Phosphorus assimilation in a stream system of the Lake Okeechobee Basin
Reddy, K.R. | Flaig, E. | Scinto, L.J. | Diaz, O. | DeBusk, T.A.
The ability to predict how streams and wetlands retain phosphorus (P) is critical to the management of watersheds that contribute nutrients to adjacent aquatic systems such as lakes. Field and laboratory experiments were conducted to determine the P assimilatory capacity of a stream (Otter Creek) in the Taylor Creek/Nubbin Slough Basin located north of Lake Okeechobee, Florida. Dominant soils in this basin are sandy Spodosols; landuse is primarily dairy farms and beef cattle pastures. Estimates of P assimilation show that sediments assimilate approximately 5 percent of the P load. Phosphorus assimilation rates in the stream were estimated using first-order relationships based on the total P concentration of the water column as a function of distance from the primary source. This method assumes minimal lateral inputs. Stream lengths required for one turnover in P assimilation were estimated to be in the range of 3-16 km. Laboratory studies using intact sediment cores indicated a P assimilation rate of 0.025 m day-1, and equilibrium P concentration of 0.16 +/- 0.03 mg L-1 in the water column. Dissolved P concentration gradients in the sediments showed upward flux of P at water column P concentration of <0.16 mg L-1. Approximately 56-77 percent of the P assimilated in the above-ground vegetation during active growth was released or translocated within six months of senesence, suggesting short-term storage in above-ground vegetation. Bottom sediments and recalcitrant detrital plant tissue provide for long-term P assimilation in the creek. Although stream sediments have the potential to adsorb P high flow rate and low contact period between water and sediment limits this process.
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