Field flume reveals aquatic vegetation's role in sediment and particulate phosphorus transport in a shallow aquatic ecosystem

Fine particles (1–100 µm), including particulate organic carbon (POC) and fine sediment, influence stream ecological functioning because they may contain or have a high affinity to sorb nitrogen and phosphorus. These particles are immobilized within stream storage areas, especially hyporheic sediments and benthic biofilms. However, fine particles are also known to remobilize under all flow conditions. This combination of downstream transport and transient retention, influenced by stream geomorphology, controls the distribution of residence times over which fine particles influence stream ecosystems. The main objective of this study was to quantify immobilization and remobilization rates of fine particles in a third‐order sand‐and‐gravel bed stream (Difficult Run, Virginia, USA) within different geomorphic units of the stream (i.e., pool, lateral cavity, and thalweg). During our field injection experiment, a thunderstorm‐driven spate allowed us to observe fine particle dynamics during both base flow and in response to increased flow. Solute and fine particles were measured within stream surface waters, pore waters, sediment cores, and biofilms on cobbles. Measurements were taken at four different subsurface locations with varying geomorphology and at multiple depths. Approximately 68% of injected fine particles were retained during base flow until the onset of the spate. Retention was evident even after the spate, with 15.4% of the fine particles deposited during base flow still retained within benthic biofilms on cobbles and 14.9% within hyporheic sediment after the spate. Thus, through the combination of short‐term remobilization and long‐term retention, fine particles can serve as sources of carbon and nutrients to downstream ecosystems over a range of time scales.

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“…Harvey et al . [] identified entrainment of fine sediment from canopies of submerged plants as a substantial contributor. O'Connor et al .…”

Section: Introductionmentioning

confidence: 99%

Fine particle retention within stream storage areas at base flow and in response to a storm event

Drummond

Larsen

González‐Pinzón

et al. 2017

Water Resources Research

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“…For example, hydraulic disturbance of algal, periphyton, and microbial biofilm communities is increasingly being studied to understand how stream ecosystems recover from floods [ Valett et al , 1994; Battin et al , 2003; Arnon et al , 2010; O'Connor et al , 2012]. Attention is increasingly being given to understanding how these factors affect dissolved oxygen uptake and accompanying biogeochemical reactions in the hyporheic zone [ O'Connor and Hondzo , 2008], transport of nutrients associated with fine particulates [ Harvey et al , 2011], metal cycling [ Brigham et al , 2009] and transport and fate of pathogenic bacteria [ Searcy et al , 2006]. These topics also are integral to understanding organic matter cycling and metabolism [ Paul and Hall , 2002; Minshall et al , 2000; Battin et al , 2008; Newbold et al , 2005; Webster et al , 1987] and predicting how streams will respond to changing flood regimes due to land‐use and climate change [ Mulholland et al , 2008; Bukaveckas , 2007; O'Connor et al , 2010].…”

Section: Introductionmentioning

confidence: 99%

“…The combined effects of turbulent transfer, settling, and filtration in hyporheic flow paths can result in accumulation of fine particulates on and within the streambed [ Hünken and Mutz , 2007; Packman et al , 2000]. Mobilization of fine particulates from the bed is generally more difficult to predict because often thresholds in shear stress must be surpassed to initiate motion [ Harvey et al , 2011]. Frequently the streambed bed itself must be disturbed by scour or migration of bedforms in order to entrain fine particulates (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Hydrogeomorphology of the hyporheic zone: Stream solute and fine particle interactions with a dynamic streambed

et al. 2012

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[1] Hyporheic flow in streams has typically been studied separately from geomorphic processes. We investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand-bed stream before, during, and after a flood. A conservatively transported solute tracer (bromide) and a fine particles tracer (5 mm latex particles), a surrogate for fine particulate organic matter, were co-injected during base flow. The tracers were differentially stored, with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute. Tracer injections lasted 3.5 h after which we released a small flood from an upstream dam one hour later. Due to shallower storage in the bed, fine particles were rapidly entrained during the rising limb of the flood hydrograph. Rather than being flushed by the flood, we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms. Three important timescales determined the fate of solutes and fine particles: (1) flood duration, (2) relaxation time of flood-enlarged bedforms back to base flow dimensions, and (3) resulting adjustments and lag times of hyporheic flow. Recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed, i.e., below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths. Thus, physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained, which affects decomposition rate and metabolism of this southeastern Coastal Plain stream. In summary we found that dynamic interactions between hyporheic flow, bed mobility, and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates. These hydrogeomorphic relationships have implications for microbial respiration of organic matter, carbon and nutrient cycling, and fate of contaminants in streams.Citation: Harvey, J. W., et al. (2012), Hydrogeomorphology of the hyporheic zone: Stream solute and fine particle interactions with a dynamic streambed,

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“…By actively increasing skin friction drag, nutrient flux to the algal surface is greatest when the filament is photosynthesising. High surface shear stress during photosynthesis may also enhance removal of loosely attached epiphytes and detritus (Harvey et al, 2011), which again increases light availability. When not actively photosynthesising, as in filaments near the bottom of the mat in poor light conditions or where incident light is otherwise reduced, skin friction drag is less.…”

Section: Discussionmentioning

confidence: 99%

Microscale measurements reveal contrasting effects of photosynthesis and epiphytes on frictional drag on the surfaces of filamentous algae

et al. 2013

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Summary Filamentous algae are widespread in freshwater ecosystems worldwide with a significant presence in streams, rivers and lakes with sufficient light and nutrients. Although typically not a preferred food source for grazers, dense filamentous mats provide surfaces for epiphytic microorganisms that are more palatable, thus adding to stream productivity. We tested the hypothesis that epiphytes change velocity gradients, and consequently shear stress and skin friction drag, near the surface of algal filaments. Using both digital holography and particle image velocimetry to measure micrometre‐scale velocity fields, we found that the surface shear stress on filamentous algae was much greater when the algae were actively photosynthesising. The presence of attached diatoms significantly reduced surface shear stress, while those filaments were photosynthesising, compared with bare filaments. A nutrient flux model, based on boundary layer thickness and surface shear stress, predicts that nutrient flux to the surface of a photosynthesising filament under measured flow conditions will be 1.5 times greater than for a preserved (i.e. dead) filament. Modelled nutrient flux to filaments with epiphytic assemblages dominated by diatoms is 75% of the flux to bare filaments under similar flow conditions. The proposed positive feedback between photosynthesis, surface shear stress and nutrient flux could be an important biophysical mechanism that overcomes diffusion limited nutrient supply within dense algal mats, enhancing algal survival through increased nutrient flux to actively photosynthesising filaments and decreased sloughing risk for filaments with lower rates of photosynthesis (due to epiphyte coverage or other light‐limiting factors).

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Field flume reveals aquatic vegetation's role in sediment and particulate phosphorus transport in a shallow aquatic ecosystem

Cited by 23 publications

References 60 publications

Fine particle retention within stream storage areas at base flow and in response to a storm event

Fine particle retention within stream storage areas at base flow and in response to a storm event

Hydrogeomorphology of the hyporheic zone: Stream solute and fine particle interactions with a dynamic streambed

Microscale measurements reveal contrasting effects of photosynthesis and epiphytes on frictional drag on the surfaces of filamentous algae

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