Institute of Geology, Center for Earth System Research and Sustainability (CEN), University Hamburg, Hamburg 20146, Germany; Institute of Carbon Cycles, Helmholtz Centre Hereon, Geesthacht 21502, Germany.
Institute of Carbon Cycles, Helmholtz Centre Hereon, Geesthacht 21502, Germany.
Sci Total Environ. 2023 Dec 15;904:166740. doi: 10.1016/j.scitotenv.2023.166740. Epub 2023 Sep 1.
Eutrophication due to excessive nutrient inputs is a major threat to coastal ecosystems worldwide, causing harmful algae blooms, seagrass loss and hypoxia. Decisions to combat eutrophication in the North Sea were made in the 1980s. Despite significant improvements during recent decades, high nitrogen loads and resulting eutrophication problems remain. In this study, long-term changes in nitrogen inputs to the Elbe Estuary (Germany) were characterized based on nitrogen data provided by the Elbe River Basin Community from 1985 to 2019. Additionally, surface water samples were taken at the weir separating the river from the estuary from 2011 to 2021 to characterize dissolved inorganic nitrogen concentrations and nitrate stable isotope composition. The findings suggest a close coupling of river discharge with the riverine nitrogen cycle. Nitrogen loads decreased disproportionately with decreasing discharge. This decrease is due to intensified nitrogen retention in the Elbe catchment, which can double nitrogen retention compared to average discharge conditions. Phytoplankton growth was enhanced by long residence times and high light availability at low water levels. This suggests that the recent decreases in nitrogen loads in the Elbe River were not only a result of management measures in the catchment but were also amplified by a recent long-lasting drought in the catchment. Based on projections from the Intergovernmental Panel on Climate Change, more frequent and extensive droughts are anticipated, which may lead to future seasonal shifts to nitrate limitation in the lower Elbe River.
由于营养物质输入过多导致的富营养化是全球沿海生态系统的主要威胁，它会引发有害藻类大量繁殖、海草消失和缺氧等问题。上世纪 80 年代，人们针对北海的富营养化问题做出了相关决策。尽管近几十年来取得了显著改善，但高氮负荷和由此产生的富营养化问题依然存在。在这项研究中，基于 1985 年至 2019 年易北河流域共同体提供的氮数据，对易北河口（德国）的氮输入进行了长期变化的特征描述。此外，2011 年至 2021 年，在分隔河流和河口的堰处采集了地表水样本，以描述溶解无机氮浓度和硝酸盐稳定同位素组成。研究结果表明，河流流量与河流氮循环密切相关。氮负荷与流量的减少不成比例。这种减少是由于易北流域氮的强化保留，与平均流量条件相比，氮的保留量可增加一倍。长时间的停留时间和低水位下的高光照条件促进了浮游植物的生长。这表明，易北河最近氮负荷的减少不仅是流域管理措施的结果，而且还受到流域最近一次长时间干旱的放大影响。根据政府间气候变化专门委员会的预测，预计会出现更频繁和更广泛的干旱，这可能导致易北河下游未来出现硝酸盐限制的季节性转变。
