Low dissolved oxygen and high oil and grease levels will likely lead to an increase in what type of organisms?

When dissolved oxygen levels are low and oil and grease levels are high, the environmental conditions become favorable for the growth of filamentous organisms. Filamentous organisms, such as certain types of bacteria and fungi, thrive in nutrient-rich conditions where oxygen is limited. They can form long, thread-like structures that can be beneficial in breaking down complex organic materials.

The presence of high oil and grease can lead to a surplus of organic carbon, fostering conditions that support the proliferation of these filamentous organisms as they can utilize these substrates for growth. Conversely, low dissolved oxygen often creates an anaerobic environment that filamentous organisms can tolerate, allowing them to flourish even when other organisms may struggle to survive.

On the other hand, while bacteria and other microorganisms are present, they may not specifically increase in prominence as a direct response to these conditions in the same way filamentous organisms do. Stalked ciliates and protozoa typically require better aerobic conditions and may decline in number with decreased oxygen availability. Therefore, the increase in filamentous organisms in response to low dissolved oxygen and high oil and grease levels is a key characteristic of this particular environmental shift.