Stable isotope techniques in food web studies often focus on organic carbon in food sources which
are subsequently assimilated in the tissue of consumer organisms through diet. The presence of nondietary
carbonates in bulk samples can affect their d13C values, altering how their results are
interpreted. Acidification of samples is a common practice to eliminate any inorganic carbon present
prior to analysis. We examined the effects of pre-analysis acidification on two size fractions of
sediment organic matter (SOM) from marine and freshwater wetlands and pure muscle tissue of a
common freshwater invertebrate (Cherax destructor). The elemental content and isotopic ratios of
carbon and nitrogen were compared between paired samples of acidified and control treatments. Our
results showed that acidification does not affect the elemental or isotopic values of freshwater SOM.
In the marine environment acidification depleted the d13C and d15N values of the fine fraction of
saltmarsh and d15N values of mangrove fine SOM. Whilst acidification did not change the elemental
content of invertebrate muscle tissue, the d13C and d15N values were affected. We recommend to
researchers considering using acidification techniques on material prepared for stable isotope
analysis that a formal assessment of the effect of acidification on their particular sample type should
be undertaken. Further detailed investigation to understand the impact of acidification on elemental
and isotopic values of organic matter and muscular tissues is required.