Data analysis dissolved organic carbon

Dissolved arsenic is correlated with ammonia (Fig. 4), consistent with a release mechanism associated with the oxidation of organic carbon. Other chemical data not shown here provide clear evidence of iron, manganese and sulfate reduction and abundant methane in some samples indicates that methanogenesis is also occurring. It is not clear however if arsenic is released primarily by a desorption process associated with reduction of sorbed arsenic or by release after the reductive dissolution of the iron oxide sorbent. Phreeqc analysis shows PC02 between 10"12 and 10"° bars and that high arsenic waters are supersaturated with both siderite and vivianite. 

Physical methods, such as ultraviolet (UV) absorption, are attractive in that they are usually simple, readily automated and may provide real-time data. However, no suitable single physical property is common to all organic compounds. Furthermore, UV absorption may suffer interference from dissolved inorganics (bromide and nitrate see Ogura and Hanya, 1966) and particulate material. As a consequence it is necessary to resort to chemical methods. The oxidation of the organic material and subsequent determination of the produced carbon dioxide thus seems the most logical approach to DOM analysis and has been generally adopted. The oxidation procedure itself becomes the critical issue in the consideration of the available alternative methods. 

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