The ecosystem function of vegetation to attenuate export of nutrients is of substantial importance for securing water quality. This ecosystem function is at risk of deterioration due to an increasing risk of large‐scale forest dieback under climate change. The present study explores the response of the nitrogen (N) cycle of a forest catchment in the Bavarian Forest National Park, Germany, in the face of a severe bark beetle (Ips typographus Linnaeus) outbreak and resulting large‐scale forest dieback using top‐down statistical‐mechanistic modeling. Outbreaks of bark beetle killed the dominant tree species Norway spruce (Picea abies (L.) H.Karst.) in stands accounting for 55% of the catchment area. A Bayesian hierarchical model that predicts daily stream NO₃ concentration (C) over three decades with discharge (Q) and temperature (T) (C‐Q‐T relationship) outperformed alternative statistical models. A catchment model was subsequently developed to explain the C‐Q‐T relationship in top‐down fashion. Annually varying parameter estimates provide mechanistic interpretations of the catchment processes. Release of NO₃ from decaying litter after the dieback was tracked by an increase of the nutrient input parameter c_s0. The slope of C‐T relation was near zero during this period, suggesting that the nutrient release was beyond the regulating capacity of the vegetation and soils. Within a decade after the dieback, the released N was flushed out and nutrient retention capacity was restored with the regrowth of the vegetation.

中文翻译：

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大型森林冲顶对森林溪流中硝酸盐浓度的贝叶斯层次建模

植被的生态系统功能以减少养分的输出对于确保水质至关重要。由于在气候变化下大规模森林大规模荒漠化的风险增加，因此该生态系统功能面临退化的风险。本研究探讨了面对严重的树皮甲虫（Ips typographus Linnaeus）暴发以及由此导致的大规模森林砍伐的情况，德国巴伐利亚森林国家公园的森林集水区的氮（N）循环响应。统计机制建模。树皮甲虫的暴发在占集水面积55％的林分中杀死了主要的树种挪威云杉（Picea abies（L.）H.Karst。）。预测每日NO _3的贝叶斯分层模型排放（Q）和温度（T）（C‐Q‐T关系）超过三十年的浓度（C）优于其他统计模型。随后开发了一个集水区模型，以自上而下的方式解释C-Q-T关系。每年变化的参数估计值可以对流域过程进行机械解释。养分输入参数c _s0的增加跟踪了枯萎后凋落凋落物中NO _3的释放。在此期间，C-T关系的斜率接近于零，表明养分释放超出了植被和土壤的调节能力。死亡后的十年内，释放出的氮被冲走，养分保持能力随着植被的再生而恢复。