Effects of Annual and Perennial Community Dynamics on Tidal Freshwater Marsh Ecosystem Functioning

Dissertation title: EFFECTS OF ANNUAL AND PERENNIAL COMMUNITY DYNAMICS ON TIDAL FRESHWATER MARSH ECOSYSTEM FUNCTIONING Kristine Noel Hopfensperger, Doctor of Philosophy, 2007 Dissertation directed by: Dr. Katharina A.M. Engelhardt Dr. Sujay S. Kaushal Program of Marine, Estuarine, Environmental Science Tidal freshwater marshes are complex systems with many linkages between the physical, chemical, and biological components. Understanding how the community dynamics of a tidal freshwater marsh affect ecosystem processes may be applicable towards restoring properly functioning wetlands that improve the filtration of excess nutrients and toxins, subsequently improving water quality for downstream areas. The first question explored is why annual species exist in a marsh dominated by perennials. Annual species may exist through facilitation or competition with neighboring species, or through relationships with abiotic variables including elevation and seed rain. Through many field and greenhouse studies, I have determined that competition between annual and perennial species may exist, but abiotic factors are driving the vegetative composition of the marsh. Understanding if annual patches move through time is imperative for relating the plant community to ecosystem processes. To explore the temporal community dynamics, I examined the composition of the belowground marsh seed bank and the aboveground vegetation composition for three years. I have learned that the seed bank partially drives the vegetation composition. Furthermore, additional environmental factors may play a role in determining aboveground vegetation composition. I examined differences in the ecosystem processes of denitrification and its influencing variables among communities dominated by annual species, perennial species, and a mixture of the two. No differences in denitrification rates existed among community types; however organic nitrogen, which is driven by vegetation increased with denitrification rates. Communities readily move through space and time and may influence nutrient cycling in tidal freshwater marshes. Therefore, restoration managers should take into consideration species that maximize nitrogen removal and the variables that control their spatial and temporal movement when planning restoration designs and alternatives. EFFECTS OF ANNUAL AND PERENNIAL COMMUNITY DYNAMICS ON TIDAL FRESHWATER MARSH ECOSYSTEM FUNCTIONING