Distribution and Influent Factors of Nitrate Concentration in Groundwater

NAKANO Takuji, YASUMOTO Jun, TERASAWA Haruna, NAWA Norio

doi:10.11408/jsidre.81.283

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Other Title

地下水中硝酸性窒素濃度の時空間分布と形成要因について
地下水中硝酸性窒素濃度の時空間分布と形成要因について : 沖縄県本島南部琉球石灰岩分布地域を例として
チカスイチュウショウサンセイチッソノウドノジクウカンブンプトケイセイヨウインニツイテ : オキナワケンホントウナンブリュウキュウセッカイガンブンプチイキオレイトシテ
— Case study on Ryukyu limestone region in southern part of Okinawa, Japan —
― 沖縄県本島南部琉球石灰岩分布地域を例として ―

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Abstract

Temporal and spatial dynamics of nitrate (NO₃^--N) in groundwater are investigated in the southern part of Okinawa Main Island, Japan, where Ryukyu limestone is extensively distributed. Influent factors of NO₃^--N formation are also examined on the basis of observed data in groundwater of the study area. It is found that probability distribution of NO₃^--N concentrations agree with normal distribution and the 75 per cent probability of NO₃^--N concentration is a little higher than the upper value (10mgL^-1) of environmental quality criteria. It is considered that NO₃^--N concentrations are influenced by nitrogen load accompanied with groundwater flow from the upstream to the downstream of the study area. It is also found that NO₃^--N concentration formation is assumed to depend on two factors, that, mixing-inflow actions and denitrification-dilution actions under conditions of groundwater flow caused by completion of the subsurface dam. It is suggested that nitrogen load from agricultural land in this area influences the long-term fluctuation of NO₃^--N concentrations in groundwater. It is recognized that groundwater level participates annual fluctuation of NO₃^--N concentrations in groundwater.

Journal

Transactions of The Japanese Society of Irrigation, Drainage and Rural Engineering

Transactions of The Japanese Society of Irrigation, Drainage and Rural Engineering 81 (4), 283-291, 2013

The Japanese Society of Irrigation, Drainage and Rural Engineering

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