Savannah River Ecology Laboratory, University of Georgia, P. O. Drawer E, Aiken, SC 29802, USA.
Environ Pollut. 2020 Jan;256:113387. doi: 10.1016/j.envpol.2019.113387. Epub 2019 Oct 22.
Constructed wetland effectiveness is often assessed by measuring reductions of contaminant concentrations in influent versus departing effluent, but this can be complicated by fluctuations in contaminant content/chemistry and hydrology. We assessed effectiveness of a constructed wetland at protecting downstream biota from accumulating elevated metal concentrations-particularly copper and zinc in effluents from a nuclear materials processing facility. Contaminants distributed throughout a constructed wetland system and two reference wetlands were assessed using six dragonfly nymph genera (Anax, Erythemis, Libellula, Pachydiplax, Tramea, and Plathemis) as biomonitors. Additionally, the crayfish, Cambarus latimanus, were analyzed from the receiving and two reference streams. Concentrations of Cu, Zn, Pb, Mn, Cr, Cd, and Al were evaluated in 597 dragonfly nymph and 149 crayfish whole-body composite samples. Dragonfly genera varied substantially in metal accumulation and the ability to identify elevated metal levels throughout components of the constructed wetland. Genera more closely associated with bottom sediments tended to accumulate higher levels of metals with Libellula, Pachydiplax, and Erythemis often accumulating highest concentrations and differing most among sites. This, combined with their abundance and broad distributions make the latter two species suitable candidates as biomonitors for constructed wetlands. As expected, dragonfly nymphs accumulated higher metal concentrations in the constructed wetland than reference sites. However, dragonfly nymphs often accumulated as high of metal concentrations downstream as upstream of the water treatment cells. Moreover, crayfish from the receiving stream near the constructed wetland accumulated substantially higher Cu concentrations than from downstream locations or reference streams. Despite reducing metal concentrations at base flow and maintaining regulatory compliance, metal fluxes from the wetland were sufficient to increase accumulation in downstream biota. Future work should evaluate the causes of downstream accumulation as the next step necessary to develop plans to improve the metal sequestering efficiency of the wetland under variable flow regimes.
人工湿地的效果通常通过测量进水与出水的污染物浓度降低来评估，但这可能因污染物含量/化学性质和水文学的波动而变得复杂。我们评估了人工湿地在保护下游生物免受积累升高的金属浓度影响方面的效果-特别是从核材料处理设施流出物中的铜和锌。使用六种蜻蜓若虫属（Anax、Erythemis、Libellula、Pachydiplax、Tramea 和 Plathemis）作为生物监测器，评估了分布在人工湿地系统和两个参考湿地中的污染物。此外，还分析了来自接收溪流和两个参考溪流的小龙虾 Cambarus latimanus。在 597 个蜻蜓若虫和 149 个小龙虾全身体复合样本中评估了 Cu、Zn、Pb、Mn、Cr、Cd 和 Al 的浓度。蜻蜓属在金属积累方面差异很大，并且能够识别人工湿地各个组成部分中的升高金属水平。与底泥更密切相关的属往往积累更高水平的金属，而 Libellula、Pachydiplax 和 Erythemis 通常积累最高浓度，并且在不同地点之间差异最大。这与它们的丰富度和广泛分布相结合，使后两个物种成为人工湿地生物监测的合适候选者。如预期的那样，蜻蜓若虫在人工湿地中的金属浓度高于参考地点。然而，蜻蜓若虫的金属浓度在处理细胞上游和下游都很高。此外，来自人工湿地附近接收溪流的小龙虾的 Cu 浓度比下游位置或参考溪流的浓度高得多。尽管人工湿地在基流时减少了金属浓度并维持了法规遵从性，但从湿地流出的金属通量足以增加下游生物的积累。未来的工作应该评估下游积累的原因，这是开发在可变流量条件下提高湿地金属固定效率计划的必要下一步。
