w(Abstract)
@Diffusive equilibrium in thin films was used to study the cycling
of phosphorus and nitrogen at the sediment-water interface in
situ and with minimal disturbance to redox conditions. Soluble
reactive phosphate (SRP), nitrate, nitrite, ammonium, sulfate,
iron, and manganese profiles were measured in a rural stream,
12 m upstream, adjacent to, and 8 m downstream of a septic tank
discharge. Sewage fungus adjacent to the discharge resulted in
anoxic conditions directly above the sediment. SRP and ammonium
increased with depth through the fungus layer to environmentally
significant concentrations (440 and 1800ƒÊM, respectively) due
to release at the sediment surface. This compared to only 0.8ƒÊM
of SRP and 2.0ƒÊM of ammonium in the water column upstream of the
discharge. Concomitant removal of ammonium, nitrite and nitrate
within 0.5 cm below the fungus-water interface provided evidence
for anaerobic ammonium oxidation (anammox). gHotspotsh of porewater
SRP (up to 350ƒÊM) at the downstream site demonstrated potential
in-stream storage of the elevated P concentrations from the effluent.
These results provide direct in situ evidence of phosphorus and
nitrogen release from river-bed sediments under anoxic conditions
created by sewage-fungus, and highlight the wider importance of
redox conditions and rural point sources on in-stream nutrient
cycling.x
Introduction
Experimental section
@Study site
@Reach characterization
@DET probes
Results and discussion
@Reach characterization
@DET gel profiles
@Wider implications
Acknowledgments
Supporting information available
Literature cited