Iron (Fe) and phosphorus (P) dynamics in sediments have direct and indirect impacts on water quality. However, the mobility of P and Fe in reservoir sediments in Eucalyptus plantation region remains unclear. This study examined P and Fe pollution in sediments in a Eucalyptus plantation region using the novel planar optode, the ZrO-Chelex DGT, and the DIFS model. Direct in situ investigations showed that the levels of labile P and Fe were smaller in the Eucalyptus species-dominated sediments (X2) compared to sediments without Eucalyptus species (X1). The mean concentration of labile P and Fe decreased by 25% and 42% from X1 to X2. The decrement was insignificant (p = 0.20) in the surface sediment concentration for labile P. The significant disparity for DGT-Fe (Fe2+) (p = 0.03) observed in the surface sediments could be attributed to the Eucalyptus species’ elevated organic matter (tannins) concentration at X2, which reacted and consumed labile Fe. For both regions, the maximum concentration of labile P and Fe occurred in November (autumn). The reductive decomposition of Fe/Mn oxides was recognized as the main driver for their high P efflux in July and November. Low concentration of labile P and Fe was observed in December (winter) due to the adsorption of Fe/Mn oxides. The concentration of labile Fe synchronizes uniformly with that of labile P in both sediments indicating the existence of a coupling relationship (r > 0.8, p < 0.01) in both regions. The positive diffusion fluxes in both regions suggested that the sediments release labile P and Fe. The fluxes of labile P and Fe in both regions were substantially higher (p < 0.05) in the summer (anoxic period) than winter (aerobic period), indicating that hypoxia and redox conditions influenced the seasonal efflux of labile P and Fe. From the DIFS model, the replenishment ability of reactive P was higher during the anoxic period (R = 0.7, k1 = 79.4 day− 1, k-1 = 0.2 day− 1) than the aerobic period (R = 0.4, k1 = 14.2 day− 1, k-1 = 0.1 day− 1), suggesting that oxygen inhibited the efflux of P in the sediments. Our results indicated that hypoxia, Eucalyptus species (organic matter (tannins)), and redox conditions influenced the seasonal mobility of sediment labile P and Fe. Our findings provided an insight into the mobility of labile P and Fe in Eucalyptus-dominated sediments and, moreover, serves as a reference for developing future studies on Eucalyptus-dominated sediments.

中文翻译：

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桉树人工林储层沉积物中铁和磷的季节动态

沉积物中铁（Fe）和磷（P）的动态对水质有直接和间接的影响。然而，桉树人工林储层沉积物中磷和铁的迁移率仍不清楚。这项研究使用新型平面光电二极管，ZrO-Chelex DGT和DIFS模型检查了桉树人工林沉积物中的磷和铁污染。直接原位调查显示，与没有桉树物种的沉积物（X1）相比，以桉树物种为主的沉积物（X2）中不稳定的P和Fe含量要低。从X1到X2，不稳定的P和Fe的平均浓度分别降低了25％和42％。对于不稳定的P，表面沉积物浓度的降低幅度很小（p = 0.20）.DGT-Fe（Fe2 +）的显着差异（p = 0。03）在表面沉积物中观察到的现象可能是由于桉树种在X2处有机物（单宁酸）浓度升高而引起的，从而使不稳定的铁反应并消耗掉了。对于这两个地区，不稳定的P和Fe的最大浓度发生在11月（秋季）。Fe / Mn氧化物的还原分解被认为是7月和11月高P外排的主要驱动力。由于Fe / Mn氧化物的吸附，在12月（冬季）观察到低浓度的不稳定P和Fe。两个沉积物中不稳定的Fe的浓度与不稳定P的浓度均匀一致，这表明两个区域都存在耦合关系（r> 0.8，p <0.01）。两个区域的正扩散通量都表明沉积物释放出不稳定的P和Fe。夏季（缺氧时期）两个区域中不稳定的P和Fe的通量都明显高于冬季（有氧时期）（p <0.05），表明缺氧和氧化还原条件影响了不稳定P和Fe的季节性流出。根据DIFS模型，在缺氧期间（R = 0.7，k1 = 79.4天-1，k-1 = 0.2天-1）的反应性P的补充能力要比有氧期间（R = 0.4，k1 = 14.2）高第1天，k-1 = 0.1第1天），表明氧气抑制了沉积物中P的流出。我们的结果表明，低氧，桉树种（有机物（单宁））和氧化还原条件影响了不稳定的P和Fe沉积物的季节性迁移。我们的发现提供了对桉树为主的沉积物中不稳定的P和Fe迁移率的见解，此外，