Papers by Marco Ghisalberti
At Mistaken Point, Newfoundland, Canada, rangeomorph ''fronds'' dominate the earliest (579-565 mi... more At Mistaken Point, Newfoundland, Canada, rangeomorph ''fronds'' dominate the earliest (579-565 million years ago) fossil communities of large (0.1 to 2 m height) multicellular benthic eukaryotes. They lived in low-flow environments, fueled by uptake [1-3] of dissolved reactants (osmotrophy). However, prokaryotes are effective osmotrophs, and the advantage of taller eukaryotic osmotrophs in this deepwater community context has not been addressed. We reconstructed flow-velocity profiles and vertical mixing using canopy flow models appropriate to the densities of the observed communities. Further modeling of processes at
Coastal Engineering
Aquatic vegetation in the coastal zone dissipates wave energy and provides a form of natural coas... more Aquatic vegetation in the coastal zone dissipates wave energy and provides a form of natural coastal protection against storm waves. The capacity of aquatic vegetation to attenuate incident waves depends on the extent to which wave energy is dissipated by small-scale hydrodynamic interactions within a canopy, which in turn depends on the work done by drag forces exerted by the canopy. Canopy drag forces (and hence rates of wave dissipation) are conventionally parameterised using a drag coefficient. Existing empirical models for predicting are usually dependent solely on either Reynolds number or Keulegan-Carpenter number , and hence neglect the potential effect of vegetation canopy density and the interactions between adjacent stems. This study uses high-resolution numerical simulations to investigate the dynamics of wave-driven oscillatory flow through emergent canopies (modelled as arrays of rigid cylinders). The simulations cover a wide range of. The influence of two mechanisms in modifying canopy drag, namely the effects of blockage and sheltering, are evaluated. The blockage effect is found to be the dominant mechanism responsible for increasing the canopy drag coefficients at high for medium to high density canopies; however, the sheltering effect plays only a minimal role in reducing the drag coefficient of the very sparse canopies. We show that Cd for canopies at high can be robustly estimated using a new modified drag formulation for the same canopies in unidirectional flow. Conversely, in the limit of the low , Cd is close to that of a single isolated cylinder at the same. The results of this study can be used as a basis for developing new predictive formulations for specifying bulk canopy drag coefficients, and in turn quantifying wave attenuation by vegetation.
Global change biology, May 19, 2018
Climate change is increasing the threat of erosion and flooding along coastlines globally. Engine... more Climate change is increasing the threat of erosion and flooding along coastlines globally. Engineering solutions (e.g. seawalls and breakwaters) in response to protecting coastal communities and associated infrastructure are increasingly becoming economically and ecologically unsustainable. This has led to recommendations to create or restore natural habitats, such as sand dunes, saltmarsh, mangroves, seagrass and kelp beds, and coral and shellfish reefs, to provide coastal protection in place of (or to complement) artificial structures. Coastal managers are frequently faced with the problem of an eroding coastline, which requires a decision on what mitigation options are most appropriate to implement. A barrier to uptake of nature-based coastal defence is stringent evaluation of the effectiveness in comparison to artificial protection structures. Here, we assess the current evidence for the efficacy of nature-based vs. artificial coastal protection and discuss future research needs...
Frontiers in Marine Science
Journal of Geophysical Research: Earth Surface
Sediment produced on fringing coral reefs that is transported along the bed or in suspension affe... more Sediment produced on fringing coral reefs that is transported along the bed or in suspension affects ecological reef communities as well as the morphological development of the reef, lagoon, and adjacent shoreline. This study quantified the physical process contribution and relative importance of sea-swell waves, infragravity waves, and mean currents to the spatial and temporal variability of sediment in suspension. Estimates of bed shear stresses demonstrate that sea-swell waves are the key driver of the suspended sediment concentration (SSC) variability spatially (reef flat, lagoon, and channels) but cannot fully describe the SSC variability alone. The comparatively small but statistically significant contribution to the bed shear stress by infragravity waves and currents, along with the spatial availability of sediment of a suitable size and volume, is also important. Although intratidal variability in SSC occurs in the different reef zones, the majority of the variability occurs over longer slowly varying (subtidal) timescales, which is related to the arrival of large swell waves at a reef location. The predominant flow pathway, which can transport suspended sediment, consists of cross-reef flow across the reef flat that diverges in the lagoon and returns offshore through channels. This pathway is primarily due to subtidal variations in wave-driven flows but can also be driven alongshore by wind stresses when the incident waves are small. Higher frequency (intratidal) current variability also occurs due to both tidal flows and variations in the water depth that influence wave transmission across the reef and wave-driven currents.
Frontiers in Marine Science, 2015
Journal of Fluid Mechanics, 2015
2011 GSA Annual Meeting in Minneapolis, Oct 10, 2011
Rangeomorph “fronds” at Mistaken Point lived in an aphotic low-flow environment fueled by “osmotr... more Rangeomorph “fronds” at Mistaken Point lived in an aphotic low-flow environment fueled by “osmotrophic” uptake and oxidation of reduced reactants (such as organic carbon or sulfide). However, the advantage of rangeomorphs relative to competing osmotrophic prokaryotes has not been assessed. In a novel application, we use canopy flow models to reconstruct and parameterize flow in this community. Flow reconstructions are based on distribution and size of individuals on ash-fall preserved on event-bed surfaces as well as sedimentologic ...
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineer... more Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.. Includes bibliographical references (p. 113-119).. Environmental aquatic flows are seldom free of vegetative influence. However, the impact of submerged ...
Environmental Fluid Mechanics, 2010
Obstructed shear flows (i.e. those over permeable media) are common in the environment. An archet... more Obstructed shear flows (i.e. those over permeable media) are common in the environment. An archetypal example, flow over a submerged vegetation canopy, is investigated here. Like any flow through complex geometry, canopy flows are characterised by strong spatial gradients. The focus of this experimental study is the three-dimensionality of aquatic canopy flow, in particular that of the coherent interfacial vortices that govern mixing into and out of the canopy. It is shown here that the vortices have a finite lateral scale that is comparable to their vertical scale; both are of the order of the drag length scale of the canopy, (C D a) −1 , where a is the frontal area density and C D is a bulk drag coefficient. The finite lateral extent of the vortices generates strong lateral hydrodynamic gradients, both instantaneously and in the long-term. The instantaneous gradients, which can contribute greatly to the dispersion of dissolved and particulate species, are far more pronounced. Finally, the potential for canopies to generate differential roughness secondary circulation is examined. In the consideration of vertical scalar transport, this circulation can be of the same order as turbulent diffusion.
Journal of Fluid Mechanics, 2009
The Proceedings of the Coastal Sediments 2015, 2015
Large bottom roughness is a characteristic of most coral reef environments and this has been show... more Large bottom roughness is a characteristic of most coral reef environments and this has been shown to have a substantial impact on hydrodynamic processes in these environments. In this paper, we evaluate suspended sediment concentration (SSC) data as well detailed hydrodynamic data over a coral reef flat in Ningaloo Reef, Western Australia, to understand how this bottom roughness affects these processes. A well-developed logarithmic velocity layer consistently developed above a canopy layer during the experiment. Estimates of bottom stresses from these logarithmic profiles were comparable with estimates obtained directly from turbulent Reynolds stresses, and an order of magnitude greater than those typically reported for sandy beach environments having similar flow. Nevertheless, the sediment grain size distribution of the suspended load was very fine relative to what should be mobilized by these stresses, indicated the large roughness substantially suppressed sediment transport.
Journal of Geophysical Research: Oceans, 2013
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Papers by Marco Ghisalberti
Wastewater stabilisation ponds (WSPs) are highly productive systems designed to treat wastewater using only natural biological and chemical processes, but they are known to operate at different levels of efficiency. Phytoplankton, microbial communities and hydraulics play important roles for ecosystem functionality of these pond systems. Although WSPs have been used for many decades, they are still considered as ‘black box’ systems as very little is known about the fundamental ecological processes which occur within them. However, a better understanding of how these highly productive ecosystems function is important, as treated wastewater is commonly discharged into streams, rivers, and oceans, and subject to strict water quality guidelines.