Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. What are the three components of sediment load in a stream? (B)

Short answer

The three components of sediment load in a stream are: (1) suspended load, referring to fine-grained particles suspended in the water column, (2) bedload, referring to coarse-grained particles transported along the streambed, and (3) dissolved load, referring to soluble substances dissolved in water.

Step-by-step solution

Understand what sediment load refers to

Sediment load is the total amount of solid material, such as sand, silt, and clay, that is transported by a stream. It is a crucial factor in stream dynamics, as it can influence the shape and behavior of the water channel, and it is an essential parameter in various environmental processes.

Identify the three components of sediment load

The sediment load in a stream consists of three main components: (1) suspended load, (2) bedload, and (3) dissolved load.

Describe each component

(1) Suspended load: This component refers to the fine-grained particles (such as clay and silt) that are suspended in the water column due to the turbulence and flow velocity of the stream. They are carried along with the flow without settling down to the bottom. (2) Bedload: This component refers to the coarse-grained particles (such as sand, gravel, and larger rocks) that are transported along the streambed. They typically move by rolling, sliding, or hopping/bouncing along the bottom, driven by the force of water. (3) Dissolved load: This component refers to the soluble substances, such as various minerals and ions originating from rock weathering and other sources, that are dissolved in water. They are transported in the stream as invisible components and may precipitate later downstream or be utilized by organisms in the stream ecosystem. In conclusion, the three components of sediment load in a stream are suspended load, bedload, and dissolved load. Each of them plays a vital role in shaping the stream's morphology and influencing diverse environmental processes.

Key concepts

Suspended Load

Suspended load is all about the tiny particles that float in the water as it flows downstream. Imagine these particles like the fine dust you see floating in a sunbeam through a window. They are so light that the turbulence and speed of the water keep them from sinking.
This mixture usually includes clay, silt, and very fine sand, all suspended because of the movement and energy of the stream.
The key points of suspended load are:

• Flow Velocity: The speed of the water is crucial. Faster-moving water can carry larger or more particles.
• Turbulence: Swirling, turbulent water mixes up particles, keeping them in suspension.
• Fine Particles: Because they are light and small, they do not settle quickly.

The suspended load significantly impacts water quality and the amount of light penetrating through the stream, affecting aquatic life.

Bedload

Bedload consists of heavier, coarser particles that move along the bottom of a stream. These are not transported by the flow continuously but move in short jumps or rolls along the streambed.
You can think of this like marbles rolling along a sidewalk. The stream uses its energy to push these particles along, especially during high flow conditions.
Some aspects of bedload include:

• Particle Size: Typically includes sand, gravel, and larger rocks, which require more energy to move.
• Transportation Methods: They may roll, hop, or slide, depending on their size and the water's speed.
• Stream Energy: Higher water flow increases a stream's ability to transport larger particles.

Bedload plays a crucial role in changing the physical shape of a stream over time, by eroding banks and altering the streambed itself.

Dissolved Load

Dissolved load refers to materials that are essentially mixed into the water at a molecular level, making them invisible to the naked eye. These are typically ions and minerals that come from rock weathering nearby or upstream.
Unlike suspended and bedload, dissolved load doesn't depend heavily on water speed or turbulence for movement.
Here's what you should know about dissolved load:

• Invisible:** Since it's dissolved, you can't see these particles as you do with suspended and bedload.
• Consistence: Includes various minerals such as calcium, sodium, and bicarbonate among others.
• Availability: These ions are used by aquatic life or might precipitate to form solid deposits down the stream.

This component is critical for stream chemistry and can affect everything from water hardness to nutrient availability for plants and animals.