Bioturbation has a limited effect on phosphorus burial in salt marsh sediments

It has been hypothesized that the evolution of animals during the Ediacaran-Cambrian transition stimulated the burial of phosphorus in marine sediments. This assumption is centrally based on data compilations from marine sediments deposited under oxic and anoxic bottom waters. Since anoxia excludes the presence of infauna and sediment reworking, the observed differences in P burial are assumed to be driven by the presence of bioturbators. This reasoning however ignores the potentially confounding impact of bottom-water oxygenation on phosphorus burial. Here, our goal is to test the idea that bioturbation increases the burial of organic and inorganic phosphorus (P-org and P-inorg, respectively) while accounting for bottom-water oxygenation. We present solid-phase phosphorus speciation data from salt marsh ponds with and without bioturbation (Blakeney salt marsh, Norfolk, UK). In both cases, the pond sediments are exposed to oxygenated bottom waters, and so the only difference is the presence or absence of bioturbating macrofauna. Our data reveal that the rate of P-org and P-inorg burial are indistinguishable between bioturbated and non-bioturbated sediments. A large terrestrial fraction of organic matter and higher sedimentation velocity than generally found in marine sediments (0.3 +/- 0.1 cm yr(-1)) may partially impact these results. However, the absence of a clear effect of bioturbation on total P burial puts into question the presumed importance of bioturbation for phosphorus burial.

Automated summary

The hypothesis that animal evolution during the Ediacaran-Cambrian transition led to increased phosphorus burial in marine sediments is based on data from oxic and anoxic environments. However, this study found that bioturbation did not significantly impact phosphorus burial in oxygenated bottom waters, challenging the assumed importance of bioturbation.