Total Organic Carbon

Water Quality Measurement  | Chemical Parameter

Lake Pend Oreille | Pend Oreille River

Total Organic Carbon (TOC) is equivalent to the amount of dissolved carbon dioxide and carbonic acid salts, present in the water body. Testing for TOC can help determine the amount of decaying natural organic matter (NOM) present in the water body. NOM can chemically react with the chlorine used during water treatment processes, increasing the amount of carcinogens in the treated water. In this case, it is important to test for elevated TOC levels to assure an additional safeness for drinking water sources. Total Organic Carbon sources include naturally decaying organic matter, agricultural runoff, and stormwater runoff.

How to use the graph: View data for only one month by clicking on that month in the legend. Supplemental information is provided by hovering over a data point. 

For a link to IDEQ’s Water Quality Standards, click here.

For an explanation on Box Plots, click here.

Total organic carbon (TOC) is equal to the total concentration of dissolved (DOC) and particulate organic carbon (POC) present in a sample. Generally, the rate at which DOC and POC enter a lake changes seasonally and tends to increase with precipitation events and autumn decomposition of leaf fall (Wetzel 2001).

High TOC levels indicate high rates of organic material decomposition (e.g., plants, algae); so it is more common to see higher TOC concentrations in backwater sloughs, ponds, or swamps. Higher-than-average TOC levels may also indicate pollution. For example, a high TOC load at the mouth of a tributary may indicate high rates of erosion upstream. On the other hand, clearcutting of forests within drainage basins can limit DOC entering a lake (Wetzel 2001).

Some sources of total organic carbon include decaying natural organic matter

  • Leaf fall (tributary streams)
  • Bacterial degradation of organic matter
  • Inputs of domestic and industrial organic wastes
  • Phytoplankton and algae
  • Agriculture and stormwater runoff

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