Phosphorus and Sulfur Cycles

The phosphorus and sulfur cycles move two essential and pollution-relevant elements through rocks, waters, soils, and the atmosphere, with contrasting chemistries that shape ecosystems.

Definition

The global cycling of phosphorus and sulfur through geological, aquatic, terrestrial, and, for sulfur, atmospheric reservoirs.

Scope

This topic covers the sedimentary phosphorus cycle driven by weathering and burial, the redox-active sulfur cycle spanning sulfate, sulfide, and atmospheric sulfur species, and the roles of both elements as nutrients and as agents of pollution and acidification.

Core questions

• Why does phosphorus cycle without a major gaseous phase?
• How does redox chemistry structure the sulfur cycle?
• How do these elements act as nutrients and as pollutants?
• How have humans altered the phosphorus and sulfur cycles?

Key theories

Sedimentary versus redox-driven cycling

Phosphorus follows a slow sedimentary cycle of weathering, uptake, and burial with no significant gas phase, while sulfur cycles rapidly through redox transformations and an active atmospheric component.

Mechanisms

Phosphorus is released by rock weathering, taken up by organisms, and ultimately buried in sediments, often limiting productivity. Sulfur cycles through microbial oxidation and reduction among sulfate and sulfide, volatile emissions of reduced sulfur, and atmospheric oxidation to sulfate that returns in deposition.

Clinical relevance

Phosphorus is a key limiting nutrient and a driver of eutrophication and a finite fertilizer resource, while sulfur chemistry links to acid deposition and to climate through sulfate aerosols.

History

Recognition of phosphorus as the common limiting nutrient and of the microbial sulfur cycle's role in sediments and the atmosphere developed through 20th-century biogeochemistry, with later attention to fertilizer and pollution impacts.

Key figures

• William H. Schlesinger

Seminal works

• schlesinger2013
• vanLoon2017

Frequently asked questions

Why is phosphorus considered a finite resource?

Because it has no gaseous cycle and accumulates in sediments, the readily mined phosphate-rock reserves used for fertilizer are limited and not quickly renewed.