Turbidity, Total Suspended Solids & Water Clarity
Total suspended solids (TSS) are particles that are larger than 2 microns found in the water column. Anything smaller than 2 microns (average filter size) is considered a dissolved solid. Most suspended solids are made up of inorganic materials, though bacteria and algae can also contribute to the total solids concentration 3.
These solids include anything drifting or floating in the water, from sediment, silt,and sand to plankton and algae 1. Organic particles from decomposing materials can also contribute to the TSS concentration. As algae, plants and animals decay, the decomposition process allows small organic particles to break away and enter the water column as suspended solids 17. Even chemical precipitates are considered a form of suspended solids 20. Total suspended solids are a significant factor in observing water clarity 3. The more solids present in the water, the less clear the water will be.
Some suspended solids can settle out into sediment at the bottom of a body of water over a period of time 3. Heavier particles, such as gravel and sand, often settle out when they enter an area of low or no water flow. Although this settling improves water clarity, the increased silt can smother benthic organisms and eggs 1. The remaining particles that do not settle out are called colloidal or nonsettleable solids 4. These suspended solids are either too small or too light to settle to the bottom.
Settleable solids are also known as bedded sediments, or bedload 37. These sediments can vary from larger sand and gravel to fine silt and clay, depending on the flow rate of water. Sometimes these sediments can move downstream even without rejoining the suspended solids concentration. When settleable solids are moved along the bottom of a body of water by a strong flow, it is called bedload transport 7.