SPEAK OUR LANGUAGE

• CELL – Core Experience Learning Lab
• SDR – Scientist Data Record

ASK WHY

Great scientists question the world around them. We encourage our LabLearner students to do the same. In anticipation of this, we explain the importance of learning the concepts in the Ask Why section within the CELL. Our hope is that these explanations help students understand why science matters.

BRANCH OUT

Each Investigation introduces students to a different branch of science or STEM (Science, Technology, Engineering, Mathematics) career that utilizes the scientific concepts of the CELL. These real-world connections will help students see the relevance of what they are learning. STEM connections are also integrated into each Performance Assessment.

GET FOCUSED

The Focus Questions in each Investigation are designed to help teachers and students focus on the important concepts. By the end of the CELL, students should be able to answer the following questions:

Investigation 1:

• How do the abiotic factors of water velocity and discharge affect a watershed? Water velocity is the distance water travels per time. Discharge is the volume of water that flows into an area per time. As water velocity increases, discharge increases. Increases in water velocity and discharge from headwaters of a watershed may lead to flooding downstream.

Investigation 2:

• How do the abiotic factors of water velocity, sedimentation, and turbidity affect a watershed? Water with a higher velocity will have higher turbidity, leading to more sediment suspended in the water.
• How does water velocity affect sedimentation and turbidity in a watershed? Water with a higher velocity will have higher turbidity. More sediment will be suspended in the water and less sedimentation will occur (less sediment will settle out on the bottom).

Investigation 3:

• How do the abiotic factors of temperature, water velocity, salinity, and dissolved oxygen affect a watershed? Dissolved oxygen increases with decreasing temperature, decreasing salinity, and increasing water velocity.

Note: These are succinct responses to the Focus Questions and are placed here for easy reference. Fully developed responses to the Focus Questions can be found on each PostLab page.

Note: Some questions may be revisited as the CELL progresses. As students acquire additional knowledge, their responses should reflect this.

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced within the CELL. These terms should be used, as appropriate, by teachers and students during everyday classroom discourse.

Note: Additional words may be bolded within the Backgrounds. These words are not Key Terms and are strictly emphasized for exposure at this time.

Investigation 1:

• Watershed: a land area that slopes downward and drains water into one primary waterway or reservoir; made of a series of brooks, streams, creeks, and rivers.
• Velocity: the time it takes for a given particle to travel a given distance; measured in meters per second.
• Discharge: the rate at which a volume of water flows past a point over some unit of time.

Investigation 2:

• Sedimentation: the process of depositing sediment.
• Turbidity: a measure of the cloudiness of water.

Investigation 3:

• Estuary: a place where a river runs into an ocean and fresh and saltwater mix, for example, a bay or salt marsh.
• Salinity: the concentration of ions (or salts) dissolved in water.

EXTEND YOUR THINKING

A watershed, or drainage basin, is a land area that slopes downward and drains water into one primary waterway or reservoir. Watersheds consist of a series of brooks, streams, creeks, and rivers. The boundaries of a watershed can be identified by locating the highest elevations of land around the primary waterway or reservoir. The Mississippi River watershed is the largest watershed in the United States. It is fed by tributaries that extend from the Appalachian Mountains to the Rocky Mountains.

Several abiotic factors affect the structure and function of watersheds. These include water velocity, water turbidity, sedimentation, dissolved oxygen, and salinity. All of these factors are important in determining what organisms can live in a given area of a watershed.

The speed and direction of water flow in a stream channel is water velocity. Water velocity is defined as the time it takes for a given particle of water to travel a given distance, and it is measured in units such as meters per second or feet per second. Water velocity is affected by the position of water in a stream channel, the type of flow, the amount of water in a stream channel, and the area of a stream channel.

Water velocity varies depending on the position of the water in a stream. For example, the velocity of water in the middle of a stream is different than the velocity of water at the edges of a stream. In a straight stream channel, the highest water velocity is in the center of the channel, and water velocity slows at the edges of the channel. In a meandering (curved) stream channel, water velocity is fastest on the outside of a bend and slowest on the inside of a bend.

There are two main types of water flow, laminar flow, and turbulent flow. These are illustrated in Figure 1. Flow becomes more turbulent as water flows over rocks and other large sediments. The turbulent flow slows water velocity because it takes a given particle longer to cover a certain distance. Stream channel roughness decreases downstream as sediment becomes smaller, causing less turbulent flow.

Discharge is the volume of water that passes a given point during a specific time interval. It is usually measured in m3/s (cubic meters per second) or ft3/s (cubic feet per second). The discharge of a stream varies during the seasons. For example, discharge downstream could increase when melting snow adds more water to tributaries or when a major storm occurs. Discharge is directly related to water velocity:

As discharge increases, either velocity increases or the width or depth of the channel must increase. This can lead to flooding downstream. As water changes depth, it can also lead to changes in temperature and light penetration which can lead to changes in habitat for living organisms.

Watersheds contain sediment, loose insoluble materials such a rock fragments, soil, and organic matter. Sediment is often formed by the erosion of the stream channel itself or by eroded material from the surrounding land. Sediment can be suspended in and carried by the moving water. The amount of material that can be suspended is a function of water velocity. For a sediment particle to be transported, the water velocity must be higher than the settling velocity of the particle. Most sediment is suspended when water velocities are highest. If the water velocity of a stream channel decreases, the ability of water to keep particles in suspension is lowered. Sediment particles begin to settle out of the water, depositing on the bottom of the stream channel. This process is called sedimentation. Streams ultimately deposit most of the material they carry as water velocity decreases, forming watershed structures like alluvial fans and deltas.

Turbidity is a measure of the cloudiness of water and is due to suspended particles in the water. Sedimentation and turbidity are indirectly proportional. Turbidity increases with an increase in water velocity or an increase in turbulent flow, whereas sedimentation increases with a decrease in water velocity or a decrease in a turbulent flow. Turbidity is one measure of water quality in lakes and streams. Turbidity may increase due to increased nutrient input from the watershed, increased erosion, increases in bacteria or algae, heavy rain, or increased boating. Increases in turbidity can have a negative impact on water ecosystems. Increased sediment in the water can hold heat, raising the temperature of the water. Turbidity decreases the ability of sunlight to penetrate the water, leading to decreased photosynthesis by submerged vegetation and ultimately decreased dissolved oxygen content of the water.

One of the most crucial abiotic factors to the health of watershed ecosystems and overall water quality is dissolved oxygen content. Dissolved oxygen is the amount of oxygen that is dissolved in water. It is measured in units of milligrams (mg) of oxygen per liter (L) of water. Aquatic organisms depend on dissolved oxygen to live. Oxygen dissolves into water in two ways: through diffusion at the air/water interface and from production from the photosynthesis of aquatic plants. The amount of oxygen that stays dissolved is dependent on the temperature of the water. As water temperature increases, the concentration of dissolved oxygen decreases. Water velocity also has an effect on dissolved oxygen content. As water velocity increases, there is more turbulent flow and an increased surface area of water is exposed to air. This increase in surface area increases the amount of dissolved oxygen in the water.

Salinity is the concentration of ions or salts dissolved in water. Typical ions found in water include sodium, magnesium, calcium, and chloride. These ions enter the water through erosion of rocks and through the mixing of seawater with fresh water in an estuary. Salinity has a direct effect on many aquatic plants and animals. As the salinity of water increases, many aquatic organisms cannot maintain their internal ionic balance. Salinity also has an indirect effect on water quality. As salinity increases, more ions enter solution. Water has a higher affinity for chloride and other ions than for oxygen, so less oxygen is able to dissolve in the water. Dissolved oxygen content decreases with increasing salinity.