Phosphorus accumulation and stability in sediments of surface-flow constructed wetlands

Edge-of-Field Technologies for Phosphorus Retention from Agricultural Drainage Discharge

“…Johannesson et al [69] found that only 22% on average of the P retained in the sediments was stable (i.e., Ca-bound P or residual P), while the P fraction bound to Fe and Al-thus potentially labile-was almost 40% (Figure 3). Mendes et al [80], in turn, found higher fractions of P bound to Fe and Al in the sediments, accounting from 58 to 100%, which is considered unstable depending on the pH and redox conditions (Figure 3).…”

“…This way, DRP can be released under certain conditions, including low sorption capacity of the soil, non-neutral pH, reducing conditions Surface-flow constructed wetlands are widely known as sinks of PP due to sedimentation of suspended particles and organic material [76,79]. Thus, the accretion of deposited material at the bottom forming a sediment layer constitutes the main retention mechanism, which is generally the case for most of the P retained [69,70,80]. Thereby, the pool of P in the sediments is generally the largest and represents a long-term retention.…”

“…A small fraction, however, is retained in the long-term as refractory organic P, which contributes to new soil material [79] (Figure 3). The stability of DRP retained by chemical interactions with P sorption sites at the soil is variable and depends on the geochemical characteristics, pH and redox conditions as well as on the concentration gradient across the soil-water interface [80,87,88]. This way, DRP can be released under certain conditions, including low sorption capacity of the soil, non-neutral pH, reducing conditions The stability of DRP retained by chemical interactions with P sorption sites at the soil is variable and depends on the geochemical characteristics, pH and redox conditions as well as on the concentration gradient across the soil-water interface [80,87,88].…”

“…The stability of DRP retained by chemical interactions with P sorption sites at the soil is variable and depends on the geochemical characteristics, pH and redox conditions as well as on the concentration gradient across the soil-water interface [80,87,88]. This way, DRP can be released under certain conditions, including low sorption capacity of the soil, non-neutral pH, reducing conditions The stability of DRP retained by chemical interactions with P sorption sites at the soil is variable and depends on the geochemical characteristics, pH and redox conditions as well as on the concentration gradient across the soil-water interface [80,87,88]. This way, DRP can be released under certain conditions, including low sorption capacity of the soil, non-neutral pH, reducing conditions ( Figure 3) and low P concentration in the overlying water.…”

“…Calcium is the major P sorbent in SFCWs with mineral alkaline soils. Iron and Al oxides, on the other hand, are the most common P sorbents in SFCWs with mineral acidic soils, and the concentrations of these largely affect the stability of P. The P sorption capacity (Equation 8, where Fe ox and Al ox are oxalate extractable Fe and Al) is a pedotransfer function which is commonly used to estimate the quantity of amorphous Fe and Al oxides (i.e., the fraction of oxides with higher sorption capacity due to larger reactive surface area) in mineral acidic soils [80,87,103]. Therefore, SFCWs receiving large loads of Fe and Al oxides may benefit by increasing the P sorption capacity in the sediments and ensure long-term retention.…”