We compared the oxygen isotope ratio of dissolved phosphate \(\left( {\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }} } \right)\) in two rivers with different land-cover and geological features (Ado River and Yasu River) within Lake Biwa basin, central Japan, to explore what factor primarily characterizes the \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\). Mean values of \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) in river water were 19.0 ± 2.4‰ (n = 7) in Ado River and 13.1 ± 2.3‰ (n = 15) in Yasu River, which were significantly different. Comparisons of \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) between river water and potential sources of phosphate revealed that in the Ado River, the \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) was similar to that in rocks from the accretionary complex and decreased with increasing sedimentary rock coverage. In the Yasu River, the \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) was low in the upper forested areas, but increased with paddy field coverage. These results demonstrate that river \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) strongly reflects inputs from geological substances, but is also impacted by land-use activities and varies with anthropogenic land coverage in the watershed. Thus, river \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) relates to land or bedrock coverage differentially in each river. Regression analysis showed that residuals of the \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) tended to converge to zero with increasing drainage area, suggesting that river \(\delta^{{{18}}} {\text{O}}_{{{\text{PO}}_{{4}} }}\) more explicitly reflects land-cover and geological features on a larger watershed scale.

中文翻译：

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表征河流水中磷酸盐氧同位素比率的因素：流域间比较方法

我们比较了溶解磷酸盐的氧同位素比\（\ left（{\ delta ^ {{{{18}}} {\ text {O}} _ {{{\ text {PO}} _ {{4}}}} } \ right）\）在日本中部琵琶湖盆地内的两条具有不同土地覆盖和地质特征的河流（阿多河和Yasu河）中，以探究哪些因素是\\\\ delta ^ {{{{18}}的主要特征} {\ text {O}} _ {{{\ text {PO}} _ {{4}}}} \）。河水中\（\ delta ^ {{{{18}}} {\ text {O}} _ {{\ text {PO}} _ {{4}}}} \\的平均值为19.0±2.4‰ 阿多河（n = 7）和 Yasu河（n = 15）的差异为13.1±2.3‰（n = 15），两者之间存在显着差异。的比较\（\三角洲^ {{{18}}} {\文本{ö}} _ {{{\文本{PO}} _ {{4}}}} \）河流水和潜在的磷酸盐来源之间的关系表明，在阿多河中，\（\ delta ^ {{{{18}}} {\ text {O}} _ {{{\ text {PO}} _ {{4} }}} \）与增生复合物中的岩石相似，并且随着沉积岩石覆盖率的增加而减小。在Yasu河中，\（\ delta ^ {{{{18}}} {\ text {O}} _ {{{\ text {PO}} _ {{4}}}} \\）的上方较低林地，但随着稻田覆盖率的增加而增加。这些结果表明，河流\（\ delta ^ {{{{18}}} {\ text {O}} _ {{{\ text {PO}} _ {{4}}}} \\）强烈反映了地质物质的输入，但也受到土地利用活动的影响，并随流域中人为的土地覆盖率而变化。因此，河\（\ delta ^ {{{{18}}} {\ text {O}} _ {{{\ text {PO}} _ {{4}}}} \}与每条河流的土地或基岩覆盖率不同。回归分析显示\（\ delta ^ {{{{18}}} {\ text {O}} _ {{{\ text {PO}} _ {{4}}}} \\）的残差趋于收敛到零随流域面积，这表明河流\（\三角洲^ {{{18}}} {\文本{ö}} _ {{{\文本{PO}} _ {{4}}}} \）更明确地在更大的分水岭上反映出土地覆盖和地质特征。