APA (7th ed.) Citation

Sigel, A., Sigel, H., & Sigel, R. K. O. Biogeochemical cycles of elements.

Chicago Style (17th ed.) Citation

Sigel, Astrid, Helmut Sigel, and Roland K. O. Sigel. Biogeochemical Cycles of Elements.

MLA (8th ed.) Citation

Sigel, Astrid, et al. Biogeochemical Cycles of Elements.