Photostability and photolability of dissolved organic matter upon irradiation of natural water samples under simulated sunlight

Abstract.

In this study the photostability/photolability of Dissolved Organic Matter (DOM) was assessed in both lake and groundwater. DOM in groundwater can undergo significant irradiation when drawn to the surface for agricultural purposes. DOM was generally photostable in lake and photolabile in groundwater, with a more elevated rate constant of DOM disappearance in groundwater samples with higher Non-Purgeable Organic Carbon (NPOC). DOM in lake water became photolabile upon acidification. The parallel decrease of both Total Organic Carbon (TOC) and NPOC suggests that actual photomineralisation took place in the samples. The ^•OH radicals play a secondary role into DOM photomineralisation in lake water, despite the fact that their generation rate considerably increases at acidic pH. The role of ^•OH is also minor in the photomineralisation of DOM contained in nitrate-rich groundwater.