Abstract
Seagrass meadows are a primary structuring feature in many estuaries because of their ability to provide refuge for resident and transient fauna, trap and stabilize sediments, and mediate/regulate diagenetic reactions in sediments. This study focuses on the dynamic interactions between seagrasses and associated sediments and their impact on porewater chemistry. Microelectrode vertical profiling using a non-stripping, gold-mercury amalgam sensing tip made possible the observation of fine-scale (<1 mm) chemical changes, both spatial and temporal, for the important redox reactive elements O₂, Mn²⁺, Fe²⁺, and H₂S, in the sediments. Sediments vegetated with Zostera marina seagrass and nearby (<1 m) unvegetated sediments in Yaquina Bay, OR were analyzed to quantify differences in the vertical distributions of the concentrations of these redox elements. Overall, profiles showed a distinct decrease in concentrations of sulfide relative to dark conditions with exposure to light (200 []E/m²/s). Previous studies of seagrass porewater chemistry have reported average concentrations within porewater sections that are typically on the vertical scale of 1 cm or larger. However, use of microelectrodes to produce approximately an order of magnitude better spatial resolution revealed differences in the chemical composition of porewater at this finer vertical scale. Furthermore, frequent differences in porewater chemistry of similar magnitude to vertical variabilities occurred between different profiles on the order of only a few centimeters apart, demonstrating small-scale lateral heterogeneity. This study highlights the advantages in using high resolution spatio-temporal data for comparisons with one dimensional steady-state diagenetic models. A multi-dimensional model will be necessary for accurately describing processes occurring in seagrass sediments at the relevant spatial scale for biogeochemical processes.
Hebert, Andrew Brian (2002). Microscale effects of light on redox zonation in seagrass sediments. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2002 -THESIS -H43.