Abstract Sub-daily variations in the rates and dominance of the main controls of stream dissolved organic carbon (DOC) concentration (production, mobility and instream processes) have the potential to create a subtle sub-daily rhythm of DOC variation in streams. We used high-frequency data, covering the spring-summer-autumn period, which included discharge, specific conductivity, pH, groundwater levels, temperature, evapotranspiration and solar radiation to investigate the interplay between factors potentially driving diel DOC cycles in northern catchments. We focused on a peatland dominated 1st order stream (0.65 km 2 ) before investigating the propagation of the signals downstream to a 2nd order stream (3.2 km 2 ), with a lower percentage of peat fringing the stream channel. DOC cycles in the 1st order stream had a median peak time of 14:00 h and temporally varying amplitude, with a median of 0.61 mg l −1 . Results supported the hypothesis that diel DOC cycles at the site are driven by hydrological processes, specifically the viscosity-effect theory: viscosity-driven increases in flow from the riparian area in the afternoon flush DOC from the peat to the stream. The temporal variability in the amplitude of the diel DOC cycle was controlled by antecedent temperature. Downstream, the diel DOC signal was weaker, with around 4-fold lower amplitudes and minima in the afternoon. The lower proportion of riparian peat downstream appeared to reduce the influence of terrestrial processes on DOC cycles. In-stream photodegradation and decomposition likely became more dominant as connectivity between DOC sources and stream reduced. The study highlighted that even in climates such as the Scottish Highlands, where energy input is relatively low and precipitation frequent, sub-daily hydrological and biogeochemical rhythms occur. Unravelling the intricacy of such diel cycles is fundamental to fully understanding stream functioning and the global carbon cycle.

中文翻译：

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潮湿、低能量、北部集水区中的时空模式 DOC 循环：突出和质疑集水区功能的亚日节律

摘要 河流溶解有机碳 (DOC) 浓度（生产、流动性和入流过程）的主要控制的速率和优势的亚日变化有可能在溪流中产生微妙的亚日节律 DOC 变化。我们使用了涵盖春夏秋冬的高频数据，其中包括流量、比电导率、pH 值、地下水位、温度、蒸散和太阳辐射，以研究可能驱动北方集水区 DOC 循环的因素之间的相互作用。我们专注于泥炭地主导的一阶流 (0.65 km 2 )，然后调查信号向下游传播到二阶流 (3.2 km 2 )，泥炭边缘流道的比例较低。一阶流中的 DOC 循环的平均峰值时间为 14：00 h 和随时间变化的幅度，中值为 0.61 mg l -1 。结果支持了现场的 DOC 循环是由水文过程驱动的假设，特别是粘度效应理论：下午从河岸地区的粘度驱动的流量增加将 DOC 从泥炭冲洗到溪流。diel DOC 循环幅度的时间变异性受前期温度控制。在下游，diel DOC 信号较弱，下午的幅度和最小值降低了约 4 倍。下游河岸泥炭的比例较低似乎减少了陆地过程对 DOC 循环的影响。随着 DOC 源和流之间的连接性降低，流内光降解和分解可能变得更加重要。该研究强调，即使在能量输入相对较低且降水频繁的苏格兰高地等气候中，也会发生次日水文和生物地球化学节律。解开这种复杂的昼夜循环是充分理解河流功能和全球碳循环的基础。