Freshwater Streams
Figure 1: Stoneflies are commonly found in cool, flowing streams and are indicative of good water quality.
Karen Jackson, ©2020, Clemson Extension
Healthy streams provide countless benefits to both the community and the environment. These benefits include recreational opportunities, reduced downstream flooding, and increased property values. Additionally, across the United States, surface waters account for up to 70% of the drinking water. Locally, surface water provides 1.9 million residents of South Carolina with water for drinking. For aquatic insects such as stoneflies, dragonflies, and mayflies, streams serve as both permanent habitats for stages of development and refugia during flooding and drought (figure 1). Organisms outside of the stream benefit as well, as insects emerging from the water serve as valuable sources of food. These are just a few examples of the ecosystem services healthy streams offer, and small headwater streams account for many of them. Headwater streams are increasingly threatened by development, loss of floodplain connectivity, and increases in impervious surfaces. These changes can lead to loss of land and property values, impairments to drinking water, and intensified flooding. Proper practices by homeowners can limit stream degradation and help protect waterways.
What are Headwater Streams
Figure 2: Perennial streams flow all year long.
Karen Jackson, ©2020, Clemson Extension
Small but often overlooked, headwater streams are of great importance to the ecosystem and community. In the United States, these streams represent 79% of the overall stream network. So, what is a headwater stream? A headwater stream is considered a “first-order” stream. The smallest flows from upland areas, as well as springs and seep sources that maintain defined stream beds throughout the year are first-order streams. Where two first-order streams combine, a second-order stream is designated. A wetland outside of the floodplain and streams with a variety of permanence can be considered a headwater stream. Flow permanence break streams into three categories: perennial, intermittent, and ephemeral. Perennial streams flow year-round and are found below the water table (figure 2). Intermittent streams flow during the wet season when the water table is above the stream bed but are generally dry during the hotter months when the water table is low. Ephemeral streams only flow after rain events or snowmelt. Some ephemeral streams flow so infrequently that there may not be water in the stream bed for up to a year.
Importance of Headwater Streams
One of the most essential benefits of headwater streams is their capacity to mitigate the effects of flooding. When a headwater stream is healthy, it intercepts and delays rainwater from reaching larger streams. However, increases to impervious cover prevent water from infiltrating into the ground and results in large volumes of water released over short amounts of time (figure 3). Infiltration is one way stream systems help mitigate flooding. Headwaters not only decrease the volume of floodwater; they also slow down water through channel diversity of channel substrate, meandering, and floodplain access. Natural channels help prevent downstream erosion, excessive sedimentation, and flooding, unlike artificial concrete channels and pipes, which help to move water downstream quickly (figure 4). In times of drought, healthy headwater streams feed larger streams and eventually rivers, maintaining a continuous supply of water.
Figure 3: A hydrograph showing the difference in stormwater runoff
Figure 4. Streams that have been converted into concrete-lined systems increase the velocity of water and cause downstream flooding.
Karen Jackson, ©2020, Clemson Extension
Headwater streams with intact riparian buffers also benefit the ecosystem by limiting the amount of sediment reaching larger waterways. Riparian buffers are areas of natural vegetation adjacent to the stream that filters pollutants, including sediments. Excessive sedimentation can cause numerous water quality issues. Suspended sediment can inhibit plant growth and can also carry excess nutrients and bacteria into the stream, which can cause water quality issues such as loss of oxygen that harms aquatic organisms. Specifically, bacteria can adsorb to sediment particles, such as sand and silt, and enter waterways when erosion occurs. This can then be resuspended in the system after storm events and persist up to six weeks in streams.
Threats to Headwater Streams
Land changes can negatively influence headwater streams. The most significant impact is from urban development and the conversion of natural stream channels to culverts and concrete-lined channels. Urban development often increases the area of impervious surfaces in the form of driveways, rooftops, and sidewalks. These surfaces do not allow water to infiltrate into the ground, instead, causing vast quantities of water to run off of the landscape into nearby stream channels. The conversion of a stream bed to an artificial system may results in the loss of aquatic habitat and faster moving water, ultimately leading to channel erosion and downstream flooding.
Often, the loss of healthy headwater stream systems means a loss of species. One of the many threatened or endangered species dependent on headwater systems is the Webster’s Salamander (figure 5). This species has declined due to loss of habitat. The Carolina Heelsplitter also depends on headwaters streams for refugia. The loss of habitat has significantly reduced the viability of this species to just eleven surviving populations. These are only two examples of species completely reliant on these smaller, often overlooked systems. The exact percentage of the 130,000 freshwater animal and plant species dependent on these headwaters systems is still unknown.
Figure 5: Webster’s Salamander, although completely terrestrial, are found in forests bordering rocky, small order streams.
Photo Credit: Alan Cressler.
Protecting Headwater Streams and Riparian Areas
Fortunately, there are many actions homeowners with streams on their properties can take to help protect these vital resources. Maintaining streamside buffers is a simple practice that does not require training or specialized equipment. Riparian buffers are areas of natural vegetation adjacent to the stream that helps to improve or maintain water quality. They prevent stream erosion and help to moderate water temperature by providing shade for aquatic life. Buffers also remove pesticide and fertilizer contaminants from runoff before entering a stream. Buffer widths may vary depending on the location, but up to 30 meters can help to preserve aquatic habitat, limit sediment, and remove nutrients. The use of pesticides and fertilizers near riparian buffer zones should be limited, and only herbicides that are labeled for use in aquatic habitats should be applied.
Intact, healthy headwater streams are essential to maintaining water quality and quantity. Without these properly functioning systems, flooding will affect homes and property values, drinking water will be compromised, and aquatic organisms will be imperiled. As more habitat and natural space are lost to accommodate our growing population, preserving our headwater streams becomes even more imperative.
Originally published 07/20
