Indicators: Sediment Diatoms

What are sediment diatoms?

Diatoms are a type of single-celled algae that have cell walls made of silica (glass). They are found in almost all aquatic habitats including lakes, ponds, streams, rivers, and the ocean. Most diatoms live as free-floating cells in the open water, but some live on the bottom (benthos), attached to surfaces such as plants or rocks, or in the bottom sediment. These surface-attached diatoms represent a significant part of the periphyton, which is a mixture of algae, cyanobacteria, microbes and detritus that is attached to submerged surfaces.

Why are sediment diatoms important?

Diatoms can photosynthesize which means they can convert dissolved carbon dioxide in the water into oxygen that is essential for the survival of fish and other aquatic organisms. They also serve as a major source of atmospheric oxygen for the planet, and a key food source for higher organisms in the food chain, such as zooplankton, molluscs, and fish. Diatoms also play a crucial role in the nutrient cycling of marine and lake waters.

What can sediment diatoms tell us about the quality of the water?

There are many sediment diatom species, and each species has a range and tolerance for environmental factors, such as pH, nutrients, and salinity, and for different types of human disturbance. Some species thrive in nutrient-rich polluted waters, while others prefer low-nutrient conditions. Because diatoms are so diverse and highly sensitive to changes in environmental conditions and human disturbances, this makes them excellent indicators of water quality and ecosystem health. By looking at the diatom species composition and their abundance in a river, lake, or pond, scientists can determine the quality of the water found there.