9:30 AM - 9:45 AM
[AHW32-09] The quantitative evaluation of bio-available particulate phosphorus discharged from Yasu River.
Keywords:particulate phosphorus, bioavailability, watersheds
River water samples were collected in 5 sites in Yasu river from one to four weeks interval from April 2014 to May 2015. Drainage from paddy fields were collected from Koka city, where locates in middle part of Yasu river watershed 3 times from May 2015 to July 2015. River water during rainfall events was also collected at 2 times in down stream site and 1time in up stream forested site in Yasu river watersheds. We separated several fractions of PP from suspended sediment (SS) by sequential extraction methods (1M ammonium chloride, 0.11M bicarbonate dithionite (BD), 1M NaOH, 0.5M HCl extraction) in water sample. SRP extracted from the particle fraction was determined by the molybdenum-blue method. We assumed that SRP extracted by ammonium chloride (NH4Cl-SRP) and bicarbonate dithionite (BD-SRP) were bio-available PP because NH4Cl-SRP release SRP in low SRP concentration environment and BD-SRP release SRP in reductive condition.
PP concentrations in Yasu river were higher during ploughing period and rainfall events. BD-SRP was dominant in base-flow in Yasu river, however NH4Cl-SRP was also important in small rainfall event (15.5 mm) at ploughing period, and non reactive phosphorus (NRP) extracted by NaOH (NaOH-NRP) was also important at large rainfall (97 mm) in August. We will discuss the source of these fraction of PP and estimate the amount of discharge rate of those.