Wednesday, May 20, 2009

Ask the Wandering Limnologist

Here is a question posed to The Wandering Limnologist by the owner of a newly-created 15 acre lake regarding aquatic plants:

Dear Wandering Limnologist,
I have a newly created lake that is full for the first time this spring and have been reading many sources regarding lake management. Some books say that the key to clear water is to have plants growing that stabilizes the bottom. One article besides dealing specifically with phosphorus gives the impression as many other conflicting articles do – that "all vegetation is bad". How do you keep a stable bottom with "good plants" and limit the bad?

Signed,
Weedless in SE New York

Dear Weedless:

There are a certain amount of nutrients in a lake acting like fertilizer to make green things grow - green things being algae & phytoplankton and aquatic plants. If you have no aquatic plants then all those nutrients go into phytoplankton and algae growth, causing cloudy water (green, green-brown, or brown). What you have been reading could also be talking about stabilizing lake bottom sediments, shallow water sediments, and lake shorelines. Without plants, wave action will resuspend sediments into the lake causing cloudiness (brown).

Lake ecosystems & lake management are not simple things. If anyone tells you verbally or in something you read that "doing this one thing" fixes all your problems or even solves one problem, be very suspect. For instance, say you had too many plants. Someone tells you that grass carp will fix your problem. It is true that grass carp eat plants. But they preferentially select and eat tastier (to them) plants first and maybe you didn't want to get rid of the tasty plant but another more troublesome plant. Furthermore, no one knows how many grass carp is the correct number. Too few and nothing happens, so the tendency is to throw in too many (there is no correct magic number). So the grass carp eat up all the tasty plants, then all the 2nd tastiest plants and so on until they eat up ALL the plants. Now your lake has no plants. Yea! But then all that phosphorus that was in the plants comes out as fish poop and with no plants you get algae and plankton and your lake is a green algae mess. And with no plants the bass can find and eat up all the small and young fish and you get no more new fish that can grow up to be big fish. And so on.

That is just on example how a "quick and easy fix" can cause more problems than it solves. So do yourself and your lake a favor, support your local lake expert. All kidding aside, don't be led around by simple statements and claims when it comes to your lake. Trust the experience of a certified lake manager when I say it is almost always more expensive to clean up a lake than it is to prevent it from getting messed up in the first place.

Oh, and the short answer is, yes you need plants in your lake to stabilize the shore and provide refuge for baby fish. You really just need to stabilize the shallow, near-shore area and there are plenty of plants that will only grow in shallow water and therefore NOT spread across the whole lake. You don't need or want plants covering the entire bottom of the lake because there aren't many deep water plants that only grow a few inches. They all want to shoot up to the surface.

So, as with the grass carp example, you have to be careful what you plant and introduce into the lake. As pretty as they are, AVOID WATERLILIES AT ALL COSTS. If you want some water lilies, plant them in buckets that you place in the lake so they won't spread everywhere! There are good sources for obtaining aquatic plants and I recommend that we create an aquatic plant planting plan for your new lake.

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Submit your questions to The Wandering Limnologist at wanderinglimnologist@lakestewardship.org

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