Kelp, cobbles, and currents: Biologic reduction of coarse grain entrainment stress

Masteller, Claire; Finnegan, N. J.; Warrick, Jonathan A.; Miller, Ian

doi:10.1130/g36616.1

Cited by 8 publications

(5 citation statements)

References 27 publications

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“…Put simply, the use of a single value of critical Shields stress in the prediction of bed load flux does not fully capture the complex processes that control bed load transport rates. Previous studies have shown that variability in critical shear stress may be due to changes in bed pocket geometry [ Wiberg and Smith , ; Kirchner et al ., ], grain exposure and protrusion [ Fenton and Abbott , ; Kirchner et al ., ], bed grain size distribution [ Parker and Sutherland , ; Ferguson , ; Wilcock and Crowe , ], channel slope [ Lamb et al ., ], and even biological organisms [ Albertson et al ., ; Masteller et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Interplay between grain protrusion and sediment entrainment in an experimental flume

2017

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Bed load sediment transport is typically formulated as a nonlinear function of the shear stress exerted on the bed in excess of a critical value. However, due to the inherent spatial variability in grain packing and protrusion on water‐worked beds, the critical stress used in transport models represents a spatial averaging of the critical entrainment stresses of many individual particles on the bed. We perform a series of flume experiments in which we quantify, for the first time, the evolution of topography on the particle scale during low‐flow periods. We link this topography to subsequent bed load sediment transport rates and explore implications for particle critical stresses. We exploit the observed dependence of bed load flux on antecedent low‐flow duration to isolate the relationship between grain protrusion and bed load flux over a wide array of transport rates at the same applied stress. A synthesis of high‐resolution bed topography surveys and bed load flux data show that bed load transport rates characteristic of gravel channels are governed by the portion of grains that protrude highest above the bed and that this portion corresponds to ~1–5% of the total bed elevation distribution in our experiments. This result supports the argument that only a small portion of grain entrainment thresholds for a riverbed is exceeded during transport. Further, these results emphasize that subtle changes in bed topography can have dramatic effects on bed load sediment transport. We also find that transport of these highest protruding particles enhances the local erosion of surrounding grains.

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Section: Introductionmentioning

confidence: 99%

Interplay between grain protrusion and sediment entrainment in an experimental flume

2017

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“…Fine sediments and sedimentation may reduce habitat suitability for these sessile organisms by inhibiting feeding strategies. Large kelps such as A. clathratum additionally require a stable foundation for holdfast attachment to endure currents and storm surge (Morrison et al, 2009;Watanabe et al, 2014;Masteller et al, 2015). In contrast, E. parma would preferentially inhabit coarse sand areas (Stanley and James, 1971;Sisson et al, 2002), enabling filtering where coarse sand traps particulate matter for consumption without excess fouling (Bland et al, 2019), and burying to avoid predation (Manderson et al, 1999;Pappal et al, 2012) and damaging storm surge (O'Neill, 1978).…”

Section: Discussionmentioning

confidence: 99%

Spatial distribution of benthic flora and fauna of coastal placentia bay, an ecologically and biologically significant area of the island of newfoundland, atlantic Canada

Mackin-McLaughlin

Nemani²,

Misiuk³

et al. 2022

Front. Environ. Sci.

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Coastal habitats have the potential to be biodiversity hotspots that provide important ecosystem services, but also hotspots for human development and exploitation. Continued use of coastal ecosystem services requires establishing baselines that capture the present state of the benthos. This study employs habitat mapping to establish a baseline describing the spatial distribution of benthic organisms along the western coast of Placentia Bay, an Ecologically and Biologically Significant Area (EBSA) in Newfoundland, Canada. The influence of seafloor characteristics on the distribution of four dominant epifaunal assemblages and two macrophyte species were modelled using two machine learning techniques: the well-established Random Forest and the newer Light Gradient Boosting Machine. When investigating model performance, the inclusion of fine-scale (<1 m) substrate information from the benthic videos was found to consistently improve model accuracy. Predictive maps developed here suggest that the majority of the surveyed areas consisted of a species-rich epifaunal assemblage dominated by ophiuroids, porifera, and hydrozoans, as well as prominent coverage by Agarum clathratum and non-geniculate crustose coralline algae. These maps establish a baseline that enables future monitoring of Placentia Bay’s coastal ecosystem, helping to conserve the biodiversity and ecosystem services this area provides.

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“…In response to the reduction in river sediment flux, up to 160 m of shoreline retreat occurred along the Elwha River delta between 1939 and 2006 21,26 . Shoreline retreat resulted in the development of the cobble low tide terrace as noted above, and this naturally armored feature was formed from relic clasts exposed during the erosion of the coastal plain and also large clasts transported to the lower shoreface from kelp-mediated transport 26,35,39 .…”

Section: The Elwha Littoral Systemmentioning

confidence: 96%

World’s largest dam removal reverses coastal erosion

Warrick

Stevens

Miller

et al. 2019

Sci Rep

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Coastal erosion outpaces land generation along many of the world’s deltas and a significant percentage of shorelines, and human-caused alterations to coastal sediment budgets can be important drivers of this erosion. For sediment-starved and erosion-prone coasts, large-scale enhancement of sediment supply may be an important, but poorly understood, management option. Here we provide new topographic measurements that show patterns and trends of beach accretion following the restoration of sediment supply from a massive dam removal project. River sediment was initially deposited in intertidal-to-subtidal deltaic lobes, and this sediment was reworked by ocean waves into subaerial river mouth bars over time scales of several months. These river mouth bars welded to the shoreline and then initiated waves of sediment accretion along adjacent upcoast and downcoast beaches. Although the downcoast shoreline has a high wave-angle setting, the sedimentation waves straightened the downcoast shoreline rather than forming self-organized quasi-periodic instabilities, which suggests that simple coastal evolution theory did not hold under these conditions. Combined with other mega-nourishment projects, these findings provide new understanding of littoral responses to the restoration of sediment supplies.

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Kelp, cobbles, and currents: Biologic reduction of coarse grain entrainment stress

Cited by 8 publications

References 27 publications

Interplay between grain protrusion and sediment entrainment in an experimental flume

Interplay between grain protrusion and sediment entrainment in an experimental flume

Spatial distribution of benthic flora and fauna of coastal placentia bay, an ecologically and biologically significant area of the island of newfoundland, atlantic Canada

World’s largest dam removal reverses coastal erosion

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