Resumen de Microbial Denitrification and the Hardy-Weinberg law

Jan Graffelman , R. De Wit

• An application of compositional data analysis in the fields of bio-geochemistry and microbial ecology is presented. In the surface layer of aquatic sediments, bacterial processes contribute to the conversion of bound nitrogen into nitrogen gas. These natural processes represent a way to reduce the negative impacts of nutrient over-enrichment (eutrophication) and, therefore, have been the subject of many biogeochemical and ecological studies. By using isotope tracking experiments with 15N the contribution of the different bacterial processes to the nitrogen conversion can be investigated. Massspectrometry measurements of nitrogen gas produced by incubated sediments samples produces compositional data sets consisting of 3-part compositions of nitrogen gas containing 28N2, 29 N2 and 30N2. Under the null hypothesis of 100% classical microbial denitrification, these 3 parts are expected to occur in Hardy-Weinberg proportions. We use tools from compositional data analysis such as ternary diagrams and isometric log-ratio transformations of the data to test this hypothesis. We found evidence that classical denitrification, although probably predominant, coexisted with other processes like Anammox coupled to ammonium oxidizers, and had to reject the Hardy-Weinberg law as a model for the data.