Sediment resuspension in coastal environments
A new erosion device has been developed to measure
sediment resuspension rates. Shear is generated via
pumping of a porous piston over the sediment surface.
Resuspension is measured with image analysis and
with turbidity sensors in the chamber. Coupled with
measurements of particle settling, this approach allows
us to evaluate benthic-pelagic particle flux at aquaculture
sites and other coastal environments. Postdoc Tony Walker
is interacting in this research as well as many others below.
Research Interests - J. Grant
Spatial distribution of Arctic benthos
Estimation of energy flow through benthic communities
is dependent on estimating their biomass. Remote samplers
such as grabs do a poor job of estimating epibenthic fauna,
especially in the Arctic The underwater camera system shown with me on Ellesmere Island was used to obtain bottom images for quantification of benthic epifauna.
Seston depletion by cultured suspension-feeders in Tracadie Bay, Prince Edward Island
Using both ArcGIS as well as STEM GIS, we have generate an extensive temporal and spatial database of benthic and pelagic variables in this system. In addition we have a validated 2D circulation model of the bay generated with AquaDyn. The hydrodynamic model has been coupled with a bioenergetic model of mussels to generate maps of seston depletion in the bay, as a tool in regulating culture to sustainable limits This figure shows GIS layers of sediment sulfides and acoustic return for various locations in the bay
Ecosystem models of mussel culture in Magdalen Islands, Quebec
Shallow lagoons of the Magdalen Islands (Gulf of St. Lawrence) are ideal for suspended culture of blue mussels. Working with colleagues at the University of Quebec (Rimouski) led by Vladimir Koutitionsky and DFO (Institut Maurice Lamontagne), we are producing box models as well as detailed spatial models of physical oceanography, trophic structure, and the role of mussels in ecosystem carbon flow. There is a substantial field effort on particle fluxes, benthic metabolism, and seston dynamics, including extensive in situ instrumentation.
Carrying capacity of mussel culture in Saldanha Bay, South Africa
Upwelling systems of coastal South Africa support rich marine ecosystems (including penguins), and allow rapid growht of cultured mussels. Using raft culture, mussels can be cultivated in less than 1 year. There are few bays along this coast, and Saldanha Bay has multiple resource users. We have been working to incoporate upwelling into an ecosystem model of primary production, using a fully coupled biological-physical model anchored in a 3D circulation model. In addition, we have developed raft-scale models of seston depletion since food limitation may occur at a very local level. Advice on optimal culture levels is being generated by an international research team including partners from France, Norway, Portugal, Netherlands, Canada, and New Zealand.
Habitat mapping and aquaculture management (funded by AquaNet and ACOA)
Environmental assessment of activities in the coastal zone are evolving from single point study sites to more comprehensive views. Using various in-water sensors, habitat mapping provides a means of quantifying habitat extent and boundaries. Geographical information systems (computer mapping) and their analytical capacities are central to this research. The Acrobat (see above) is used to map water column variables such as chlorophyll, oxygen, and turbidity. An echosounder is used to map benthic habitats for variables such as sediment type and macrophyte beds. We are applying these technologies to potential aquaculture sites in Guysborough County, Nova Scotia to assess the value of more ecosystem-based approaches to characterization of the environment. This figure provides an example of mapped chlorophyll in a mussel farm in the Magdalen Islands
Acrobat towed sensor array
Developed by Peter Cranford at the Department of Fisheries and Oceans (adjunct Dalhousie Oceanography), the Acrobat Light Towed Vehicle (LTV) can be towed behind a variety of vessels to map temperature, salinity, depth, oxygen , chlorophyll, turbidity, optical plankton counts, and other variables. It provides essential spatial data used in assessing water quality and the effects of aquaculture or other activities on the water column (see habitat mapping below). It also provides groundtruth data for remote sensing.
Settling rates of particle aggregates
Organic-mineral aggregates have complex composition and settling rate, which regulates their benthic pelagic flux and role in bioegeochemical sites. Their fragility makes settling velocity difficult to measure. We developed a special sampling bottle which inverts on deck to record settling via digital video. Image analysis is used to measure fall velocity anf particle size. The device has been used in a variety of temperate and arctic locations.
Canadian Arctic Shelf Exchange Study (CASES)
This international Research Network funded by NSERC seeks to examine the coupling between the MacKenzie River, the major North American river input to the Arctic Ocean, and the shelf of the Beaufort Sea. The majority of work in CASES involved benthic and pelagic studies offshore including overwintering of the ship in ice. Our work in CASES was mostly base in Kugmalik Bay at the river mouth. We undertook acoustic surveys, Acrobat transects, particle settling experiments, and benthic sampling. Shown at left is a scene from
Tuktoyuktuk, our local base of operations. Dogs are owned by our guide, outfitter James Pokiak.
