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Rivers and Streams
More about rivers and streams:
Rivers and streams are the general terms used to describe natural and man-made bodies of moving water. Rivers are larger than streams and empty into large waterbodies such as oceans and lakes. River and stream systems consist of numerous tributaries joined together to form a main channel. The tributaries (streams) are identified by their stream order, denoted by its position in the system (see table below). Learn more about rivers and streams by the links below.
There are three main types of streams:
Ephemeral streams regularly exist for short periods of time, usually during a rainy period, and may have defined channels even when they are dry.
Intermittent streams flow at different times of the year, or seasonally, when there is enough water from either rainfall, springs, or other surface sources such as melting snow or even discharge from a wastewater treatment facility.
Perennial streams are those that flow year-round.
| Stream Order | Characteristics |
|---|---|
| First Order | not connected to any other tributaries |
| Second Order | connected to one other stream/tributary |
| Third Order | joining of two second order streams |
- Large River Systems
- Lotic Ecosystems of the Streambed
- In the Lifetime of Rivers and Streams
- What makes a Healthy River, Stream, or Lake?
Large River Systems
Slow-moving lotic ecosystems are very similar to those of lentic environments in terms of aquatic plant and animal life. As in lakes and ponds, phytoplankton is the dominant vegetation in the open water of slow-moving lotic environments. Phytoplankton (microscopic plants) living in this environment have a higher rate of productivity (reproduction occurs often) than their counterparts in fast-moving water.
This is partly due to the slower waters' leaving more detritus and other nutrients to be picked up by microscopic organisms and the water bottom, rather than be swept downstream.
The consumers of any given lotic environment vary in diversity according to water conditions and available vegetation. Although phytoplankton communities are large in lotic environments, they do not become as dense as they do in lentic environments. Fast-moving rivers and streams prevent much primary production due to fast currents and turbulence and therefore, low level consumers are also very sparse.
Sections of rivers and streams where water flow is somewhat slowed by a rocky shoal or sand bar create areas of choppy water called riffles. Common juvenile species of fish such as trout rely on these somewhat safe places to feed upon the drifting zooplankton and aquatic insects and hide from larger consumers until they are large enough to escape predators.
Some of the most productive and protective habitats in slower moving
waters are "backwater" areas. The backwaters are the floodplain
and wetlands next to the river that provide a refuge and spawning area
for many fish. Visit American
Rivers 
to
learn more about large river systems.
Lotic Ecosystems of the Streambed
The benthic habitat of lotic environments is found in the streambed. The streambed is comprised of various physical and organic materials where erosion and/or deposition is a continuous characteristic. Erosion and deposition may occur simultaneously and alternately at different locations in the same streambed. Where channels are exceptionally deep and taper slowly to meet the relatively flattened streambed, habitats may form on the slopes of the channel. These habitats are referred to as littoral habitats. Shallow channels may dry up periodically in accordance with weather changes. The streambed is then exposed to open air and may take on the characteristics of a wetland.
Silt and organic materials settle and accumulate in the streambed of slowly flowing rivers and streams. These materials decay and become the primary food resource for the invertebrates inhabiting the streambed. Productivity in this habitat depends upon the breakdown of these organic materials by herbivores. Not all organic materials are used by bottom dwelling organisms, a substantial amount becomes part of the streambed in the form of peat.
In faster moving rivers and streams, organic materials do not accumulate so easily. Primary production occurs in a different type of habitat found in the riffle regions where there are shoals and rocky regions for organisms to adhere to. Therefore, plants that can root themselves into the streambed dominate these regions. By plants, we are referring mostly to forms of algae, often microscopic and filamentous, that can cover rocks and debris that have settled into the streambed during summer months. If you have ever stepped into a stream, the green, slippery slime on the rocks in the streambed is representative of this type of algae.
Although the filamentous algae seems well anchored, strong currents can easily lift it from the streambed and carry it downstream where it becomes a food resource for low level consumers. One factor that greatly influences the productivity of a river or stream is the width of the channel; a direct relationship exists between stream width and richness of bottom organisms. Bottom dwelling organisms are very important to the ecosystem as they provide food for other, larger benthic animals through consuming detritus.
Slow-moving streams are dominated by aquatic insects and invertebrates. Most aquatic insects are in their larval and nymph forms such as the blackfly, caddisfly, and stonefly. Adult water beetles and waterbugs are also abundant. Insect larvae and nymphs provide the primary food source for many fish species, including American eel, brown bullhead catfish, and trout. Representatives of crustaceans, rotifers, and nematodes (flat worms) are sometimes present. Leech, worm and mollusk (especially freshwater mussels) abundance varies with river and stream conditions, but generally favors low phosphate conditions (oligotrophic). Larger animals found in slow moving streams and rivers include newts, tadpoles and frogs. The important characteristic of all life in streams and rivers is adaptability to withstand currents.
In the Lifetime of Rivers and Streams
Streams may originate in two ways, either flowing from headwaters such as lakes, or from springs or groundwater seepage. The direction of stream flow is dependent upon the slope and obstructions of the landscape. Flow velocity is also determined by the associated land gradient, which when steep, not only speeds flow, but increases sediment load and deposition.
Over time, rivers and streams may change greatly in appearance. Where gradients are steep and near the source of the river or stream, water travels in a straight channel, velocity is high and much sediment is carried. Upon reaching level ground, velocity decreases and sediments are dropped in the form of silt, mud, and sand.
As a river or stream channel builds up or erodes the surrounding floodplain, it meanders, creating loops of varying sizes in the channel. When meanders become extremely distorted they can be severed, becoming independent oxbow lakes. Once a river reaches the stage where it has built up a floodplain and meanders, it is referred to as mature.
Maturity is not permanent. Should the river come upon a geological obstacle, major climatic change, tectonic event, or man-made obstacle resulting in a waterfall or rapids rather then a meander, the river may be rejuvenated. That is, the river is not characteristically mature anymore, but holds characteristics similar to those of "immature" rivers and streams near their sources.
Taking Shape
Rivers and streams represent lotic environments and therefore must
have continuously flowing water. Flowing water creates currents within
the stream or river that wear away the sides of the channel, slowly shaping
it over time. Currents are also responsible for moving and mixing organic
and chemical substances as they enter the water through erosion and transport
through weather (precipitation and wind) and animals (eg. birds dropping
seeds and plant matter). The speed and subsequent ability of currents
to alter the channel is determined primarily by the age of the river or
stream. Young streams tend to have higher velocities and therefore erode
their channels at faster rates. Mature streams are slower and current
is more dependent on the terrain of the channel. Nutrient levels and sediment
loads often vary throughout the different locations along the course of
a mature river/stream and therefore affect velocity and current.
Physical Characteristics
The conditions of river and stream water vary greatly with season,
weather changes, and solar intensity. Water characteristics affected by
these outside influences include conductivity, temperature, turbidity,
and chemical composition (i.e., dissolved nutrient concentrations). Interactions
between air and water give rise to changes in surface agitation and gas
exchange of oxygen and carbon-dioxide. Land-water interactions elate to
erosion, nutrient influxes, and channel alteration. The constant stirring
of the channel bottom by underwater currents also affect erosion, nutrient
flow, and turbidity.
What makes a Healthy River, Stream, or Lake?
There are many things that help make waters healthy: natural flows, diverse habitat, and unpolluted waters. Flow, chemistry, biological interactions, sources of energy (food), and habitat are all important. Water resource integrity is more than water quality - incorporating all essential factors that comprise the character and attributes of watersheds. The concept of water resource health, or integrity, includes the five major factors of water chemistry, habitat structure, energy dynamics, biotic interactions, and hydrology (flow regime) and how these interact to produce the "goods and services" important to healthy and sustainable aquatic ecosystems.Learn about biological integrity
In terms of the importance to humans, water resource integrity pertains directly to clean and safe drinking water supplies, safe consumption of fish, assimilation of wastewater, and healthy and diverse aquatic plants, animals and other wildlife.
Biological indicators are the best and most accurate measure of the health of a river, stream, or lake. But other measures, such as chemistry and habitat, are also vital. Sometimes changes in water quality (chemistry, physical parameters such as temperature and sediments) and habitat changes can come before changes in the biological community and can help be an early warning to the biota. Water quality and habitat are also used as "diagnostic" indicators to help determine the causes and sources of problems affecting the biota.
Learn more about rivers and streams
- USEPA's American Heritage Rivers
- Missouri Botanical Gardens rivers
and streams (don't miss this incredible site)
- U.S. Geological Survey rivers and streams
- National Park Service National Wild and Scenic Rivers System
- American Rivers all
about rivers
- Center for Global Environmental Education - Rivers of Life
- Minnesota Shorelands Management Rivers Primer
- The River Network on-line
library
- NaturServe Rivers
of Life