Reclamation Culture Alters Sediment Phosphorus Speciation and Ecological Risk in Coastal Zone of Southeastern China

Sediment phosphorus (P) speciation plays a critical role in coastal wetland ecosystems, while the response of P speciation to reclamation culture remains unclear. In this study, sediment P species (total P [TP], organic P [Org-P], inorganic P [IP], iron- and aluminum-bound P [Fe/Al-P], calcium-bound P [Ca-P], loosely adsorbed P [Lsor-P], P sorption index [PSI], and P adsorption saturation [DPS] are investigated in the natural marsh wetland, 3-year and 15-year reclamation culture ponds. Sediment P pollution level and eutrophication risk are evaluated based on the single-factor standard index (S_i) and eutrophication risk index (ERI). Furthermore, a simulation experiment is conducted to reveal the effects of baits input and overlying water aeration on sediment P species and ecological risk. Measured sediment TP, Org-P, IP, Fe/Al-P, Ca-P, and Lsor-P concentrations are significantly higher in 15-year culture ponds than in 3-year culture ponds and natural marsh wetland. Sediment PSI is lower in reclamation culture ponds than in natural marsh wetland, while DPS is just opposite. The S_i and ERI are higher in 15-year culture ponds than in natural marsh wetland, suggesting that reclamation culture significantly increases sediment P pollution level and eutrophication risk. A short-term simulation experiment further indicates that baits input and overlying water aeration can alter sediment P dynamics and increase sediment P loading. Overall, these results confirm that reclamation culture can make more available P accumulation and thus increase eutrophication risk of adjacent coastal water.