Correction to “Carbon sequestration and greenhouse gas emissions in urban turf”

Abstract

[1] In the paper “Carbon sequestration and greenhouse gas emissions in urban turf” by A. Townsend-Small and C.I. Czimczik (Geophysical Research Letters, 37, L02707, doi:10.1029/2009GL041675, 2010), we discovered an error in the calculation of carbon dioxide (CO2) emissions from fuel consumption during turfgrass maintenance. The data for fuel consumption and park area described in the original publication are correct. Park management contractors use about 2700 gallons of gasoline per month to maintain a total park area of about 2 × 106 m2 [Townsend-Small and Czimczik, 2010]. We assumed that one gallon of gasoline equaled 2421 g C [Environmental Protection Agency, 2005] and a combustion efficiency of 85% [Lal, 2004]. This results in CO2 emissions from fuel usage of 122 g CO2 m−2 yr−1, not 1469 g CO2 m−2 yr−1 as originally reported [Townsend-Small and Czimczik, 2010], or about 24% of the organic carbon (OC) storage per m−2 shown in ornamental lawns (Figure 3 of the current study). [2] This changes the total global warming potential (GWP) of both ornamental lawns and athletic fields (Figure 3b). Based on this correction, the total GWP of ornamental lawns ranges from −108 g CO2 m−2 yr−1 for the low fertilization scenario (10 g N m−2 yr−1) to +285 g CO2 m−2 yr−1 for the high fertilizer scenario (75 g N m−2 yr−1). In athletic fields, which do not store OC in soils, there is a positive GWP ranging from +405 to +798 g CO2 m−2 yr−1 for the low and high fertilizer scenarios, respectively. Our estimates of global warming potential also have errors associated with our measurements of carbon sequestration and N2O production (error bars in Figure 3). Ornamental lawn OC sequestration ranges from −513 +37 to −513 −73 g CO2 m−2 yr−1, with uncertainties estimated from calculating OC sequestration rates based on the standard error (SE) of OC stocks at each time point. N2O emissions range from 45 +108 to 45 −25 g CO2 m−2 yr−1 at a fertilization rate of 10 g N m−2 yr−1 and from 145 + 109 to 145 − 73 g CO2 m−2 yr−1 at a fertilization rate of 75 g N m−2 yr−1. Uncertainties in N2O emissions were calculated from the SE of flux during fertilizer pulses and the 25% or 75% interquartile of the baseline flux. [3] This reanalysis shows that there may be a potential for urban ornamental lawns to sequester atmospheric CO2 if they are managed conservatively (Figure 3b). However, intensive management practices such as frequent application of inorganic fertilizers, irrigation, and fuel consumption from mowing and leaf blowing all decrease the likelihood that urban turfgrass can mitigate greenhouse gas emissions in cities.