The seafloor plays a critical role in the elemental cycling within shallow water ecosystems. An ubiquitous feature in these aquatic sediments is the sequential depletion of terminal electron acceptors (oxygen, nitrate, Mn & Fe oxides, sulfate). However, particularly in the coastal ocean, with abundant macrofauna or wave-induced mixing, sediment biogeochemistry can be highly dynamic and heterogeneous.

irrig sm
Burrowed sediment-water interface: core top and simulated oxygen distribution in a burrow

Macrofaunal Effects on Benthic Exchange Fluxes

Although the coastal benthos has been relatively well studied, the quantitative role of infauna in modifying critical ecosystem services such as nutrient cycling remains still poorly constrained. This stems largely from difficulties in scaling biogeochemical dynamics observed at the plot (sub-mm - m) scale to the larger framework of coastal ecosystems. We quantify small-scale dynamics of infaunal activities and their ecological interactions under controlled conditions and incorporate these data into models of sediment biogeochemistry (click here for more information). Ongoing work also studies the effect of early diagenesis and biological mixing on N isotopic signatures. 

Iron Dynamics in Soils

Fe cycling has been implicated in a wide array of soil chemical processes including the bioavailability of nutrients (e.g., sorption of phosphate), transport and toxicity of pollutants (e.g., sorption of speciation of heavy metals) and degradation of carbon compounds. In collaboration with A. Thompson (UGA) and M. Scherer (U. Iowa), we investigate changes in soil quality related to soil iron (e.g., P availability, carbon transformation rates, etc.) under oscillating redox conditions, as can occur when rainfall or irrigation results in intermittent saturation and draining of microsites. 

To quantify the impact of redox oscillations on a wide range of soil microbial, nutrient, contaminant and physico-chemical properties, we evaluate Fe transformation rates and Fe mineral composition under a range of redox oscillation frequencies and develop numerical models to describe the Fe, C and P response to oscillations and changes in oscillation frequency.