Heather Charles, M.S. Graduate, 2007

Heather.Charles(at)umb.edu

Thesis title: EFFECTS OF WARMING AND ALTERED PRECIPITATION ON PLANT AND NUTRIENT DYNAMICS OF A NEW ENGLAND SALT MARSH Abstract: Salt marshes are highly productive ecosystems, valuable for their contributions in exporting biomass and nutrients to estuaries, storing carbon, protecting coastlines, and filtering pollutants. Current climate models predict substantial increases in average global temperatures and associated regional shifts in precipitation patterns over the next century. Salt marsh structure and function, and consequently ability to continue to provide benefits, may be affected by these changes. I conducted a manipulative experiment to help predict the future for salt marshes, given imminent climate change. Plots were established in a brackish marsh in Massachusetts in two plant communities: Spartina patens/Distichlis spicata and short form Spartina alterniflora. These plant communities experienced one of five climate manipulations: warming via passive open-topped chambers, doubled precipitation, warming and doubled precipitation, extreme drought via rainout shelter, or ambient conditions. Warming increased total aboveground biomass of the S. alterniflora community (24%), but not the S. patens/D. spicata community. Drought also increased total biomass of the S. alterniflora community (53%) and live S. patens (69%), perhaps by alleviating waterlogging of sediments. Warming increased stem heights of S. alterniflora (8%), S. patens (8%), and D. spicata (15%). Photosynthetic rates and flowering phenology showed minimal effects. Decomposition was accelerated by increased precipitation and slowed by drought, particularly in the S. patens/D. spicata community, likely due to increased microbial activity. Warming marginally accelerated decomposition in the S. alterniflora community. Porewater salinity, sulfide, ammonium, and phosphate concentrations showed no treatment effects in either plant community. These results suggest that salt marshes may be resilient to future changes in temperature and precipitation. If production increases or stays at current levels in the future, marshes will have a greater ability to keep pace with sea level rise, however increased decomposition could offset this. Provided that marshes are not inundated by flooding due to sea level rise, increases in biomass and stem heights suggest marshes may continue to export carbon and nutrients to coastal waters, and may be able to increase their carbon storage capability by increasing plant growth under future climate conditions.