Geochemical characteristics of runoff from acid sulfate soils in the northern area of Okinawa Island, Japan

Abstract

The oxidation of pyrite in acid sulfate soils (ASS) produces high concentration of strong acid (H 2 SO 4 ) in the soil. The acid reacts with soil minerals and dissolves aluminum and other acid-soluble metals. During rainfall, they are flushed and discharged into terrestrial and aquatic environments. The authors examined the chemical characteristics of the runoffs from ASS in Arashiyama and in Ooshitai, which are located in the northern part of Okinawa Island and evaluated their potential effects on surrounding environments.The results show that the runoffs were very acidic with pH range of 2.87 to 4.29, and minimum values were close to the pH values of the soils. The dominant species were SO 4 2-, Al 3+ , and Fe 2+ and they were well correlated with pH. The acidity of the runoffs caused dissolution of metals in the following order: Mn > Zn > Cu = Cd. The quality of runoffs was found to be poor and was mainly governed by the interaction of rain and soil. A comparison between the stream waters collected during rain event and on fine day showed a marked changes in stream water chemistry during rainfall as follows: alkalinity was reduced by 3.7 times, sulfate concentration was increased by 3 times whereas pH was decreased by 0.18 units. These changes are attributed to the contamination by runoff from ASS. Moreover brown flocky sediments were observed to have covered entire streambed at the discharging point. The chemical composition of the sediments shows that as those of runoffs, they were dominated by Fe, Al, and SO 4 . These results indicate that the sediments were mainly formed as the results of mixing runoffs and stream water.

Assessment of hydrogeochemical characteristics of groundwater quality in the vicinity of Okpara coal and Obwetti fireclay mines, near Enugu town, Nigeria

“…It was also found that while ratios of Na to Cl and SO 4 to Cl generally increased, the ratios of Ca to Mg decreased. This kind of deviation has been attributed to ion adsorption/exchange processes due to the dissolution of drainage materials (Vuai 2001;Vuai et al 2003). Generally, the ratio of SO 4 to Cl in the analyzed water samples deviates remarkably from those of the river and seawater.…”

Dissolved aluminum and silica release on the interaction of Okinawan subtropical red soil and seawater at different salinities: Experimental and field observations

“…The low content of base cations in GRC soil compared to ORGC soil could be partly contributed by leaching of base cations due to high annual rainfall (2155 mm), which is usually acidic with pH of 4.66 to 4.73 (Vuai et al, 2003b). When the atmospheric acidic deposition contacts with surface soil, it depletes labile pools of nutrient cations (i.e., Ca 2+ , Mg 2+ ), accumulates sulfur and nitrogen, and mobilizes inorganic monomeric aluminum (Driscoll et al, 2003).…”

“…Al inputs to surface waters appear to be associated largely with particulate matter derived from soil/sediment (Driscoll and Postek, 1996). However, occurrence of acidic precipitation in Okinawa Island (Vuai et al, 2003b) may also contributed Al content on surface waters because strong acid anions such as SO 4 2-and NO 3 -are readily transporting H + and Al out of the soil during acidic rainfall (Reuss et al, 1987;Driscoll et al, 2003).…”

Photochemical Formation of Hydroxyl Radicals in Red Soil-Polluted Seawater on the North of Okinawa Island, Japan

“…Red soil pollution was recognized in the 1980s as being responsible for causing major damage to the coastal ecosystems, e.g., corals. The dominant chemical components of red soil are SiO 2 (79%), followed by Al 2 O 3 (10%) and Fe 2 O 3 (3.9-5.3%) (Vuai et al 2003). Natural waters equilibrated with red soil have been reported to have considerable pH variation ranging from 3.8 to 8.1, depending on its amount in natural waters (Vuai et al 2003;Kombo et al 2005).…”