Graduate Research Fellows - Rich Gwozdz
NOAA/Padilla Bay NERR Graduate Research Fellow
Sediment accretion in eelgrasses
Richard Gwozdz
M.Sc Candidate, Western Washington University
Huxley College of the Environment
Bellingham, WA
Sedimentation accretion in an eelgrass dominated estuary and implications for estuarine sustainability: a field and modeling study.
BACKGROUND
Seagrasses affect seafloor elevation in several ways. The leaves of plants in large seagrass meadows slow the movement of water around the plants, causing suspended sediments to drop out of the water column. Sediments then collect around the base of plants where they are often trapped by roots and rhizomes. Organic material consisting of root, rhizomes, and detrital organisms also accumulates on this surface. This accumulation of organic material further contributes to sediment accretion.
Fig. 1. Zostera marina and Zostera japonica in Padilla Bay, WA
Current sediment accretion rates in Padilla Bay seagrass beds (Fig. 1) may not be sufficient to maintain seafloor elevation given predicted increases in sea-level rise. A proposed diversion of Skagit River floodwater into the Swinomish channel, which discharges directly into the Padilla Bay, may alter current rates of sediment delivery. The geological and biological consequences of large pulses of freshwater and sediment on Padilla Bay seagrass beds are unknown at this time.
This research is designed to answer the following questions:
- How fast are sediments accreting in Padilla Bay eelgrass meadows?
- How have accumulation rates changed over time in Padilla Bay and are there different rates of accretion in Zostera marina compared to Zostera japonica at similar tidal elevations?
- How does seagrass growth and belowground biomass production contribute to rates of sediment accretion?
This research will contribute to an existing computer model of Zostera growth and modify an existing relative elevation model of Padilla Bay mudflats. The development of these models will be used to investigate the effects of sea level rise, elevation gain, and sedimentation rates on the maintenance of Padilla Bay seagrass beds. Further application of these models may be used to predict how environmental alterations, such as floodwater diversions, eutrophication, and proposed management plans may alter seagrass habitat.
Fig. 2. Taking measurements at Zostera japonica sites.
METHODS
Study sites will be established within a Zostera japonica meadow (invasive Japanese eelgrass) and within a Zostera marina meadow (native eelgrass) at similar tidal locations (Fig. 2). Sedimentation rates will be measured monthly for one year using filter paper traps. Mineral and organic sedimentation will be measured from these samples as well. Historic sedimentation rates will be determined using 137 Cs radioactive dating of sediment in cores. Additional analyses of these cores include measurements of bulk core density, percent organic matter by weight, percent of mineral matter by weight, and distribution of volume. Below-ground net primary productivity of eelgrass will be measured using core samples taken seasonally over a one-year period. Above-ground productivity will be measured in August to verify previous research in Padilla Bay for use in the model.
Upon collection of all field data, a model of Zostera spp. productivity in Padilla Bay will be constructed, initialized, and calibrated and sensitivity analyses will be conducted.
PROJECT SIGNIFICANCE
This study will address habitat conservation issues by illustrating the effects of sea level rise, elevation gain, and sedimentation rates on the maintenance of Padilla Bay seagrass beds. Models developed from this research will be valuable for assessing management programs designed to sustain seagrasses within estuaries.
Fig. 3. Rich Gwozdz in Padilla Bay near his study area.
BIOGRAPHICAL INFORMATION
Rich Gwozdz is a Master's student in the graduate program at Huxley College of the Environment at Western Washington University (Fig. 3). His graduate professor is Dr. John Rybczyk in the Department of Environmental Science at Western Washington University. Rich is a recipient of a Padilla Bay NERR Graduate Research Fellowship awarded through the Estuarine Reserves Division of NOAA. For more information, or questions about this research, contact the Reserve.