Climate change and riparian management are major drivers of hydrological change, with important implications for nutrient fluxes in lowland streams. However, the coupling of hydrological and nutrient dynamics is complex due to time-variant flow paths, interacting biogeochemical processes and variation in land use, fertilization levels and management measures. Here, we assessed the long-term (30 year) changes in climate, discharge, groundwater levels and stream water quality in a mixed land use catchment (Demnitzer Mill Creek catchment, DMC) in northern Germany. The catchment was subject to wetland restoration and subsequent beaver (Castor fiber) recolonization over the last 15 years. Climatic variability is the primary driver of the hydrological regime, with discharge and groundwater variations closely coupled to increases in annual air temperature and fluctuations of annual rainfall. Over the past 8 years, stream flows have been greatly reduced during a prolonged drought period. Meanwhile, beaver dams have also moderated flow regimes and facilitated groundwater recharge. In terms of water quality regimes, the concentration-discharge (C-Q) relationship for nitrate (NO₃-N) and soluble reactive phosphate (SRP) showed positive and negative chemodynamic behavior respectively, whilst dissolved organic carbon (DOC) exhibited chemostatic behavior. These differences were dictated by the intrinsic properties of each solute in terms of contrasting catchment storage and immobilization processes. Moreover, the changing hydrological conditions regulated such patterns and strengthened the C-Q relationships for nutrients during the drought. As an integrated result of drought and wetland restoration, nutrient concentrations and fluxes in stream water have been reduced in recent years. Headwater catchments like DMC, where much of the hydrochemical signature of larger, downstream river networks are generated, are critical observatories for integrating understanding of the linkages between water quality and land management in an era of climate change.

气候变化和河岸管理是水文变化的主要驱动因素，对低地溪流的养分通量具有重要影响。然而，由于随时间变化的流动路径、相互作用的生物地球化学过程以及土地利用、施肥水平和管理措施的变化，水文和养分动态的耦合是复杂的。在这里，我们评估了德国北部混合土地利用集水区（Demnitzer Mill Creek 集水区，DMC）的气候、排放、地下水位和溪流水质的长期（30 年）变化。流域受到湿地恢复和随后的海狸（蓖麻纤维) 过去 15 年的重新殖民。气候变化是水文状况的主要驱动因素，排放和地下水变化与年气温升高和年降雨量波动密切相关。在过去的 8 年中，由于长期干旱，河流流量大大减少。同时，海狸水坝也调节了水流状态并促进了地下水的补给。在水质状况方面，硝酸盐 (NO ₃-N) 和可溶性活性磷酸盐 (SRP) 分别显示出正负化学动力学行为，而溶解有机碳 (DOC) 则表现出趋化行为。这些差异是由每个溶质在对比集水储存和固定过程方面的内在特性决定的。此外，不断变化的水文条件调节了这种模式，并加强了干旱期间养分的 CQ 关系。作为干旱和湿地恢复的综合结果，近年来河流水中的养分浓度和通量有所降低。像 DMC 这样的上游集水区，在那里产生了较大的下游河流网络的大部分水化学特征，