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.

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).

We measure the TOC of the water each time we collect data – once a month for five months out of the year (June – October). The bars represent the upper quartile (75% of the data taken at this site falls below this line), the median (or mid-point of the data) for each site, first quartile (25% of the data taken at this site falls below this line), and the box represents the middle 50% of the data.

Use our interactive graph to check out all the data we have collected since 2012. Hover over a data point to see more information or try clicking on the name of a month to see all the data for just one month! 

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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