[A-HW27] Biodiversity, nutrients and other materials in ecosystems from headwaters to coasts

[AHW27-P12] ASSESSMENT OF THE LEVELS OF PHOSPHORUS AND ITS VARIOUS FORMS AS WELL AS THE DETERMINATION OF THE SEASONAL PHOSPHORUS PATTERNS IN WATER FROM YAMATO RIVER

*DAVID NYAMWEYA MOENGA¹, Shin-ichi Onodera¹, Mitsuyo Saito¹, Takuya Ishida¹, Sharon Bih Kimbi¹, Muhammad Shahinur Rahman¹, Wanna Zaw¹ (1.Graduate School of Advanced Science and Engineering, , Hiroshima University)

Keywords: phosphorus forms, industrialization, urbanization, temporal, Yamato River, Osaka Bay

This study was conducted to assess the concentration levels of various forms of phosphorus (p) as well as the determination of their seasonal patterns in water from Yamato River. Yamato River is one of the major rivers that flow into Osaka Bay. Phosphorus (p), an extremely essential element makes up the components responsible for different cell functions in humans and other living beings. Similarly, it helps to maintain and increase crop yield in agriculture although, excessive application of fertilizers and animal manure leads to its increase in aquatic environments where it is responsible for eutrophication and subsequent deterioration of water quality. Industrialization and urbanization are also known to deposit significant amounts of various forms of phosphorus into the ecosystem. Transportation of phosphorus in freshwater environments is aided through fine sediments while its amount depends on the catchment characteristics i.e. geology, land use and hydrometeorological conditions. Variations of various forms of phosphorus present in water and suspended sediments from Yamato River were assessed with an intention to identify their likely sources and their short and long-term temporal variations. River water samples were collected at a water collection point of Yamato River from October 2022 to December 2024 and analyzed for total phosphorus (TP), total dissolved phosphorus (TDP), particulate inorganic phosphorus (PIP) using the molybdenum blue method and the sequential extraction method (SEDEX) for various forms of phosphorus. Area precipitation and water level data were obtained from the Sakai and Oriono weather stations over the same period to assess their relationships with the phosphorus concentrations. Obtained results showed varying amounts of (p) species with varying water levels. The average TP concentration obtained was 0.33 mg/L (0.14 mg/L - 0.84 mg/L), TPP was 0.11 mg/L (0.05 mg/L - 0.44 mg/L), PIP was 0.08 mg/L (0.04 mg/L - 0.30 mg/L), POP was 0.03 mg/L (0.00 mg/L - 0.14 mg/L) and TDP was 0.18 mg/L (0.00 mg/L - 0.34 mg/L). The lowest TP values corresponded to low water level seasons while occasional increments were observed with increased water levels. The values remained constantly above average with sustained water levels. The phosphorus in the Yamato River water may have been as a result of application of fertilizers and animal manure in the agricultural lands, sewage and industrial waste discharge and surface runoffs being washed into the river. The highest water level over the study period was 2.42 m while the lowest was 0.06 m corresponding to the highest (105.5 mm) and the lowest (0.0 mm) precipitation respectively. This showed that precipitation had a direct impact on the Yamato River water levels.
Acknowledgement
This work was supported by the Asia-Pacific Network for Global Change Research (No. CRRP2019-09MYOnodera) and the Research grant of restoration and creation in a coastal environment in Osaka Bay area PI: Mitsuyo Saito, No. 060003.