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Project Looks to Bolster Productivity in the Kootenai River

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     Fertilizer. Nitrogen and phosphorous. It’s the same stuff many of us put on our lawns to make them greener and healthier, and even grow faster. But there are other uses for these two key organic nutrients, and one of them happens to be enhancing altered aquatic ecosystems.

     Generally, many pristine freshwater systems are naturally phosphorous-limited, whereas marine ecosystems are often nitrogen-limited. In the Pacific Northwest, the biologically available amounts of phosphorous regulate overall ecosystem growth. Nutrients have a powerful control over the growth of an aquatic system. The growth of algae, aquatic invertebrates and eventually fish are all regulated by the availability of nitrogen and  phosphorous.

     A number of streams, rivers and lakes in the Pacific Northwest have become nutrient-poor for a variety of reasons. Water diversions, impoundments, diking of the riverbanks, channelization, wetland drainage and the collapse of migratory fish populations all contribute to a nutrient-poor system. For some streams, the decay of kokanee carcasses once their spawning run ends, provides 99% of the nutrient input that particular stream receives all year. A single kokanee carcass helps to maintain the productivity of an ecosystem, and maybe even provide food for next year’s juvenile fish.

     This is where nutrient enhancement can be used to rehabilitate streams, rivers and lakes. The north arm of Kootenay Lake in British Columbia was fertilized with a carefully measured mixture of nitrogen and phosphorous to aid the waning Gerrard rainbow trout population. Previous kokanee numbers had dropped considerably for a number of reasons, and this was the primary food for the Gerrard rainbow trout. Today, the north arm kokanee population has increased, from several hundred thousand to several million fish, and the project has been a huge success. During the fall kokanee run, the hundreds of thousands of fish in the Meadow Creek spawning channel on the west side of the lake’s north arm can verify that fact.

     Many scientific studies have proven that the regulated and controlled addition of nitrogen and phosphorous to an aquatic ecosystem can have beneficial results. The addition of nutrients to a stream or river follows the simple food chain theory: an increase in nutrients triggers an increase in algae, which in turn is a food source for aquatic invertebrates. This increase in algae causes an increase in aquatic invertebrates, and an increase in aquatic invertebrate numbers means more food for fish. More fish food availability generally leads to higher fish growth rates and a lower mortality rate. Ecologists refer to this phenomenon as “bottom-up” regulation.

     Nitrogen and phosphorous were added to the Keogh River in British Columbia, and the results included increased algae growth and increased aquatic invertebrate numbers. This increase in aquatic invertebrate numbers means more available food for juvenile salmonids, such as steelhead and coho salmon. Artic grayling in the Kuparuk River, in Alaska, showed an increase in growth after the addition of nutrients. In this case, fish growth was attributed to the increase in aquatic invertebrates as food items. Many other studies in British Columbia, Alaska and Scandanavia have shown nutrient addition to increase the overall productivity of the system.

     Nutrient enhancement is not for all ecosystems. Systems that have suffered severe nutrient losses, perhaps due to the loss of migratory fish population or wetland drainage, are more apt to benefit from nutrient additions. An over-abundance of nutrients in a system could prove detrimental. Excess algae, de-oxygenation and fish population shifts are results of “eutrophication,” or too many nutrients. Lakes and rivers in the Midwest are naturally prone to eutrophication.

     Closer to home, the Kootenai Tribe of Idaho is currently conducting a nutrient study in the Kootenai River in Bonners Ferry. The purpose of this study is to evaluate the feasibility of nutrient enhancement on a small scale in the Kootenai River. Water quality reports have shown the Kootenai River to be extremely phosphorous-limited.

     The system in which these nutrient tests are taking place is called a “mecocosm,” meaning “middle-world.” Troughs made of Plexiglas are suspended in the mainstem Kootenai River between two pontoons, and these troughs are filled with rocks in order to simulate the river’s natural substrate. Also housed within each of these troughs are ten juvenile Kootenai River white sturgeon, which are from the 200 year-class at the tribe’s sturgeon hatchery. Nutrients are delivered to some of the troughs via a pump.

     This mecocosm will aid biologists in determining if nutrients could bolster the low productivity in the Kootenai River. AS with the successful Kootenay Lake nutrification program, the goal is to restore Kootenai River productivity back to natural, pre-impoundment levels. Algae growth, aquatic invertebrate densities and fish growth will be evaluated to see what benefits, if any nutrient addition has in the Kootenai River.

     The mecocosm is currently anchored just upstream of the Hwy. 95 bridge in downtown Bonners Ferry. It will be running until Oct. 12, when the aquatic “growing season” has slowed down, and the mecocosm will be run again next summer from July to October.

     Nutrient enhancement could prove to be a very powerful tool in bolstering productivity in the Kootenai River and its tributaries.


Genny Hoyle is a graduate student, currently working with the Kootenai Tribe of Idaho on their nutrient study in Bonners Ferry.

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