2.3. Impairment of Water Quality

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.

Contaminated solids from sediment can be resuspended into the water through processes such as storms or strong currents. This resuspension causes chemicals attached to these solids to enter the water column. After some time, the particles can settle back to the bottom. This back-and-forth movement of solids and dissolved chemicals impairs water quality because it introduces contaminants into the water, affecting its purity.

Imagine stirring up a glass of muddy water. When you push the spoon through the mud at the bottom, tiny particles cloud the water, making it hard to see through. Similarly, when sediment is disturbed, it releases pollutants that were trapped in the sediment, leading to dirty water.

If I take this entire water sample and extract, I will get the combination of chemical that is attached to the water as well as on the solid.

When sediment is stirred up and solids are suspended in the water, the concentration of chemicals in the water is not just from what is dissolved in the water, but also from what is attached to the solids. This means measuring water quality must consider both the dissolved and the particulate-bound chemicals to understand the true level of contamination.

Think about a sponge soaked in juice. When you squeeze the sponge, both the liquid within it and some bits of the sponge itself come out, creating a juice mixture. Similarly, when sediment is disturbed, both the dissolved chemicals and those bound to particles are released into the water.

Bioturbation is the transport caused by biological agent. This transport of chemicals in the sediment is due to biological agents, but what do you mean by biological agents?

Bioturbation refers to the process by which living organisms, like worms and crabs, disturb the sediment. These organisms dig through the sediment, which can enhance the movement of chemicals buried in the sediment to the water above. This biological activity makes the sediment structure less compact and allows chemicals to more easily move upward into the water column, further contributing to pollution.

Imagine a gardener mixing compost into the soil. As they dig in, they not only aerate the soil, but also bring nutrients closer to the surface where plants can access them. In a similar way, organisms that burrow in the sediment can bring trapped contaminants to the water surface.

What they do is they are feeding at the sediment, the sediment is sent in and the chemical goes in.

The actions of organisms such as worms not only mix the sediment but also involve them consuming the sediment. As they ingest and process this material, they can transform the chemicals present, contributing to chemical cycling in the ecosystem and potentially increasing the concentration of certain pollutants in the water.

Similar to how a cow grazing in a field digests grass and alters its composition, through the process of bioturbation, these organisms change how chemicals are presented in sediments and can influence their availability in the water.

Now, advection is bulk flow of material coming out, unlike soil, sediments have very little opportunity of advection.

Advection refers to the process where substances such as pollutants are carried along with the flow of water. In sediments, this process is less common due to the saturated nature of sediments, but biological activity that produces gases like methane can create small channels that help facilitate the upward movement of contaminants along with these gas bubbles.

Think of a sponge full of water that you press down. As air bubbles are released from the sponge, they can carry tiny bits of liquid upward. Similarly, the formation of bubbles in sediment can transport contaminants to the surface, where they mix with water.

Sediments at different locations are very different. If you look at sediments in coastal regions... If somebody dumps, in India large number of industries are located on the coast.

Different environments have distinct sediment types that influence how contaminants behave. For instance, sandy sediments in coastal areas tend to have less capacity for chemical absorption compared to clay-rich sediments found in rivers or lakes, leading to varied pollution dynamics and risks in different ecosystems.

Consider how sand on a beach can quickly drain water while mud in a lake retains it. Similarly, the ability of sediments to store and release contaminants varies greatly based on their composition, affecting overall water quality.

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