Degradation of dissolved organic matter in permeable sediments

Degradation of dissolved organic matter in permeable sediments Lindsay Chipman, Markus Huettel, Katie Higgs, Matt Laschet ABSTRACT: Coastal seawater is characterized by high concentrations of dissolved organic matter (DOM) and is pumped by bottom currents through the upper layers of permeable sand sediments that cover large areas of the continental shelf. Within these sediments, DOM is exposed to enzymes of a large and diverse microbial community that colonize the sand grains. We tested the hypothesis that a fraction of the DOM is degraded while passing through the sediment. Through a combination of in-situ measurements in the Gulf of Mexico and laboratory column reactor experiments, we examined the role of filtration processes on DOM degradation. Our results show that filtration through permeable shelf sediments promotes the degradation of DOM. HYPOTHESIS: DOM is degraded as it flows through sediment by microbes that inhabit the sand grains. Lab Work Field Work SITES: Gulf and Bay sides of St. George Island, FL Gulf of Mexico FLUME EXPERIMENT: Degradation of phytoplankton at the surface leads to transport of DOC into the sediment where water is forced into the bed Apalachicola Bay TIME SERIES: Compares DOC concentrations of the water column and pore water in an exposed and a sheltered site COLUMN REACTOR EXPERIMENTS: DOC is degraded by the microbial community present in natural sediment. Degradation rates depend on pore water flow. DIC produced from degradation of DOC in water and in sediment DOC degradation in sterile and natural sediment CONCLUSIONS: Our results show that filtration through permeable shelf sediments promotes the generation and degradation of dissolved organic matter and makes nearshore sands in the Gulf of Mexico a biocatalytic converter for DOM. Depending on the season, these sediments can act as sources or sinks of DOM. . DOC concentrations in the water DOC in pore water column at the bay and gulf sites ADVECTION CHAMBER INCUBATIONS: To show the seasonal dynamics of the DOC fluxes, and to demonstrate their dependency on the environmental settings. Under nutrient-limited conditions, phytobenthos produced large quantities of DOM that caused positive DOM fluxes in late summer during the day. Acknowledgements: Dr. Thorsten Dittmar, Dr. David Thistle, Dr. Yang Wang, Dr. Yingfeng Xu, Dr. William Cooper, Cooper Lab, Dr. Kostka, Kostka Lab