Estonian University of Life Sciences, Kreutzwaldi 5, 51006 Tartu, Estonia; Ecosystems and Environment Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, Viikinkaari 1, FI-00014 Helsinki, Finland.
Freshwater Research, 3421 Hwy 117, Baysville, Ontario P0B 1A0, Canada.
Sci Total Environ. 2022 Jul 10;829:154572. doi: 10.1016/j.scitotenv.2022.154572. Epub 2022 Mar 17.
Sediment phosphorus (P) recycling is one of the key issues in lake water quality management. We studied sediment P mobility in Võrtsjärv, a large shallow lake in Estonia using both sorption experiments and long-term (1985-2020) monitoring data of the lake. Over the years studied, the lake has undergone a decline in external phosphorus loading (EL), while no improvement in phytoplankton indicators was observed. The results of the sorption experiments revealed that it may be successfully used as a tool to determine P forms involved in P retention, as up to 100% of the P from the water column was detected in sediments. Incubation of wet sediment is preferred to dry because of the sensitivity of organic P to desiccation. In the sediments of Võrtsjärv, the labile P (Lab-P) and iron bound (Fe-P) fractions are the major forms of the mobile pool that supply internal P load as sediment released P. The internal P load calculated from summer total P (TP) increases (IL) in the water column was on average 42%, but could reach 240% of EL at extreme environmental conditions. IL was correlated with the active area, which resembles the area involved in redox-related P release in polymictic lakes, and with the mean bottom shear stress in summer. IL showed a similar decreasing pattern as the external P load over the years 1985-2020, and was likely driven by the decrease of the pool of releasable P. Similarly, the decreases in sediment loading by P retention in our P sorption experiment were associated with decreases in the concentration of the potentially mobile P forms (mainly Lab-P and Fe-P). These results show that changes in external P loading can successfully control internal P loading and are useful in water quality management of large lakes.
沉积物磷（P）再循环是湖泊水质管理的关键问题之一。我们使用吸附实验和湖泊长期（1985-2020 年）监测数据研究了爱沙尼亚大型浅水湖 Võrtsjärv 的沉积物 P 迁移。在研究的这些年中，湖泊的外部磷负荷（EL）有所下降，但浮游植物指标没有改善。吸附实验的结果表明，它可以成功地用作确定参与磷保留的磷形态的工具，因为高达 100%的水柱磷被检测到在沉积物中。由于有机磷对干燥的敏感性，湿沉积物的孵育优于干沉积物。在 Võrtsjärv 的沉积物中，活性磷（Lab-P）和铁结合（Fe-P）是移动库的主要形式，作为沉积物释放的 P，它们为内部 P 负荷提供供应。从水柱夏季总磷（TP）增加（IL）计算得出的内部 P 负荷平均占 EL 的 42%，但在极端环境条件下可达到 EL 的 240%。IL 与活跃面积相关，类似于多营养型湖泊中与氧化还原相关的 P 释放所涉及的面积，并且与夏季底部剪切应力的平均值相关。IL 随着外部 P 负荷在 1985-2020 年间的逐年下降呈现出相似的下降模式，这可能是由于可释放 P 池的减少所致。同样，我们的磷吸附实验中磷保留导致的沉积物负荷减少与潜在可移动磷形式（主要是 Lab-P 和 Fe-P）浓度的减少有关。这些结果表明，外部 P 负荷的变化可以成功地控制内部 P 负荷，并且在大型湖泊的水质管理中很有用。
