Investigating Microbial Nitrogen Cycling in the Northwest Arm, Halifax Harbour and in Wastewater Treatment Facilities Using Natural Abundance Stable Isotopes in Nitrate, Nitrite, and Ammonium.

Abstract

Using a 3-year time series of concentrations of nitrate, nitrite and ammonium and natural abundance stable isotopes in nitrate, this project identifies seasonal trends and major sources of fixed nitrogen to the Northwest Arm, Halifax Harbour. The highest nitrate concentrations were at Horseshoe Island during late winter and early spring from accumulated atmospheric deposition sourced nitrate on melting ice cover. Isotopic measurements were also taken at three different wastewater treatment facilities primary, secondary, and tertiary treatment levels. There was no significant change in influent (δ15NNH4 = 8-10‰), and effluent (δ15NNH4 = 7-9‰) in primary treatment. δ15NNH4 in secondary effluent measured between 15-22‰ seasonally and in tertiary treatment, effluent δ15NNH4 measured 46‰ ± 8‰. In secondary treatment, effluent δ15NNO3 measured between 10‰ to 11‰ seasonally, and δ18ONO3 between 2‰ to 3‰. In tertiary treatment δ15NNO3 measured 14-19‰ seasonally and δ18ONO3 between -2‰ and -15‰.