Physicochemical assessment and phosphorus storage of canal sediments within the Everglades Agricultural Area, Florida

Excess nutrients such as phosphorus (P) transported from the Everglades Agricultural Area (EAA) in South Florida, USA, to downstream water bodies have been identified as contributing to trophic imbalances within the Florida Everglades. Decades of farming drainage from the EAA has led to accumulation of sediments in regional canals which may be transported to downstream ecosystems and act as potential internal source of P. Intact sediment cores were collected from three main conveyance and three farm canals within the EAA. Physicochemical assessment, mineralogy, P speciation, and storage were determined for surface and subsurface layers. The main conveyance canal sediments had higher total P (TP) concentrations (1,280 +/- 360 mg kg(-1)) than the farm canals (960 +/- 540 mg kg(-1)), while farm canal sediments showed higher organic matter content (28-53 %) compared to the main canal (24-27 %) sediments. The minerals found in main conveyance canal sediments were similar to those found in Lake Okeechobee. The labile KCl-P fraction comprised < 2 % of TP from all canal sediments, while NaOH-Pi (i = inorganic) fraction consisted of 1-14 % of TP. The majority of P in the canal sediments was contained in the HCl-P fraction (Ca-P and Mg-P), comprising > 50 % of TP in the main and farm canal sediments. An estimated 73 metric tons (mt) of P was stored in the 0-10-cm layer of the three main conveyance canals within the EAA boundary of which 57-mt P is reactive and potentially available for release at different time scales. The EAA canal sediments are highly organic with low bulk density and susceptible of being transported to downstream ecosystems. Many factors can impact the potential release of the reactive stored P, including redox potential of sediments as well as the overlying water column P concentration. Further investigation of potential P release from these sediments is warranted.