# Characteristics of Arsenic Leached from Sediments: Agricultural Implications of Abandoned Mines
###### Abstract  
Heavy metals, including arsenic from abandoned mines, are easily transported with sediment and deposited in waterbodies such as reservoirs and lakes, creating critical water quality issues when they are released. Understanding the leaching of heavy metals is necessary for developing efficient water quality improvement plans. This study investigated how arsenic leaches from different soil and sediment types and responds to hydrologic conditions to identify areas susceptible to arsenic contamination. In this study, batch- and column-leaching tests and sequential extraction procedures were used to examine arsenic leaching processes in detail. The results showed that most arsenic-loaded sediments accumulated in the vicinity of a reservoir inlet, and arsenic in reservoir beds have a higher leaching potential than those from agricultural land and stream beds. Arsenic deposited at the bottom of reservoirs had higher mobility than that in the other soils and sediments, and arsenic leaching was closely associated with the acidity of water. In addition, arsenic leaching was found to be responsive to seasons (wet or dry) as its mobilization is controlled by organic compounds that vary over time. The results suggested that temporal variations in the hydrochemical composition of reservoir water should be considered when defining a management plan for reservoir water quality. arsenic; leaching; sediment; heavy metal; reservoir; abandoned mine +
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chloride (Cl), and sulfate (SO\({}_{4}\)) [14; 15; 16], as well as heavy metal leaching from various media, including sewage sludge [6; 17; 18], industrial waste [19], coral ash [20; 21; 22], tropical soils [23], and mine tailings [24; 25]. However, the previous research has mainly considered the waterbodies of streams and rivers or relatively large-scale lakes and reservoirs [22; 23; 26], and the leaching of arsenic from the bottom of an irrigation reservoir has not been a focus of previous studies even though it has significant implications for agriculture. Small agricultural reservoirs have a relatively small storage capacity, and the water level changes frequently depending on the hydrological process with rainfall related watershed runoff and irrigation. Hence, the sediments of the reservoir are exposed to various environmental conditions, e.g., such as air during drought periods, and become submerged in water when high water levels are present. As arsenic leaching processes are sensitive to the physical and chemical conditions to which they are exposed, it is important to have a detailed understanding of how the processes respond to various environments under these water conditions. In addition, as various studies stressed and analyzed deposition [27] and diffusive gradient [28; 29; 30; 31] characteristics related to the arsenic bioavailability (heavy metals and other persistent pollutants) in water and sediments, we considered the seasonal effects (differences of the water quality between wet season and dry season, especially soluble organic matter) on arsenic leaching characteristics. In this study, we examined the process by which arsenic leaches from reservoir sediments with the goal of providing data required to develop an arsenic management plan for reservoirs and demonstrating the implications of arsenic-contaminated sediments on the quality of water in an agricultural reservoir. In this study, we compared the characteristics of soil and sediment samples which were taken at a paddy field and in the beds of a downstream stream and reservoir in an agricultural watershed. Multiple tests, including tests and sequential extractions, were conducted in a detailed investigation of the arsenic leaching process. In addition, to understand the long-term impacts of arsenic leaching on water quality, column-leaching tests were also applied to sediments deposited in the reservoir bed.