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Nutrient restoration program going well on Kootenay and Arrow Lakes, says FWCP

On February 8, the Fish and Wildlife Compensation Program (FWCP) held an online information session on its Nutrient Restoration Program (NRP) on Kootenay Lake and Arrow Lakes Reservoir.

Marley Bassett, a fish restoration biologist with the Ministry of Water, Land, and Resource Stewardship, touched on the nutrient history of Kootenay and Arrow Lakes, then talked about what the program is doing to promote healthy food webs through nutrient application.

History

“The Columbia Basin Watershed is a very heavily regulated system,” Bassett began. “There’s a lot of dams and it’s managed quite extensively.”

Kootenay Lake is regulated by two dams: Duncan Dam (built in 1967) on the north arm, and Libby Dam (built in 1973) on the south arm. It takes about two years for all the water in Kootenay Lake to be refreshed.

Arrow Lakes Reservoir used to be two separate lakes, upper and lower, connected by a river, but it was flooded in 1969 when the Hugh Keenleyside Dam was built just north of Castlegar. The two dams that regulate Arrow Lakes are Mica Dam (built in 1973) which created Kinbasket Reservoir, and Revelstoke Dam (built in 1983). It takes about one year for all the water in Arrow Lakes Reservoir to be refreshed completely.

The lakes are cold, deep, and naturally nutrient poor. The dams have also caused significant nutrient loss, most notably phosphorus, which comes from the soil and is washed into the lakes from rivers and streams. The other key nutrient is nitrogen, which comes from the atmosphere via precipitation. Though Kootenay Lake used to get an influx of phosphorus from a fertilizer plant, it was shut down in the 1980s. Between the dams, the closing of the plant, and the naturally nutrient poor waters, Kootenay and Arrow Lakes began to suffer.

Food web

When it comes to the NRP, Bassett said it’s important to go back to the basics: the food web.

Nutrients are the base of the food web and without the proper amount of phosphorus and nitrogen, organisms higher up the chain like kokanee salmon, are impacted.

Nutrients move up through the food web via phytoplankton—free-floating microscopic algae, or plants. Phytoplankton are fed by phosphorus and nitrogen. They also photosynthesize to create energy.

Phytoplankton are then consumed by zooplankton—free-floating, microscopic animals. There are two types, copepods and cladocerans. Copepods are abundant and around all year, though they don’t have much nutritional value. In contrast, cladocerans are not around all the time, but have much higher nutritional value and are preferred by fish. A type of cladocerans that it particularly tasty for fish are daphnia, whose reproduction is triggered by seasonal changes. They are most abundant in July and August.

Another piece of the food web are mysids, an introduced species to Kootenay and Arrow Lakes. Mysids are small, shrimp-like crustaceans that feed on zooplankton. They were introduced in 1949 in an attempt to increase prey for juvenile rainbow trout.

Kokanee, land-locked sockeye salmon, are next in the food web. Kokanee are a keystone species, meaning that changes in their numbers can fundamentally change the ecosystem. Many other species such as rainbow and bull trout, bears, and birds, rely on kokanee for food.

When the fertilizer plant shut down in the 1980s, combined with the dams cutting off the natural flow of nutrients into the lakes, kokanee stocks began to decline. Without kokanee, the organisms that feed on them also suffered.

Nutrient restoration

“The Nutrient Restoration Program began as an experiment in 1992 in the north arm of Kootenay Lake with the objective of restoring lost nutrients,” said Bassett. It then expanded to Arrow Lakes Reservoir in 1999.

The goal was to ensure that there are enough nutrients to move up the food web to support fish populations, particularly the keystone kokanee. Phytoplankton absorb the added nutrients, and the food web carries it up from there.

Phosphorus and nitrogen are deposited weekly, from spring to early fall, into Kootenay Lake through the ‘tug and barge’ method, in a few specific zones.

The Shelter Bay-Galena Bay ferry is used to apply nutrients to Arrow Lakes. Since the reservoir flows north to south, the nutrients can be deposited in one spot and the flow of the water can take care of spreading it through the rest of the lake. Doses happen more often in Arrow Lakes Reservoir, between one and seven applications per week.

The NRP is a balancing act though; adding too many nutrients can cause too much algae to grow, which is just as detrimental to the ecosystem as too few nutrients.

Is it working?

Bassett said an independent review of the program found that the program is working. Adding nutrients improves food conditions for kokanee – especially their favourite food, daphnia. And the bottom-up approach has the unique outcome of benefitting the whole food web.

The costly project is funded by the Fish and Wildlife Compensation Program (FWCP), BC Hydro, in-kind support from the Province, and the Kootenai Tribe of Idaho, which receives funding from the Bonneville Power Administration. Funds also come from the Northwest Power and Conservation Council’s Columbia Basin Fish and Wildlife Program, Waterbridge Ferries Inc., Columbia Power, and Arrow Lakes Power Corporation.

Rachael Lesosky, Local Journalism Initiative Reporter, Valley Voice