Abstract
The objective of our research was to analyze the environmental factors determining short-term fluctuation in the concentration of suspended and/or dissolved matters in rivers. We conducted the analysis by using the 10 year water quality and precipitation monitoring data of short-term variation in four fixed rivers. All water-quality parameters were extracted by time-series analysis. We found that the particulate matter concentrations were affected by 2 days of rain, while the major ion concentrations were affected by 3 days of rain. However, the nutrient concentrations were affected by only 1 day of rain. After a rain event, suspended matter concentrations increased as a result of turbid water inflow. On the other hand, the major ion concentrations were diluted by rainwater after flooding. The dynamics in the nutrient concentration after rain differed among nutrient species and rivers. Meanwhile, in larger rivers, nutrient concentrations were affected by instream processes such as nutrient uptake by algae. Most of the above findings were confirmed by the direct observation data of two runoff events. Our results showed that the short-term variation in river water quality could be determined and evaluated by the time-series analysis of monitoring data without the need for direct frequent runoff sampling.
