03/03/09

(This page describes the TMDL process in more detail than the "Troubled Waters" page.)

What are those weeds in Peltier Lake? Why is the lake sometimes so green and rotten? The first thing an aquatic biologist will say is those are not weeds in the lake, those are aquatic plants, specifically, Curlyleaf Pondweed (Potamogeton crispus) and Eurasian Watermilfoil (Myriophyllum spicatum) and others. Trouble with water quality in the lake has multiple causes, but the effects of one invasive aquatic plant is easily seen. The non-native Curlyleaf Pondweed is a problem.  This exotic grows earlier than native species so it becomes dominant. In late June with warmer water, it dies and releases nutrients into the lake. But before it dies, it produces millions of seeds called turions that get ready to grow the next year.

Algae (image at left) loves the nutrients from the decomposing Curlyleaf and so it blooms in huge quantities creating scum and smell. Sometimes blue-green algae blooms can be toxic so caution on the part of people and pets is advised. The algae blocks the light and tends to knock back all submerged aquatic plants, even the exotic invasive Eurasian Watermilfoil. Other lakes have huge problems with Eurasian Watermilfoil when it covers areas with thick surface mats of vegetation.

So the south part of Peltier Lake has a vicious cycle where Curlyleaf and algae help each other create an environment that discourages anything else from taking hold. A lake should have beneficial aquatic plants to absorb nutrients and avoid algae blooms. In the spring, Peltier Lake can look quite good because all the aquatic plants are healthy. But by midsummer, algae and its scum take over when the plants die and release nutrients.  

Another player in the lake is Eurasian Watermilfoil. This exotic first appeared in 2000 and has been expanding its presence in the lake ever since. Every year it seems to increase its density and range but the algae in July knocks it back. But the Milfoil hangs on till next year’s clear spring waters. The lake is so full of algae, not even exotic Eurasian Watermilfoil grows well.

What might be done about these and other problems with water quality?

By the Clean Water Act, the Minnesota Pollution Control Agency (MPCA) has designated Peltier, Centerville, George Watch, Marshan, and Reshanau lakes in the Rice Creek Chain of Lakes Regional Park Reserve as “impaired waters.” A Total Maximum Daily Load (TMDL) study is a process to improve waters listed as impaired. This study looks at lake loading of nutrients and makes recommendations to bring the lake into compliance with water quality standards.

On July 31, 2008, water resource experts, Matt Kocian of the Rice Creek Watershed District (RCWD), Gary Oberts of Emmons & Oliver, Inc, and Joe Bischoff of Wenck Associates presented TMDL information and strategies to improve the impaired waters.

The TMDL process has these steps:
Assess waters
Determined whether impaired
Place water body on impaired list
Monitor, study water body further
Complete pollutant load allocation formula
Develop restoration strategy
Implement strategy
Monitor changes in water quality
Next steps and/or delist

The process is currently at the “Develop restoration strategy” step. The diagram below illustrates the steps in the process.

Peltier lake is in a category of “shallow” lakes which act different than “deep” lakes. Shallow lakes tend to exist in one of two states, turbid or clear. Peltier is solidly locked in the “turbid” state right now and the goal of the TMDL and restoration strategy is to move it into the “clear” state.

The following diagram illustrates characteristics of the clear-water state and the turbid-water state. A strategy is biomanipulating the lake to minimize the algae. (Nutrients in the sediments and watershed must be reduced too, so this diagram does not show everything.) Peltier lake is turbid and has some pike predator fish, a lots of carp, minnows and pan fish, few invertebrates, way too much algae, almost no beneficial submerged plants, and sediments full of nutrients. This situation means the small number of predator fish allow too many minnows and pan fish who in turn eat most of the invertebrates. Invertebrates eat the algae, but with very few invertebrates around, algae thrive. The carp stir up the bottom releasing nutrients there and hamper beneficial aquatic plant growth. The huge algae population blocks the light further preventing beneficial aquatic plants which would help stabilize the sediments and absorb nutrients. 

In the clear-water state, a large population of predator fish reduces the minnow and pan fish population. This allows the invertebrates to flourish and eat the algae. Beneficial aquatic plants could then flourish, stabilize the sediments and absorb nutrients.

Algae is generally limited by the amount of phosphorus nutrient in the lake. With excessive phosphorus, there is excessive algae. In Peltier Lake, phosphorus is internal and external. Internal phosphorus is already in the lake sediments or in a cycle with non-native aquatic plants like the Curlyleaf. External sources of phosphorous come from the watershed. The diagram below shows the amounts from each source: 62% from internal sources, 14% from Upper Rice Creek, 15% from Hardwood Creek, and 8% from Clearwater Creek.

Going from the clear-water state to a turbid-water state is easy. But Peltier Lake needs to go the other way which is not so easy. One strategy under consideration is a lake drawdown. Keeping the lake down over winter might kill much of the non-native aquatic plants. Keeping it down over summer could reduce the nutrients in the sediments. But first, external sources have to be addressed or phosphorus might just accumulate in the sediments again and little would be gained.  Strategies in the TMDL consider: water level changes, fish management, chemical treatment, macrophyte control, aeration/circulation, habitat restoration, sediment removal, wetland restoration, low impact development, bioretention, detention ponding, local/RCWD rules, buffers, and infiltration/filtration.

The public can help. Runoff into the lake adds to the nutrient loading. Consider the following: planting raingardens to reduce runoff; keeping lawn clippings and vegetation off the street so they won’t wash into the lake; not mowing next to wetlands; keeping high speed boat traffic far from shore and shallow water; respecting the no-wake zone by the island; establishing buffers and natural vegetation on shorelines to reduce nutrients going into the lake and not fertilizing by the lake. See www.BlueThumb.org for more information.

If all this fails, a new invention claims to produce oil from algae. But that is another story. Hopefully, the TMDL process will improve the water quality in the Chain of Lakes offering everyone improved natural resources!

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