Efficiency of a constructed wetland for retention of sediment-associated phosphorus

Abstract

A constructed wetland (2.1 ha; 2% of catchment area) in southeast Sweden, in a catchment with 35% arable land on clay soils, was investigated with respect to phosphorus (P) retention, focusing on particulate P (PP) and sediment accretion. The aims were to i) estimate P retention and identify the dominating retention processes; ii) investigate how well estimates of P retention based on inflow-outflow measurements compared with the amount of P accumulated in the sediment.In-and outflow of P was measured during four years with continuous flow measurements and flow proportional weekly composite samples. P in the accumulated sediment was estimated based on core samples and analyzed using sequential fractionation. Total P load during four years was 65 kg/ha and intensive sampling events detected 69% as PP. Based on inflow-outflow estimates the mean P retention was 2.8 kg/ha/yr, or 17%, but the amount of P accumulated in the inlet zone equated 78% of the TP load. This discrepancy showed the need to add studies of sediment accumulation to inflow-outflow estimates for an improved understanding of the P retention.The dominating P forms in the sediment were organic P (38%) and P associated with iron or aluminum (39%), i.e. potentially mobile forms. In areas colonized by Typha latifolia, the amount of P in the upper sediment layer (390 kg) was more than double the total P load of 136 kg.Cycling and release in those areas is a potential source of P that deserves further attention.3

Phosphorus and particle retention in constructed wetlands—A catchment comparison

“…This possible error in the retention estimate would be relatively more important in low loaded wetlands, and in sections with dense stands of emergent plants (c.f. Johannesson et al, 2011). A difference in sediment composition that supports this discussion was indeed observed in two of the wetlands in the current study (Fig.…”

Phosphorus Retention in a Newly Constructed Wetland Receiving Agricultural Tile Drainage Water

“…A possible reason for this could be that the long period with ice cover caused anoxia that reduced iron in the wetland sediment, which released the P bound to iron. Similar observations were made in another Swedish FWS wetland, where it was suggested that accumulated litter and organic sediment caused the development of anoxic conditions, with the subsequent release of iron‐bound P during ice cover periods (Johannesson et al, 2011).…”

Characterization of biogenic phosphorus in outflow water from constructed wetlands

“…For instance, Johannesson et al (2011) showed that the PP concentration in the outflow from a constructed wetland was stable even though the PP concentration in the inflow fluctuated drastically. This indicates a background production of PP in the wetlands.…”