Effect of climate change on humic substances and associated impacts on the quality of surface water and groundwater: A review.

Humic substances (HS), a highly transformed part of non-living natural organic matter (NOM), comprise up to 70% of the soil organic matter (SOM), 50-80% of dissolved organic matter (DOM) in surface water, and 25% of DOM in groundwater. They considerably contribute to climate change (CC) by generating greenhouse gases (GHG). On the other hand, CC affects HS, their structure and reactivity. HS important role in global warming has been recognized and extensively studied. However, much less attention has been paid so far to effects on the freshwater quality, which may result from the climate induced impact on HS, and HS interactions with contaminants in soil, surface water and groundwater. It is expected that an increased temperature and enhanced biodegradation of SOM will lead to an increase in the production of DOM, while the flooding and runoff will export it from soil to rivers, lakes, and groundwater. Microbial growth will be stimulated and biodegradation of pollutants in water can be enhanced. However, there may be also negative effects, including an inhibition of solar disinfection in brown lakes. The CC induced desorption from soil and sediments, as well as re-mobilization of metals and organic pollutants are anticipated. In-situ treatment of surface water and groundwater may be affected. Quality of the source freshwater is expected to deteriorate and drinking water production may become more expensive. Many of the possible effects of CC described in this article have yet to be explored and understood. Enormous potential for interesting, multidisciplinary studies in the important research areas has been presented.