Graduate School of Advanced Science and Engineering, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan.
School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan.
Environ Sci Technol. 2024 Mar 26;58(12):5372-5382. doi: 10.1021/acs.est.3c07170. Epub 2024 Mar 15.
Long-term phosphorus (P) fertilization results in P accumulation in agricultural soil and increases the risk of P leaching into water bodies. However, evaluating P leaching into groundwater is challenging, especially in clay soil with a high P sorption capacity. This study examined whether the combination of PO oxygen isotope (δO) analysis and the P saturation ratio (PSR) was useful to identify P enrichment mechanisms in groundwater. We investigated the groundwater and possible P sources in Kubi, western Japan, with intensive citrus cultivation. Shallow groundwater had oxic conditions with high PO concentrations, and orchard soil P accumulation was high compared with forest soil. Although the soil had a high P sorption capacity, the PSR was above the threshold, indicating a high risk of P leaching from the surface orchard soil. The shallow groundwater δO values were higher than the expected isotopic equilibrium with pyrophosphatase. The high PSR and δO orchard soil values indicated that P leaching from orchard soil was the major P enrichment mechanism. The Bayesian mixing model estimated that 76.6% of the P supplied from the orchard soil was recycled by microorganisms. This demonstrates the utility of δO and the PSR to evaluate the P source and biological recycling in groundwater.
长期施用磷肥会导致农业土壤中磷的积累，增加磷向水体淋失的风险。然而，评估磷向地下水淋失的情况具有挑战性，特别是在磷吸附能力高的黏土土壤中。本研究通过对日本西部久比地区集约化柑橘种植区的地下水和潜在磷源进行调查，探讨了 PO 氧同位素（δO）分析与磷饱和度比（PSR）相结合，用以识别地下水中磷富集机制的有效性。该地区浅层地下水呈氧化状态，PO 浓度较高，果园土壤磷积累量高于林地土壤。尽管土壤具有较高的磷吸附能力，但 PSR 高于阈值，表明表层果园土壤存在较高的磷淋失风险。浅层地下水中的 δO 值高于预期的焦磷酸酶同位素平衡值。高 PSR 和 δO 果园土壤值表明，从果园土壤淋失的磷是磷富集的主要机制。贝叶斯混合模型估计，76.6%来自果园土壤的磷通过微生物被循环利用。这证明了 δO 和 PSR 可用于评估地下水的磷来源和生物循环。
