You are here:
A DIAGENETIC MODEL FOR SEDIMENT-SEAGRASS INTERACTIONS
Citation:
Eldridge, P M. AND J. Morse. A DIAGENETIC MODEL FOR SEDIMENT-SEAGRASS INTERACTIONS. MARINE CHEMISTRY. Elsevier Science BV, Amsterdam, Netherlands, 70:89-103, (2000).
Description:
The objective of this modeling effort was to better understand the dynamic relationship between seagrass beds and their sedimentary environment using a diagenetic model. The model was developed and optimized for sediments in the Laguna Madre, TX, which is one of the world's largest (~140 km long) negative estuaries with close to 85% of the basin floor covered with seagrass beds. Although high levels of organic matter decomposition occur in the near-surface sediments, the model was unable to produce enough metabolism to satisfy dissolved inorganic carbon (DIC) profiles from organic matter oxidation alone. Carbon isotope analyses of DIC verified that carbonate mineral dissolution contributes more than 50% of DIC added to porewaters during early diagenesis and is especially important betrween ~5 cm. In comparison to unvegetated areas, a common characteristic of seagrass bed sediments was their low sulfide concentrations in the seagrass rootzone. Model simulations indicate that rootzone fluxes of O2 are essential to maintaining non-toxic levels of sulfide and consequently promote healthy conditions for seagrass growth. Further, the model simulations suggest that the position of maximum organic matter metabolism relative to the position of the seagrass rootzone can be used to prodict several properties of seagrass sediment geochemistry. These predictions include the comparative role of anaerobic and aerobic metabolism, the sulfide to ammonium ratio, and the presence or abasences of sulfides in the rootzone. In summary, the results of this model clearly demonstrate a dynamic interaction between seagrasses and diagenetic processes in the underlying sediments. The primary impact of these interactions is to lower sedimentary sulfide concentrations below toxic levels for seagrasses. Such interactions not only modify the sedimentary record but also play an important role influences the health and productivity of seagrasses.