Nitrogen and Carbon Transformations in the Chickasawhatchee Swamp

Research Team: Dr. Stephen P. Opsahl (Assistant Scientist), David W. Hicks (Scientist), Christopher Wheeler (Research Technician III), Brian Clayton (Monitoring Technician), and Joanna Jenkins (Research Technician)

Aquatic microorganisms are the major processors of organic and inorganic matter in aquatic ecosystems and significantly improve water quality by remineralizing excess nitrogen and organic carbon, or by transferring it into food webs. Measurements of oxygen consumption within a water sample provide an index of microbiological activity that can be used to gauge the level of microbial processing. Oxygen consumption and, thus, levels of microbial activity vary geographically and temporally. Various levels of nutrient amendments determine whether nitrogen, carbon or phosphorous is limiting the overall activity of microorganisms. Coupled with water budget and water chemistry information, these data and analyses will provide a better understanding of how the various subsystems within the Chickasawhatchee Swamp contribute to improved water quality under different environmental regimes including flooding, drought, and nonpoint source runoff.

Dissolved organic carbon (DOC) in swamps consists primarily of remnants of terrestrial vegetation, and is typically more concentrated than in lakes and rivers due to extensive leaching of abundant litterfall. Recently, molecular-level analysis of DOC for lignin, a biopolymer unique to vascular plants, has proven useful for fingerprinting water from different drainage basins. These distinctions are based on fundamental differences in lignin composition between angiosperms (e.g. deciduous trees), gymnosperms (e.g. pine trees), and grasses. Lignin composition also holds great promise as an indicator of surface water and groundwater interactions. Groundwater typically has low DOC concentrations and is clear, while surface waters have relatively high DOC concentrations with a distinct tea color that is indicative of plant contributions. Measurements of DOC, lignin composition, d¹³C, and UV/visible absorbance properties can be used to characterize the organic matter in different regions within the Chickasawhatchee Swamp. These studies will provide information regarding the natural history of water during its residence within the Chickasawhatchee Swamp, and will also help delineate which subsystems are more important for improving water quality and why.

Following are specific elements of this component of the project:

Collect representative water samples on a periodic basis from the streams, wetlands, and the water-table and Upper Floridan aquifers.
Determine the water chemistry of each water source.
Conduct oxygen consumption experiments using waters collected at different stages of the hydrograph.
Conduct nutrient amendment experiments to determine if carbon, phosphorous, or nitrogen are limiting microorganism activity.
Conduct experiments to determine relative lignin concentrations in the waters within the Swamp.
Determine if surface waters and ground waters of the Chickasawhatchee Swamp can be distinguished based on organic carbon composition.
Develop a conceptual understanding of the origin of groundwater in the Upper Floridan aquifer within the Swamp based on the presence or absence of lignin.

Research in progress, publications forthcoming.

Funded by: The Joseph W. Jones Ecological Research Center