Weed Control in Lower Beverley Lake

(Musings About the Role of Phosphorus)

Several years ago we asked our members and others interested in the lake to identify problems, priorities, and concerns. We received over 60 excellent responses, and complaints about “excessive weeds” were quite frequent and vigorous.

Lake weeds fall into three general categories. They are (1) bottom weeds which are rooted in the bottom and remain below the surface, (2) emergent weeds which are rooted on the bottom but emerge from the lake surface and grow further and flower in open air, and (3) weeds which float and are not rooted and drift about under and on the surface. These weeds are all advanced flowering plants. A much more simple form of plant life which may be “weed-like” is the vast array of single and multiple-cell algae blooms which may appear as green scum, particles in the water, or just turbidity.

While at this time we do not have good data on nutrient loading in our lake water, the sheer mass and abundance of lake weeds suggests high lake water nutrient loads. Plants have various nutrient requirements, but nitrates, phosphates, and potassium are the most prominent. When you buy plant fertilizer in the garden store, you may see the formulation label of “10-10-10” or “5-10-15” on the container. In this latter example you are buying various bulk and fillers plus 5% nitrogen, 10% phosphorous, and 15% potassium.

If Lower Beverly Lake were pure, distilled water, it would take many tons and/or truckloads of nitrates and potassium to enrich the lake sufficiently to promote plant growth. Phosphorous, though, is quite a different story. In a typical natural and undeveloped freshwater lake, there is only about 1 part per billion (ppb) of phosphorous. When a lake gets up to concentrations of 3 ppb you begin to see plant growth response. I would make the guess that our lake water might run at 10 to 20 ppb phosphates. In any case you are dealing with relatively tiny total quantities of phosphate. Lower Beverly Lake contains about 70 million cubic meters of water. To achieve a total concentration of 3 ppb you only need one 55 gallon drum (like the blue plastic barrels) of phosphate in all of Lower Beverly Lake. The point is that the total quantities of phosphorous in the lake occur in tiny and manageable amounts. We may be able to manage lake weeds by attempting to control phosphorous levels.

Where does the phosphorous come from?

The U.S. Environmental Protection Agency estimates that 50% to 60% of all phosphate pollution in the freshwater lakes of the U.S. comes from detergents.* This includes laundry, dishwater, and soaps. It may also include the relatively harsh cleaning material sometimes known as “washing soda” which is trisodium-phosphate.

Other potential sources of phosphorous are lawn fertilizers, agricultural fertilizers, animal manures (agricultural and wild), oil pollution, chemical toilets, whey, feed mill discharges, and deficient septic systems. Problems with phosphates from these sources are at least addressable, and the detergent source seems especially susceptible to some sort of serious phosphate reduction campaign. Considering area geology, it is unlikely that there are important sources of phosphorous leaching from underlying bedrock.

The following steps are suggested:

Make a list of detergent and soap products which are phosphate-free. Urge all members and lake users to consider these products.
Applaud the trend for 4-cycle outboard engines. If there are 1000 gallons of gasoline burned each year by 2-cycle engines, that represents at least 20 gallons of oil in the lake. Careless oil drain practices and lakeshore disposal will add to that figure.
Promote the application of minimum fertilizer on lawns. If shore-side owners must fertilize, promote use of low phosphorous blends.
Start a program of lake water sampling and measurement for phosphates, especially focusing on the feeder inlets to the lake.
Continue to press the Town Council to include Lower Beverley Lake in its septic system inspection program.
Inquire about the results of past or ongoing measurements of lake water condition. These measurements might have been conducted by federal, province, town, or conservation authority level.
Consider entering into a cooperative agreement with some agency (possibly one of the conservation authorities) to make Lower Beverley Lake a “poster” example of lake phosphorous cleanup.

*Dr. David Schindler is a leading water ecologist and researcher at the University of Alberta. He claims that hundreds of Canadian lakes are now burdened with excess levels of phosphorous, including the tenth largest freshwater lake in the world (Lake Winnipeg). A 2007 report by Environment Canada called phosphorous “a national freshwater-quality issue,” finding that one-third of southern Canada’s water monitoring sites exceeded the safety threshold for fish and other water life