PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Historical variations in nitrogen source to wetlands.

ELLIOTT, EMILY¹, BRUSH, G.¹, ¹

ABSTRACT- Nitrogen isotopes (¹⁵N/¹⁴N) have been used to elucidate nitrate sources to ecosystems using surface water, ground water, and food web analysis. Previous work has also shown the importance of land use in determining both nitrogen cycling rates and nitrogen isotope ratios of soil, vegetation, and surface waters. This research investigates the use of nitrogen isotopes as indicators of nitrogen source to terrestrial wetlands, over extended temporal and spatial scales. Sediment cores extracted from wetlands throughout the Chesapeake Bay watershed are used to reconstruct changes in sedimentation rates, land cover, and nitrogen source to wetland biota since European settlement (300 years). The ¹⁵N of sedimentary organic matter is used to indicate the relative importance of various nitrogen sources (e.g., human or animal waste, atmospheric deposition). Changes in land use and sedimentation rates are reconstructed using palynology and historical records. Preliminary results from a Coastal Plain wetland show a marked decrease in the ¹⁵N of organic matter with depth, from +7 ‰ in surface sediments, to +2 ‰ at 95cm, likely indicating the influence of anthropogenic inputs (e.g. animal or human waste) in more recent sediments. Although this technique cannot precisely distinguish between sources and fractionating processes that result in similar isotopic ratios (e.g., waste-derived nitrate and enhanced denitrification), it is a useful tool, coupled with palynology and historical research, for understanding changes in nitrogen cycling through complex systems over long temporal scales.

KEY WORDS: nitrogen, isotope, land use, wetlands