et al., 1998). The segmented model produced a C sequestration rate of 0.099 kg C m−2 yr−1 , for the initial 21.5 years, and 0 kg C m−2 yr−1 thereafter. This higher C accumulation rate was comparable to residential turf land use (Table 2). Residential turf often receives varying levels of nutrient, and water management (Osmond and Hardy, 2004) which benefits biomass production and facilitates soil C accumulation (Conant et al., 2001; Pouyat et al., 2009; Golubiewski, 2006). Highway VFS/VSs receive fertilizers and lime at establishment but rarely thereafter. Run-on from adjoining impermeable road surfaces increases water content relative to a non-irrigated lawn. Hence, during storm events the VFS/VS is exposed to extra water and accompanying nutrients. Another key difference between residential turf and highway VFS/VSs is mowing. Nearly half of residents remove grass clippings and therefore remove the ability for turf to accumulate soil C (Osmond and Hardy, 2004); grass clippings remain post-mowing in highway VFS/VSs. Per Qian et al. (2003) when turf clippings were left on site, the turf increased C sequestration by 11–59% when compared to turf where clippings were removed during mowing. Perhaps the grass clippings left on highway VFS/VSs and the additional runon water/nutrients both offset the absence of either fertilizer or irrigation.

Fig. 4. Segmented regression model results for Piedmont VFS/VSs.

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4. Discussion and conclusions Global quantification of terrestrial C stocks fails to identify specific urban land uses like roadside VFS/VSs and wetland swales. This study offers C density values to quantify the unique and extensive roadside environment, which is currently unaccounted for. Average soil C densities within roadway VFS/VSs ranged from 2.55 ± 0.13 to 4.14 ± 0.15 kg C m−2 through a 0.2 m sample depth within the Piedmont and Coastal Plain, respectively. Wetland swales were found to have a higher C density (5.04 ± 0.73 kg C m−2 ) than dry swales (3.05 ± 0.13 kg C m−2 ). Thus, swales should be valued differently per their hydrologic condition, if C accounting is implemented. Piedmont VFS/VSs were the only SCM examined to have a temporal relationship with C density. The C sequestration rate within Piedmont VFS/VSs was measured at 0.099 kg C m−2 yr−1 until the C plateau at age = 21.5 years. Utilizing the segmented model, roadway VFS/VSs were estimated to reach a C maximum of 3.34 kg C m−2 . The age range where VFS/VSs reach C maximum presented herein were comparable to literature values for grasslands and turf (Table 2). Currently, no roadside soil data are available in other regions to which C density or C accumulation rates found along NC highways can be directly compared; however the C density of roadside VFS/VSs was comparable to literature values for grasslands, and accumulation rates from this study were similar to grassland and turf values. Perhaps grasslands could be a surrogate land use for roadway VFS/VSs if no specific roadside data were available. While no data regarding C sequestration in roadway soils have been reported in refereed literature, the Federal Highway Administration conducted a feasibility study to discern sequestration potential of vegetated ROWs and assumed a C sequestration rate of 0.17 kg C m−2 yr−1 for VFS/VSs (USDOT-FHWA, 2010). When compared to the segmented model, the C accumulation rate presented herein (0.099 kg C m−2 yr−1 ), the FHWA model would substantially overestimate the C sequestration rate by a factor of 1.7. Furthermore, the rate assumed by the FHWA was not constrained to a timeframe. Utilizing the timeframe of maximum accumulation (21.5 yr), the Piedmont VFS/VS would accumulate 2.13 kg C m−2 (segmented model). If the FHWA C sequestration rate were applied using the 37-year timespan, it would predict an accumulation of 6.29 kg C m−2 , which is roughly three times the amount predicted in this study for the Piedmont. Since there was no increase in C in the Coastal Plain, the FHWA C sequestration rate grossly overestimates the ability of this practice to sequester C. Consequently, it is important for any agency wishing to account for roadway vegetation and soil as a C sink to consider an appropriate timeframe when applying C accumulation rates. If an agency were granting C credits (or C offsets) for roadside VFS/VSs, the results associated with this research are more conservative than those associated with the FHWA calculator. This paper offers a tool for agencies like the Federal Highway Administration and State Departments of Transportation to estimate and predict the maximum C density of grassed roadside soils. The maximum C density value allows agencies to quantify the net C source or sink associated with converting native or long standing vegetation to roadside VFS/VSs or wetland swales. Native C density of existing land uses prior to roadway and VFS/VS construction were not sampled herein; consequently, the net effects of land use change were not reported. It would be advantageous to sample existing soil prior to land use conversion and then monitor the C density within roadway VFS/VSs to discern the effects of land use conversion. Future studies should focus on other climatic and topographic regions and vegetation type, which would allow agencies

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to better estimate and predict the C sequestration potential of their roadways. Acknowledgments The authors thank staff from North Carolina Department of Transportation (NCDOT)’s Highway Stormwater Program, particularly Matt Lauffer and Ernie Hahn. Funding for this project was provided by the NCDOT Highway Stormwater Program. References Blake, G.R., Hartge, K.H., 1986. Bulk density. In: Methods of Soil Analysis: Part 1 – Physical and Mineralogical Methods. American Society of Agronomy, Inc., Madison, WI, pp. 363–375. Bouchard, N.R., 2012. Do roadside stormwater control measures (SCMs) offer a possible carbon sink? Thesis. North Carolina State University, Raleigh, NC. Conant, R.T., Paustian, K., Elliott, E.T., 2001. Grassland management and conversion into grassland: effects on soil carbon. Ecol. Appl. 11 (2), 343–355. Davies, Z.G., Edmondson, J.L., Heinemeyer, A., Leake, J.R., Gaston, K.J., 2011. Mapping an urban ecosystem service: quantifying above-ground carbon storage at a citywide scale. J. Appl. Ecol. 48 (5), 1125–1134. Deletic, A., Fletcher, T.D., 2006. Performance of grass filters used for stormwater treatment – a field and modelling study. J. Hydrol. 317, 261–275. Gee, G.W., Bauder, J.W., 1986. Particle-size analysis. In: Methods of Soil Analysis: Part 1 – Physical and Mineralogical Methods. American Society of Agronomy, Inc., Madison, WI, pp. 383–411. Golubiewski, N.E., 2006. Urbanization increases grassland carbon pools: effects of landscaping in Colorado’s front range. Ecol. Appl. 16 (2), 555–571. Griffith, G.E., Omernik, J.M., Comstock, J.A., Shafale, M.P., McNab, W.H., Lenat, D.R., Glover, J.B., Shelburne, V.B., 2002. Ecoregions of North Carolina and South Carolina. (2 sided color poster with map, descriptive text, summary tables, and photographs). U.S. Geological Survey, Reston, VA, Scale 1:1,500,000. Grimm, N.B., Faeth, S.H., Golubiewski, N.E., Redman, C.L., Wu, J., Bai, X., Briggs, J.M., 2008. Global change and the ecology of cities. Science 319 (5864), 756–760. IPCC, 2007. 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. IPCC, 2001. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom/New York, NY, USA. Jastrow, J., Amonette, J., Bailey, V., 2007. Mechanisms controlling soil carbon turnover and their potential application for enhancing carbon sequestration. Clim. Change 80 (1), 5–23. Johnson, D.W., Knoepp, J.D., Swank, W.T., Shan, J., Morris, L.A., Van Lear, D.H., Kapeluck, P.R., 2002. Effects of forest management on soil carbon: results of some long-term resampling studies. Environ. Pollut. 116 (Suppl. 1), S201–S208. Kaye, J., McCulley, R., Burke, I., 2005. Carbon fluxes, nitrogen cycling, and soil microbial communities in adjacent urban, native and agricultural ecosystems RID A-1420-2009. Global Change Biol. 11 (4), 575–587. Lal, R., 2004. Soil carbon sequestration to mitigate climate change. Geoderma 123 (1–2), 1–22. Line, D.E., Hunt, W.F., 2009. Performance of a bioretention area and a level spreadergrass filter strip at two highway sites in North Carolina. J. Irrig. Drain. Eng. (ASCE) 135 (2), 217–224. Litynski, J.T., Klara, S.M., McIlvried, H.G., Srivastava, R.D., 2006. The United States Department of Energy’s regional carbon sequestration partnerships program: a collaborative approach to carbon management. Environ. Int. 32 (1), 128–144. Moore, T.C., Hunt, W.F., Burchell, M.R., Hathaway, J.M., 2011. Organic nitrogen exports from urban stormwater wetlands in North Carolina. Ecol. Eng. 37 (4), 589–594. Moore, T.L.C., Hunt, W.F., 2012. Ecosystem service provision by stormwater wetlands and ponds – a means for evaluation? Water Res. 46, 6811–6823. Murray, B., Sohngen, B., Ross, M., 2007. Economic consequences of consideration of permanence, leakage and additionality for soil carbon sequestration projects. Clim. Change 80 (1), 127–143. NCDC. 2012. U.S. Annual Station Normals (1981–2012). Weather Stations USC00314962 (Lewiston, NC), USC00319467 (Wilmington, NC), USC00316422 (Richlands, NC), USW00093807 (Winston-Salem, NC), USC00319079 (Raleigh, NC), USC00311975 (Concord, NC). National Climatic Data Center, US Department of Commerce. http://www.ncdc.noaa.gov Neill, C., Cerri, C., Melillo, J., Feigl, B., Steudler, P., Moraes, J., Piccolo, M., 1998. Stocks and dynamics of soil carbon following deforestation for pasture in Rondonia. In: Soil Processes and the Carbon Cycle. CRC Press, Boca Raton, pp. 9–28. Osmond, D.L., Hardy, D.H., 2004. Characterization of turf practices in five North Carolina communities. J. Environ. Qual. 33 (2), 565–575. Post, W.M., Amonette, J.E., Birdsey, R., Garten, C.T., Izaurralde, R.C., Jardine, P.M., Jastrow, J., Lal, R., Marland, G., McCarl, B.A., Thomson, A.M., West, T.O., Wullschleger, S.D., Metting, B.F., 2009. Terrestrial Biological Carbon Sequestration: Science

232

N.R. Bouchard et al. / Ecological Engineering 54 (2013) 227–232

for Enhancement and Implementation. Geophysical Monograph Series 183, pp. 73–88. Post, W.M., Kwon, K.C., 2009. Soil carbon sequestration and land-use change: processes and potential. Global Change Biol. 6 (3), 317–327. Pouyat, R., Yesilonis, I., Golubiewski, N., 2009. A comparison of soil organic carbon stocks between residential turf grass and native soil. Urban Ecosyst. 12 (1), 45–62. Qian, Y., Follett, R., Kimble, J., 2010. Soil organic carbon input from urban turfgrasses. Soil Sci. Soc. Am. J. 74 (2), 366–371. Qian, Y.L., Bandaranayake, W., Parton, W.J., Mecham, B., Harivandi, M.A., Mosier, A.R., 2003. Long-term effects of clipping and nitrogen management in turfgrass on soil organic carbon and nitrogen dynamics. J. Environ. Qual. 32 (5), 1694–1700. Department of Transportation Federal Highway Administration (USDOT-FHWA), 2010. U.S. Highways and Climate Change: Carbon Sequestration Pilot Program. U.S. Department of Transportation Federal Highway Administration.

Unger, P.W., 2009. Soil total carbon content, aggregation, bulk density, and penetration resistance of croplands and nearby grasslands. In: Lal, R., Follett, R.F. (Eds.), Soil Carbon Sequestration and the Greenhouse Effect. Soil Science Society of America, Inc., Madison, WI, pp. 123–140. United Nations, Department of Economic and Social Affairs, Population Division, 2010. World Urbanization Prospects, The 2009 Revision: Highlights. West, T.O., Marland, G., King, A.W., Post, W.M., Jain, A.K., Andrasko, K., 2004. Carbon management response curves: estimates of temporal soil carbon dynamics. Environ. Manage. 33 (4), 507–518. Winston, R.J., Hunt, W.F., Kennedy, S.G., Wright, J.D., Lauffer, M.S., 2012. Field evaluation of stormwater control measures for highway runoff treatment. J. Environ. Eng. 138 (1), 101–111. Wu, J., Allan, C., Saunders, W., Evett, J., 1998. Characterization and pollutant loading estimation for highway runoff. J. Environ. Eng. 124 (7), 584–592.