Question

If you collect a jar of water from a stream, what part of its load will settle to the bottom of the jar? What portion will remain in the water indefinitely? What part of the stream's load would probably not be represented in your sample?

Short answer

Most of what settles is the bed load; the dissolved load stays indefinitely, and large bed load is often missing.

Step-by-step solution

Understand the Stream Load Types

Stream load is the material that a stream transports, which consists of dissolved load, suspended load, and bed load. The dissolved load is made up of soluble materials, the suspended load consists of fine particles like silt and clay, and the bed load includes larger particles such as sand, gravel, and stones.

Identify What Settles

When you collect water from a stream and let it sit undisturbed, typically the bed load, which consists of larger particles, will settle to the bottom of the jar because these particles are too heavy to stay suspended.

Analyze What Remains Suspended

The suspended load, usually consisting of fine particles like silt and clay, will stay in the water column for a time but may eventually settle to the bottom if left undisturbed for long enough. However, initially, these particles will remain suspended.

Determine What Remains Dissolved

The dissolved load consists of materials like salts and other soluble compounds that remain in solution indefinitely and do not settle out. This load remains completely unaltered in the jar.

Recognize Missing Load

The bed load, particularly larger particles and materials that move along the stream bed by rolling or bouncing, is likely not represented in your sample as these materials are typically too large to be included in the jar, which usually captures only water and suspended sediments.

Key concepts

Dissolved Load

When you think of a stream, imagine it as a natural blender mixing various materials. The dissolved load is like the sugar dissolved in your tea. You can't see it, but it's there, making the stream unique.
The dissolved load consists of soluble materials. This includes elements and compounds, like ions from salts and minerals dissolved in the water. These materials are in solution and are not visible to the naked eye.
Since they are dissolved, they do not settle. They move with the stream indefinitely. This makes them a permanent part of any water sample collected from a stream. Even if a jar sits for days, these materials remain suspended in the solution without settling at the bottom. They are the invisible travelers in the stream's journey.

Suspended Load

Look at a river after a rainy day, and you'll notice it might look muddy. This cloudy appearance is due to the suspended load. These are tiny particles, including silt, clay, and other small particles, suspended within the stream.
The suspended load can stay in the water for quite some time. These particles are light enough to float within the water, moving along with the current. However, if you were to collect some stream water in a jar and leave it alone, over time, the finer particles might start to settle towards the bottom.
This settling happens very slowly, especially for the smallest particles like silt and clay. Initially, they remain suspended, giving the water a murky look. Over time, as they settle in still water, the clarity of the water improves. But in a fast-moving stream, these particles dance along, rarely finding rest.

Bed Load

When considering the massive rocks and gravel at the bottom of a streambed, you're observing the bed load. Imagine powerful currents strong enough to roll or push these particles along the stream bed.
The bed load consists of larger particles such as sand, gravel, and stones. These are too heavy to be carried in suspension. Instead, they bounce, roll, and slide along the bottom as the stream flows.
In a water sample you collect, you likely won't see the bed load. These materials are not easily lifted except during high flow conditions, like floods, when the stream's energy is high enough. In normal conditions, the larger, heavier particles are left on the streambed and are generally absent in a simple jar sample.