Measurement

Total Suspended Solids

The total amount of particulate material suspended in lake water, including sediment, algae, and organic matter, measured in milligrams per liter.

What It Means for Your Lake

Total suspended solids (TSS) measures the concentration of all particulate material in a water sample, expressed in milligrams per liter (mg/L). In lake water, suspended solids consist of inorganic particles (silt, clay, and sand), organic particles (algae cells, zooplankton fragments, and decomposing plant material), and precipitated minerals (calcium carbonate in hard-water lakes). TSS directly affects water clarity, higher TSS means murkier water. In Minnesota and Wisconsin lakes, TSS typically ranges from less than 2 mg/L in clear oligotrophic lakes to over 50 mg/L in turbid prairie lakes and wind-mixed shallow lakes. The sources of suspended solids differ by lake type. In deep, nutrient-poor lakes, TSS is dominated by algae cells and is closely correlated with chlorophyll-a. In shallow lakes, wind-driven resuspension of bottom sediments can be the dominant source, particularly in lakes less than 15 feet deep where wave energy reaches the lake bottom. In lakes receiving significant tributary inflow, erosion from the watershed contributes inorganic sediment, especially during spring snowmelt and after heavy rainfall events. Agricultural lakes in southern Minnesota and central Wisconsin often have high TSS due to a combination of algae growth and sediment inputs from eroding cropland. TSS affects more than just clarity, suspended particles carry adsorbed phosphorus into lakes, reduce light penetration for aquatic plants, and can smother fish spawning habitat. Reducing TSS in lakes generally requires addressing both nutrient inputs (to reduce algae-related TSS) and erosion sources in the watershed (to reduce sediment-related TSS).

Frequently Asked Questions