What happens when rivers meet the sea? As climate change shifts weather patterns and rates of glacial melt, Hakai Institute researchers are tracking the impacts of terrestrial freshwater on marine ecosystems.
In society and politics, a time-honored adage is “follow the money.” When it comes to understanding coastal marine ecosystems, there’s a similar dictum: follow the water. This means, in large part, tracking the flow of freshwater that ends up in the sea.
Why should we follow the water? The short answer is that marine ecosystems and many of the organisms that make them up—from algal diatoms to salmon and beyond—are profoundly affected by the freshwater that enters their habitats via rivers and streams.
At the 2023 State of the Pacific Ocean (SOPO) conference in Victoria, British Columbia, Hakai Institute researchers presented their ongoing findings to participants and stakeholders from universities, First Nations, and many other groups and organizations, including the Pacific Salmon Commission and Fisheries and Oceans Canada.
Using data from the Kwakshua Watersheds Observatory and oceanography surveys, the SOPO presentation linked freshwater inputs on British Columbia’s Central Coast to particular watershed types and highlighted the effects of seasonal freshwater on ocean biogeochemistry.
This view from the terminus of a small glacier looks down over Bute Inlet in British Columbia. Bedrock newly exposed by melting is visible just below the retreating ice. Photo by Ian Giesbrecht
As one might expect, the amount of terrestrial runoff into the ocean is massive, even when glacial meltwater is excluded.
Kwakshua Watersheds Observatory data allowed Hakai Institute researchers to estimate that in a single year, seven small, non-glacial watersheds on Calvert and Hecate Islands—together draining an area of less than 48 square kilometers—delivered an average of over 109 million cubic meters of water into the ocean. That’s more than 43,000 Olympic swimming pools of freshwater annually from a tiny section of the Central Coast.
The Hakai Institute’s research on freshwater inputs into the marine environment is part of a decade-long effort in oceanography and watershed field studies that is filling significant research gaps and ties in with the institute’s role in the five-year Coastal Rainforest Margins Research Network. Funded by the National Science Foundation and Tula, the network was steered by representatives from Alaska, British Columbia, Alberta, and the lower forty-eight.
“For Hakai, nothing is more place-based and appropriate for us to study than the interaction of watersheds with the coastal ocean,” says Tula codirector Eric Peterson. “In keeping with our motto ‘ice fields to cceans,’ we understand ecosystems by following the water, in the particular interface where the Pacific meets the temperate rainforest on the coastal margin.”
There’s often an artificial barrier between research on terrestrial and marine environments, says Peterson. “That barrier militates against getting a cohesive view, and the Hakai Institute has the mandate and opportunity to step confidently across that barrier.”
A tale of two rivers: left, tea-colored rivers and streams from forested wetlands, like this one on Calvert Island flowing into Kwakshua Channel, provide a rich source of organic carbon to marine food webs; right, the Klinaklini River shows the milky appearance caused by an abundance of powdered minerals, common in glacier-fed waters. Photos by Ian Giesbrecht
Freshwater runoff plays a fundamental role in oceans whether it comes from glaciated or forested watersheds. In the latter case, rain and melted snow collects in lower-elevation wetlands and percolates through the ground, steeping in a rich mix of forest detritus, moss, and soil. When rivers and streams deliver water from forested landscapes to the ocean, the water is changed—often visibly.
“That water makes its way downstream carrying a lot of carbon,” says Hakai Institute ecosystem scientist Ian Giesbrecht. “It can have a brownish or slightly orange-brown tint to it from dissolved organic matter.”
The carbon-rich tea of freshwater and dissolved organic matter is a big deal for marine organisms, but the picture wouldn’t be complete without another ingredient: the milky waters of glacial runoff.
Glaciers themselves are rivers of ice. As they flow out of the mountains they scrape the bedrock like sandpaper, enriching rivers and lakes with powdered minerals (silicates, iron, phosphorus, and others) that can can give them a cloudy, turquoise appearance.
How these waters look—brownish tea or cloudy milk—is not as important as what they do for marine ecosystems.
Glacial rivers deliver important mineral nutrients and organic matter that feed freshwater and marine food webs. Rivers in forested areas with wetlands contribute more concentrated organic matter to these systems. Illustration by Emily Damstra, based on O’Neel et al. 2015
The water that flows out of rivers and streams affects the temperature and salinity of the ocean, as well as carbon, light, and nutrient levels. Depending on where they are located and how rich their waters are with organic carbon or minerals, rivers can enhance or dilute the nutrient concentrations of the ocean. Terrestrial organic carbon is an important energy source for marine microbes, and riverine waters that are laden with it bring a powerful seasonal infusion of energy into marine food webs.
Transforming minerals into marine life begins with microscopic algae, which take up these nutrients in combination with sunlight. These algae are a type of phytoplankton, which is the primary food source for zooplankton—which in turn provide food for larger organisms, from invertebrates to fish to baleen whales.
“The abundance of phytoplankton—being at the base of the marine food web—has huge implications for higher trophic levels, such as whales, seabirds, and fish,” says Justin Belluz, a Hakai Institute research scientist.
“So it’s really important, especially under a changing climate, to start to understand these processes in order to understand how food webs stand to change moving forward.”
The disappearance of glaciers is expected to have a variety of consequences for species that depend on rivers and streams, like these chinook salmon. Photo by Tavish Campbell
Along with weather and freshwater inputs, another factor affecting the ocean is the upwelling of “source water“—deep-ocean water that upwells onto the continental shelf. Adding to the terrestrial “tea and milk” of non-glacial and glacial runoff, this source water comes laden with the organic detritus of dead organisms from deep in the water column.
“This is water that hasn’t seen the surface in decades,” says Carrie Weekes, a Hakai Institute ocean acidification research technician. “It’s really nutrient- and carbon dioxide–rich.”
Winter storms mix the water that’s been shoaled onto the shelf, notes Weekes, helping to create the conditions for explosions in the phytoplankton population when spring brings more sunlight.
“If you have nice, calm, sunny weather one to three days in a row, then all of a sudden the bloom just pops off. Those creatures are just waiting to photosynthesize, and with all those nutrients and carbon dioxide available, all they need is the sun to do it.”
These blooms of phytoplankton mainly occur in the warmer months, and can be large enough to be seen from space. They can also have immediate, and sometimes dire, effects on the health of humans and other species, via harmful algae. One phytoplankton species, a diatom called Pseudo-nitzschia seriata, contains domoic acid, a toxin that causes amnesic shellfish poisoning.
NASA satellite photo of a coccolithophore bloom in the Salish Sea in 2016. These single-celled algae produce an estimated 1.5 million tonnes of calcite per year in the world’s oceans. Photo courtesy of NASA
In the context of climate change, grasping land-sea linkages is particularly important. As freshwater inputs change due to altered climate patterns and shrinking glaciers, the effects stand to be hugely consequential for the ecosystem and food web.
It may seem that glacial loss, for example, only means the loss of beautiful ice caps in the mountains. But along with delivering nutrients, glacial meltwater cools rivers and makes them habitable and productive for many species.
A decade ago, a group of researchers led by Eddy Carmack—now senior research scientist emeritus with Fisheries and Oceans Canada—put forward the paradigm-shifting concept of the riverine coastal domain (RCD). The RCD is a band of ocean about 15 kilometers wide along the Pacific and Arctic coasts of North America and beyond where the fundamentals of life are driven by the abundance of freshwater runoff.
“Carmack’s idea of a riverine coastal domain was the kind of unifying theme of that five-year project,” says Giesbrecht, who sat on the Coastal Rainforest Margin Research Network steering committee. “Our aim was to facilitate more coordinated research on the theme of land-sea linkages.”
Giesbrecht has also authored an influential study with several collaborators: a groundbreaking analysis of watersheds on the west coast of North America. After mapping thousands of watersheds from Alaska to California, Giesbrecht grouped them into 14 types, including glaciated mountains, snow mountains, rain mountains, rain hills, and rain lowlands.
Using these categories in tandem with data from streamflow gauges that measure runoff, Giesbrecht has been able to estimate how much freshwater makes its way into certain regions of the RCD every day.
Meltwater cascades over rocks recently exposed by retreating ice, below the terminus of a small alpine glacier at the head of Bute Inlet. Photo by Ian Giesbrecht
“What oceanographers need is an estimate of the total amount of runoff into the ocean from all of those watersheds,” says Giesbrecht. “That’s where I come in, is to provide a very simple modeling approach to estimate the amount of water entering the ocean from all of the watersheds, not just the ones that are monitored.”
Ongoing research by Hakai Institute scientists will include analyzing links between the abundance of certain phytoplankton species relative to freshwater source characteristics and the subsequent carbon and nutrient availability in the ocean. As warming global temperatures influence climate—affecting rainfall, threatening to erase glacial ice completely, and even influencing deep-ocean circulation—following the water and understanding land-sea interactions has never been more critical.
