Comparison of soluble reactive phosphorus and orthophosphate concentrations in river waters

The concentrations of phosphorus determined by spectrophotometric analysis (soluble reactive phosphorus; SRP) and ion chromatography (orthophosphate only) were compared in fresh water from inflowing rivers of Lake Biwa (Shiga, Japan) and its outflow (Seta River). The high-volume sample injection and high-capacity analytical column used for ion chromatography enabled detection of orthophosphate ions at levels below 10 nmol/l. In river waters sampled from inflows to Lake Biwa, the ratios of orthophosphate to SRP ranged from 0.06 to 0.79, and varied considerably between rivers. This result shows that the fractional determination of dissolved phosphorus in natural waters is important for understanding its bioavailability.