Denitrification is a microbial process that takes place on and within sediment and results in the transformation of dissolved inorganic nitrogen to nitrogen gas (N2), which is subsequently lost to the atmosphere. In coastal waters denitrification is an important pathway for the removal of excess nitrogen. Rates of denitrification are typically quantified using either in situ benthic chambers or sediment cores incubated in the laboratory. This study assesses if these two approaches give similar fluxes and denitrification efficiencies. This dataset gives fluxes of: i) dissolved oxygen (DO); ii) nitrogen gas (N2); iii) dissolved inorganic nitrogen (DIN); iv) nitrate (NO3-); v); nitrite (NO2-) and vi) ammonium (NH4+) between the sediment and the water column. Results are obtained using core cylinders incubated in the laboratory and in situ benthic chambers. Fluxes are expressed as µmol m-2 of seafloor surface day-1. Denitrification efficiency is also reported and represents the flux of N2 as a proportion of the total flux of DIN. Studies were carried out in Port Phillip Bay at Clifton Springs and Williamstown, Victoria in March and May 2004, respectively. The flux of oxygen, ammonium, nitrate, nitrite and the denitrification efficiency was found to differ between in situ benthic chambers and laboratory incubated sediment cores. Additional experiments were conducted to assess if the abundance of macrofauna in sediments of core cylinders and benthic chambers differed; and ii) if physical disturbance associated with the collection and transport of core cylinders could account for the observed differences.
Denitrification is an important microbial process that results in the removal of nitrogen from marine systems. This study was carried out to assess if two common methods for measuring rates of denitrification in marine systems produced comparable results.
This research was supported by an Australian Research Council Linkage grant.
Various people assisted with the collection and processing of samples including A.O'Brien, J. Ahern, L. Barr. and M. Reardon.
Benthic chambers were 0.4m lengths of clear polycarbonate pipe (~ 0.29m diameter) sealed at one end. The open end of the tube was pushed into the sediment to a depth of ~ 0.1m, enclosing ~ 20L of overlying water. Core cylinders (0.11 m diameter) were 0.5m in length and made from clear perspex. Core cylinders were pushed into the sediment to a depth of 0.4m and the top sealed with a removable cap, enclosing 1L of overlying water. The top sections of both the benthic chambers and core cylinders were equipped with: i) a sampling tube; ii) pressure/water compensating tube; iii) pulsed dissolved oxygen meter and iv) a mixing paddle.
a. Dataset: This dataset gives fluxes of i) dissolved oxygen (DO); ii) orthophosphate (PO4); ii) NO2-3, iv) nitrite (NO2-); v) ammonium (NH4+); vi) orthosilicate (SiO4); vii) nitrate (NO3-); viii) nitrogen gas (N2) and ix) dissolved inorganic nitrogen (DIN) between the sediment and water column. Fluxes were measured within cores cylinders incubated in the laboratory and in situ benthic chambers. Fluxes are expressed as µmol m-2 of seafloor surface day-1. Denitrification efficiency (DE), representing the percent DIN that was transformed to N2 is also given for cores and chambers at each study site. Studies were carried out in Port Phillip Bay at Clifton Springs and Williamstown, Victoria in March and May 2004, respectively. A full description of the core cylinders and benthic chambers are given in "collectionHardware". During each study, in situ chambers were embedded into the sediment to a depth of 0.1m at five random locations. Water samples were collected from benthic chambers ~ 0.5h after installation and a further sample collected ~ 20h later, additional water samples were also collected outside each chamber as a control. Core cylinders were embedded into the sediment next to chambers to a depth of 0.4m and subsequently transported to the laboratory for incubation. Dissolved oxygen levels were monitored at regular intervals within each chamber and core cylinder. Water samples were analysed for N2, DIN, NO3-, NO2- and NH4+ and fluxes calculated.
Data files: MacreadieCliftonSpringsFluxCalculations and MacreadieWilliamstownFluxCalculations.
Columns in each dataset are: Technique (Chambers, Cores); Sample source (Ambient, Chamber (1,3, 5, 6) or Core (1,3,5,6)); Incubation time (20hrs, 45hrs);
The remaining data columns give the initial (C1) and final (C2) concentration (µmols l-1), as well as fluxes (µmols m-2 of seafloor surface day-1) for: PO4, NO2-3, NO2-, NH4+, SiO4, NO3-, N2, and DIN. The final column gives the calculated Dentrification Efficiency (DE). For O2 only the change in concentration between T1 and T2 are reported.
For more details on the methods and experimental design see Macreadie, P.I., Ross, D.J., Longmore, A.R. and Keough, M.J. (2006). Denitrification measurements of sediments using cores and chambers. Marine Ecology Progress Series, 326: 49-59.
b. Scale: Concentrations at T1 and T2 are expressed as µmol per L. Fluxes are expressed as µmol m-2 of seafloor surface day-1
c. Media Types: Not Relevant
d. Date: March 2004; sampling at Clifton Spring; May 2004, sampling at Williamstown
e. Dates of various parts of the process:
2. Processing Steps:
a. Intermediate processing steps (after data capture):
Fluxes were calculated using the following relationship
Flux = (?C/ ?T) x (V/A)
?C is the change in concentration between the two sampling events
?T is the time in days between the two sampling event
V is the volume of water (l) enclosed by the apparatus
A is the area of seafloor enclosed by the apparatus in m2
Denitrification efficiency (DE) was estimated as the proportion of N2 fluxed into the water column compared to the total concentration of inorganic nitrogen, and was calculated using the following formula:
DE = (N2/ (N2 + DIN) x 100
N2= moles of nitrogen fluxed into the water column
DIN= moles of dissolved inorganic nitrogen fluxed into the water column
b. Methods used to generate final product: Not Relevant