Aquatic Plants (Lake Weeds) Provide Important Ecosystem Services

The Importance of Lake Aquatic Vegetation
by Dr. Lorin Hatch, Widseth

One definition of a weed I’ve heard is that it is a plant out of place, which is really a human judgement. For example, some people like dandelions on their lawns, some don’t. 

Let’s turn that idea to the lakeshore, specifically the rooted plants that grow in the water. These plants can grow at depths from the shoreline to 15 feet of water. They typically don’t grow in deeper waters simply because not enough sunlight reaches those depths to drive photosynthesis and plant growth.

At first glance, what positive things do humans get directly from aquatic plants? That’s a tough question, because we don’t eat those plants or use them as bait. I would guess many people’s direct physical experience with aquatic plants is negative: stuck to boat props, getting in the way of waterskiing, washed onto the shore messing up the beach, tangled in feet when swimming, snagging our fishing lines. Which is probably why we may refer to aquatic plants in negative terms: weeds.

However, without those aquatic plants in adequate numbers and types, many of the aesthetic and recreational opportunities afforded by lakes would not exist! In other words, a healthy aquatic plant community indirectly creates our positive lake experiences: 

Plant roots help retain the lake bottom sediments from wave disturbance, reducing water turbidity (cloudiness) and nutrients that could lead to algal blooms

Plants provide habitat for juvenile fish, including a place to hide from predators

Plants are a food source for many tiny organisms near the bottom of the food chain

Plants create dissolved oxygen during winter under the ice, providing oxygen that allow fish to survive over winter

What types of activities can negatively impact these communities? Natural disturbances such as intense waves from strong storms is an example, but such impacts are minimal, and the plant community is typically left intact. Human activities such as repetitive motorboating close to or through the plant community can negatively impact them as well. It isn’t so much the propeller chewing up plants that is the issue, it is the intense wave action that tears up the bottom sediments to which the plants are anchored. Other plant disturbance extremes include the use of excessive chemicals, as well as tearing up an entire shoreline. A reasonably-sized swimming and dock area can be OK, but a balance between human wants and a healthy plant community needs to be achieved along the shoreline.

If a large area of aquatic plants is disturbed greatly, it can be very difficult to restore that plant community. It may take several years of intense restoration activities, with the ecosystem services listed above being lost during that time.

So taking care of aquatic plant communities is in our best interests, because in many ways a healthy lake aquatic plant community creates the positive recreational conditions we enjoy. To paraphrase a DNR shoreline habitat document, you don’t need to give up a sandy beach to create a natural, wildlife-friendly lakeshore. If you have 100 feet of shoreline, consider reverting 75 feet back to its natural condition (which included woody debris) and keeping 25 feet for a boat dock and swimming area. Taking care of aquatic plant communities is in our best interests because in many ways a healthy lake aquatic plant community creates the positive recreational conditions we enjoy.

Lorin Hatch has over 20 years of experience managing Minnesota lakes, streams, and wetlands. Trained as a limnologist, he has worked on issues pertaining to aquatic invasive species (AIS), lake water quality, algae, aquatic plants, stream and shoreland restoration, boat safety, loons, government relations, and funding. He is an excellent speaker and is willing to speak with your group about a multitude of lake management topics, either in person or online video.