Lake algae growth was high in 2003

POLSON - According to reports from the Yellow Bay Biological Station, algae growth in Flathead Lake increased during 2003, reaching the third highest level since measurements began in the 1970s.

Bonnie Ellis, a researcher at the biological station, presented the "State of the Lake" report at the Flathead Lakers' recent annual meeting at KwaTaqNuk Resort.

Primary productivity, Ellis said, is an indicator of water quality in the lake, with higher primary production values indicating more algae and declining water quality.

The 2003 value, she reported, was 119 grams of carbon per square meter, exceeding the water quality target of 80 grams of carbon per square meter per year set by the Flathead Basin Commission in 1997.

Targets for several water quality parameters were established by the Flathead Basin Commission to meet the "Total Maximum Daily Load" (TMDL) requirement of the federal Clean Water Act.

Growth of algae in the lake is influenced by the amount of the nutrients nitrogen and phosphorus entering the lake.

Nutrients can come from several sources, Ellis said, including runoff from land disturbances such as roads, agricultural activities, timber harvest, homes, old septic systems, driveways and other impervious surfaces throughout the watershed.

Initial experiments conducted at the biological station indicate the high primary production value in 2003 may have been due in part to smoke from last summer's forest fires.

Ammonium, Ellis explained, is the form of nitrogen most available for uptake by algae in the lake.

Ammonium can rarely be detected in Flathead Lake.

Smoke from forest fires contains high concentrations of ammonium.

With last summer's warm lake temperatures (the warmest temperature ever recorded) in addition to high light reaching deep into the lake, "the algae were poised to take advantage of the ammonium arriving from the atmosphere," according to the researcher.

Ellis also pointed out that changes in the lake's food web can have a big effect on primary production by changing how organisms cycle nutrients.

Ellis warned of another threat to Flathead Lake, should the zebra mussel be inadvertently introduced.

She described how lakes in the Midwest have been devastated by this prolific exotic species.

The Biological Station continues to monitor several other water quality parameters.

Although the highest levels of chlorophyll ever measured in Flathead Lake occurred last summer, low values during the winter months resulted in a mean annual average that met the water quality target.

However, a recorded decline in dissolved oxygen near the lake bottom did not meet the target for this parameter.

Another water quality target is to see no increases in the amount of algae attached to shoreline rocks.

The amount measured in 2003 exceeded the baseline value established in 1987. But Ellis said there are currently insufficient data to determine a trend.

Flathead Lake remains one of the cleanest large lakes in the world, Ellis concluded.

But the 2003 monitoring information points out "a number of water quality concerns" that confirm the need for continued monitoring and continued vigilance to protect the lake's water quality.

The biological station has monitored water quality in Flathead Lake continuously since 1977.