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Fine particle transport dynamics in response to wood additions in a small agricultural stream
Hydrological Processes ( IF 3.2 ) Pub Date : 2020-08-04 , DOI: 10.1002/hyp.13874
Jennifer Drummond 1, 2 , Aslan Wright‐Stow 2, 3 , Paul Franklin 2 , John Quinn 2 , Aaron Packman 4
Affiliation  

Wood additions to streams can slow water velocities and provide depositional areas for bacteria and fine particles (e.g., particulate organic carbon and nutrients sorbed to fine sediment), therefore increasing solute and particle residence times. Thus, wood additions are thought to create biogeochemical hotspots in streams. Added wood is expected to enhance in‐stream heterogeneity, result in more complex flow paths, increase natural retention of fine particles and alter the geomorphic characteristics of the stream reach. Our aim was to directly measure the impact of wood additions on fine particle transport and retention processes. We conducted conservative solute and fluorescent fine particle tracer injection studies in a small agricultural stream in the Whatawhata catchment, North Island of New Zealand in two reaches—a control reach and a reach restored 1‐year earlier by means of wood additions. Fine particles were quantified in surface water to assess reach‐scale (channel thalweg) and habitat‐scale (near wood) transport and retention. Following the injection, habitat‐scale measurements were taken in biofilms on cobbles and by stirring streambed sediment to measure fine particles available for resuspension. Tracer injection results showed that fine particle retention was greater in the restored compared to the control reach, with increased habitat‐scale particle counts and reach‐scale particle retention. Particle deposition was positively correlated with cobble biofilm biomass. We also found that the addition of wood enhanced hydraulic complexity and increased the retention of solute and fine particles near the wood, especially near a channel spanning log. Furthermore, particles were more easily remobilized from the control reach. The mean particle size remobilized after stirring the sediments was ~5 μm, a similar size to both fine particulate organic matter and many microorganisms. These results demonstrate that particles in this size range are dynamic and more likely to remobilize and transport further downstream during bed mobilization events.

中文翻译:

在小农业流中响应木材添加的细颗粒传输动力学

溪流中添加木材会减慢水的流速,并为细菌和细颗粒(例如,颗粒有机碳和吸附到细沉积物上的营养物)提供沉积区域,因此增加了溶质和颗粒的停留时间。因此,木材添加被认为会在溪流中形成生物地球化学热点。预计添加木材会增强河内异质性,导致更复杂的流路,增加细颗粒的自然保留并改变河段的地貌特征。我们的目标是直接测量木材添加对细颗粒运输和保留过程的影响。我们在Whatawhata流域的一条农业小流中进行了保守的溶质和荧光细颗粒示踪剂注入研究,新西兰北岛有两个河段-控制河段和1年前通过添加木材恢复的河段。对地表水中的细颗粒进行了定量,以评估河床规模(河道)和栖息地规模(近木材)的运输和保留。注入后,在鹅卵石上的生物膜中进行生境规模测量,并通过搅拌河床沉积物来测量可重悬的细颗粒。示踪剂注入结果表明,与对照组相比,恢复后的细颗粒保留量更大,栖息地规模的颗粒计数和范围尺度的颗粒保留都增加了。颗粒沉积与卵石生物膜生物量呈正相关。我们还发现,添加木材会增加水力复杂性,并增加溶质和细颗粒在木材附近的保留能力,特别是在通道生成日志附近。此外,粒子更容易从控制范围内移出。搅动沉淀物后重新固定的平均粒径为〜5μm,与细颗粒有机物和许多微生物相似。这些结果表明,在该尺寸范围内的颗粒是动态的,并且在床移动过程中更可能移动并向下游进一步输送。
更新日期:2020-08-04
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