A significant increase in urbanization will be observed during the next fifty years. It has been shown that urbanization impacts soil carbon (C) and nitrogen (N). Many previous studies have suggested that urban land use may increase C storage in comparison to native soil without considering the effect of impervious surfaces such as buildings and sidewalks on soil carbon. Impervious surfaces may alter soil biogeochemistry by limiting the exchange of gasses, water, and organic matter. Top soil removal results in the elimination of highly active soil biota and organic matter which have a critical role in upper soil biogeochemistry. To address this knowledge gap, for the first time, a controlled study designed with three structures; concrete slabs, simulated crawl spaces under houses , and grassed lawns was installed on 5m x 5m plots. Each treatment was replicated four times in a randomized complete block design (RCB) approach. Soil C and N beneath these surfaces have been monitored periodically for more than a year and will be sampled for another year. Parameters affecting soil carbon dynamics such as microbial activities, soil moisture, temperature, oxygen, pH, cation and anion concentration levels have been monitored as well.
Results/Conclusions
Soil carbon content beneath concrete slabs and houses was 36 percent or 0.76 Kg/m2 (±0.15; ±95%C.I), and 52 percent or 1.11 Kg/m2 (±0.15; ±95%C.I) lower than grassed reference plots respectively. Higher carbon loss beneath the houses is due to oxidation of surface soil which is not protected by vegetation or concrete. Soil carbon content decreases with depth for all the treatments. Soil carbon in surface soil (0-10cm) was 1.02 Kg/m2 (±0.15; ±95%C.I) and 0.74 Kg/m2, (±0.22; ±95%C.I) and 0.41 Kg/m2 (±0.22; ±95%C.I) higher than subsurface soil (10-20cm) for grassed reference sites, beneath concrete slab, and houses respectively. The effect of depth on soil carbon is smaller beneath impervious surfaces in comparison to grassed areas. The soil beneath the concrete slab had the lowest microbial activity possibly due to lack of oxygen and energy sources. In contrast, the soil beneath the houses had higher microbial activity in comparison to concrete slabs, however, this was still fifty-one percent lower than that of reference plots. These data may improve the current estimation of carbon storage in urban areas, thus improving carbon models which are often deficient in regard to the fate of C underneath those surfaces.