Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
Sci Total Environ. 2020 Jul 10;725:138279. doi: 10.1016/j.scitotenv.2020.138279. Epub 2020 Mar 27.
Mankind is taking advantage of numerous services by small shallow lakes such as drinking water supply, irrigation, and recreational function; however, many of these lakes suffer from eutrophication. Given the key role of phosphorus (P) in eutrophication process, one of the effective restoration methods especially for small shallow lakes is removal of sediments enriched with nutrients. In our study, we used interannual, seasonal, and spatial data to examine the changes in sediment P mobility after removal of sediments in 2016 from a 1-ha highly eutrophic lake. We measured the sediment redox potential, analyzed soluble reactive P (SRP) in the pore water and P fractional composition of the surface sediments, and calculated the diffusive flux of P in three locations in two continuous years (2017 and 2018) after the excavation. Similar measurements were done before sediment removal at central site of the lake in 2015. Removing nutrient-rich sediment also removed 6400 kg of P, and thus the potential for release of P from sediments decreased on a long-term scale. However, a large pool of releasable P was rebuilt soon after the sediment removal due to high external P loading, resulting in extensive anoxia of sediment surface and associated internal P loading as high as 1450 mg m summer. Moreover, the Fe-P and labile P fractions were the most important sources of P release, as evidenced by their considerable seasonal and interannual changes after the sediment removal. The sediment total Fe negatively correlated with diffusive flux of P, pore water SRP, and near-bottom water total P and SRP concentrations which indicated a strong linkage between sediment P dynamics and Fe after the restoration. Sediment removal could be a beneficial restoration approach, but the effects on lake water quality remain only short-term unless there is an adequate control on external loading to the lake.
人类正在利用众多小型浅湖提供的服务，如饮用水供应、灌溉和娱乐功能；然而，许多这些湖泊都受到富营养化的影响。鉴于磷（P）在富营养化过程中的关键作用，去除富含营养物质的沉积物是一种有效的恢复方法，尤其是对于小型浅湖。在我们的研究中，我们使用年际、季节性和空间数据来研究 2016 年从一个 1 公顷高度富营养化的湖泊中去除沉积物后，沉积物 P 迁移性的变化。我们测量了沉积物氧化还原电位，分析了孔隙水中的可溶解性反应磷（SRP）和表层沉积物的 P 分数组成，并在挖掘后的两个连续年份（2017 年和 2018 年）的三个位置计算了 P 的扩散通量。在 2015 年，我们在湖泊中心位置进行了类似的测量，这些测量是在去除沉积物之前进行的。去除富营养沉积物还去除了 6400 公斤的 P，因此从长期来看，沉积物中 P 的释放潜力降低了。然而，由于外部 P 负荷高，在沉积物去除后不久，就重新建立了大量可释放 P 的库，导致沉积物表面广泛缺氧，内部 P 负荷高达 1450 毫克/米夏季。此外，Fe-P 和不稳定 P 分数是 P 释放的最重要来源，这可以从它们在沉积物去除后的季节性和年际变化中得到证明。沉积物总铁与 P 的扩散通量、孔隙水 SRP 以及底层水总 P 和 SRP 浓度呈负相关，这表明恢复后沉积物 P 动态与 Fe 之间存在很强的联系。沉积物去除可能是一种有益的恢复方法，但除非对湖泊的外部负荷进行充分控制，否则对湖泊水质的影响将只是短期的。
