Phosphorus dynamics in selected wetlands and streams of the lake Okeechobee Basin

Abstract

Lake Okeechobee is becoming increasingly eutrophic, presumably due to P loading from numerous dairy operations in the Lake's northern drainage basin. Phosphorus released from this basin is transported through canals, streams, and wetlands before its discharge into the lake. This paper summarizes the results of several studies on P dynamics in wetlands and stream sediments in the Lake Okeechobee Basin with primary focus on P interaction with soil/sediment-water column and vegetation. Stream sediments and wetland soils in the basin were characterized for labile and non-labile pools of P. The labile inorganic P ( P i) pool (KCl-extractable) accounted for 0.1 to 2.3% and 0.1 to 0.7% of the total P in sediments and wetland soils, respectively. The NaOH extractable P i, representing the P associated with Fe and Al oxyhydroxides, was the dominant P i in both stream sediments and wetland soils (accounting for up to 71 and 43% total P, respectively). The NaOH- P o (humic and fulvic acid associated organic P) is considered resistant to biological breakdown and accounted for 6 to 56% of total P. Stream sediments showed higher buffer intensity for P sorption than wetlands. Phosphate sorption capacity ( S max) and buffer intensity (Kd-adsorption coefficient) were highly correlated with oxalate extractable [Fe + Al] and total organic carbon (TOC) suggesting P sorption is associated with amorphous and weakly crystalline forms of Fe and Al, and/or complexed with organic matter. Phosphorus assimilation in vegetation was found to be short-term and dependent upon plant species, P loading, and wetland hydrology. Decomposition of detrital tissue resulted in rapid release of P into the water column. Phosphorus release was rapid during decomposition of floating macrophytes, as compared to herbaceous vegetation. Phosphorus retention coefficients were positively correlated with oxalate extractable Fe and Al content of soils and sediments. The average EPC w (threshold P concentration in the water column where P retention = P release) for stream sediments was 0.10 mg p l −1 and 0.42 mg P l −1 for wetland soils. The stability of the P retained was regulated by the physico-chemical properties of the soils and sediments.