Sand-Jensen Kaj, Bruun Hans Henrik, Nielsen Tora Finderup, Christiansen Ditte M, Hartvig Per, Schou Jens C, Baastrup-Spohr Lars
Freshwater Biological Section, Department of Biology, Faculty of Natural and Life Sciences, University of Copenhagen, Copenhagen, Denmark.
Section of Ecology and Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Front Plant Sci. 2018 Feb 2;9:66. doi: 10.3389/fpls.2018.00066. eCollection 2018.
European freshwater habitats have experienced a severe loss of plant diversity, regionally and locally, over the last century or more. One important and well-established driver of change is eutrophication, which has increased with rising population density and agricultural intensification. However, reduced disturbance of lake margins may have played an additional key role. The geographical variation in water chemistry, which has set the scene for - and interacted with - anthropogenic impact, is much less well understood. We took advantage of some recently completed regional plant distribution surveys, relying on hundreds of skilled citizen scientists, and analyzed the hydrophyte richness to environment relations in five contiguous South-Scandinavian regions. For three of the regions, we also assessed changes to the freshwater flora over the latest 50-80 years. We found a considerable variation in background total phosphorus concentrations and alkalinity, both within and between regions. The prevalence of functional groups differed between regions in accordance with the environmental conditions and the species' tolerance to turbid waters. Similarly, the historical changes within regions followed the same trend in correspondence to the altered environmental conditions over time. Small submerged species decreased relative to tall submerged and floating-leaved species along the regional and historical eutrophication gradients. These changes were accompanied by systematically greater relative abundance of species of higher phosphorus prevalence. We conclude that species traits in close correspondence with anthropogenic impacts are the main determinants of local, regional and historical changes of species distribution and occupancy, while pure biogeography plays a minor role. Conservation measures, such as re-oligotrophication and re-established disturbance regimes through grazing and water level fluctuations, may help reduce the tall reed vegetation, restore the former richness of the freshwater flora and safeguard red-listed species, although extended time delays are anticipated in nutrient-rich regions, in which species only survive at minute abundance in isolated refugia.
在过去一个多世纪里，欧洲淡水栖息地在区域和局部范围内都经历了植物多样性的严重丧失。一个重要且已得到充分证实的变化驱动因素是富营养化，它随着人口密度的增加和农业集约化程度的提高而加剧。然而，湖泊边缘干扰的减少可能也起到了额外的关键作用。人们对水化学的地理变化了解较少，而这种变化既为人类活动的影响创造了条件，又与之相互作用。我们利用了一些最近完成的区域植物分布调查（这些调查依靠数百名技术娴熟的公民科学家），分析了斯堪的纳维亚半岛南部五个相邻地区水生植物丰富度与环境的关系。对于其中三个地区，我们还评估了最近50 - 80年淡水植物群的变化。我们发现，区域内和区域间的背景总磷浓度和碱度存在相当大的差异。根据环境条件和物种对浑浊水域的耐受性，不同区域功能组的优势度有所不同。同样，区域内的历史变化也随着时间环境条件的改变呈现相同趋势。沿着区域和历史富营养化梯度，小型沉水物种相对于大型沉水和浮叶物种数量减少。这些变化伴随着磷含量较高的物种相对丰度系统性地增加。我们得出结论，与人为影响密切相关的物种特征是物种分布和占有率局部、区域和历史变化的主要决定因素，而纯粹的生物地理学作用较小。诸如重新恢复贫营养状态以及通过放牧和水位波动重新建立干扰机制等保护措施，可能有助于减少高大芦苇植被，恢复淡水植物群以前的丰富度并保护列入红色名录的物种，尽管在营养丰富的地区预计会有较长的时间延迟，在这些地区物种仅在孤立的避难所以极低的数量存活。
