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Soil pH values ranged from 6.7 to 7.7 and no significant differences were found between soil depths in marsh or pond areas (Table 1). The soil bulk density was higher in the pond area than in the marsh and it was due to the lack of vegetation in the pond area. The amount of NH4+, NO3, and PO4 in the marsh areas was three to four times higher in the upper soil depth than in the lower depths, whereas, in the pond area, the nutrient concentrations did not differ much among the soil depths. The pond area was 75 cm deep and therefore anaerobic conditions prevailed in this area. Hence, nitrification did not occur as much as in the marsh area.

Table 1

Physical and chemical properties measured in two soil depths within marsh and pond areas after 12 years of swine wastewater treatment in a constructed wetland cell

 Marsh area
Pond area
Soil property0–6 cm6–12 cm0–6 cm6–12 cm
pH 6.69 (0.1)* 6.91 (0.1) 7.74 (0.1) 7.57 (0.1) 
NH4+, mg kg−1 18.6 (18.1) 3.6 (1.7) 42.8 (8.3) 56.4 (21.3) 
NO3, mg kg−1 5.0 (4.6) 2.8 (2.3) 0.2 (0.2) 0.1 (0.1) 
PO4−2, mg kg−1 322.5 (76.4) 81.0 (46.1) 137.5 (53.4) 102.0 (17.8) 
Bulk density, g cm−3 1.32 (0.1) 1.33 (0.1) 1.73  1.74  
 Marsh area
Pond area
Soil property0–6 cm6–12 cm0–6 cm6–12 cm
pH 6.69 (0.1)* 6.91 (0.1) 7.74 (0.1) 7.57 (0.1) 
NH4+, mg kg−1 18.6 (18.1) 3.6 (1.7) 42.8 (8.3) 56.4 (21.3) 
NO3, mg kg−1 5.0 (4.6) 2.8 (2.3) 0.2 (0.2) 0.1 (0.1) 
PO4−2, mg kg−1 322.5 (76.4) 81.0 (46.1) 137.5 (53.4) 102.0 (17.8) 
Bulk density, g cm−3 1.32 (0.1) 1.33 (0.1) 1.73  1.74  

*Numbers in parentheses are standard errors.

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