Soil Carbon and Nitrogen Dynamics beneath Impervious Surfaces

Core Ideas Carbon loss from soil beneath impervious surfaces would not exceed 1.92 Pg globally. Net nitrogen mineralization rates beneath impervious surfaces were primarily related to nitrification. Temporally, nitrate accumulation was evident beneath impervious surfaces. Soil microbial biomass carbon was the key factor affecting soil carbon beneath the concrete slabs. Soil carbon beneath homes was positively related to soil volumetric water content. Soil sealing by impervious surfaces is a major disturbance caused by urbanization and has been shown to reduce soil carbon and nitrogen significantly. However, the degree to which these changes are driven by the initial disturbance (i.e., top soil removal) or post‐construction processes is not clear. A controlled field study consisting of three treatments including concrete slab (SLB), home with crawl space (CRW), and control (CNT) was conducted to monitor changes in soil properties immediately after sealing and over a 15‐mo time frame. At depth 10 to 20 cm (first layer beneath the concrete slab) soil carbon decreased by 30.4% (±3.4%) from 2.3 (±0.4) kg m –2 at Month 0 to 1.57 (±0.36) kg m –2 at the end of experiment with a rate of 0.04 (±0.01) kg m –2 per month ( p = 0.001, F 1,7 = 9.27). At this depth soil, carbon and nitrogen fluctuated seasonally at CRW and CNT plots. At depth 20 to 30 cm, the soil carbon beneath the CRW (1.14 ± 0.21 kg m –2 ) was higher than that beneath the SLB (0.93 ± 0.23 kg m –2 , p = 0.01, F 2,23 = 5.26), suggesting that partially permeable impervious surfaces such as CRW can support limited inputs of carbon and organic matter. In addition to carbon and nitrogen, temporal changes of microbial biomass carbon and nitrogen mineralization rates were also monitored. Nitrogen mineralization rates also decreased below impervious surfaces as evidenced by zero net ammonium production rate. However, a significant increase in mineralization rates was observed in warm periods of the year beneath SLB treatments.