The use of an ultrafiltration technique for measurement of orthophosphate in shallow wetlands

The overestimation of orthophosphate by filterable reactive phosphorus (FRP ) measurement techniques has long been accepted. The aim of this study was to quantify that overestimation in 17 wetlands over time. Specifically an u ltrafiltration technique was used prior to the application of the molybdenu m blue phosphorus detection method to quantify orthophosphate concentration s. Samples were collected over a B-month period and analysed for total filt erable (< 0.50 <mu>m) phosphorus (TFP), filterable reactive phosphorus (FRP < 0.50 <mu>m) and ultrafiltered (< 10(3) Dal reactive phosphorus (PO4). FR P correlated well with PO4, however, FRP overestimated PO4 particularly wit h increasing colloidal phosphorus concentration. The ratio of DOC to TFP (C :P) influenced the fate of PO4 in the water, implying that DOC was forming complexes with phosphorus. The PO4 concentrations decreased with increasing C:P ratios in some of the wetlands over the B-month monitoring period. (C) 2001 Elsevier Science B.V. All rights reserved.