Transport dynamics in a sheltered estuary and connecting tidal straits: SF6 tracer study in New York Harbor

In July 2002, approximately 0.9 mol of sulfur hexafluoride (SF6) was injected into Newark Bay, NJ, a 14 km2 estuary that forms part of New York Harbor, to investigate circulation, mixing, and the transport and fate of solutes. The SF6 tracer was observed over 11 consecutive days using a high-resolution measurement system. Total tracer mass in the sheltered waters declined quasiexponentially at a rate of 0.29 +/- 0.03 d(-1). Air-water gas exchange was estimated to account for 56% of tracer mass loss, upon the basis of wind speed/gas exchange parametrizations. Large-scale tidal transfer of solutes through the Kill van Kull strait (7 km long) caused net seaward flushing contrary to the apparent residual circulation. Seaward transport via the Arthur Kill strait (20 km long) appeared to depend on longitudinal dispersion, residual circulation, and freshwater discharge and was approximately 1 order of magnitude lower. The loss rate due to flushing alone was 0.13 +/- 0.02 d(-1), indicating a mean residence time for water and solutes in Newark Bay of approximately 8 days (without gas exchange). The experiment provides direct visualization of the transport of a released contaminant, and suggests a relationship between the length and configuration of tidal straits and related transport of solutes.