Department of Geography and Geosciences, GeoZentrum Nordbayern, Friedrich- Alexander-Universität Erlangen-Nürnberg (FAU), Schlossgarten 5, Erlangen 91054, Germany.
Helmholtz Centre for Environmental Research-UFZ, Brueckstrasse 3a, D-39114 Magdeburg, Germany.
Sci Total Environ. 2022 Sep 10;838(Pt 3):156541. doi: 10.1016/j.scitotenv.2022.156541. Epub 2022 Jun 6.
Dissolved oxygen (DO) dynamics of a temperate drinking water reservoir in the Harz Mountains (Germany) were investigated over a time period of 18 months. Via depth profiles in a fortnightly sampling resolution we were able to trace DO and temperature dynamics including the formation and breakdown of a Metalimnetic Oxygen Minimum (MOM) by means of DO concentration, saturation patterns and stable isotope ratios of dissolved oxygen (expressed as δO). Over the evaluation period, 19.4 % of the samples collected had δO values compatible with atmospheric equilibration (+24.6 ‰ ± 0.4 ‰). With values smaller and larger than this threshold, the remaining δO values showed that 40.8 % of our samples were dominated by photosynthesis and 39.8 % by respiration. From December to April the reservoir was mixed and DO consumption by respiration exceeded production via photosynthesis. During stratification period, quantification of respiration/photosynthesis rates (R/P) confirmed the epilimnion as a photosynthetic (i.e. net-autotrophic) environment while the hypolimnion was heterotrophic and dominated by respiration at various degrees. Samples of the MOM zone showed the highest R/P ratios and had among the most positive δO signals caused by respiration. This study showed that combinations of DO concentrations and their isotope ratios are promising to quantify critical zones of respiration and photosynthesis in aquatic environments.
在 18 个月的时间内，研究了哈茨山脉（德国）一个温带饮用水水库的溶解氧（DO）动态。通过每两周进行一次深度剖面采样，我们能够追踪 DO 和温度动态，包括通过 DO 浓度、饱和度模式和溶解氧的稳定同位素比值（表示为δO）来追踪成层区氧最小值（MOM）的形成和破坏。在评估期间，收集的样本中有 19.4%的δO 值与大气平衡（+24.6 ‰ ± 0.4 ‰）兼容。其余的δO 值小于或大于这个阈值，表明我们的样本中有 40.8%是由光合作用主导的，39.8%是由呼吸作用主导的。从 12 月到 4 月，水库混合，呼吸作用消耗的 DO 超过光合作用产生的 DO。在分层期间，呼吸/光合作用比率（R/P）的定量证实了上混合层是光合作用（即净自养）环境，而下混合层是异养的，在不同程度上主要由呼吸作用主导。MOM 区的样本显示出最高的 R/P 比值，并且具有由呼吸作用引起的最正的δO 信号之一。本研究表明，DO 浓度及其同位素比值的组合有望量化水生环境中呼吸和光合作用的关键区。
