Grace Rogansky and Olivia Wyatt
A stillwater ecosystem, also called a lacustrine ecosystem or lentic ecosystem, is any standing water, like a pond or lake. Other examples include ditches, seeps, seasonal pools, and basin marshes. This kind of ecosystem does not have flowing water and can be contrasted with a lotic ecosystem. Lotic ecosystems are free flowing and moving, and examples of which are rivers, streams, brooks, runs, channels and springs. Stillwater ecosystems usually do not have a source because they form in places where the groundwater reaches the earth’s surface. While some lakes and ponds are created by humans for various reasons, such as commercial and recreational use, they are often formed due to an oversaturation of water that remains above the Earth’s surface. The climate of stillwater ecosystems range in temperature and depends on their geographical region.
Ponds support a variety of rooted aquatic plants, are relatively shallow, and have a lot of light penetration. Lakes, in contrast, are larger and deeper and have a large temperature range and stratified light penetration. Ponds tend to experience a lot of imbalances (ex. evaporation, wind, precipitation), so inhabitants must be able to adapt to survive in those conditions. Thanks to increased light penetration, ponds have a great deal of diverse plant species. Lakes have similar imbalances and inhabitants must be able to adapt to the changes, but they are more gradual.
There are normally four zones that can be found in a still water ecosystem: littoral, limnetic, profundal, and benthic. The littoral zone is shallow water where light can penetrate to the bottom and support bottom dwelling animals and rooted plants. It contains plants such as reeds and cattails. The leaves of these plants form a good hideout for insects and fish. The littoral zone also supports frogs and reptiles. It is found on the banks or boundaries of the water. The limnetic zone is slightly deeper, and still has considerable light penetration to support plants and animals. It extends a few meters into the water. Lots of fish reside here, with some plants that will freely float on the water. Algae and plankton usually thrive in this zone. The profundal zone is even deeper, with little or no sunlight, where dark- adapted organisms are supported. This zone tends to be colder. Organisms that live here depend on the drifting organic matter for food. The benthic zone is the deepest part of the water, and is farthest from the banks. There is no sunlight in this zone. Worms, bacteria, decomposers, and other scavengers live here.
Animals Found in Stillwater Ecosystems
Mammals that can be found on the edges and outer regions of still-water ecosystems include beavers, muskrats, otters, racoons, bears and white-tailed deer. Turtles, alligators, salamanders, snakes, newts, toads and frogs, such as spring peepers, also live in these areas. There is an abundance of bird species, including, swans, great blue herons, great egrets, mallard ducks, Canada geese, and many others. At the Stillwater National Wildlife Refuge alone more than 280 species of birds have been sighted. There are a variety of insects including ants, bees, wasps, dragonflies, flies, mosquitos, and water striders. Invertebrates are diverse in this environment and include copepods, water fleas, crayfish, mollusks, shrimp, snails, earthworms and zooplankton. Fish are found throughout all four zones of stillwater ecosystems, and it is said that 43 percent of the world’s fish species rely on freshwater ecosystems. Where the species are located within the ecosystem is dependent on their needs. Small fish, such as minnows, need shallow water, while sturgeon and pike have to be in large lakes or rivers because of their size. Salmon and trout need lots of oxygen so they typically live in flowing streams, while catfish and carp live in muddy ponds or smaller lakes.
Issues within Stillwater Ecosystems
There are many issues within the stillwater ecosystems today, and the sad part is the majority of them are caused by humans. The first issue that will be discussed is oil spills. Oil spills are a threat to stillwater ecosystems and marsh environments are the most sensitive. Stillwater spills are less publicized than oil spills in the ocean, even though the effects here are more severe and occur more often. The oil tends to pool in the water and can remain there for long periods of time, taking years to restore the ecosystem to a balanced state. An oil spill in a lake or pond is harmful because sediment traps oil and can affect the organisms that live there, leading bottom dwellers, like worms, insects and shellfish, to feed off of the contaminated sediment. Oil spills also impact shoreline plants that provide important functions for life in and around the water by coating them in oil. These plants serve as food sources, nesting areas, and shelter for animals, impacting the animals that live there and often devastating fisheries located in freshwater ecosystems. Water bugs and floating plants are threatened by oil slicks on the surface of the water.
Damming is a very prevalent issue as well, because it cuts off the flow of water in the lotic Stillwater ecosystems, creating problems for the ecosystem as a whole and wreaking havoc on the species. Dams are created for hydropower, water storage, and for more anthropocentric desires like fishery reservoirs and to make leisure activities such as boating easier. Over 90,000 dams are in the United States today, and although convenient for human activity, they have severely damaged our stillwater ecosystems. The damming of these free flowing bodies of water raises the temperature of the water making it no longer suitable for many species, increases toxic chemical levels, and makes it impossible for fish such as salmon and many other species to complete their natural migratory and reproduction patterns. Damming and other human caused issues have also led to the increases of algae in stillwater ecosystems.
Another problem in this environment is algae. Movement in water discourages algae blooms, so stillwater ecosystems are an ideal breeding ground for algae. A change in the water’s color to green can indicate an algae bloom, with the most common types being filamentous algae (also known as pond scum), planktonic algae, and macrophyte algae. They are aesthetically unappealing and also harbor toxins. Algae growth is usually caused by a combination of factors, with the biggest factor being pollution such as fertilizer runoff or contaminated soil. Runoffs deposit high levels of nitrogen and phosphorus into water which creates the perfect environment for algae to thrive. Algae blooms can also be caused by a change in water temperature. It grows in warm water, and water temperature can be increased by levels of floating sediment, exposure to sunlight, and season changes. These intense algal blooms cause eutrophication. Eutrophication is when too much algae and other plant life blooms at once so there are too many nutrients in the body of water. This dense gross of plant life releases a great deal of phosphorus and nitrogen, and uses up a great deal of the oxygen in the water, so there is not enough for the animal life, causing them to die.
Invasive species are also a threat to these ecosystems and are believed to be the greatest global threat to native fish communities and their ecosystems. Some introductions of non-native species are intentional, such as those used to provide new fisheries or to control mosquito populations. However, unintentional introductions are the biggest threat. Non-native species being deposited into these ecosystems almost always ends in disaster, like with zebra mussels, Eurasian watermilfoil, and even common carp. Zebra mussels are extremely dangerous because of how quickly they can take over whole ecosystems, and take out other species and filter feeders, They can cause the destruction of habitats, introduction of diseases and parasites, and predation and competition with native species. This is such a large problem that there is actually a branch of the US Fish and Wildlife Service equipped with just the job of dealing with invasive species control.
Overfishing continues to be an increasing problem with stillwater ecosystems, especially in lakes. In many developing countries, human population growth is driving a need for protein sources and alternative income, and fish in these ecosystems are the most accessible resources to meet these needs. Other causes of overfishing are market pressures, technology development, lack of appropriate policies, accidental by-catches, and unregulated trade of wild species and tropical fish. There is a need in these areas for sustainable fishing practices and management, as well as knowledge of indigenous fish and conservation plans.
Policies addressing issues
Many policies concerning Stillwater bodies of water address conservation, illegal trade, commercial exploitation, habitat destruction, and environmental contaminants. The US Fish and Wildlife Service and the Bureau of Land Management patrol and enforce these policies. A few example policies are the Migratory Bird Treaty Act, Bald and Golden Eagle Protection Act, Archaeological Resource Protection Act, Clean Water Act, and the Endangered Species Act. All of these are very important and aim at helping the species and ecosystems.
A specific example of one of the policies discussed above is the Clean Water Act (CWA). It was originally passed in 1948 as the Federal Water Pollution Control Act, but the act was reorganized and expanded to its current version in 1972. It aims to protect US waters and wetlands and to improve wastewater treatment procedures. It also implements pollution control programs and outlines national water quality criteria recommendations for pollutants in surface waters. The CWA puts limits and guidelines in place for the disposal of pollutants, which protects some stillwater ecosystems from habitat destruction and the death of their inhabitants.
What you can do
There are many ways for you to get involved and help this ecosystem! One of the biggest problems that stillwater ecosystems are facing is pollution. Individuals can take measures in their own lives to avoid contributing to this growing problem. One thing to keep in mind that is often overlooked is keeping your car repaired. Oil spots from leaking cars on driveways and parking lots end up in the watershed and have the potential to harm the ecosystem. It is also important to be careful when adding oil to your car, making sure that any used and leftover oil is properly disposed of or recycled when possible. Also, when visiting freshwater ecosystems for recreational activities, be sure to treat the space with respect and care. This entails not destroying plant life or overfishing, being cognizant of restricted areas and rules, and cleaning up your trash and any other pollution you may see when visiting this space.
Water diversion and withdrawal is another big problem that stillwater ecosystems are facing. Because of a growing global population, large quantities of water are withdrawn or diverted directly from freshwater ecosystems like ponds and lakes, or the underlying water table itself. Many communities in the world are facing water stress and human water needs are expected to continue to increase. This withdrawal harms stillwater ecosystems as it lowers lake water levels, leading to loss of habitats, particularly edge habitats that are used for reproduction in many species. Withdrawal of the water table results in damage to wetlands, even if that habitat is protected, and in some cases can completely dry them up. Withdrawn water is often returned to systems in the form of household water with pollutants and an altered temperature. One way to combat this problem at home is to always turn off faucets, and fix them when they are leaking. Don’t let the faucet run needlessly while you wash dishes, wash your hands or face, brush your teeth, or shave. According to the Environmental Protection Agency (EPA), bathroom faucets run at about 2 gallons of water a minute, and turning them off when not needed can save hundreds of gallons a month. Fixing leaks is equally important, as a slow drip from a leaking faucet can waste as much as 20 gallons of water a day, and leaky toilets can waste 200 gallons a day.
In a similar way, fertilizers and pesticides used on a garden can end up in the watershed and pollute ecosystems. They add copious amounts of nitrogen to lakes and ponds which contributes to the expansion of algae blooms. This causes an imbalance in the chemistry of the water and can cause fish kills along with other problems. Natural fertilizers and bug sprays can be a perfect alternative to toxic chemicals. If chemicals are required for the task you are completing, limit your usage if possible and ensure that your chemical usage will not end up in the water cycle. It is also important to make sure you dispose of household chemicals and medicines correctly. Most towns have programs for this that you can look into. One important thing to note is not to flush medicine down the toilet, as traces of these substances are starting to turn up in local drinking water and watersheds. It is also best to use natural cleaning products for similar reasons.
A unique way to save water is to learn how to repurpose it. For example, when using a colander for washing produce or draining pasta, capture it and water plants with it. You can do the same when waiting for hot water to come on. If you are going to invest in new appliances, go for low flow and high efficiency ones. And of course, one thing that is always stated when discussing this topic: try to shorten your showers. Use a timer and limit them to 5-7 minutes.
Sources: Aquatic Environmental Consultants , Enchanted Learning, Encyclopedia Britannica, Environmental Protection Agency, eSchoolToday, Exploring Nature, Forbes, Greener Ideal, IUCN Freshwater Fish Specialist Group, National Oceanic and Atmospheric Administration, Sciencing, World Wildlife Fund, US Fish and Wildlife Service