Total Suspended Solids

Suspended solids settle out as mud deposits on the banks of the Red River after flood events.

The amount of particles that suspend in a sample of water is called total suspended solids (TSS). To remain permanently suspended in water (or suspended for a long period of time), particles have to be light in weight (they must have a relatively low density or specific gravity), be relatively small in size, and/or have a surface area that is large in relation to their weight (have a shape like a sheet of paper). The greater the TSS in the water, the higher its turbidity and the lower its transparency (clarity).

Measuring TSS
TSS can be estimated from measurements of turbidity or transparency, but an accurate TSS measurement involves carefully weighing the amount of suspended material from a water sample. To accomplish this, a sample of water is first run through a filter. The filter and the material trapped on the filter are dried in an oven. The dried material is then weighed, and the weight of the TSS is determined by subtracting the weight of the filter. TSS is reported in milligrams per liter (mg/L; weight of the suspended solids per volume of water).

TSS in the Red River
TSS is relatively high for the mainstem Red River and the lower reaches of its tributaries, reflecting the muddy soils in the central Red River Valley. In the Fargo Moorhead (FM) area, TSS varies seasonally, with highs in summer (greater than 100 mg/L). This reflects the influx of sediment from runoff and bank erosion. In the winter, when the ground is frozen and precipitation is stored in snow, the TSS level drops to nearly zero.

Graph of total suspended solids (mg/L) for the Red River in the FM metro area for the period March 2000 to October 2002.