Interactions of Thalassia testudinum and sediment biogeochemistry in Santa Rosa Sound, NW Florida

Abstract

Thalassia testudinum belowground biomass weights, leaf weights, leaf growth rates, areal shoot densities (m⁻²), and leaf C:N:P ratios were compared to a set of biogeochemical parameters to gain information on seagrass–sediment interactions that may influence seagrass growth. Data were compiled from three surveys conducted in Santa Rosa Sound, located in northwest Florida, at three different meadows in sequential years. Biomass measurements and leaf growth rates decreased between stations along transects from shallow to deeper water. Belowground biomass weights decreased and leaf C:P ratios increased with temperature reflecting a seasonal growth pattern. The T. testudinum parameters were highly correlated with each other. Sulfate reduction rates (at times exceeding 1000 nmol ml⁻¹ day⁻¹) were among the highest recorded for seagrass beds with temperature accounting for 79% of the variation. Even though sulfate reduction rates were high, total Fe:reduced S ratios indicated sufficient Fe to account for all reduced S as pyrite. Sediment Fe, C, N, and organic P concentrations increased with sediment depth, whereas inorganic P decreased with depth, suggesting burial of organic P and root uptake of inorganic P. Leaf C:N:P ratios indicated P-limited growth for two surveys. NH₄ ⁺ was detected in water above the sediment surface during some surveys demonstrating T. testudinum meadows at times may serve as sources of inorganic N to the water column. Plant parameters correlated with concentrations of sediment organic C and N, Fe, S, and porewater NH₄ ⁺. These results highlight the importance of the organic matter and Fe contents of sediments to seagrass growth.

Keywords:

• Biogeochemistry
• seagrass
• sediments
• sulfate reduction

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

We thank the GED field and dive teams for their assistance with sample collections; Jed Campbell, Will Davis, Peggy Harris, Becky Hemmer, Deborah Santavy, and Sherry Vickery; Brad Blackwell, and George Smith for additional technical support; and Paul Soderlind for preparation of figures. The information in this document has been funded wholly or in part by the US Environmental Protection Agency. It has been subjected to review by the National Health and Environmental Effects Research Laboratory and approved for publication. Approval does not signify that the contents reflect the views of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. This is contribution no. 1344 from USEPA NHEERL Gulf Erology Division.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark