Coastal nutrient loads from point sources such as rivers are mostly well-monitored. This is not the case for diffuse nutrient inputs from coastal catchments unconnected to rivers, despite the potential for high inputs due to intensive land use. The German Baltic Sea coastline consists of numerous peatlands that have been diked and drained. However, some of the dikes have been removed in order to re-establish the hydrological connection to the Baltic Sea, restore local biodiversity, and promote natural CO₂ uptake. Since these peatlands were used for agriculture, their rewetting may release accumulated nutrients, leading to nutrient export into the Baltic Sea and intensified coastal eutrophication. Data on these potential nutrient exports are mostly lacking. Therefore, this study investigated nutrient exports from two former agricultural, coastal peatlands: Drammendorfer Wiesen, rewetted in 2019, and Karrendorfer Wiesen, rewetted in 1993. Nutrients (NO₃^–, NO₂^–, NH₄⁺, PO₄^3–), nitrous oxide (N₂O), particulate organic matter (POM, comprising POC and PON; δ¹³C-POC), chlorophyll-a, and nitrification rates were analyzed in surface water and porewater sampled weekly to monthly in 2019 and 2020 to compare the effects of different time scales after rewetting on nutrient cycling and potential exports. NH₄⁺, NO₂⁻, and PO₄³⁻ concentrations were higher in the porewater than in the overlying water at both sites, while nutrient concentrations were generally higher at the recently rewetted Drammendorfer Wiesen than at the Karrendorfer Wiesen. NO₃⁻ concentrations in porewater, however, were lower than in the overlying water, indicating NO₃⁻ retention within the peat, likely due to denitrification. Nitrification rates and N₂O concentrations were generally low, except for a high N₂O peak immediately after rewetting. These results suggest that denitrification was the dominant process of N₂O production at the study sites. Both peatlands exported nutrients to their adjacent bays of the Baltic Sea; however, N exports were 75% lower in the longer-rewetted peatland. Compared to major Baltic Sea rivers, both sites exported larger area-normalized nutrient loads. Our study highlights the need to monitor the impact of rewetting measures over time to obtain accurate estimates of nutrient exports, better assess negative effects on coastal waters, and to improve peatland management.

来自河流等点源的沿海养分负荷大多受到良好监测。尽管由于土地集约化利用而可能产生高投入，但来自与河流不相连的沿海集水区的扩散养分输入的情况并非如此。德国波罗的海海岸线由许多已筑堤和排水的泥炭地组成。然而，为了重新建立与波罗的海的水文联系、恢复当地生物多样性并促进自然二氧化碳 ₂ 吸收，一些堤坝已被拆除。由于这些泥炭地被用于农业，其再润湿可能会释放积累的养分，导致养分流入波罗的海并加剧沿海富营养化。关于这些潜在营养素出口的数据大多缺乏。因此，本研究调查了两个前农业沿海泥炭地的养分输出：Drammendorfer Wiesen（2019 年重新湿润）和 Karrendorfer Wiesen（1993 年重新湿润）。养分（NO ₃ ^– 、NO < b3> ^– , NH ₄ ⁺ , PO ₄ ^3– ), 一氧化二氮 (对地表水和孔隙水采样的 N ₂ O）、颗粒有机物（POM，包括 POC 和 PON；δ ¹³ C-POC）、叶绿素-a 和硝化速率进行分析2019 年和 2020 年每周到每月一次，比较再润湿后不同时间尺度对养分循环和潜在出口的影响。 NH ₄ ⁺ 、NO ₂ ⁻ 和 PO ₄ ³⁻ 浓度为两个地点的孔隙水中的营养物浓度均高于上覆水中的营养物浓度，而最近再润湿的 Drammendorfer Wiesen 的营养物浓度通常高于 Karrendorfer Wiesen 的营养物浓度。 然而，孔隙水中的 NO ₃ ⁻ 浓度低于上覆水中的浓度，表明 NO ₃ ⁻ 保留在泥炭内，可能是反硝化作用造成的。除了再润湿后立即出现较高的 N ₂ O 峰值外，硝化速率和 N ₂ O 浓度普遍较低。这些结果表明反硝化是研究地点 N ₂ O 产生的主要过程。这两个泥炭地都向邻近的波罗的海海湾输出养分。然而，在较长时间再湿润的泥炭地中，氮出口量降低了 75%。与波罗的海的主要河流相比，这两个地点输出了更大的面积归一化养分负荷。我们的研究强调需要随着时间的推移监测再润湿措施的影响，以获得养分输出的准确估计，更好地评估对沿海水域的负面影响，并改善泥炭地管理。