Author(s): Shuzo Nishida; Kohei Tsugita; Yusuke Nakatani
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Keywords: Groundwater use; Pumping; Water quality; Nutrient transport; Urban are
Abstract: Groundwater supplies fresh water and transports nutrients in coastal zones. However, the influence of groundwater pumped to the surface on the nutrient cycle is not quantitatively understood yet. To quantify nutrient transport by groundwater pumping in an artificial transport system, such as the water supply and sewage system, we analyzed the water qualities indices and discharge rates of pumped groundwater in Osaka Prefecture, Japan. Water samples were collected from 48 pumping wells and 2 major rivers in Osaka Prefecture. The dissolved inorganic nutrient concentrations of the pumped groundwater were 0–16 mg/L (NH 4 –N), 0–4.9 mg/L ([NO 2 +NO 3 ]–N), 0–1.5 mg/L (PO 4 –P), and 9.2–40.1 mg/L (SiO 2 –Si). NH 4 –N and PO4–P concentrations were high in the middle region of the study area. Such high concentrations were considered to be caused by advection and decomposition of organic matter in clay layers. [NO 2 +NO 3 ]–N concentrations were high near agricultural areas because of the infiltration of fertilizer in the aquifer. The resulting nutrient transport showed higher values in the northern and southwestern regions of the study area than in other regions. SiO 2 –Si concentrations, they were 3–10 times higher than in river waters. In Osaka Prefecture, pumping discharge was highest in the early 1960s and thereafter decreased to about one-third in recent year due to regulation of the pumping of groundwater in an effort to prevent ground subsidence. Nutrient transport decreased in proportion with the decrease in pumping discharge. This suggests that changes in nutrient transport because of groundwater use affect water quality and ecosystems in coastal zones.
Year: 2014