Eagle River Watershed Council: Life under the surface
Courtesy photo
When you think of our rivers and streams here in Eagle County, what do you see? A beautiful blue stream with wildlife on either side of it? Are people enjoying the river? What about the iconic cutthroat trout that swim through our rivers?
All of those are critical aspects of our river systems, but I am going to challenge you to think smaller. How small? Small enough to see the tiny bugs that are integral to river ecosystems. These bugs are called macroinvertebrates or macros, for short. From the Greek prefix, “macro” means large — in this case, large enough to see without a microscope. Invertebrate means without a backbone. These macroinvertebrates are critical not only to local rivers but to freshwater bodies of water everywhere.
There are thousands of macroinvertebrates, but three common ones we see here in Eagle County are scuds, stoneflies and mayflies. Today, we’ll focus on the life cycle of mayflies.
Like other macroinvertebrates, mayflies start their lives as eggs. This egg stage can last as little as a couple of days, or as long as a few weeks as they grow and prepare to hatch. Once they are developed enough, they emerge into the nymph stage as recognizable insects. This is the longest life cycle stage and can last up to two years. Nymphs usually stay at the bottom of the river, also known as the benthic level. This is a critical development stage.
Mayfly nymphs consume plants, like leaf litter and algae, and use those nutrients to grow. They support healthy, functional river food chains and are consumed by fish, otters, birds and other species. This is also known as nutrient cycling, and it refers to moving nutrients from organic matter of the environment to animals, such as leaf debris that becomes energy for mayflies, and eventually, fish. This keeps the river ecosystem at an equilibrium by allowing nutrients to freely move.
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Because mayflies are a species sensitive to water pollution, evaluating their population numbers in the nymph stage can be helpful in gaining an understanding of water quality trends. Mayflies are a favorite for water quality indicators because they are easily identifiable and common to our region in areas with good water quality. There are a lot of variables that can impact water quality such as high sediment loads, low oxygen levels or human-caused impacts. A few examples of human-caused impacts are trash, pesticides and fertilizers.
On the flip side, leeches and midges are more pollution-tolerant and can withstand higher levels of pollution, like pesticides. By inventorying species of macroinvertebrates annually, data can be collected that helps to tell the story of the impacts of pollution as well as efforts to improve water quality in local waterways. A local example is the efforts of Restore the Gore in the Town of Vail, where education, outreach, and policy have improved water quality and allowed sensitive species, like mayflies, to return. It is important to remember that even pollution-tolerant macros are critical to the ecosystem and can be found in areas of good water quality.
If water quality is healthy during the nymph phase and mayflies fully mature, they are ready to reproduce. To do so, they make their way to the surface of the river and enter the sub-imago stage. They will shed their skin and lay on top of the water, waiting for their newly-available wings to dry out. This isn’t easy sunbathing — they are very vulnerable to attacks from fish and other predators during this stage.
Once their wings are dry, they fly out of the water and are ready to mate. This is the shortest stage of their life cycle and may last only minutes. Why? Adult mayflies do not have a way to eat or digest food. They are relying solely on energy reserves.
If the timing is right in some locations, hundreds to thousands of mayflies can be seen leaving the water to mate in the air — it is a spectacular sight. This generally occurs between May and June. After mating, the female mayfly will return to the surface of the water, and release her eggs as the final process. Male mayflies often land on shore before expiring. The cycle starts again with a new generation.
From our high alpine streams to the Eagle River flowing near town, macroinvertebrates need clean water to do what they do. Remember, you have a direct impact on the health of our watershed. To protect not just the small bugs that rely on clean water, but also our water sources, we’ve put together some tips for taking action:
- Be aware of what enters our storm drains. Remember that anything that ends up on the ground, like oil, soap or fertilizers will end up in local waterways.
- Protect riparian areas. Only walk on established paths near the river to reduce damage to sensitive riparian plants and streambanks. This helps us to reduce the amount of sediment that enters waterways and supports places where wildlife can thrive to benefit the watershed.
- Use less water, especially in late summer. When flows get too low, water temperatures rise which can negatively impact macros and fish. To learn more about reducing your water use please visit beyondlawn.org.
Next time you are down by the river or exploring mountain streams, look closely and see if you can find any of those little bugs that keep our waterways going.
Rose Sandell is the education and outreach coordinator for Eagle River Watershed Council. The Watershed Council has a mission to advocate for the health and conservation of the Upper Colorado and Eagle River basins through research, education, and projects. Contact the Watershed Council at 970-827-5406 or visit ERWC.org.
