PARENT SESSION
Oral Session #68: Nutrient Cycling. Presiding: D. Johnson.
Thursday, August 9, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Iron-phosphorus cycling in southeastern Piedmont lakes.
Mayhew, Mary1, Parker, Amanda1, Rasmussen, Todd1, 1
ABSTRACT- A small impoundment in the Southeastern Piedmont was fertilized on three occasions during the summer of 2000. Liquid fertilizer (8L of 11-37-0) was directly broadcast over the pond in the first two treatments. A mixture of liquid fertilizer (8L of 11-37-0) and iron-rich clay subsoil (55 kg) was allowed to sorb for 24-hours before being mixed with sufficient water to form a slurry. The slurry was then broadcast as the third treatment. The system response to each nutrient addition was measured using the Environmental Process and Control Laboratory, which measured a variety of water quality parameters at subhourly intervals over a four-month period. Ammonium (NH4), phosphate (PO4) and turbidity (TUR) are reported here. Response to the first two fertilizations showed similar, immediate increases in PO4 and NH4 (maxima greater than 1 mg/L for both in less than two hours). The third (fertilizer-clay slurry) treatment produced no detectable increase in PO4 (<0.01 mg/L) and a minimal increase in NH4 (<0.1 mg/L). These data support the hypotheses that 1) suspended colloidal iron sequesters phosphate and 2) clay soils with high cation exchange capacities sequester ammonium in aquatic systems. These mechanisms of nutrient sequestration have important implications for bioavailability in Piedmont systems: nonpoint sediment-bound nutrients are less available than nutrients from point-sources.
KEY WORDS: phosphorus, iron, nutrient cycling, lakes