Title
25-Year Record of Nutrient Loading to a Large, Oligotrophic Lake -- Flathead Lake
Abstract
Flathead Lake is one of the 300 largest lakes in the world. The Flathead Basin is 22,241 sq. km and is drained by six 5th-order tributaries of the main-stem Flathead River. Almost half (42%) of the Basin is included in National Park and Wilderness protection. Nutrient loading to Flathead Lake from all major tributaries and atmospheric deposition was measured over a period of 25 years. During the last two decades as much as 45% of the annual phosphorus and 24% of the nitrogen load was fallout from the atmosphere, mainly from fugitive dust from local rural roads, smoke particulates from forest fires and agricultural burning inside and often far outside the Flathead Basin. Pelagic primary production (in-lake growth of algae) is limited by availability of nitrogen and phosphorus. Nitrogen loading from human sources upstream of Flathead Lake has steadily increased over the last three decades, and daily nitrogen loading weakly correlates with increasing primary production.
Presenter: Scott Relyea of the Flathead Lake Biological Station
Start Date
1-4-2005 1:00 PM
End Date
1-4-2005 3:00 PM
Document Type
Poster
25-Year Record of Nutrient Loading to a Large, Oligotrophic Lake -- Flathead Lake
Flathead Lake is one of the 300 largest lakes in the world. The Flathead Basin is 22,241 sq. km and is drained by six 5th-order tributaries of the main-stem Flathead River. Almost half (42%) of the Basin is included in National Park and Wilderness protection. Nutrient loading to Flathead Lake from all major tributaries and atmospheric deposition was measured over a period of 25 years. During the last two decades as much as 45% of the annual phosphorus and 24% of the nitrogen load was fallout from the atmosphere, mainly from fugitive dust from local rural roads, smoke particulates from forest fires and agricultural burning inside and often far outside the Flathead Basin. Pelagic primary production (in-lake growth of algae) is limited by availability of nitrogen and phosphorus. Nitrogen loading from human sources upstream of Flathead Lake has steadily increased over the last three decades, and daily nitrogen loading weakly correlates with increasing primary production.
Presenter: Scott Relyea of the Flathead Lake Biological Station