5:15 PM - 7:15 PM
[MIS22-P03] Elucidation of the nutrient supply route and dynamics of the Tama River's Wando/Tamari using a multi-environment tracer
Keywords:Tama River, Wando/Tamari, Environmental tracers, nutrient
<Introduction>
Wando (Backwater) and Tamari (Pond) are semi-enclosed bodies of water that exist on the floodplains on the sides of rivers, and are often found in the middle and lower reaches of rivers. In Japan, while the size of Wando and Tamari are small, ranging from dozens of meters to several hundred meters, due to the effects of channel straightening and the construction of embankments, they have been shown to contribute to the diversification of river ecosystems by functioning as habitat and as refuge during floods (Denda et al., 2002). In other countries, large floodplain waters with a length of several kilometers exist, and in addition to biodiversity, research has been conducted on water cycle analysis, nutrient dynamics, and biological production (Bondar-Kunze et al., 2009), and the importance of interactions such as material exchange with river surface water has been demonstrated. However, in the case of Japanese Wando-Tamari, which are affected by groundwater recharge from the underlying layer, there is the possibility of forming a diverse water environment due to the influence of biogeochemical processes caused by differences in the recharge source and the route underground.
Therefore, in this study, we aim to establish a method for classifying Wando-Tamari according to their characteristics by using multiple environmental tracers for the Wando discharge point and the central part of the Tamari, and obtaining complementary data on the origin and supply route of water and nutrients.
<Materials and Methods>
Using satellite images, we selected about 50 Wando/Tamari sites along the Tama river (15 km to 55 km from the mouth of the river), and conducted water sampling and surveys three times between February 2024 and March 2025 (2024 winter, 2024 summer, 2025 winter). In addition, water samples were also collected from the main stream of the Tama river (approx. 16 locations) and springs around the Tama river (approx. 50 locations) for comparison with the water quality of the Wando and Tamari. On-site measurements of electrical conductivity (EC), water temperature, pH, and dissolved oxygen(DO) were taken, and samples were filtered through 0.22 µm or 0.45 µm filters for analysis, and then refrigerated, frozen or processed in the laboratory. Nutrients were measured using a colorimetric method with an AACS II automatic analyzer, etc., to determine the concentrations of phosphate (PO43-), nitrate (NO3-), nitrite (NO2-), ammonium (NH4+), and silicate (DSi). In addition, in the Wando-Tamari area, the concentration of Chl.a, which was collected from a certain amount of water using a GF/F filter and extracted with DMF, was measured. We measured various ions (Cl-, NO3-, SO42-, Ca2+, Mg2+, Na+, K+) as environmental tracers using ion chromatography, and measured the concentration of 222Rn using a static concentration electrostatic collector radon monitor (Durridge Co.), and the concentration of colored dissolved organic matter (CDOM) using a CDOM logger.
<Result and Discussion>
The concentrations of various nutrients in the Wando and Tamari estuaries differed greatly between locations (Wando DSi: 50-175 µmol/L, NO3-: 39-402 µmol/L, PO43-: 0.05-12 µmol/L, Tamari DSi: 28-157 µmol/L, NO3-: 5.4-370 µmol/L, PO43- ), and also differs from the trend of increasing nutrient concentrations in the downstream direction of the main river, so it is highly likely that the internal environment, origin of the water, supply route, etc. are creating these differences. As with previous studies, the 222Rn concentration used as an indicator of the origin of the water in the Wando and Tamari was two orders of magnitude higher than that of the river water in most shallow groundwater, so it is expected that the degree of shallow groundwater inflow into the Wando can be clarified. In addition, river water clearly showed higher concentrations of CDOM than shallow groundwater.
As various nutrients (DSi, NO3-, PO43-) were found to be related to 222Rn and CDOM concentrations, it is thought that the mixing state of river water and shallow groundwater in many of the Wando is affecting the internal nutrient conditions. However, it is difficult to classify the NO3- concentration in both river water and shallow groundwater because it is high, and there is no relationship between environmental tracers and nutrient in the Tamari, so it is necessary to conduct additional surveys using environmental tracers such as nitrate stable isotope ratios.
<Acknowledgment>
This study was supported by the River Fund The River Foundation, Japan.
Wando (Backwater) and Tamari (Pond) are semi-enclosed bodies of water that exist on the floodplains on the sides of rivers, and are often found in the middle and lower reaches of rivers. In Japan, while the size of Wando and Tamari are small, ranging from dozens of meters to several hundred meters, due to the effects of channel straightening and the construction of embankments, they have been shown to contribute to the diversification of river ecosystems by functioning as habitat and as refuge during floods (Denda et al., 2002). In other countries, large floodplain waters with a length of several kilometers exist, and in addition to biodiversity, research has been conducted on water cycle analysis, nutrient dynamics, and biological production (Bondar-Kunze et al., 2009), and the importance of interactions such as material exchange with river surface water has been demonstrated. However, in the case of Japanese Wando-Tamari, which are affected by groundwater recharge from the underlying layer, there is the possibility of forming a diverse water environment due to the influence of biogeochemical processes caused by differences in the recharge source and the route underground.
Therefore, in this study, we aim to establish a method for classifying Wando-Tamari according to their characteristics by using multiple environmental tracers for the Wando discharge point and the central part of the Tamari, and obtaining complementary data on the origin and supply route of water and nutrients.
<Materials and Methods>
Using satellite images, we selected about 50 Wando/Tamari sites along the Tama river (15 km to 55 km from the mouth of the river), and conducted water sampling and surveys three times between February 2024 and March 2025 (2024 winter, 2024 summer, 2025 winter). In addition, water samples were also collected from the main stream of the Tama river (approx. 16 locations) and springs around the Tama river (approx. 50 locations) for comparison with the water quality of the Wando and Tamari. On-site measurements of electrical conductivity (EC), water temperature, pH, and dissolved oxygen(DO) were taken, and samples were filtered through 0.22 µm or 0.45 µm filters for analysis, and then refrigerated, frozen or processed in the laboratory. Nutrients were measured using a colorimetric method with an AACS II automatic analyzer, etc., to determine the concentrations of phosphate (PO43-), nitrate (NO3-), nitrite (NO2-), ammonium (NH4+), and silicate (DSi). In addition, in the Wando-Tamari area, the concentration of Chl.a, which was collected from a certain amount of water using a GF/F filter and extracted with DMF, was measured. We measured various ions (Cl-, NO3-, SO42-, Ca2+, Mg2+, Na+, K+) as environmental tracers using ion chromatography, and measured the concentration of 222Rn using a static concentration electrostatic collector radon monitor (Durridge Co.), and the concentration of colored dissolved organic matter (CDOM) using a CDOM logger.
<Result and Discussion>
The concentrations of various nutrients in the Wando and Tamari estuaries differed greatly between locations (Wando DSi: 50-175 µmol/L, NO3-: 39-402 µmol/L, PO43-: 0.05-12 µmol/L, Tamari DSi: 28-157 µmol/L, NO3-: 5.4-370 µmol/L, PO43- ), and also differs from the trend of increasing nutrient concentrations in the downstream direction of the main river, so it is highly likely that the internal environment, origin of the water, supply route, etc. are creating these differences. As with previous studies, the 222Rn concentration used as an indicator of the origin of the water in the Wando and Tamari was two orders of magnitude higher than that of the river water in most shallow groundwater, so it is expected that the degree of shallow groundwater inflow into the Wando can be clarified. In addition, river water clearly showed higher concentrations of CDOM than shallow groundwater.
As various nutrients (DSi, NO3-, PO43-) were found to be related to 222Rn and CDOM concentrations, it is thought that the mixing state of river water and shallow groundwater in many of the Wando is affecting the internal nutrient conditions. However, it is difficult to classify the NO3- concentration in both river water and shallow groundwater because it is high, and there is no relationship between environmental tracers and nutrient in the Tamari, so it is necessary to conduct additional surveys using environmental tracers such as nitrate stable isotope ratios.
<Acknowledgment>
This study was supported by the River Fund The River Foundation, Japan.