Comparison of suspended nitrogen and phosphorus concentrations in stream water from adjacent watersheds with different turbidity levels in Ashoro Research Forest

Chiwa Masaaki, Nakamura Takuma

doi:10.15017/7344002

Limited information is available on the particulate forms of nitrogen and phosphorus in runoff from forests. Nonetheless, assessment of particulate content may be crucial for accurately quantifying nitrogen and phosphorus runoff from forested areas. In this study, we examined turbidity, major ionic constituents, and particulate nitrogen and phosphorus in two adjacent streams with different turbidity levels within the Ashoro Research Forest and assessed how turbidity influences particulate nitrogen and phosphorus concentrations. To investigate seasonal variations, samples were collected at different times of the year. The results showed that in low turbidity stream water (mean turbidity 0.11 FTU), the proportions of particulate nitrogen and phosphorus relative to total nitrogen and phosphorus were low (2.4% and 1.9%, respectively), whereas in high turbidity stream water (mean turbidity 6.3 FTU), these proportions were substantially higher (28% and 68%, respectively). Concentrations of particulate nitrogen and phosphorus were positively associated with turbidity levels. Temporal variability was more pronounced for the suspended component than for the dissolved component. These results suggest that the need to measure particulate nitrogen and phosphorus concentrations is influenced by river water turbidity, and that a higher frequency of water sampling may be required to estimate particulate matter discharge compared to that required for dissolved matter discharge.

Comparison of suspended nitrogen and phosphorus concentrations in stream water from adjacent watersheds with different turbidity levels in Ashoro Research Forest

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