IMPACT OF CITRUS AGRICULTURE ON THE QUALITY OF WATER RESOURCE IN A SMALL STEEP ISLAND, SETO INLAND SEA, JAPAN

Abstract

Groundwater is an extremely valuable resource thus its pollution a call for concern. Amongst the major threats, agricultural leachates often contribute significantly to groundwater pollution. This paper reports an investigation on the effects of citrus agriculture on the groundwater quality aspects of Osakishimojima island. Fifty-one groundwater samples were collected and analyzed for major ions and nutrients. The Gibbs diagram revealed that the overall hydrogeochemical environment of the study area is controlled by rock-water interaction. Two main hydrochemical facies (CaMg-HCO₃ and CaMg-SO₄) were identified. 48 groundwater samples showed PO₄³⁻-P content (0.06 - 3.2 mg/L), which exceeds WHO’s recommended maximum permissible limit. High contamination of PO₄³⁻-P was noticed at depth zones between 3 to 6 m while the highest concentrations were found at depths of 5 m. NO₃⁻-N contamination of groundwater was also observed to decrease with depth. High levels of PO₄³⁻-P in groundwater may be as a result of heavy fertilizer application by farmers.