Quantification of Groundwater-Derived Nutrients Into Beach Ridge Drainage Using Radon Mass Balance Model

Abstract

Groundwater discharge can be a significant pathway for dissolved nutrients to surface water and thus can bring forth important implications to the coastal biogeochemical cycles. Discrete sampling of radon concentrations at several locations along an interridge drainage off Setiu Wetlands were carried out to estimate the fluxes of groundwater discharge. The 222 Rn mass balance results show that groundwater discharge in the drainage is estimated to be 6649 m 3 day -1 , made up of ~33% of total water discharge and has contributed 2.88×10 2 molday -1 , 1.23×10 2 molday -1 and 0.75molday -1 of ammonium-nitrogen, nitrate-nitrogen and nitrite-nitrogen, respectively into the surface water drainage. Strong correlation between radon and ammonium suggested that the source of nutrient in drainage is groundwater-based, derived probably from the nearby damaged or leaking residential septic tanks and from agricultural practices of oil palm plantation.Keywords: groundwater-surface water interaction, water quality, beach ridge drainage, Setiu, Malaysia Abstrak Pelepasan air bawah tanah merupakan satu laluan penting untuk nutrien ke air permukaan. Proses ini mampu membawa implikasi yang penting terhadap kitaran biogeokimia di pesisiran pantai. Pensampelan radon di sepanjang saluran pematang pasir telah dijalankan untuk menentukan kadar pelepasan air bawah tanah. Hasil model keseimbangan jisim 222 Rn telah menunjukkan kadar pelepasan air bawah tanah di saluran adalah sebanyak 6649 m 3 hari -1 dan nilai ini merangkumi ~33% daripada jumlah pelepasan air. Pelepasan air bawah tanah juga menyumbang sebanyak 2.88×10 2 mol hari -1 amonium-nitrogen, 1.23×10 2 mol hari -1 nitrit-nitrogen dan 0.75 mol hari -1 dan nitrit-nitrogen ke air permukaan saluran. Kolerasi antara kepekatan radon dan ammonium di saluran juga mencadangkan sumber nutrien berasal dari air bawah tanah yang kemungkinan tercemar oleh sisa pembuangan kumbahan dari kawasan kediaman berdekatan dan rembesan pertanian dari ladang kelapa sawit di sekitarnya.Kata kunci: interaksi air bawah tanah-air permukaan, kualiti air, saluran pematang pasir, Setiu, Malaysia