Mitigating the exchange flux of sedimented phosphorus in invasive water Hyacinth (Pontederia crassipes) bloom system using a biogenic waste material

Calcium rich materials have been studied as sediment capping agents, but the high cost and the potential toxicity of extraneous metal ion constituents have been identified as impediments to field-scale applications. Therefore, Gastropod shell (GS), a biogenic waste material predominated with calcium mineral phase is assessed as a sediment capping agent in P. crassipes bloom system. Using the overlying water and sediment samples collected from a P. crassipes bloom system, the P-binding capacity of thermally treated GS was evaluated. Two microcosm aquatic systems (i.e., oxic and anoxic systems), with GS amended and unamended sediment, were created. The systems were incubated for fifty (50) days and the temporal trend in the physicochemical characteristics, and nutrient exchange flux across the sediment-water interface were monitored. The proof-of-concept was tested using pot experiment in a screenhouse. The two reactive materials showed significant capacity to sequestrate both the aqueous and sediment phase P, but the GS₁₀₀₀ showed better performance. The GS amended sediment trapped the sedimented P, and precluded the release into the overlying water phase, but a significant increase in the pH value of the overlying water was noted. In the field trial, the GS₁₀₀₀ amended sediment mitigated the exchange flux of sedimented P, which led to the death of the P. crassipes within twenty-four (24) days. Further studies are recommended to ascertain the role of extreme pH value created by the sediment amendment on the growth profile of P. crassipes.