2.2. Failed Processes Evaluation

So, we were looking at the exchange between the sediment-water. So, the mechanisms of release what we had talked about one is by diffusion. So, it is diffusion inside the sediment plus conductive mass transfer at the interface. The second thing that we talked about is resuspension.

In this chunk, we begin by discussing the exchange process between sediment and water, introducing two primary mechanisms of chemical release: diffusion and resuspension. Diffusion occurs within the sediment and across the sediment-water interface, allowing contaminants to move from a higher concentration area to a lower concentration area. On the other hand, resuspension occurs when solid particles in the sediment are lifted into the water column, allowing the contaminants they carry to spread into the water body.

Imagine a sponge soaked in food coloring. When you press the sponge (which represents sediment) into clean water, the color (contaminants) diffuses into the water. If you shake the sponge, bits of it get released into the water (resuspension), causing the water to change color as the pigment disperses.

When this cloud of particles goes downstream several things happen. The contaminated solids are suspended into water and while they are there, the desorption of chemical from the water occurs. Then this particle also settles back.

This chunk explores what happens when resuspended particles travel downstream. When these particles (which contain contaminants) are suspended in the water, they can release chemicals into the water (a process known as desorption). Eventually, the particles may settle back down to the sediment, but during their time in suspension, they have the potential to impact water quality significantly.

Think of stirring up a jar of chocolate syrup that has settled at the bottom. Initially, the syrup particles are at the bottom, but once stirred, they mix with water, affecting its color and flavor. The syrup eventually settles again, but could change the overall quality of the water in the jar while suspended.

In order to estimate the effect of this, one needs to estimate what is the resuspension that is happening? How much of resuspension happens? That is not in the core purview of this course.

Here, we acknowledge the complexity of quantifying resuspension effects. Although estimating the amount of resuspension is crucial for understanding its impact on water quality, it falls outside the main focus of the course. Those interested would need to delve into sediment transport and hydrology to understand the energy dynamics behind resuspension.

Consider a researcher trying to gauge the number of times dust particles are stirred up in a room. While they can see the dust circulating (resuspension), measuring exactly how much has been suspended and how it affects air quality would require specialized tools and methods, much like the case with sediment resuspension.

The other consequence to this is once a particle is suspended, it can desorb, it can transfer from the solid phase to a liquid phase, when it comes to liquid phase, it can also go to the atmosphere.

This chunk introduces bioturbation as an additional mechanism of chemical transport in sediments caused by living organisms, such as worms. When these organisms disturb the sediment, they can cause contaminants to release from the sediment into the water. This process is significant because it can alter where contaminants are found and how they affect different environments.

Picture a baker mixing ingredients in a bowl. As they fold the batter repeatedly, ingredients that were settled at the bottom (like chocolate chips or nuts) get mixed throughout, making the entire mixture more contaminated. In nature, organisms like worms perform a similar function in sediment, causing chemicals to disperse from their original location into the water.

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