Quantifying the Drivers of the Increasing Colored Organic Matter in Boreal Surface Waters

Abstract

Long-term monitoring of surface water quality has shown increasing concentrations of colored dissolved organic matter (CDOM) across large parts of the northern latitudes. This has increased purification costs for domestic water works. Appropriate abatement actions require better knowledge of the governing factors for the increase, and this has motivated a growing scientific interest in understanding the factors and mechanisms promoting the CDOM increase. A proposed water color model for an important raw water source for Oslo, Norway, is based on the precipitation's amount and mobile ion concentration. The model explained more than 93% of the temporal variation in CDOM between 1983 and 2008. The model structure was also tested on three adjacent raw water sources and was found to explain 75-82% of the CDOM development throughout the same period. The long-term trend of increasing CDOM was closely related to the decline in sulfate and chloride concentrations in precipitation. Furthermore, interannual fluctuations in CDOM were explained by variation in predominant water flow paths, depending on amounts and intensity of precipitation, both of which are predicted to increase in several parts of the northern latitudes according to climate change scenarios.

DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

“…No significant trends in discharge could be identified, verifying results of Lischeid (2001a). Thus, in the catchment under study here, changes in hydrology as a cause for increased DOC concentrations, as proposed by other studies (Haaland et al, 2010;Köhler et al, 2008), are not very likely.…”

“…The aim of this study was to find support for the hypothesis that the long-term increase in DOC exports from catchments is not only due to a decline in sulfate or acid rain deposition or due to a decrease in ionic strength (Clark et al, 2010;Hruska et al, 2009), but also by changes in biogeochemical processes and DOC mobilisation processes and hydrological flow paths in the source areas (e.g., Haaland et al, 2010;Clark et al, 2012). Many studies have so far investigated DOC exports from catchments and the controls thereof (Clark et al, 2010), but fewer studies are available investigating the DOC source areas and the DOC in runoff in a complementary approach (Worrall et al, 2008;Clark et al, 2008Clark et al, , 2012.…”

Decadal oscillations of the aquatic chemistry of river waters in Latvia

“…Signs of oscillations with 20, 11, 8-9, 3-5 and 2 years long periods can be observed, that generally corresponds to the results of earlier studies (Glazacheva, 1988;Klavins et al, 2002a). Increase of water color, known also as brownification, was frequently reported in many lakes and rivers of the Northern hemisphere (Driscoll et al, 2003;Frey and Smith, 2005;Monteith et al, 2007;Erlandsson et al, 2008;Haaland et al, 2010), including Latvian rivers as well (Klavins et al, 2012). Our data show that despite low data quality and short period of observations , statistically significant upward trends of color values can be found in both rivers (Table 3).…”

Simulating Dissolved Organic Carbon Dynamics at the Swedish Integrated Monitoring Sites with the Integrated Catchments Model for Carbon, INCA-C

“…However, over-reliance on simple models and purely statistical criteria may lead to overly simplistic views of the environment. If nothing else, it can be argued that more than 30 years of research into surface water DOC, and its links to acidification, acidity, climate and hydrology (Krug and Frink 1983;Laudon et al 1999;Erlandsson et al 2008Erlandsson et al , 2010Lepistö et al 2008;Clark et al 2010;Haaland et al 2010;Haei et al 2010;Löfgren et al 2010b;Löfgren and Zetterberg 2011), has shown that numerous factors influence or covary with surface water DOC. So, we must conclude that, on the basis of our current understanding, reality is over-determined but that models can be a useful tool for environmental hypothesis testing and understanding.…”

“…Changes in [DOC] in surface waters may have important consequences for drinking water in Fennoscandia (Haaland et al 2010). The costs of water treatment for human consumption and the production of potentially carcinogenic trihalomethane compounds are correlated with [DOC] (Christman et al 1983).…”