UVM Theses and Dissertations
Format:
Print
Author:
Hayden, Melissa J.
Dept./Program:
Plant and Soil Science
Year:
2004
Degree:
M.S.
Abstract:
Atmospheric deposition of nitrogenous compounds to natural ecosystems has the potential to significantly alter ecosystem functioning and species composition. These effects can be especially deleterious in ecosystems in which species are adapted to a low nutrient regime, such as ombrotrophic peatlands. By evaluating the fate of additional nitrogen inputs to these systems, it may be possible to estimate the threat of increased nitrogen loadings to these delicate natural areas. This study utilized the acetylene inhibition technique to estimate the relative importance of denitrification in nitrogen removal from a primarily ombrotrophic peatland ecosystem. Rates were measured using both an in situ field chamber technique and an ex situ soil core technique.
Net nitrification was also measured in an attempt to evaluate this process as a source of nitrate for denitrifiers. Estimates of mean rates of denitrification ranged from -2.76 to 84.0 ng N₂O-N cm-³ hr-¹ (roughly equivalent to -150 to 4800 ug N₂O-N m-² hr-¹) using the acetylene-amended core technique and from -8.30 to 5.98 ug N₂O-N m-² hr-¹ using the acetylene-amended chamber technique. It is likely that core denitrification rates were elevated over natural field levels due to the effects of disturbance on substrate availability, and that chamber rates, while providing a more accurate estimate of denitrification rates, were low due to diffusional constraints on acetylene and N₂O in this water-logged peat soil.
. Rates of net nitrification could not be accurately determined due to the preponderance of nitrate concentrations measured below the detection limit of the analytical instrument. There was very little free nitrate available in peat extracts or in pore water in this peatland. This in combination with the low rates of net nitrification and the low rates of in situ denitrification measured in this study, suggests that inorganic N turnover in this wetland is low, and organic N may be the dominant form of nitrogen in this peatland. Results showed that nitrate was a limiting factor for denitrification in this peatland, with mean rates from nitrate-amended cores ranging from 13.1 to 260 ng N₂0- N cm-³ hr-¹, and it is expected that increases in nitrogen loadings will increase denitrification rates in this ecosystem.
Net nitrification was also measured in an attempt to evaluate this process as a source of nitrate for denitrifiers. Estimates of mean rates of denitrification ranged from -2.76 to 84.0 ng N₂O-N cm-³ hr-¹ (roughly equivalent to -150 to 4800 ug N₂O-N m-² hr-¹) using the acetylene-amended core technique and from -8.30 to 5.98 ug N₂O-N m-² hr-¹ using the acetylene-amended chamber technique. It is likely that core denitrification rates were elevated over natural field levels due to the effects of disturbance on substrate availability, and that chamber rates, while providing a more accurate estimate of denitrification rates, were low due to diffusional constraints on acetylene and N₂O in this water-logged peat soil.
. Rates of net nitrification could not be accurately determined due to the preponderance of nitrate concentrations measured below the detection limit of the analytical instrument. There was very little free nitrate available in peat extracts or in pore water in this peatland. This in combination with the low rates of net nitrification and the low rates of in situ denitrification measured in this study, suggests that inorganic N turnover in this wetland is low, and organic N may be the dominant form of nitrogen in this peatland. Results showed that nitrate was a limiting factor for denitrification in this peatland, with mean rates from nitrate-amended cores ranging from 13.1 to 260 ng N₂0- N cm-³ hr-¹, and it is expected that increases in nitrogen loadings will increase denitrification rates in this ecosystem.