Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Environmental conditions may positively or negatively influence production, reproduction, and restoration of submerged aquatic vegetation (SAV). As SAV populations decline, it is important to understand the potential impacts of the environment on the natural processes of reproduction. The objectives of this study are to provide fundamental information on sexual reproduction in a dominant species of freshwater SAV, Vallisneria americana, in the Chesapeake Bay observe the changes in environmental conditions in an established V. americana bed over an entire growing season (April-October), quantify the effects of similar environmental conditions on V. americana seed germination under controlled laboratory conditions, and finally to synthesize this information in order to develop a series of criteria for V. americana restoration in the Chesapeake Bay. Light, dissolved oxygen, temperature, salinity, sediment composition, V. americana production (biomass, density) and reproduction (flowering) were measured in a persistently vegetated SAV bed located in a tidal freshwater tributary to the Chesapeake Bay over the 2004 growing season. In addition, the effects of these same parameters on germination of V. americana seeds were quantified separately under controlled laboratory conditions. Production of V. americana biomass in Nanjemoy Creek increased significantly when water temperatures increased above a threshold of 25 ºC. Flowering occurred during periods of peak biomass (August and September) and resulted in the production of up to 71 seed pods m-2 at the end of the growing season. Despite the potential production of thousands of seeds m-2, < one percent were retained in the seed bank and remained viable after a period of 12 months. Germination of V. americana seeds was enhanced (greater overall germination and shorter time to germination) under oxygenated conditions, at temperatures > 22 ºC, at salinities of 0 psu, and when sediments were composed of ≤ 3 percent organic content and > 40 percent sand. Light (< 160 μmol m-2 s-1) and burial depth (down to 10 cm) had no significant effect on germination. Based on the synthesis of field and laboratory data, criteria for restoration of V. americana using seeds in Chesapeake Bay should include temperatures greater than 13 ºC, salinities ≤ 5 psu, and sediment containing ≤ 3 percent organic content and > 40 percent sand. This research provides the initial steps to determine which environmental factors affect germination of V. americana seeds and may increase the efficiency of current restoration practices for this species and provide a mechanism for increased success of current and potential larger scale projects.



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