The Main Points
- Some sedimentary load is a normal part of aquatic ecosystems.
- Excess suspended solids can damage an aquatic ecosystem.
- TSS analysis provides data that can be used to make routine environmental management decisions but does not provide detailed geological information.
Sediments being carried through the water in a river or stream are a natural part of ecological cycles. Dirt and soil wash away from one location and get deposited in another location. Dam construction, stream bank modification, water diversion and even sea-level rise can impede sediment flow. At its most extreme, this robs coastal regions of the material needed to replace land lost to the ocean. The most famous example of this problem is found along the Gulf Coast of the United States where over the last 80 years some 2,000 square miles of the marshes have disappeared.
The opposite problem is called “sediment stress” where excessive amounts of sediment damage aquatic life. Suspended sediments can prevent sunlight from reaching aquatic plants, clog the gills of fish and damage shellfish. Cloudy or muddy looking water is considered unattractive and is unsuited for recreation. Pollutants such as pesticides and petroleum products can be transported far from their point of origin if they bind to small sediment particles.
Each river or stream will have a natural amount of suspended sediment (which is also called the “sediment flux”) that depends on the surrounding topography and potential for erosion. Although an occasional excess or periodic sediment shortage is a normal part of the ecosystem function, persistent changes to the natural flux should be investigated.
Measuring total suspended solids consists of passing a water sample through a pre-weighed filter. Small particles are trapped on the filter which is then dried and re-weighed. Results are expressed in units of milligrams per liter.
TSS is usually sufficient for making routine environmental management decisions but does not provide detailed geological information about the suspended particles. Silt, clay, sand, algae and bits of plant material are all trapped on the filter and become part of the TSS measurement.
More advanced analysis is needed reveal the exact make-up of the sediment such as the proportions of sand, silt and clay. Mineral content can be used to trace the origins of the suspended particles. Chemical analysis can determine if there are dangerous pollutants bound to the sediment particles. Analyzing the naturally occurring organic materials that are bound to the sediment particles can tell us something about the surrounding ecosystem. There are also some advanced analysis techniques to determine the age of the suspended materials.