Mapping Eelgrass to Measure the Health of Our Coastal Waters

When a child has a fever, the first thing a parent does is take their temperature.  In the world of science, it’s not quite so simple, but researchers at Nova Scotia Community College are now using novel, specialized equipment, to assess the health of our bays and estuaries.

Dr. Tim Webster and his team at the college’s Applied Research Division are using topo-bathymetric lidar sensor equipment – purchased with the support of the Nova Scotia Research and Innovation Trust – to map the cover material on the Atlantic coastal seabed.

“The Department of Fisheries and Oceans uses the distribution of eelgrass as an ecosystem health indicator for bays and estuaries, making it an important measurement,” says Dr. Webster. “We’ve been in the field using the radar, testing our ability to map and monitor this species of aquatic vegetation.”

Researchers use the lidar sensor equipment to measure depth. A reflected green laser pulse provides detailed information about the cover of the seabed – literally shining a light on the bright sand reflecting against the contrasting dark vegetation. The resulting “greyscale image” can be matched with a map of the underwater terrain to provide an even richer dataset to work from.

Left map is a combination of bathymetry and lidar intensity of the reflected green laser (dark and light blue tones) from the seabed. Middle images represent ground truth samples and photos of eelgrass on the bottom. Right map is the distribution of eelgrass from the lidar with ground truth points indicating 80% accuracy.

Left map is a combination of bathymetry and lidar intensity of the reflected green laser (dark and light blue tones) from the seabed. Middle images represent ground truth samples and photos of eelgrass on the bottom. Right map is the distribution of eelgrass from the lidar with ground truth points indicating 80% accuracy. (Photo courtesy of NSCC)

Several recent projects have helped define new techniques to effectively map eelgrass.

“In our Tabusintac study area in northern New Brunswick, three independent teams pulled data off the seabed using underwater cameras to check for the presence or absence of eelgrass on the bottom. This information was compared to our results of mapping eelgrass with the radar and helped validate the group’s assessment for the entire bay.”

Dr. Webster and his colleagues also spent a week in September 2014 in the field gathering data throughout New Brunswick and along nine study sites. Work is continuing to assess the results.

The purchase on the lidar sensor equipment was made possible by an investment of $1.6 million, equally shared by Nova Scotia Research and Innovation Trust and Canada Foundation for Innovation.

Dr. Webster believes the team’s initial efforts only scratch the surface of the potential for the equipment to assist in research supporting the sustainability of our natural resources.

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