Question

What are three components of sediment load in a stream?

Short answer

The three components of sediment load in a stream are: 1. Suspended load: fine particles such as silt and clay, carried in the water column and move at the same velocity as the water. 2. Bed load: larger sediment particles like sand and gravel, transported along the bottom of the stream through a process called "saltation." 3. Dissolved load: dissolved minerals and ions transported in the water molecules, typically making up the smallest portion of sediment load.

Step-by-step solution

Component 1: Suspended Load

Suspended load is the fine particles such as silt and clay that are carried in the water column of a stream. These particles are small enough to be kept suspended in the water by the turbulent motion of the stream, and they move at about the same velocity as the water. Suspended load typically makes up the largest portion of a stream's sediment load.

Component 2: Bed Load

Bed load consists of larger sediment particles such as sand, gravel, and sometimes even boulders that move along the bottom of the stream. These particles are too heavy to be carried in suspension and are instead transported through a process called "saltation." In saltation, particles are lifted off the stream bed by the water's force, and then they fall back to the bed, creating a sort of hopping or jumping motion.

Component 3: Dissolved Load

Dissolved load refers to the dissolved minerals and ions that are transported in the water itself. Dissolved load is carried in solution, meaning that these substances are dissolved in the water molecules and cannot be seen or felt. Some dissolved load materials, such as calcium and magnesium, can later form precipitates when the water becomes saturated. Dissolved load typically makes up the smallest portion of a stream's sediment load.

Key concepts

Suspended Load

Suspended load refers to the fine particles, typically silt and clay, that are light enough to be carried throughout the water column of a stream. Because these particles are so small, the turbulent motion of the stream's flow easily keeps them suspended in the water instead of settling to the bottom.

Suspended particles generally move at the same speed as the water itself. This movement is a big reason why suspended load often makes up the largest portion of a stream's sediment load.

Imagine stirring a glass of water with fine sediment at the bottom. When you stir it vigorously, the sediment clouds the water because it remains suspended throughout the liquid. This is similar to how suspended load works in a natural watercourse.

• Key Terms: silt, clay, turbulence
• Characteristic: Largest portion of sediment load
• Movement: Same velocity as water

Bed Load

The bed load of a stream is composed of heavier materials like sand, gravel, and sometimes even larger boulders. Because these particles are too hefty to remain suspended, they are instead transported along the stream bed.

This movement occurs through a process known as "saltation," which involves particles being lifted off the bed due to water's force and eventually settling back down. Think of it like a dance where the stream lifts a particle, it briefly hops into the flow, and then gently lands back onto the streambed.

Bed load undergoes a continuous cycle of erosion and deposition as water levels and velocities change. This process reshapes the landscape by altering the streambed over time.

• Key Terms: sand, gravel, saltation
• Characteristic: Moves along the bottom
• Movement: Lifted by water's force

Dissolved Load

Dissolved load consists of minerals and ions dissolved completely in the stream's water. They are transported in solution, meaning that they have become part of the water's own chemical makeup, rendering them invisible and undetectable by touch.

Common components of dissolved load include ions like calcium, magnesium, and bicarbonates. These materials often originate from the erosion of minerals or from groundwater that joins the stream flow.

Even though dissolved load makes up the smallest share of a stream's sediment, it plays an essential role in aquatic chemistry and nutrient cycles. It can further contribute to processes like mineral precipitation when conditions become favorable.

• Key Terms: minerals, ions, solution
• Characteristic: Invisible, smallest portion
• Origin: Mineral erosion, groundwater