Annis Water Resources Institute, Grand Valley State University, 740 West Shoreline Drive, Muskegon, MI 49441, USA.
Sci Total Environ. 2019 Feb 10;650(Pt 2):1969-1979. doi: 10.1016/j.scitotenv.2018.09.298. Epub 2018 Sep 24.
Many riverine wetlands have been drained for the creation of agricultural land; however, global declines in freshwater biodiversity have begun to motivate wetland restoration projects around the world. Legacy phosphorus (P) increases the risk that wetland restoration may liberate excess P to the water column and connecting waterbodies, resulting in a trade-off of restored habitat for degraded water quality. To avoid this trade-off, we dredged a former agricultural parcel prior to hydrologic reconnection, and evaluated restoration success by comparing sediment P dynamics before and after dredging. First, results from P adsorption isotherm experiments suggested that after dredging, the sediment would act as a sink for dissolved P only when water column soluble reactive phosphorus (SRP) concentrations exceeded 40 μg L. Additionally, the dredging depth (~1 m on average) exposed sediment with significantly reduced P sorption capacities. Second, P release rates were measured in sediment cores that were incubated under two water temperatures (ambient; +2 °C) and two oxygen levels (oxic; hypoxic). Average maximum total phosphorus (TP) release rates ranged from 40 to 85 mg m d before dredging and from 0 to 7 mg m d after dredging, resulting in a 95-99% reduction in TP release rates after dredging. Similar reductions were measured also for SRP release rates. The significant reduction in sediment P release after dredging now creates a high potential for this restored wetland to reduce net P loads into downstream waters by facilitating the deposition and burial of particulate P. We conclude that sediment dredging can be a useful technique for balancing the goals of habitat restoration and water quality improvements in wetlands restored on former agricultural lands.
许多河流湿地已被排干用于农业用地的开发；然而，全球淡水资源生物多样性的减少已开始促使世界各地开展湿地恢复项目。遗留的磷（P）增加了湿地恢复可能会将过量的 P 释放到水柱和相连水体中的风险，从而导致恢复的栖息地与退化的水质之间存在权衡。为了避免这种权衡，我们在水文重新连接之前疏浚了以前的农业用地，并通过比较疏浚前后的沉积物 P 动态来评估恢复的成功。首先，通过 P 吸附等温线实验的结果表明，疏浚后，只有当水柱可溶性反应磷（SRP）浓度超过 40μg/L 时，沉积物才会成为溶解 P 的汇。此外，疏浚深度（平均约 1m）使具有显著降低的 P 吸附能力的沉积物暴露出来。其次，在两种水温（环境温度；+2°C）和两种氧水平（好氧；缺氧）下，通过在沉积物芯中测量磷释放率。在疏浚之前，平均最大总磷（TP）释放率范围为 40 至 85mg/m/d，疏浚之后为 0 至 7mg/m/d，TP 释放率降低了 95-99%。SRP 释放率也有类似的降低。疏浚后沉积物 P 释放的显著减少，现在为通过促进颗粒 P 的沉积和埋藏，为恢复后的湿地减少进入下游水体的净 P 负荷创造了很高的潜力。我们的结论是，沉积物疏浚可以成为一种有用的技术，用于平衡在以前的农业用地上恢复的湿地的生境恢复和水质改善目标。
