Fig. 2. Change over time in (a) Pb content (HBEF, Oie r² = 0.91, p < 0.001, OaA r² = 0.17, p = 0.74; BEF, Oie r² = 0.55, p = 0.004, OaA r² = 0.10, p = 0.90); (b) Pb concentration (HBEF, Oie r² = 0.99, p < 0.001, OaA r² = 0.07, p = 0.47; BEF, Oie r² = 0.72, p < 0.001, OaA r² = 0.21, p = 0.08); and (c) organic mass (HBEF, Oie r² = 0.54, p = 0.04, OaA r² = 0.07, p = 0.29; BEF, Oie r² = 0.10, p = 0.86, OaA r² = 0.06, p = 0.56) of Oie and Oa-A horizons at Hubbard Brook and Bartlett Experimental Forests.