Seasonal variation in phosphorus removal processes within reed beds - Mass balance investigations

  • Headley T
  • Huett D
  • Davison L
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Abstract

The phosphorus (P) removal processes in two pairs of High and Low
Loaded reed beds were investigated during five periods within a 27-month
study. The uptake/release of P was measured in seven mass balance
compartments. With the exception of the first year of operation,
the reed beds consistently removed over 96% of the influent P load,
with total phosphorus (TIP) concentrations being reduced from 0.5
mg/L to generally less than 0.005 mg/L across the range of loading
rates and seasons studied. During the first year, uptake by Phragmites
australis accounted for greater than 75% of P removed, and was equally
distributed between above and below-ground biomass. During the second
and third years, three seasonal stages were identified in the uptake
and cycling of P by P. australis. A period of rapid above-ground
growth and uptake occurred during spring fuelled partly by P reserves
accumulated in rhizomes during the previous year. During summer,
uptake by above-ground biomass was governed by the influent P loading
rate, while the amount of P held in below-ground biomass remained
relatively stable. During autumn and winter, P appeared to be translocated
from senescent shoots to reserves in the rhizomes. Approximately
85% of the below-ground biomass P occurred in the top 20 cm of the
substrate. Gravel fixation increased in importance from 12% in the
first year to approximately 30% of P removed in the second year,
with a highly significant correlation between the influent P loading
rate and P fixed by the gravel. The weakly-bound P fraction from
a sequential extraction was the dominant form of P fixed by the gravel.
HCl extracts were inappropriate for the examination of sorption processes
as they dissolved large amounts of mineral P from within the basaltic
gravel. The bottom 30 cm of the substrate became the most important
site for gravel fixation during the second year. Incorporation of
P into the detritus/microbiota/other compartment increased after
the first year to become one of the most important P removal processes,
probably consisting mainly of leaf litter and slowly accreted organic
sediments.

Author-supplied keywords

  • Mass balance
  • Phosphorus removal
  • Reed bed

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  • ISSN: 02731223
  • PUI: 37368917
  • SGR: 0242552260
  • SCOPUS: 2-s2.0-0242552260

Authors

  • T. R. Headley

  • David O. Huett

  • L. Davison

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