2 The Roles of Algae in Biogeochemistry

Biogeochemistry is the study of chemical interactions between the atmosphere, hydrosphere (aquatic systems), lithosphere (crustal minerals), and biosphere (living organisms). Algae have played significant roles in Earth’s biogeochemistry for billions of years and continue to do so today. For example, ancient cyanobacteria generated Earth’s first oxygen atmosphere. Ancient algae also produced important fossil fuel deposits and massive carbonate rock formations that reduced atmospheric carbon dioxide levels. Modern algae produce about half of the atmosphere’s oxygen and powerfully influence the cycling of carbon, nitrogen, phosphorus, sulfur, and other elements, affecting other organisms in diverse ways. On the basis of these effects, experts have suggested that algae could be used in engineered systems to produce renewable sources of energy and remove mineral pollutants from water. Some have even proposed that algal growth could be manipulated to mitigate human effects on atmospheric chemistry, helping to moderate climate change. An understanding of algal roles in biogeochemistry is thus important in understanding Earth’s past, as well as present and future global ecological issues.

This chapter begins by discussing algal production of atmospheric oxygen and then covers the roles of algae in global biogeochemical cycles. This background will be useful in understanding interactions that occur between algae and other organisms (the focus of Chapter 3) and the technological applications of algae (Chapter 4).