Pm. Gale et al., PHOSPHORUS RETENTION BY WETLAND SOILS USED FOR TREATED WASTE-WATER DISPOSAL, Journal of environmental quality, 23(2), 1994, pp. 370-377
Wetlands function as buffers for nutrients loaded from terrestrial eco
systems through drainage and surface discharges. The objectives of our
study were to (i) determine the P retention capacity of representativ
e wetland soils being used for disposal of treated wastewater and (ii)
relate P retention characteristics to selected physicochemical proper
ties to evaluate likely mechanisms of P removal in the soils. Intact s
oil cores (0-40 cm) and bulk soil samples (0-15 cm) were collected fro
m a system of natural and constructed wetlands currently being used fo
r disposal of treated wastewater. Floodwater P concentrations of the i
ntact soil cores were monitored over time to determine the rate of P r
emoval. Batch experiments were conducted to determine maximum P retent
ion capacity of the soils. Soil samples were analyzed for inorganic P
pool sizes, and selected physicochemical properties. During a 21 d hyd
raulic retention time, the constructed wetlands (sandy, low organic ma
tter soils) retained 52 to 66% of added P, as compared with 46 to 47%
retained by the natural wetlands (high organic matter soils). The P re
tention maximum, as estimated using the Langmuir model, ranged from 19
6% to 1821 mg P kg(-1) (aerobic incubations) and from 32 to 1415 mg P
kg(-1) (anaerobic incubations). The P sorption maximum for these soils
could be predicted by batch equilibration with a single high P soluti
on. Anaerobic conditions increased P solubility. Organic P pools and t
he Fe-Al-bound fraction seemed to control P chemistry in these natural
and constructed wetlands.