Use of an urban fjord as a living laboratory for understanding impacts of hypoxia on nitrous oxide production and iodine cycling, and for testing of mitigation strategies.

Abstract

The Bedford Basin is a a 70 m deep, seasonally stratified and hypoxic semi-enclosed fjord on the West Atlantic coast (Nova Scotia, Canada). The basin is connected to the Atlantic Ocean (Scotian Shelf) via a narrow 20 m deep sill that restricts exchange and mixing of surface and bottom waters. Bedford Basin is located in an urban setting (Halifax) and receives considerable wastewater input. The Basin has benefitted from a weekly multidisiciplinary time-series of physical, chemical and microbiological data over several decades. Over the past decade, the intensity of hypoxia has increased due to warmer winters and reduced convective renewal of the deeper water. The presentation will highlight understanding of physical-microbiological-chemical interactions, and sediment-water exchanges, that affect the concentration and speciation of nitrogen and iodine species in relation to variable levels of oxygen. A focus will be on interannual and short-term variability in production of nitrous oxide and iodide in relation to variations in oxygen, microbial diversity and sediment-water exchange. The potential of coastal basins to act as living laboratories for  studying complex, redox-dependent processes through comprehensive, multidisciplinary, time-series study will be demonstrated. The closely related potential of urban fjords to act as testbeds for evaluation of emerging approaches to the mitigation of coastal hypoxia will be emphasized.