# Meaning of the C in the unit "mg C L-1"

Could somebody tell me what the "C" signifies in the unit mg C L-1? I was wondering if it stood for concentration but it seems redundant as litres are mentioned. Thanks.

The paper which uses the unit is "Dissolved Organic Carbon Thresholds Affect Mercury Bioaccumulation in Arctic Lakes" by French et al. 2014.

• Likely they are specifying carbon in units milligram per liter. Jun 30 '14 at 0:01

Given the subject matter of the paper, I'd assume that it stands for carbon, and the whole expression refers to milligrams of carbon (or organic carbon) per litre of lake water.

If the "C" stands for carbon, then the "unit" doesn't conform to the SI standard, which states that units should not contain extraneous information. That information should instead be in the name of the relevant quantity. See http://physics.nist.gov/Pubs/SP811/sec07.html for more information.

• The litre isn't an SI unit either. SI units of volume are based on lengths cubed. The correct SI unit would be g/m3 carbon (in water!). mg/dm3 is also a common substiute for mg/L in laboratory work because a m3 of water just seems an absurdly large quantity. As they've already broken another guideline of the referenced style guide, it's not surprising that they chose something that scans better in English mg C L-1 over the slightly less natural mgL-1 C (in H2O). Note also that their ordering avoids the need to laboriously point out that we're talking about litres of water, not carbon Jun 30 '14 at 3:54
• @steveverrill I think kg/m³ would actually be the strict SI formulation, since the kg is the base unit of mass in SI (despite having a prefix!). In any case, it's pretty common in my experience for publications to deviate from strict SI.
– Pont
Jun 30 '14 at 6:57