RICE — A dry start to the summer means algae in some area lakes and rivers has become par for the course, including on Little Rock Lake.
Lake systems rely on a balanced ratio of nitrogen and phosphorus. Rain typically provides nitrogen, Department of Natural Resources area fisheries manager Eric Altena said Wednesday. Without rain, the system is without that contribution of fresh nitrogen.
“If that balance gets out of kilter, you end up having a(n algae) bloom, because the phosphorus gets more prevalent,” Altena said.
The U.S. Drought Monitor categorizes most of Benton County as abnormally dry, while Stearns County is abnormally dry in the east and experiencing moderate drought in the western portion of the county, according to data through July 9.
Abnormally dry areas developed or expanded in several parts of the Midwest, including central Minnesota, the weekly drought summary said.
According to the Department of Natural Resources’ May hydrologic conditions report, St. Cloud this year had the ninth driest May on record, short more than 2 inches of rain from normal. National Weather Service records show St. Cloud was short about 1.5 inches of rain from June’s normal, and what rain did come arrived mostly in the last three days of the month.
“Good” algae uses a lot of nitrogen, Altena said, and if more nitrogen is not provided by rain, green algae and even blue-green algae can take hold.
This is part of the natural cycle; lakes typically start the spring with a closer balance, with more nitrogen and less phosphorus. But as summer progresses, unless rain helps maintain that balance, it shifts. And shallow lakes, like Little Rock Lake, are sensitive, “fickle” and “tempermental,” Altena said.
“This year was very prevalent, when we did not have the rainfall amounts, that we actually had algal blooms even in the better-quality lakes,” Altena said.
Blooms in lakes with better water quality tend to be filamentous algae — the slimy, stringy algae that can coat plants or grow on rocks in slow-flowing rivers.
“We saw many of that in our lakes this spring, and that was primarily due to the fact that we had a drought,” Altena said.
In a normal year, area rivers would have relatively high flows through June, Altena said. That means the water clarity is lower and algal growth does not necessarily occur. But when sun exposure allows things to grow, algae makes that list.
He said he received several calls about a large plume of duckweed — tiny, free-floating plants — that rain flushed down the Platte River from the Rice-Skunk Lakes and into the Mississippi River. It is also common to get more complaints about dead fish on shorelines in drought years, he said.
But recent rain could have given Little Rock Creek a shot of nitrogen and runoff water, Altena said.
In healthy lake ecosystems, clearer water allows plants to thrive. In turn, even if there is an influx of phosphorus, those plants help use that phosphorus up, mitigating algae blooms, Altena said.
Ultimately, this is the goal for Little Rock Lake: to change the system from a shallow lake with dirty water to a more clear-water state with good vegetation, he said. A drawdown of the Mississippi River above the Sartell dam last summer was part of that process.
Altena said a plant survey conducted in Little Rock Lake in June showed more plants than the previous year. Additionally, despite the green tint and some algae build-up on the windblown side, the lake is still usable.
“It’s trending in the right direction,” Altena said.
He has high hopes for Little Rock Lake, but reminds people that improvements will take time. To expect instantaneous change is “pretty unrealistic.”
“This is like being punched in the stomach for 107 years for Little Rock Lake, and all we did was kind of give it a little bit of a break and try to nudge it in the right direction so it could hopefully help itself,” Altena said.
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