Ammonium and nitrate uptake by leaves of the seagrass Thalassia testudinum: impact of hydrodynamic regime and epiphyte cover on uptake rates

Cornelisen, Christopher D.; Thomas, Florence I. M.

doi:10.1016/j.jmarsys.2003.05.008

Cited by 77 publications

(77 citation statements)

References 52 publications

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“…The background 15 N signature of epiphytes was determined from samples collected from canopies outside of the flume at each experimental site. Previous results indicated that DIN uptake by a seagrass tissue is dependent on the degree to which it is colonized (Cornelisen & Thomas 2004). Grass uptake values would thus reflect the combined and complicating effects of diffusive transfer and epiphytic competition.…”

Section: Uptake Sample Collection and Processingmentioning

confidence: 99%

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Uptake of dissolved inorganic nitrogen by shallow seagrass communities exposed to wave-driven unsteady flow

Weitzman

Aveni-Deforge²,

Koseff³

et al. 2013

Mar. Ecol. Prog. Ser.

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In natural seagrass systems, regular oscillatory motion -like that caused by surface wind-waves -enhances uptake of dissolved inorganic nitrogen (DIN) relative to current-driven, unidirectional flows. A mobile field flume was deployed to measure the uptake of DIN by intact shallow seagrass communities exposed to unidirectional, oscillatory, and combined flows. The flume volume was spiked with 15 N-labeled DIN to measure nutrient uptake rate constants for the entire system (S) and to determine height-specific nutrient uptake rates of seagrass epiphytes (ρ). In oscillatory and combined flows, S depended positively on the water speed, but also inversely on a modified Keulegan-Carpenter number (KC). This ratio compares the wave-orbital excursion distance to canopy element spacing. Experiments characterized by relatively low KC values were associated with significantly higher uptake efficiencies than experiments characterized by high KC values. Uptake efficiencies for high KC conditions were similar to those measured in comparable unidirectional flows. Measured canopy flow attenuation was also found to increase with KC, a result in line with expectations from a parameterized conceptual model. Damping variability alone could not explain the observed oscillatory flow uptake enhancement however, a result that seemingly highlights the role of both element flexural response and unsteady boundary layer mechanics in the exchange process. In all flow conditions, DIN uptake rates of epiphytes harvested from the bottom of the blades (ρ bot ) were lower than those for epiphytes harvested from the upper portion of the blades (ρ top ). While uptake by the top epiphytes exhibited flow dependency, uptake by bottom epiphytes did not.

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Section: Uptake Sample Collection and Processingmentioning

confidence: 99%

“…Encrusting organisms colonize the vertical extent of the seagrass blades. Epiphytes were composed of diatoms, blue-green algae, par ticulates, red macroalgae, and coralline algae (see Cornelisen & Thomas 2004.…”

Section: Site and Field Flumementioning

confidence: 99%

Uptake of dissolved inorganic nitrogen by shallow seagrass communities exposed to wave-driven unsteady flow

Weitzman

Aveni-Deforge²,

Koseff³

et al. 2013

Mar. Ecol. Prog. Ser.

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“…The interaction of flows with seagrass meadows affects many ecological processes such as the transport and interception of pollen by seagrass carpels (e.g., Ackerman 2002), the supply of dissolved nutrients to seagrass leaves (e.g., Cornelisen and Thomas 2004), and sediment nutrient dynamics (Rose and Dawes 1999). Abdelrhman (2003) has provided a mathematical model of many of these effects.…”

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confidence: 99%

Hydrodynamics of model Posidonia oceanica patches in shallow water

2005

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The hydrodynamics of simulated patches of the Mediterranean seagrass Posidonia oceanica were studied in laboratory flume experiments in which the height of the pronated canopy was always greater than half the total water depth. The effects of variations in speed (from 0.08 m s Ϫ1 to 0.24 m s Ϫ1) and patch configuration on the hydrodynamics were investigated. Significant speeds penetrated the patches to approximately half their height. Reducing speed did not change the flow patterns observed, except to weaken and blur them. Flow encountering a single patch formed a turbulent wake at the height of the top of the canopy. Within this wake, the vertical shear stress decreased monotonically downstream, but the Reynolds stress increased initially and then decayed. When a second patch was positioned within the region where Reynolds stress increased (referred to as the ''06 patch''), the wake center penetrated it, causing average turbulent velocities with horizontal components 3.3 times higher and vertical components 4.2 times higher than in the upstream patch. When this patch was positioned where the Reynolds stress decayed (referred to as the ''14 patch''), the wake center rose above it. Nevertheless, the turbulence in the 14 patch had horizontal components 12% higher and vertical components 22% higher on average than in the 06 patch because its upstream end was closer to the Reynolds stress maximum. Thus the ratio of the patch separation to the length of wake in which the Reynolds stress increased was identified as central to quantifying the turbulence within the downstream patch. The increased turbulence is likely to be important in determining sedimentary and ecological patch characteristics by increasing retention of particulates in suspension and thus reducing depositional rates of, for example, larvae, nutrients, and dead organic matter.

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“…Acoustic Doppler velocimetry-ADV is often used in studies of turbulent processes in limnology (e.g., Cornelisen and Thomas 2004;Tritico and Hotchkiss 2005;Venditti and Bauer 2005), oceanography (e.g., Yahel et al 2002;Talke and Stacey 2003;Butt et al 2004), and benthic ecology (e.g., Eckman et al 1990;Friedrichs et al 2000). The technique has been employed in a range of flow conditions, including natural stream environments (Lane et al 1998;Mutz 2000;Carollo et al 2002), estuaries (Kim et al 2000), natural and artificial wave environments (Osborne et al 1997;Doering and Baryla 2002), and artificial channels (Cheng and Chiew 1998;Car-bonneau and Bergeron 2000;Nikora and Goring 2000;Lawless and Robert 2001).…”

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confidence: 99%

The accuracy of acoustic Doppler velocimetry measurements in turbulent boundary layer flows over a smooth bed

Dombroski

Crimaldi

2007

Limnology & Ocean Methods

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Acoustic Doppler velocimetry (ADV) is a popular technique for quantifying turbulent fluid flows in aquatic, marine, and laboratory environments. The technique relies on the Doppler shift principle to measure the velocity of suspended scattering particles that are assumed to move passively with the flow. Descriptions of ADV principles of operation are given by Lohrmann et al. (1994), Sontek (1997), and Voulgaris and Trowbridge (1998. The velocimeter employed in this evaluation is a SonTek 16 MHz MicroADV with the ADVField signal processing hardware enclosed in a splash-proof housing. This is a newer generation instrument that is advertised as having better spatial and temporal characteristics than the original SonTek 10 MHz and 5 MHz Ocean probes. These attributes make the 16 MHz model ideal for laboratory and turbulence measurements; however all of the models are available with ADVField processors enabling the probe to be used in the field. Acoustic instruments have a sampling volume (located at the intersection of the transmitting and receiving beams) that is large compared to the smallest scales of motion in turbulent flows. This limits the resolution and signal-to-noise (SNR) performance of the instrument, particularly in flows with smallscale turbulence and large velocity gradients. Thus, the ADV technique is subject to certain limitations in different flow regions and conditions. In this study, we evaluate ADV system performance by using the instrument to measure controlled laboratory flows. ADV results are compared to laser Doppler velocimetry (LDV) measurements in the same flow and to direct numerical simulations (DNS) of similar flows. The mean flow rates are designed to mimic those typically found in natural marine and aquatic systems so as to provide a useful guide for users interested in field and laboratory study. AbstractAn evaluation of acoustic Doppler velocimetry (ADV) in the near-bed region of turbulent boundary layer flows is presented. Acoustic instruments have large sampling volumes compared with the smallest scales of motion in turbulent flows. This limits the accuracy of the technique, especially when making measurements close to the bed or in flows where large spatial gradients are present. These limitations are quantified by comparing ADV results to laser Doppler velocimetry (LDV) measurements from the same flow, and to direct numerical simulations of similar flows. A SonTek 16 MHz ADVField system was used in the evaluation. Measurements were made in a turbulent boundary layer over a smooth bed in a laboratory flume. The instrument was evaluated in both a fast and slow flow case with free stream velocities similar to those found in many natural environments. Additionally, results from an assessment of ADV sample volume size and position are reported. Mean velocities were within 5% accuracy down to 0.7 cm from the bed for the fast flow case and 1 cm for the slow flow case. ADV-derived Reynolds stresses matched well with those from LDV to within 1-2 cm of the bed, however turbulence intens...

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Ammonium and nitrate uptake by leaves of the seagrass Thalassia testudinum: impact of hydrodynamic regime and epiphyte cover on uptake rates

Cited by 77 publications

References 52 publications

Uptake of dissolved inorganic nitrogen by shallow seagrass communities exposed to wave-driven unsteady flow

Uptake of dissolved inorganic nitrogen by shallow seagrass communities exposed to wave-driven unsteady flow

Hydrodynamics of model Posidonia oceanica patches in shallow water

The accuracy of acoustic Doppler velocimetry measurements in turbulent boundary layer flows over a smooth bed

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