Looking at the Fraser plume

This unusual ecosystem is a cloud of turbid river water, full of sand and silt, which floats over the heavier salt water of the ocean.

The Fraser river is running high as snow melt pours off the mountains. We are close to the peak of freshet season. As the river water flows into the salty waters of the Georgia Strait, it forms an unusual ecosystem: the Fraser river plume.

The plume is a cloud of turbid river water, full of sand and silt, which floats over the heavier salt water of the ocean. During an ebbing tide, the plume reaches as far as Galiano Island and the line of demarcation is easily seen from ferries crossing the Strait. As the tide floods in, the silty, yet light, river water and the clear, heavy, salt water become mixed. This process, repeated twice daily, effectively creates two types of plume: one predominantly fresh water, the other, brackish remnants of earlier ebb tides.

The salt wedge toe, nudging into the estuary at high tide, allows nutrients to be brought to the surface from the deep, cold ocean. This increases the density of phytoplankton, microscopic plant matter that drives the marine food chain. The tiny plankton are consumed by microscopic animals, such as copepods. Small fish and crustaceans prey on them, and are, in turn, eaten by larger fish, birds, and marine mammals. The edge of the plume is an excellent place to watch for wildlife, such as loons, grebes, porpoises and orcas.

The plume is a key part of the estuary, allowing life to thrive. The murkiness of the plume allows juvenile fish to take refuge from predators. By moving between river and estuarine plumes, salmon smolts can gradually adjust to increasing levels of salinity and temperature, before making their migration out to sea. In the late summer, the plume is less strong, allowing returning salmon to adjust before they head up river to spawn.

It is essential that coastal shores affected by the plume are maintained in a natural state, to allow the full functioning of the ecosystems. There are many conservation issues. For example, the barriers presented by the major causeways on Roberts Bank are of considerable concern. They disrupt natural tidal flows and block salmon migration. Strong consideration should be given to providing openings for wildlife corridors.

Anne Murray is a local naturalist and author of two books on the Fraser delta: A Nature Guide to Boundary Bay, and Tracing Our Past ~ A Heritage Guide to Boundary Bay; see www.natureguidesbc.com and Anne’s blog www.natureguidesbc.wordpress.com.

 

Just Posted

New police force in Surrey must avoid VPD, RCMP errors made in Pickton case: Oppal

Boots are scheduled to be on the ground by spring 2021

PHOTOS: Surrey designer uses toilet paper to make a dress for annual Toronto show

‘The dress is very experimental and avante garde,’ says Guildford-based Alex S. Yu

Police issue warning after four overdoses in North Delta

Police and emergency health services use naloxone to revive four overdose victims Thursday morning

Surrey reacts to policing plan getting the green light

Former mayor, councillors and residents weigh in on the Public Safety Minister approving the transition

Trudeau vows to stand firm against ‘increasingly assertive’ China

China has accused Canada of meddling in its affairs

Conan turns to the Property Brothers for tips on buying Greenland

Jonathan Scott suggests removing glaciers and mountains to bring in ‘more natural light’

Forests minister visits B.C. town rocked by multiple mill shutdowns

A third of Mackenzie turns out for rally, not much to cheer about

B.C. sockeye returns drop as official calls 2019 ‘extremely challenging’

Federal government says officials are seeing the same thing off Alaska and Washington state

North Van music teacher accused of sexual misconduct involving girls

Police believe other victims could be out there after the arrest of Lamar Victor Alviar

B.C. family stranded in Croatia desperate to come home

Funds being raised to bring back mom and two children

B.C. man on trial for daughters’ murders says an intruder broke in

Andrew Berry takes stand in his defense for December 2017 deaths of young daughters

‘Plenty of time for a deal’: Teachers’ union expects kids back in school on Sept. 3

BCTF says class size, composition at the heart of the issue

Most Read