Institute of Geography & Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.
Faculty of Oceanography and Geography, University of Gdansk, Poland.
Sci Total Environ. 2021 Feb 10;755(Pt 2):143713. doi: 10.1016/j.scitotenv.2020.143713. Epub 2020 Nov 14.
Eutrophication and anoxia are increasing in lakes worldwide. However, our understanding of variations of primary productivity and anoxia in lakes over thousands of years is limited. Long-term records are needed to understand the natural variability of lake ecosystems and to improve our understanding of drivers of productivity and anoxia. In this study, we used the varved sediment record of Lake Żabińskie, Poland to answer the following research questions: 1) How have primary production and water column oxygen concentrations varied during the past 10,800 years?; 2) what role did natural and anthropogenic forces have in driving changes in primary production or lake mixing regime? Recently developed hyperspectral imaging (HSI) techniques were used to quantify sedimentary chloropigments-a and bacteriopheopigments-a (Bphe-a) at sub-annual resolution. These data, combined with elemental data from micro X-ray fluorescence (μ-XRF) and pigment assemblage data from high-performance liquid chromatography (HPLC) measurements, were used to reconstruct paleolimnological conditions. Bphe-a was used as an indicator of anoxia, and its presence suggests that an extensive anoxic zone was present nearly continuously from 10.8 to 2.8 ka BP. Anoxic conditions, driven by thermal stratification, were promoted by closed forest cover during that time, which limited wind-driven mixing of the water column. After 2.8 ka BP, water column oxygenation occurred more frequently, particularly during periods of increased human agricultural activity and forest opening. Pronounced anoxia was again present continuously from ~610 to 1470 CE, concurrent with a period of reforestation. After ~1610 CE, deforestation caused increases in erosion rates, algal production, and water column oxygenation. Pigment assemblages indicate that the algal community during the past 150 years was different from any other time during the Holocene. This study demonstrates a clear link between lake biogeochemical processes and forest cover and shows the potential of HSI to produce extremely high-resolution records of past productivity and redox conditions from varved lake sediments.
富营养化和缺氧现象在世界各地的湖泊中日益严重。然而，我们对于数千年来湖泊初级生产力和缺氧变化的理解是有限的。为了了解湖泊生态系统的自然变异性，并更好地理解生产力和缺氧的驱动因素，我们需要长期的记录。在这项研究中，我们使用波兰 Żabińskie 湖的纹层沉积物记录来回答以下研究问题：1）在过去的 10800 年中，初级生产力和水柱氧浓度是如何变化的？；2）自然和人为因素在驱动初级生产力或湖泊混合状态的变化方面发挥了什么作用？最近开发的高光谱成像（HSI）技术被用于以亚年分辨率量化沉积物中的叶绿素-a 和细菌叶绿素-a（Bphe-a）。这些数据与来自微 X 射线荧光（μ-XRF）的元素数据以及来自高效液相色谱（HPLC）测量的色素组合数据相结合，用于重建古湖泊条件。Bphe-a 被用作缺氧的指标，其存在表明从 10800 年到 2800 年前，几乎连续存在广泛的缺氧区。在那段时间里，由于热分层，缺氧条件由封闭的森林覆盖所驱动，这限制了水柱的风驱动混合。在 2800 年前之后，水柱的充氧更为频繁，特别是在人类农业活动增加和森林开放期间。从大约 610 年到 1470 年 CE，再次出现明显的持续缺氧，与重新造林时期相吻合。大约 1610 年 CE 之后，森林砍伐导致侵蚀率、藻类生产力和水柱充氧的增加。色素组合表明，过去 150 年的藻类群落与全新世的任何其他时期都不同。这项研究表明湖泊生物地球化学过程与森林覆盖之间存在明显联系，并展示了 HSI 从纹层湖泊沉积物中产生过去生产力和氧化还原条件的极高分辨率记录的潜力。
