Physical disturbances in streams have important effects on rates of gross primary production (GPP) and ecosystem respiration (ER). Underlying lithology can control sediment size, amount, and evolution in the stream, influencing substrate stability and in turn benthic organisms. We assessed patterns of disturbance and recovery for metabolic processes of GPP and ER associated with periods of increased flow and suspended sediment flux between December and April in two streams in the Oregon Coast Range with differing lithologies (basalt and sandstone). The results of whole-stream metabolism modelling indicate that the two study streams have varying patterns of response and recovery rates after storm events. Both streams were heterotrophic during the entirety of the study period with changes in heterotrophy driven by changes in ER. Poststorm GPP decreased in both streams, but the basalt basin had greater proportional decreases and recovered slower than the sandstone basin. This result was unexpected and appeared to be associated with lower light availability in the basalt basin driven by increased turbidity during storm events; the coarser basalt substrate weathers into smaller size fractions than the finer sandstone substrate, remaining in suspension over longer periods and limiting light availability to benthic primary producers. The rates of ER in the sandstone basin did not change from prestorm to poststorm, whereas rates of ER in the basalt basin had varying responses. Overall, our results indicated that the underlying lithology of small mountain streams can drive variability in GPP by controlling sediment size and light availability during storms events.

中文翻译：

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岩性对源头系统河流代谢的影响

河流中的物理干扰对初级生产总值 (GPP) 和生态系统呼吸 (ER) 的速率有重要影响。底层岩性可以控制河流中沉积物的大小、数量和演化，影响底物稳定性，进而影响底栖生物。我们评估了 GPP 和 ER 代谢过程的扰动和恢复模式，这些过程与 12 月和 4 月期间俄勒冈海岸山脉具有不同岩性（玄武岩和砂岩）的两条溪流中流量增加和悬浮沉积物通量增加有关。全流代谢模型的结果表明，两个研究流在风暴事件后具有不同的响应模式和恢复率。在整个研究期间，两条溪流都是异养的，异养的变化是由 ER 的变化驱动的。两个河流的风暴后 GPP 均下降，但玄武岩盆地的比例下降幅度更大，恢复速度比砂岩盆地慢。这一结果是出乎意料的，似乎与风暴事件期间浊度增加导致玄武岩盆地的光照可用性降低有关；较粗的玄武岩基质比较细的砂岩基质风化成更小的尺寸部分，保持悬浮的时间更长，限制了底栖初级生产者的光照。从风暴前到风暴后，砂岩盆地的 ER 率没有变化，而玄武岩盆地的 ER 率有不同的响应。总的来说，我们的结果表明，小山溪的潜在岩性可以通过控制风暴事件期间的沉积物大小和光照可用性来驱动 GPP 的变化。