Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
Sci Total Environ. 2024 Aug 25;940:173570. doi: 10.1016/j.scitotenv.2024.173570. Epub 2024 May 31.
Global change may introduce fundamental alterations in phytoplankton biomass and community structure that can alter the productivity of northern lakes. In this study, we utilized Swedish and Finnish monitoring data from lakes that are spatially (135 lakes) and temporally (1995-2019, 110 lakes) extensive to assess how phytoplankton biomass (PB) of dominant phytoplankton groups related to changes in water temperature, pH and key nutrients [total phosphorus (TP), total nitrogen (TN), total organic carbon (TOC), iron (Fe)] along spatial (Fennoscandia) and temporal (25 years) gradients. Using a machine learning approach, we found that TP was the most important determinant of total PB and biomass of a specific species of Raphidophyceae - Gonyostomum semen - and Cyanobacteria (both typically with adverse impacts on food-webs and water quality) in spatial analyses, while Fe and pH were second in importance for G. semen and TN and pH were second and third in importance for Cyanobacteria. However, in temporal analyses, decreasing Fe and increasing pH and TOC were associated with a decrease in G. semen and an increase in Cyanobacteria. In addition, in many lakes increasing TOC seemed to have generated browning to an extent that significantly reduced PB. The identified discrepancy between the spatial and temporal results suggests that substitutions of data for space-for-time may not be adequate to characterize long-term effects of global change on phytoplankton. Further, we found that total PB exhibited contrasting temporal trends (increasing in northern- and decreasing in southern Fennoscandia), with the decline in total PB being more pronounced than the increase. Among phytoplankton, G. semen biomass showed the strongest decline, while cyanobacterial biomass showed the strongest increase over 25 years. Our findings suggest that progressing browning and changes in Fe and pH promote significant temporal changes in PB and shifts in phytoplankton community structures in northern lakes.
全球变化可能会对浮游植物生物量和群落结构造成根本改变，从而改变北方湖泊的生产力。在这项研究中，我们利用瑞典和芬兰的监测数据，这些数据在空间（135 个湖泊）和时间（1995-2019 年，110 个湖泊）上都很广泛，以评估浮游植物生物量（PB）与水温、pH 值和关键养分[总磷（TP）、总氮（TN）、总有机碳（TOC）、铁（Fe）]变化的关系，这些变化包括空间（芬诺斯堪的亚）和时间（25 年）梯度。使用机器学习方法，我们发现 TP 是总 PB 和特定红藻 - 鱼腥藻属生物量以及蓝藻（两者通常对食物网和水质有不利影响）的最重要决定因素，在空间分析中，而 Fe 和 pH 对鱼腥藻属的重要性次之，TN 和 pH 对蓝藻的重要性次之和第三。然而，在时间分析中，Fe 的减少、pH 和 TOC 的增加与鱼腥藻属的减少和蓝藻的增加有关。此外，在许多湖泊中，TOC 的增加似乎导致了褐变程度的增加，从而显著降低了 PB。空间和时间结果之间的差异表明，用空间替代时间的数据可能不足以描述全球变化对浮游植物的长期影响。此外，我们发现总 PB 表现出相反的时间趋势（在芬诺斯堪的亚北部增加，在南部减少），总 PB 的减少比增加更为明显。在浮游植物中，鱼腥藻属的生物量下降最为明显，而蓝藻的生物量在 25 年内增加最为明显。我们的研究结果表明，不断加剧的褐变以及 Fe 和 pH 的变化促进了北方湖泊 PB 和浮游植物群落结构的显著时间变化。
