Soil Extractable Lead (Pb) Levels Associated With Increased Soil Carbon Content in Mid‐Atlantic Turfgrass Soils

Abstract The effects of multiple global change factors on soil carbon (C) stocks are difficult to capture in short‐term experiments, but urbanization and other localized characteristics impose long‐term, gradual increases in temperature, carbon dioxide and ozone with observable in situ effects. We conducted an observational study in 62 golf courses at varying distances from urbanized areas in the temperate, mesic, mid‐Atlantic U.S., measuring soil carbon stocks in minimally managed areas where cool‐season turfgrasses had grown without disturbance for at least 25 years. In 2009–2010, soils were sampled to 30 cm depth and site and management variables were recorded. Total and permanganate oxidizable soil carbon were quantified and potential explanatory factors were explored using multiple regression analysis. Extractable soil lead (Pb) was strongly and positively correlated with total soil C (Pb incremental R 2 = 30.3%) above a threshold of ca. 4 mg/kg soil extracted. Increasing minimum daily temperature in February and cation exchange capacity were also positively correlated with total soil carbon (incremental R 2 = 2.8% for each factor). These findings suggest that atmospherically deposited Pb atoms chemically associated with and stabilized soil carbon in these soils. Large quantities of Pb were deposited atmospherically over the last century. If the effects observed here are widespread (i.e., in other regions and ecosystems), legacy Pb may impact soil carbon at a scale relevant to global carbon cycle modeling and uncertainty. Further exploration of Pb effects on soil C mineralization is urgently needed to improve quantitative models and our understanding of soil C dynamics.