Jg. Cooke, NUTRIENT TRANSFORMATIONS IN A NATURAL WETLAND RECEIVING SEWAGE EFFLUENT AND THE IMPLICATIONS FOR WASTE TREATMENT, Water science and technology, 29(4), 1994, pp. 209-217
Citations number
17
Categorie Soggetti
Water Resources","Environmental Sciences","Engineering, Civil
The processes influencing nutrient (phosphorus and nitrogen) renovatio
n in a natural wetland which had received oxidation pond effluent for
twelve years were studied, and compared with current literature percep
tions. Mass transport studies showed that 30-70% of the influent P was
removed from the water column, which was much greater than published
values suggest could be predicted for this highly loaded (approximatel
y 34 g p m-2 y-1) system. Sediment traps studies showed that depositio
n of particulate P immediately downstream of confluences with arms of
the wetland not impacted by sewage effluent (natural wetlands) was the
dominant cause of P removal. Separation of the deposited-P into chemi
cally definable fractions along with studies on the water chemistry, s
uggested that P deposition was associated with iron-organic complexes
contributed dominantly from the natural wetlands. Considerable spatial
and temporal heterogeneity was also demonstrated for nitrogen transfo
rmations. During summer most of the influent-N was in nitrate form whi
ch was all transformed during passage through the wetland. Isotope (N-
15) dilution studies indicated that approximately 60-70% was denitrifi
ed, 25-35% converted to ammonium (dissimilatory reduction), and 5-10%
assimilated. For most of the year, however, influent N was mainly in r
educed forms. Despite this, significant quantities of nitrate were exp
orted from the wetland especially at higher flows in spring-early summ
er. Assays on the sediment showed that there was a marked increase in
nitrification activity at the confluence with natural wetlands. It is
suggested that marked changes in sediment redox potential at these con
fluence sites provide ideal conditions for nitrification of sorbed amm
onium which is subsequently flushed from the system in 'flood events'.
The distribution and type of nutrient processing observed in this wet
land are attributable to its configuration. The implication of these r
esults to the sustainability of nutrient renovation in wetland treatme
nt systems is discussed.