This is an interactive adapted from Kentucky’s Natural Heritage: An Illustrated Guide to Biodiversity that gives students an opportunity to explore headwater streams, medium streams/rivers and large rivers, which are all systems that are part of lotic communities. Students can click or touch any of the systems to learn about it and the various organisms that live there.
Similar to lentic communities, lotic communities are also aquatic. However, lotic communities are systems of moving water such as creeks, streams, and rivers. The water in a lotic community must flow in one direction from source to mouth. Some other characteristics of the water in a lotic community are atmospheric gases such as oxygen, areas that are thick with sediment that has been stirred up, and temperature change.
Lotic communities often start in areas known as headwater streams. These can be small permanent streams or temporary streams that are formed after a rainfall. The headwater streams twist and turn as they flow into medium streams/rivers where the water becomes wider and warmer. Due to the sunlight and warmth of the water in these areas, food is easily produced through photosynthesis. Finally, the water continues flowing downstream into large rivers formed from many tributaries. At this point, the water widens, the current slows, and the river doesn't twist and turn as much.
As the water flows from headwater streams to large rivers, they form the two major zones of the lotic community: rapids and pools. Rapids are the areas where the current moves quickly enough to keep materials from building up on the bottom. Usually, they can be detected by the rough broken water surface they create. Pools are areas where the current slows down enough for debris and silt to collect on the bottom. These areas usually have the appearance of smooth or calm surface water.
Each part of the lotic community meets the needs of a variety of species. Headwater streams are home to smaller aquatic species such as crayfish, mayfly larvae, and minnows. Species such as the gar prefer the slower moving currents and deeper waters of the larger streams and rivers because they are larger and prey on other fish. Each of these species plays an important roll in the lotic community food chain and ecosystems.
Why do the headwaters have a direct impact on the health of the water downstream?
After looking at the different types of aquatic life found in each system, discuss some of the major differences you see among them. What are some reasons for such major differences in species found from headwaters to rivers?