Isotopic distribution of bioavailable Sr, Nd, and Pb in Chungcheongbuk-do Province, Korea

Background Mapping the distribution of bioavailable isotope ratios across landscapes serves as an efficient geochemical tool for delineating the origins and migration trajectories of humans and animals. Chungcheongbuk-do Province in central Korea, known for its geological diversity and inland location isolated from coastal influences, provides an ideal area to study the contributions of geological and environmental factors to the isotope landscape (isoscape). This study analyzed the distribution of bioavailable Sr, Nd, and Pb isotopes in the province using plant and soil data obtained in this study and from previous works. Findings Chungcheongbuk-do features diverse geological elements, including Precambrian basement, Paleozoic metasedimentary rocks, and Mesozoic granitoids and volcano-sedimentary sequences. The 87 Sr/ 86 Sr ratios of bulk soil samples from 44 sites primarily range from 0.781 to 0.706, with two ratios exceeding 0.9 originating from Precambrian basement and Cretaceous granitoid areas. Fractions of soils treated with 1 M ammonium nitrate and acetic acid exhibit indistinguishable 87 Sr/ 86 Sr ratios (R 2 = 0.99, except for one point), spanning from 0.804 to 0.707. Plant 87 Sr/ 86 Sr ratios demonstrate a robust positive correlation with leachate ratios (for ammonium nitrate data, ( 87 Sr/ 86 Sr) plant = 0.938 × ( 87 Sr/ 86 Sr) leachate + 0.045, R 2 = 0.98). The ε Nd values of bulk soils from Precambrian basement areas (–18 to –30) plot against Sm/Nd ratios around the reference line corresponding to 3 Ga, while other bulk soil samples (ε Nd = –1 to –21) align with a younger (~ 2 Ga) reference line. Plant ε Nd values, ranging from –4 to –24, exhibit a prominent positive correlation with ammonium nitrate leachates ( plant ε Nd = 0.77 × leachate ε Nd – 3.83, R 2 = 0.89). Plant samples do not show consistent variation between 87 Sr/ 86 Sr and ε Nd . The 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios of bulk soils show a ~ 2 Ga trend, typical for Korean basement rocks. The Pb isotopic ratios of ammonium nitrate and acetic acid leachates match perfectly with each other (R 2 = 0.99). The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of plant samples vary narrowly (19.2–17.9; 15.8–15.5; 39.0–38.0) and are distinctly different from those of bulk soils (24.4–17.9; 16.5–15.6; 42.5–37.9) and their leachates (23.1–17.7; 16.2–15.6; 41.0–38.1). Plant and soil data from this study and previous works were used to construct Sr and Nd isoscapes, em