抄録
Nitrogen and phosphorus supplied from Sasagase and Kurashiki Rivers to Lake Kojima, Japan contribute to internal production of chemical oxygen demand (COD) in the lake. It is necessary to gather the information on their characteristics based on which we can decrease the COD value. Then, concentrations of nitrate (NO3--N) and phosphate (PO43--P) were measured once a month at 21 sampling points along the rivers from Feb 2001 to Jan 2002. As results, the average concentrations of NO3--N and PO43--P at most points in Kurashiki River were higher than those at each sampling point in Sasagase River. In addition, monthly concentration-changes of NO3--N and PO43--P at each sampling point was as follows; 1) monthly changes in the NO3--N concentration were similar to those of PO43--P at the sampling point where irrigation water was introduced in the summer, 2) the NO3--N concentration changed in inverse proportion to the PO43--P concentration at the sampling points where phosphate was released from the sediments under the condition of low-dissolved oxygen in the summer, 3) monthly changes in the NO3--N concentration were independent of those in the PO43--P concentration at the sampling point where it was affected by some non-specific sources.
