Three Rivers Edition Staff - 08/31/2004
WHITEHALL — The Jefferson River Watershed Council (JRWC) has completed an aquatic insect survey on the Jefferson River.
The survey duplicates one conducted by Montana Fish, Wildlife & Parks in 1978.
The Watershed Council is collecting the information for two reasons:
1) to establish a base-line condition on the river.
2) to determine changes to the river ecosystem over the past 25 years. The JRWC hired a non-biased consultant to collect the data and strives to obtain good scientific information for decision-making.
McGuire Consulting of Kennewick, Wash. conducted the survey. Data was collected during August and October of 2003 in the same locations as the 1978 survey.
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Looking at aquatic insects also known as macroinvertebrates provides a good indicator of river health. Insects such as mayflies, caddisflies and stoneflies indicate a healthy river system. Midges and other non-insect species are found in streams with more degraded environments.
The survey reports that biological integrity of the Jefferson was slightly impaired at Hells Canyon but is severely impaired at Waterloo and Silver Star. Significant impacts are reported at Cardwell and Three Forks.
"The severity of the impacts appeared proportional to the amount of streambed dewatered during the previous summer," according to biologist Dan McGuire.
The good news is the river supports a rich number of aquatic insects. Caddis flies were the most common insect at Hells Canyon, Silver Star and Three Forks. Mayflies were the most abundant at Cardwell. This means that the river is supporting a good diversity of aquatic insects important to the trout fishery.
The valley has been in a drought since 1998 and this affects the flows of the river. The survey confirms that environmental stress was present throughout the 2003 season. Environmental stress to the river includes increased nutrient loads, low dissolved oxygen, increased water temperatures, and substrate embeddedness. All of these factors are related to a low flow condition.
The insect community has shifted from 1978 to species that are more tolerant of warmer water temperatures and more nutrient rich environment.
The flow pattern is a major factor in the health of the river. When the flow is low, the river becomes more susceptible to nutrient loading. The nutrient loading along with increased water temperatures and limited scouring of the streambed, changes the composition of the aquatic insect community. In order for the Jefferson River to return to "blue ribbon trout stream status," the streambed needs to be inundated throughout the year.
The JRWC is working to keep minimum flows in the river through its Drought Management Plan. The committee wants to thank all of those people in the valley who have supported this plan for the past four years.
A complete copy of the report is available electronically free of charge. A hard copy (paper) is available for $5. For more information about the Jefferson River Watershed Council visit www.JeffersonRiverWC.homestead.com.
