[A-HW32] Material transportation and cycling in aquatic ecosystems; from headwaters to coastal areas

[AHW32-P10] Nitrate and Phosphate Contamination of Groundwater in Small and Steep Sedimentary Rock Island

*Sharon Bih Kimbi¹, Shingo Nozaki¹, Shin-ichi Onodera¹, Kunyang Wang¹, Yusuke Tomozawa¹ (1.Graduate School of Integrate Arts and Sciences, Hiroshima University)

Keywords:nitrate contamination, phosphate, sedimentary rock, mountain catchment

Over the past years, there has been a constant trend towards greater agricultural intensification and higher agricultural productivity which has been accompanied by a significant increase in the use of inorganic nitrogen and phosphorus in fertilizers. Nitrogen in particular the very soluble nitrate, is vital for life and is found naturally in soil and water however because many crop plants require large quantities of nitrogen to produce high yields, additional nitrogen in the form of fertilizer is applied to crops which easily dissolves into percolating water. Phosphorus on the other hand is less mobile and reaches surface water due to erosion with the bounded soil particles. These different pathways cause a problem with water protection, because elimination of one water pollution source may aggravate another. Phosphates are essential for growth of plants and animals but human activities have altered its natural cycle. Phosphate in excess causes nutrient boost which often equates to excessive algae growth. The present study was carried out in Osaki-Shimojima which is one of the island in the Seto island sea famous for citrus fruit cultivation. The aim of this study was to assess the impact of agriculture, with special attention on nitrate and phosphate contamination of the groundwater quality and to propose mitigative methods for implementing nitrogen-phosphate reduction measures. A total of 49 water samples were collected during the month of October, 2019 and subject to nutrient analysis using the Automatic Nutrient Analyzer. The startling results showed both high nitrate and phosphate concentrations in groundwater. Thus an unfavorable N: P ratio in supplied nutrients were detected. Severe shortage of phosphorus in applied fertilizers maybe one of the major factors causing leaching of nitrogen due to limited possibilities of its consumption by plants.