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How Can We Assess the Health of a Lake, River, or Forest?


Since March, we've been getting questions in as part of our Curious North series.

Jaron Childs from Tomahawk recently asked: What signs can we look for to help assess the health of a lake, river, or forest in northern Wisconsin?

The Masked Biologist answers his question for this week's Wildlife Matters.

What follows is a very brief answer to a very complex question about how to evaluate habitat health.

Lake health could take up volumes of books, so there is no way to answer it simply here. In briefest terms, lake quality is water quality. There are some simple ways to evaluate the health of your lake without testing equipment. Water clarity is a great example. Measuring how far down into the water you can see a black and white secchi disk can give you a great index of water clarity. Plants you find in the lake can also give you an indication of health. Exotic or invasive plants like curlyleaf pondweed, Eurasian water milfoil or purple loosestrife can drain the health from a water body. If you have high quality native aquatic plants, you probably have a pretty healthy lake. Emergent plants would include arrowleaf and wild rice. Submergent plants might include native bladderworts and pondweeds. From a wildlife standpoint, you might see wild celery, lotus or duckweed that attracts insects as well as ducks and other birds that feed on them. If you have invasive species of fish or wildlife, like rusty crayfish, they can really reduce the health of the lake by destroying plants, stirring up sediment, or displacing native species. Some invasive species might seem like they are improving the lakes, but the harm is still there. For example, zebra mussels have made the great lakes clearer than they had been in recent history. In this case, though, the clear water is an indicator of a decline in health. The removal of suspended nutrients and microflora changes the entire aquatic food chain.You can also take some measurements like dissolved oxygen, phosphorous content, and heavy metals if you wanted to go into greater depth in evaluating the health of your lake.

Rivers are very similar in some aspects. Instead of a secchi disk, you use a clarity tube. It is basically a clear pipe with a small black and white disk at the bottom. You fill it up, look through the tube, and slowly let the water out until you can see the disk. The remaining water in the tube is measured and that is your water clarity. Plants are also important for a healthy river, especially up here in the headwaters area of Wisconsin. Any sediment, contaminants, invasive species or waste we discharge up here will impact everyone downstream of us. Even simply spreading road salt makes the river unhealthy. One tablespoon of road salt pollutes five gallons of water, and we use salt on our roads all winter across the north.

Finally, a healthy forest can take many different forms. Trying to force a forest to grow species that do not naturally occur or thrive there will result in unhealthy trees. When forest landowners start pine plantations, they will often work hard to clear and prepare the site, plant the trees, trim up the branches, and thin the trees over time to make sure the remaining trees stay healthy. On public lands, like county, state, and federal forests, the managers work hard to keep forests healthy. They strive for a variety of timber stands of appropriate species, making sure they have older trees, younger trees, and new regeneration. If you are walking in a forest this time of year, you can usually tell how healthy a forest is by listening for bird songs. If all you hear are crows or ravens, your species richness and composition might be out of balance. When I walk in a healthy northern forest this time of year, I hear grouse drumming and turkeys gobbling. I hear flickers, chickadees, towhees and warblers. All sorts of different bird species will occupy healthy forests. Soon, you can look down for health instead of up. You can look to see what kinds of flowers and plants you find growing. Native flowers thrive in healthy soils when deer populations are within well-managed levels. Trilliums, for example, do well when deer populations are lower and struggle when deer populations increase. And, like the lakes and rivers, invasive plant and insect species can have a significant negative impact on individual species and forests in general.

This is just a quick glimpse into a very simplified way of looking at basic habitat health. You can contact resource professionals that daily work with our lakes, rivers, and forests to get more information or specifics.

Striving to make new things familiar and familiar things new, this is the Masked Biologist coming to you from the heart of Wisconsin’s great Northwoods.

Do you have a question for the Masked Biologist? Submit it below to our Curious North series and it could be featured in an upcoming commentary.


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The Masked Biologist is a weekly commentator on WXPR talking about natural resources and wildlife in the Northwoods. He is anonymous so that he can separate his professional life as a biologist from his personal feelings about the natural world.
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