Savannah River Ecology Laboratory, Warnell School of Forestry and Natural Resources, University of Georgia, PO Drawer E, Aiken, SC, 29802, USA.
Savannah River Ecology Laboratory, University of Georgia, PO Drawer E, Aiken, SC, 29802, USA.
Environ Monit Assess. 2022 Jul 7;194(8):571. doi: 10.1007/s10661-022-10258-7.
Metal biogeochemistry in the sediment, water, and the sediment-water interface (SWI) was studied in a free water surface constructed wetland. Concentrations of labile copper (Cu), zinc (Zn), sulfate, chloride, and dissolved organic carbon (DOC) were measured with the diffusive gradients in thin film (DGT) and peeper. A good agreement between peeper- and DGT-measured metals was observed for Cu (regression r = 0.3, 95% CI of the slopes > 0), but not for Zn (95% CI of the slopes overlapped with 0), which was attributed to the different complexed compounds between Cu and Zn in porewater. The depth profile of labile metals in sediment porewater varied with time and was consistent with the solid-phase metal deposition, showing higher concentrations in the surface layer (3 to - 3 cm) than in the bottom layer (- 4 to - 13 cm). The depth-averaged labile Cu and Zn concentrations measured by DGT were 1.0 and 3.1 µg/L, and labile sulfate, chloride, and DOC concentrations measured by peeper were 1.8, 3.6, and 2.1 mg/L, respectively. A sharp decrease in sulfate occurred in September when sulfate concentrations became the lowest among sampling months. This was caused by the seasonal sulfur cycles in the wetland, where the dominant sulfur reaction is sulfate reduction in warm seasons and sulfide oxidation in cold seasons. Different metal-removal mechanisms were observed in the two wetland cells; sulfur dynamics controlled the removal processes in the cell without frequent disturbance but failed to influence metal removal in the cell with frequent disturbance due to the interruption of anoxic layers. The flux ratios that compare labile element concentrations between the water column and the SWI (R-Cu, R-Zn, R-DOC, R-sulfate, and R-chloride) were generated to determine metal diffusive fluxes at the interface. Labile Zn was mostly transported from the water to the SWI during all seasons (R-Zn < 1 for all months except January). Labile Cu moved from the SWI to the water during the warm months (R-Cu < 1), which was explained by the bioturbation-induced transport of organic matter based on the positive correlations between R-Cu and R-DOC. In general, sediment can serve either as a sink or a source depending on the environmental conditions, metal speciation, and presence of living organisms. Metal flux at the SWI is a key component in the biogeochemical cycling of a constructed wetland.
在自由水面人工湿地中研究了沉积物、水和沉积物-水界面（SWI）中的金属生物地球化学。利用扩散梯度薄膜（DGT）和 peeper 测量了可利用铜（Cu）、锌（Zn）、硫酸盐、氯化物和溶解有机碳（DOC）的浓度。Cu 的 peeper 和 DGT 测量值之间存在良好的一致性（回归 r = 0.3，斜率的 95%置信区间大于 0），但 Zn 则不然（斜率的 95%置信区间与 0 重叠），这归因于孔水中 Cu 和 Zn 的不同络合化合物。沉积物孔隙水中可利用金属的深度分布随时间而变化，与固相金属沉积一致，表明表层（3 至-3 cm）的浓度高于底层（-4 至-13 cm）。用 DGT 测量的可利用 Cu 和 Zn 的平均浓度分别为 1.0 和 3.1 µg/L，用 peeper 测量的可利用硫酸盐、氯化物和 DOC 浓度分别为 1.8、3.6 和 2.1 mg/L。9 月硫酸盐浓度达到采样月份中的最低值时，硫酸盐浓度急剧下降。这是由于湿地的季节性硫循环所致，其中主要的硫反应是温暖季节的硫酸盐还原和寒冷季节的硫化物氧化。在两个湿地单元中观察到不同的金属去除机制；在没有频繁干扰的单元中，硫动态控制了去除过程，但在频繁干扰的单元中，由于缺氧层的中断，无法影响金属去除。生成了水层和 SWI 之间可利用元素浓度的通量比（R-Cu、R-Zn、R-DOC、R-硫酸盐和 R-氯化物），以确定界面处的金属扩散通量。在所有季节中，大部分可利用 Zn 都是从水输送到 SWI（除 1 月外，所有月份的 R-Zn < 1）。温暖月份可利用 Cu 从 SWI 迁移到水（R-Cu < 1），这是由于基于 R-Cu 和 R-DOC 之间的正相关关系，有机质的生物扰动引起的运输所致。一般来说，沉积物可以作为汇或源，具体取决于环境条件、金属形态和生物的存在。SWI 的金属通量是人工湿地生物地球化学循环的关键组成部分。
