『Abstract
Two methods were used to measure in-stream nitrogen loss in the
Connecticut River during studies conducted in April and August
2005. A mass balance on nitrogen inputs and output for two study
reaches (55 and 66 km), at spring high flow and at summer low
flow, was computed on the basis of total nitrogen concentrations
and measured river discharges in the Connecticut River and its
tributaries. In a 10.3 km subreach of the northern 66 km reach,
concentrations of dissolved N2 were also
measured during summer low flow and compared to modeled N2 concentrations (based on temperature and atmospheric
gas exchange rates) to determine the measured “excess” N2 that indicates denitrification. Mass balance
results showed no in-stream nitrogen loss in either reach during
April 2005, and no nitrogen loss in the southern 55 km study reach
during August 2005. In the northern 66 km reach during august
2005, however, nitrogen output was 18％ less than the total nitrogen
inputs to the reach. N2 sampling results
gave an estimated rate of N2 production that
would remove 3.3％ of the nitrogen load in the river over the 10.3
km northern sub-reach. The nitrogen losses measured in the northern
reach in August 2005 may present an approximate upper limit for
nitrogen attenuation in the Connecticut River because denitrification
processes are most active during warm summer temperatures and
because the study was performed during the annual low-flow period
when total nitrogen loads are small.
Keywords: Nitrogen; Denitrification; Mass balance; Connecticut
River』
Introduction
Materials and methods
Study area
Mass balance
Sample collection and analysis
Mass balance computations
N2 sample collection and analysis
Field sampling for N2
Determining atmospheric gas exchange
Analysis of N2: Ar samples
Analysis of SF6 and bromide
Modeling denitrification
Error analysis
Mass balance computations
N2 analysis and modeling
Results
Mass balance
Gas exchange rates
N2 modeling
Discussion
Acknowledgements
Appendix A - Uncertainty analysis computations
Mass balance
N2 analysis and modeling
Appendix B - Sample calculations for gas transfer rates
References