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[AHW31-P03] Implications of pollen found in shallow groundwater in downtown Shinagawa, central Tokyo, Japan
Keywords:Tokyo, urban groundwater, pollen, insect-pollinated flower, origin of groundwater, sewage leakage
A wide variety of pollen was detected in shallow groundwater in the Kitashinagawa area of Shinagawa Ward, Tokyo, one of the most densely populated areas in Japan. We report pollen occurrence from groundwater in August 2021 and discuss the process that brought pollen to urban groundwater.
The studied well is a tube well with a depth of 9.1 m and a diameter of approximately 10 cm. The well is capped at the top, so there is no possibility of aerial pollen entering the well. The water table was located 0.9 m below the ground surface in August 2021. The depth of the sewer main in the area is 1.2-1.9 m below the ground surface. About 90% of the surface of the ground in the Kitashinagawa area is covered with buildings and asphalt, which restrict rainwater infiltration into the ground.
Groundwater was collected from 1-2 m below the water table using a Teflon bailer, and the sample was concentrated by evaporation to approximately 1 mL for pollen analysis. Thirty eight pollen grains were detected in 1 L of groundwater, and the occurrence rate of each pollen was 34.2 % for the Cryptomeria, 14.5 % for the Quercus subgen.Quercus, and 6.6 % for the Pinus subgen.Dploxylon, which is consistent with the pollen content of the air. It is noteworthy that insect-pollinated Brassicaceae pollen accounted for 10.5% of the total.
A mixing analysis based on Cl- concentration and oxygen isotope ratio of water indicates that 52 % of the groundwater in the well in August 2021 originated from rainwater, and 48 % from sewage (human waste and domestic wastewater) (Itoh et al., 2022). Judging from a high coverage of the ground surface and low permeability (small pore size) of the geologic materials, it is unlikely that pollen entering from the ground surface passes through the vadose zone to groundwater in such a large amount. Rather, it is assumed that pollen accumulated on the road surface is directly introduced to groundwater through subsurface leakage from rainwater drainage pipes. A high percentage of insect-pollinated Brassicaceae pollen strongly suggests broccoli and cauliflower pollen in human feces is loaded into groundwater through subsurface leakage from broken sewer pipes.
The studied well is a tube well with a depth of 9.1 m and a diameter of approximately 10 cm. The well is capped at the top, so there is no possibility of aerial pollen entering the well. The water table was located 0.9 m below the ground surface in August 2021. The depth of the sewer main in the area is 1.2-1.9 m below the ground surface. About 90% of the surface of the ground in the Kitashinagawa area is covered with buildings and asphalt, which restrict rainwater infiltration into the ground.
Groundwater was collected from 1-2 m below the water table using a Teflon bailer, and the sample was concentrated by evaporation to approximately 1 mL for pollen analysis. Thirty eight pollen grains were detected in 1 L of groundwater, and the occurrence rate of each pollen was 34.2 % for the Cryptomeria, 14.5 % for the Quercus subgen.Quercus, and 6.6 % for the Pinus subgen.Dploxylon, which is consistent with the pollen content of the air. It is noteworthy that insect-pollinated Brassicaceae pollen accounted for 10.5% of the total.
A mixing analysis based on Cl- concentration and oxygen isotope ratio of water indicates that 52 % of the groundwater in the well in August 2021 originated from rainwater, and 48 % from sewage (human waste and domestic wastewater) (Itoh et al., 2022). Judging from a high coverage of the ground surface and low permeability (small pore size) of the geologic materials, it is unlikely that pollen entering from the ground surface passes through the vadose zone to groundwater in such a large amount. Rather, it is assumed that pollen accumulated on the road surface is directly introduced to groundwater through subsurface leakage from rainwater drainage pipes. A high percentage of insect-pollinated Brassicaceae pollen strongly suggests broccoli and cauliflower pollen in human feces is loaded into groundwater through subsurface leakage from broken sewer pipes.