While many are familiar with the fish and wildlife that define our landscapes there are other lesser-known critters that play a role in creating and maintaining a healthy ecosystem. This little guy isn’t flashy with brilliant plumage, a thrilling call, or a remarkable migration story. It is very difficult to see by the naked eye, doesn’t have a dramatic migration story, and isn’t tasty to eat. But you can always know where to find it … in clean clear healthy waters.
So what is this new river friend of ours?
Cymbella cistula shown here is one of the many members of the genera and among the many thousands of varieties of diatoms, or what are commonly called algae. Diatoms are microscopic cells with an outer body shaped in a dramatic and diverse array of wondrous forms. These individual diatoms can exist as individuals or group together in visible colonies (such colonies can be mistaken for a vascular plant, e.g., a plant that has circuitry like blood vessels for transporting water and nutrients through their stems … as a simpler form of life, diatoms have none of this circuitry).
Diatoms generate oxygen through photosynthesis – the process where sunlight and carbon dioxide are converted to oxygen, energy, and water. They are often referred to as planktonic (from the Greek for “wandering”) because despite some having the ability to swim about, they spend their time moving with the currents. The companion group of critters to the plant-like diatoms, or phytoplankton, are the zooplankton, the first consumer in the ocean that eats phytoplankton, also small or early life stage animals that swim or float about.
These two types of planktonic organisms are critical to freshwater and marine food webs and make up a tremendous amount of the living biomass, or organic matter, in our rivers and streams.
Algae? Phytoplankton? You may be envisioning a lake or stream covered in green, making recreation discouraging or even hazardous with certain types of algae blooming in the heat of summer. Too many nutrients from treated wastewater and lawn or farm chemicals allow many species of diatoms to excessively thrive. Impoundments behind dams are often subject to algae blooms due to the decreased flow of water and higher water temperatures. And while abundant amounts of algae generate oxygen from their photosynthesis, inevitably an excessive amount of algae biomass will crash and decay. And decay then consumes all that oxygen. What was a naturally clear and clean waterbody turns a murky green with little oxygen. And some species of diatoms generate toxins that are harmful to humans and animals, making an impoundment or lake not just unappealing to swim, but hazardous to your health. But what about our new friend Cymbella cistula? Not all diatoms are alike! And many species are quite sensitive to an abundance of nutrients and do not thrive in enriched and warmer waters. Cymbella diatoms are one of the diatoms that can really only flourish in low nutrient (“oligotropic”) conditions, waterbodies that run clear and clean. Here is where this tiny organism has an out-sized role in our work to protect and restore our waters.
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To chart a course away from polluted and degraded rivers, streams, lakes, and wetlands we need to set a destination. One destination is a waterbody that has little or no impact from humans, or what scientists and regulators call a baseline condition. Because different types of waterbodies – wetlands, estuaries, lakes, streams, and rivers – all have different chemical, biological, and physical characteristics no two types of baseline conditions are exactly the same. Pristine rivers and streams in the northeast are generally those that run clear and cold and flow through forests and areas of little human disturbance. While you may know a pristine stream when you see it, in order to make decisions about how to restore an unloved reach of river, scientists and regulators need precise and measurable indicators of what a pristine baseline condition means.
For many years those indicators were chemical measures of water cleanliness – dissolved oxygen, suspended solids, or temperature. But these indicators only describe a condition at a point in time when the measurement was taken and don’t integrate conditions over longer periods. And they can miss other problems that may be present. So these chemical measures alone are not the best for ensuring we make it to our destination of healthy water. To get the get fullest and most robust picture of the health of a river or stream we need to listen to the critters!
To make a better roadmap (rivermap?) to our destination scientists have for years been exploring what types of fish, insects, and diatoms live in the different types of waterbodies. This work over the last 30 years has created biological definitions of a waterbody’s health to complement the more simplistic chemical measures. One of those biological definitions is based on the description of the types and amounts of diatoms present different environmental conditions. In many parts of the country including here in New England scientists have now collected enough diatom data across enough waterbody types and conditions to create statistical models that show us what diatoms should be living in what types of water conditions. These data and models allow environmental professionals to design clean-up plans or demonstrate how a high-quality water body can remain in good health. In our work to ensure our rivers can be as clean and healthy as possible we rely on the most robust tools, regulations, and policies that help guide science-based decision making. Biological indicators of river health are one of those important tools. The Cymbella diatoms whose presence in these models provides a scientifically robust measure of what constitutes high-quality water are ones we need to listen and pay attention to. So the next time you are paddling down or wandering along that clear and cold stream give a nod to that other “wanderer” helping guide us on our journey to clean and healthy water for all!
A version of this blog was first published in the Spring 2024 edition of Estuary, a quarterly magazine for people who care about the Connecticut River; its history, health, and ecology—present and future. Find out how you can subscribe at estuarymagainze. com
