Carbon Isotope Records From Wetland Plants, and Implications for Paleohydrological Reconstructions

The carbon isotopic record of temperate tree-rings, are controlled by changes in water stress, which causes an increase in water-use-efficiency that results in a relative carbon isotope enrichment. Hence a relative decrease in rainfall during the growing season, would result in a water-stressed condition. However, plants growing in wetland environments do not necessarily respond in a similar manner. In contrast, to terrestrial plants, initial carbon isotopic results indicated that wetland plants such as pond cypress have positive relationship with precipitation. One important plant in the greater Everglades ecosystems is sawgrass ( Cladium jamaicense), which comprises an important part of the regional ecosystem. To calibrate and understand the isotopic changes that may potentially be related to changes in water level, which corresponds to hydroperiod in a temporal manner, mesocosm experiments were used to grow these plants at different water levels. 24 mesocosms were randomly assigned 4 different water treatments to simulate changes in hydroperiod and water depth, similar to the typical Everglades wet season and dry season cycle. Our initial results from this work show a strong correlation between variations in water depth and plant carbon isotope values in the shallow water treatments vs. the deeper water treatments. Further analyses are presently underway to compare assimilation with the collected carbon isotopic data. These results confirm the observations from the cypress work, and set the stage for using carbon isotopes from preserved OM and/or biomarkers to reconstruct changes in water level from wetland settings.