Goodbye Weeds, Hello Filamentous Algae Blooms

As treated aquatic vascular plants fall out of the water column, they decay and release nutrients that then become available to filamentous algae. In confined, shallow coves and bays this nutrient release commonly gives rise to filamentous algal blooms. This season these blooms will be treated prior to the 4th of July Holiday weekend for three reasons: 1. The algaecide applicator is unavailable until after the holiday, 2. The blooms are not quite done forming and would therefore avoid detection and treatment, and 3. Chemical treatments are always timed to minimize restrictions on recreational water uses by residents. Once the localized blooms have stabilized in the next few days, the algaecide applicator will be out to apply chelated copper sulfate to blooms in the designated treatment areas. We are currently watching blooms in Far West (near the north channel, and the north side of the east bay), The channel east of the island on Main, as well as the finger of Main near the Buchanan and West Royal pump and a shoreline bloom on Rush Lake.

Notice the green cloud in the lower left hand corner of this image. You guessed it, filamentous algae. The algae is blooming because it is capitalizing on the nutrients being released by treated I. Pondweed around it. At least we know the herbicide treatment was effective.

Another example of decaying aquatic plants giving rise to algal production.

In extreme cases like this shallow protected bay in Far West Lake, decaying aquatic plant matter can give rise to thick filamentous blooms. The isolated blooms like this one will be treated ASAP following the Holiday.

Looking closely at this Illinois Pondweed, one can see the browning and veination indicating that the upper portion of the plant has been successfully treated. The primative cellulose structures holding the plant erect in the water column are lysed and broken apart. The plant will fall over or out of the water column quickly as it succubmes to wind and wave action. Over the next few days and weeks it will decompose and release the nutrients it had locked up in its structures.

Treated Aquatic Plants are Slowly Falling Out

Treated native aquatic vascular plants are just now beginning to fall out of the water column in most treatment areas. Due to the relatively cool water temps(74 F as of 6-28-06) and lack of major turbulence, the plants have been hanging in there longer than they have the past two years. Plants should fall out very quickly as boat traffic intensifies over the holiday weekend. The resulting benefit will be open water for swimming, fishing, boating etc. The unfortunate but predictable side effect will be free floating clumps of aquatic vegetation washing up on beaches or getting tangled in your propeller. Currently, chemical control is our only option in minimizing the consequences of increased nutrient levels and the resulting increased plant biomass in the lakes. We are exploring the possibility of adding aquatic plant harvesters to the in-lake control efforts. These machines actually remove the vegetation, theoretically reducing plant biomass potential each year. The drawback is that they are very expensive to operate and maintain.