Assessment of sample processing methods for stable isotope analysis of aquatic food webs

Abstract

Stable isotope analysis is commonly used in studying flows of mass and energy through food webs and trophic relationships in aquatic ecosystems. However, different sample processing methods can influence the measurement of these stable isotope rates, which may result in errors in the resulting food web models and the comparing results between different studies. In particular, errors may result from four different sources, that is, preservation, separation, acidification and dehydration. The collectted particulate/dissolved organic matter, bacteria, zooplankton, algae, hydrophyte, fish and zoobenthos were rinsed with de-ionized water to clean off epibionts, and then stored at -20 degree C. Acidification by adding 1mol/L HCl drop-by-drop was needed for carbon isotope analysis in samples of sediment organic matter, invertebrates with calcareous structures, and plankton. For nitrogen analysis, acidification should be avoided. Finally, dehydration was required by the analytical methods used in the determination of isotopic abundance. Both freeze-drying and drying at 40-70 degree C were acceptable. In addition, materials preserved with formalin and ethanol stocks was suitable for current ecological applications of isotopic analysis and open up the possibility to reconstruct food webs and biogeochemical changes at scales of tens or hundreds of years. In this review we summarize different sample processing prior to the analytical determination of stable isotope ratios and the influence mechanism of some processing methods, which are fundamental for further methodology research.