Benefits of Freshwater Systems
Freshwater systems – including streams, rivers, ponds, lakes and wetlands – are important components of landscapes. The organisms that make up food webs in freshwater systems (See Image 1) are diverse and important both ecologically and economically. Many aquatic species are well known, including a variety of important fish species, but at the bottom of a water body are organisms that are members of benthic communities. The term benthos derives from the Greek word bathys, meaning deep. Benthic communities are composed of algae, bacteria, fungi, and invertebrates — organisms that transform matter and energy into LIFE — living biomass that eventually becomes food for other organisms like fish. Insects that emerge from streams and lakes also provide important nutrients and energy to neighboring forests and sustain terrestrial organisms, such as birds, spiders and lizards1,2,3. Benthic organisms have unique adaptations that allow their communities to perform valuable “ecosystem services”, such as improving water quality for drinking, sustaining commercial fisheries, offering leisure and recreational opportunities, and providing inspiration for artistic expression and spiritual renewal. When the world was relatively “empty” of humans, the bounty of these ecosystem services was so vast that it seemed limitless. However, in today’s world of 7 billion people, our footprint has grown so large that it is impairing the capacity of freshwater ecosystems to provide these valuable services.
Image 1. A stream food web. Credit: Federal Interagency Stream Restoration Working Group (1998).
Ecosystem services provided by benthic communities:
Think of benthic communities as living ‘water purifiers’. The diverse lifestyles of benthic organisms allow them to play vital roles such as cleaning water, processing detritus, and controlling harmful algae blooms. One group of organisms, the filter-feeders, is composed of a variety of species that specialize in removing particles from the water column. For example, a study on the Ashuelot River in New Hampshire4 showed that freshwater mussels (See Image 2) can filter 35% of the total daily discharge (all water flowing past the river mouth) from a flood control dam. To illustrate this point, an aquarium filled with murky water will become clear after several hours of filtering by mussels (See Image 3).
Freshwater mussels are one of the most imperiled groups of aquatic organisms in streams and rivers because much of their habitat has been altered by dredging, channeling, impoundment, and sedimentation. Mussels also are sensitive to water pollution, the spread of exotic species, and barriers to migration.
Image 2. Mussels from the Ashuelot River in New Hampshire, USA: endangered dwarfwedge mussel, Eastern elliptio (top), and Eastern lampmussel (right). Credit: E. Nedeau of Biodrawversity and The Nature Conservancy.
Image 3. Water filtration by mussels. The tank on the right contains mussels while the tank on the left does not. Water in the tanks was from the same source. Credit: R. Neves of Virginia Tech.
Aquatic plants, such as algae, diatoms, and rooted macrophytes (See Image 4), also improve water quality by removing nutrients from the water and making them available for other life forms. However, in cases where rivers are receiving excess nutrients, algal blooms can be problematic. In some cases, rooted plants can remove and degrade toxins like mercury or atrazine (a widely used herbicide). Plants also derive energy from the sun, which is then available to fuel the benthic food web in the form of organic matter.
Image 4. Aquatic algae and plants: cyanobacteria (Nostoc sp., right, credit: R. Lowe) a diatom (Gomphonema acuminatum, middle, credit: R. Lowe), and a sedge (Eleocharis sp., right) in Prairie Creek, Florida, USA.
Benthic communities break down the organic matter derived from plants – such as aquatic macrophytes and the leaves and branches of trees that fall into streams, lakes, and ponds – while removing dissolved nutrients from the water. Thus, they can also be thought of as ‘digestion systems.’ A fallen leaf eventually settles to the bottom and microbes colonize it (See Image 5). Microbes break down toxins and leaf structural components, such as cellulose and lignin. Microbes also enhance leaf nutritional value for larger benthic organisms by assimilating nitrogen and other nutrients they remove from the water. These processes are referred to as ‘conditioning.’ Once the leaf is conditioned by microbes, macroinvertebrates shred the leaf material into smaller particles while consuming small bits of it. This shredding accelerates decomposition by increasing the surface area of the leaf material for further microbial processing. The energy and material fixed during decomposition support the growth of macroinvertebrates, as well as the fish that consume invertebrates and the conditioned detritus.
Image 5. The process of leaf decomposition – a leaf falling into a stream is converted to fine particulate organic matter (FPOM), which includes leaf fragments, feces, and dissolved carbon and nutrients. Credit: modified from Allan and Castillo (2007).
Bio-indicators for watershed management
The structure and composition of a benthic community is an excellent bio-indicator of pollution and habitat quality5,6,7. Consider this: a truck dumps waste into a stream. The stream moves the toxins downstream making it difficult to pinpoint the problem. But the tiny benthic organisms on the stream bed respond quickly to pollutants and document the environmental event. For example, organisms tolerant to the pollutant increase in their abundance relative to other organisms present, whereas others that are intolerant decrease in their relative abundance or disappear altogether.
Dr. Ruth Patrick championed the cause for biological diversity through what many call the “Patrick Principle.” Her theory was that a diversity of species holds the key to understanding environmental problems that affect our world. As far back as the early 20th century, European scientists used benthic organisms to classify and assess stream and river conditions. Today, there are many indices used to assess the health of freshwater systems – and benthic organisms are the foundation for many of them. The Patrick Principal provides a foundation for the bio-indicator approach, which is used by people of all ages and levels of training to monitor, learn, and examine the quality of water and the health of aquatic ecosystems around the world.
Commercial fisheries, recreation, tourism, and land value
There’s a reason why salmon go through the risky and high energy task of migration up streams and rivers to spawn. Abundant food – in the form of small benthic organisms – and low risk of predation by larger fish make streams and rivers ideal locales for newly hatched fish. Rivers, small streams, and wetlands are thus critical for fish reproduction. The value of benthic communities to commercial fisheries, like salmon, is so great that large dams are being removed or retrofitted (See Image 6) because in some cases, the fishery is of equal or greater value than the hydropower or recreational opportunities provided by the dam.
Image 6. One of several fish ladders located at the Bonneville Dam on the Columbia River, USA. Credit: E. Guinther and Wikipedia.
Some people derive great aesthetic pleasure from recreational activities in freshwaters, such as fishing, swimming, kayaking, and canoeing. For example, fly fishing enthusiasts understand the intricacies of the benthic food web because they tie the perfect fly to “match the insect hatch” in lakes and streams (See Image 7). Others enjoy observing nature – watching dragonflies flit about, seeing waterfowl and birds of prey catch fish – or simply enjoying the relaxing sounds of water. The economies of many small towns and cities depend on healthy freshwater systems. Recreation and tourism fuel an entire industry of skilled crafts people, and gives value to the land.
The aesthetic beauty of benthic organisms, such as dragonflies, damselflies, and mayflies, has led many cultures to use them as symbols of human characteristics. The Japanese believe the dragonfly represents agility and strength, the Samurai envisioned the dragonfly as an emblem of victory, and some Native American tribes associate the dragonfly with water, fertility, and curing. Some cultures have entire fables built on animals in the benthos. An old name for damselflies was 'Devil's Darning Needles'. This stems from an old myth that if you went to sleep by a stream on a summer's day, damselflies would use their long, thin bodies to sew your eyelids shut! In another version of the same tale, dragonflies sew shut the mouths of lying children, scolding women and cursing men as they slept. A more delightful Zuni legend8 involves a dragonfly and a brother and sister who were left behind by some villagers when the corn crop failed. The little boy constructed a toy dragonfly from corn husks to cheer up his sister. The dragonfly eventually came to life and appeased the corn maidens who created a bountiful harvest of corn to welcome the villagers back.
Traditional arts such as poetry, painting and photography are inspired by freshwater ecosystems. The dragonfly is a symbol found on many Native American pottery and textiles and throughout Art Noveau (See Image 8). For some artists, benthic organisms and processes are the medium as well as the instrument of art. Much like paint on a brush, diatoms and their diverse silica shapes can be dyed and arranged to make ethereal images. Fallen leaves can be carved by hand and treated with chemicals to mimic the leaf decomposition process and create artistic designs. Caddisflies themselves become artists by constructing their cases from semi-precious stones for the purposes of making jewelry (See Image 9).
Image 8. Dragonfly imagery in pottery glasswork. A dragonfly symbol on a Hopi bowl (circa 1400-1625 A.D.) from the Sikyatiki archaeological site (left, credit: J. W. Powell and the U.S. Bureau of American Ethnology). A Tiffany lamp with a dragonfly detail (right, credit: www.antique-marks.com).
Image 9. Diatom art (left, credit: California Academy of Sciences, https://www.flickr.com/photos/casgeology), leaf carving art (top right, credits: http://www.longal-craft.com/leaf-carving-art.html, http://www.leafcarvingart.com/leaf_carving_art.htm), and caddisfly jewelry-made with gold, pearls, and semi-precious stones (bottom right, artist: H. Duprat, photo credit: J-L Fournier).
Today I saw the dragon-fly
Come from the wells where he did lie.
An inner impulse rent the veil
Of his old husk: from head to tail
Came out clear plates of sapphire mail.
He dried his wings: like gauze they grew;
Thro' crofts and pastures wet with dew
A living flash of light he flew.
- The Dragon-fly by Alfred Lord Tennyson
Interested citizens and large groups of scientists – including ecologists, entomologists, geneticists, chemists, hydrologists, and geomorphologists – are working to understand intact and threatened freshwater systems. The Society of Freshwater Science helps to improve scientific training, foster collaboration among scientists, and communicate research findings to the general public.
We encourage you to get your feet wet! Explore the benthos and our beautiful freshwater systems.
1. Nakano S, Murakami M. 2001. Reciprocal subsidies: Dynamic interdependence between terrestrial and aquatic food webs. PNAS 98 (1): 167-170.
2. Sabo JL, Power ME. 2002. River-watershed exchange: Effects of riverine subsidies on riparian lizards and their terrestrial prey. Ecology 83: 1860-1869.
3. Baxter CV, Fausch KD, Saunders WC. 2005. Tangled webs: reciprocal flows of invertebrate prey link streams and riparian zones. Freshwater Biology 50: 201–220.
4. Nedeau E. 2006. Quantitative Study of the Freshwater Mussel Community Downstream of the Surry Mountain Flood Control Dam on the Ashuelot River. Unpublished report prepared for U.S. Army Corps of Engineers, Otter Brook/Surry Mountain Lakes, Keene, NH and U.S. Fish and Wildlife Service, New England Field Office, Concord, NH.
5. Rosenberg DM, Resh VH (eds). 1993. Freshwater biomonitoring and benthic macroinvertebrates. Chapman and Hall, New York, NY.
6. Stevenson RJ, Rollins SL. 2006. Ecological assessments with benthic algae. Pages 785-804 in Methods in Stream Ecology, Second Edition, FR Hauer and GA Lamberti (eds.), Academic Press, New York, NY.
7. Carter JL, Resh VH, Hannaford MJ, Meyers MJ. 2006. Macroinvertebrates as biotic indicators of environmental quality. Pages 805-834 in Methods in Stream Ecology, Second Edition, FR Hauer and GA Lamberti (eds.), Academic Press, New York, NY.
8. The Boy Who Made Dragonfly A Zuni Myth retold by Tony Hillerman (ISBN 0-8263-0910-0)
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