In 1977, the U.S. Environmental Protection Agency National Eutrophication Survey’s Report on Hayden Lake indicated that the lake is early mesotrophic. A pivotal study in 1986 by R. Soltero confirmed that the lake is oligotrophic, tending toward mesotrophic. With such good news, why be concerned about eutrophication? Our experience of the lake tells us that what Soltero also says is true, “The water quality of Hayden Lake is remarkably good. However, Hayden Lake is susceptible to, and probably experiencing, accelerated eutrophication (nutrient enrichment) as a result of man’s activities within the drainage basin.”
The trophic States Sound More Complicated Than They Are
Nutrients in the water, specifically varying forms of nitrogen and phosphorus, encourage the growth of aquatic plants. Plants provide food, shelter, and protection for fish, foul, and other life in a vibrant ecosystem. The vitality of this food chain, often called the productivity of the system, is summarized in a water body’s trophic state. Oligotrophic lakes have low nutrients and less productive plant growth. Eutrophic lakes have abundant nutrients and high productivity. The nutrient levels and productivity of mesotrophic lakes lie in between.
Any lake’s trophic state will shift from oligotrophic through mesotrophic to eutrophic over time. As the shift in nutrients and productivity occurs, the personality of the system changes, the lifeforms sustained within the ecosystem change, and the indicators of water quality take on different values.
Nutrient enrichment can become so abundant that plant growth is no longer limited by the plant-food available, setting the ecosystem on a spiraling path. Plant life blooms and then dies. Dead-plant decay consumes dissolved oxygen. Other aquatic life struggles and only the more-tolerant species survive. Those that need an oxygen-rich environment do not. Nutrients from plant decay further enrich the water. The spiral continues.
Human Activity Hastens Natural Changes in Hayden’s Trophic State
Changes in trophic state happen naturally over time but can accelerate when human activities contribute significantly to a lake’s nutrient load. This is at the heart of the concern for Hayden Lake’s water quality and its designation as an impaired waterway.
The concentrations of phosphorus and nitrogen in the water are creeping up. Nutrients flow into the lake by way of runoff from the watershed, precipitation, and seepage from the ground around the lake. Since water leaves the lake by routes that the nutrients cannot follow – evaporation and infiltration into the aquifer – each year’s nutrient load is essentially trapped in the water column and the sediment on the bottom of the lake. Human activity intersects with the natural sources of nutrient loading and adds to their phosphorus content to varying degrees:
- Runoff from higher elevations in the watershed flows from clearcut areas to streams and into the lake
- Runoff from the slopes along the shoreline flows from rooftops, through fertilized lawns, and over roads
- Seepage flows from failing septic systems of homes around the lake
- Old nutrient-rich flood planes and cattle-grazing land are now lake-bottom soil
- Precipitation falling directly on the lake from the atmosphere carries particulates from industry including agriculture.
When considered as a whole, Hayden Lake is undeniably low in nutrients and plant productivity today. It is oligotrophic to early mesotrophic. What is also undeniable is the fact that the lake’s plant growth is changing. Anecdotally, resident after resident will recount their experience of clear-water views of a sandy lake bottom that now are obscured by plants and muck. The North Arm, in particular, shows signs of eutrophication. Its summer weed growth has impeded movement and discouraged recreation for nearly a decade. And in the summer of 2018, weed growth became an issue in shallow areas throughout the lake for the first time.
Is Hayden Lake undergoing eutrophication? Yes.
Is it currently eutrophic? No.
Can eutrophication be stopped, or slowed? There are things we can do!
Read More About the Water Quality of Hayden Lake:
- Hayden Lake Water Quality
- Idaho Water Quality Standards
- The Eutrophication of Hayden Lake
- What is TMDL?
- Phosphorus Loading Via South Shore Runoff
- Nutrient Profile of the North Arm
