Abstract
Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland waters across northern Europe and northeastern North America. This inland-water “browning” has profound physical, chemical and biological repercussions for aquatic ecosystems affecting water quality, biological community structures and aquatic productivity. Potential drivers of this “browning” trend are complex and include reductions in atmospheric acid deposition, changes in land use/cover, increased nitrogen deposition and climate change. However, because of the overlapping impacts of these stressors, their relative contributions to DOC dynamics remain unclear, and without appropriate long-term monitoring data, it has not been possible to determine whether the ongoing “browning” is unprecedented or simply a “re-browning” to pre-industrial DOC levels. Here, we demonstrate the long-term impacts of acid deposition and climate change on lake-water DOC concentrations in low and high acid-deposition areas using infrared spectroscopic techniques on ~200-year-long lake-sediment records from central Canada. We show that acid deposition suppressed naturally higher DOC concentrations during the 20th century, but that a “re-browning” of lakes is now occurring with emissions reductions in formerly high deposition areas. In contrast, in low deposition areas, climate change is forcing lakes towards new ecological states, as lake-water DOC concentrations now often exceed pre-industrial levels.
Highlights
Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland waters across northern Europe and northeastern North America
Water-monitoring data have shown strong temporal correlations between changes in water chemistry resulting from reduced acid deposition and increasing DOC concentrations[1,19], and experimental studies have demonstrated reduced DOC mobility in soils with increasing acidity[20,21]
Water-chemistry monitoring data show the recovery of Sudbury lakes from acid deposition, with increasing pH in acid-sensitive lakes and declining SO42− levels in all study lakes since the beginning of monitoring in the
Summary
Water-chemistry monitoring data show the recovery of Sudbury lakes from acid deposition, with increasing pH in acid-sensitive lakes and declining SO42− levels in all study lakes since the beginning of monitoring in the. In the ELA the current DOC increase has already surpassed pre-industrial background levels in most lakes, suggesting that climate is already the dominant driver of DOC change in low acid-deposition regions. The Sudbury region experienced similar environmental changes (increased annual air temperature by ~1.4 °C, increased rainfall by ~145 mm, and a longer growing and runoff season by ~21 days since the 1950s; Fig. 2) as the ELA. These changes will have contributed to the ongoing. These widespread fundamental changes in lakes may have large consequences for the biota in these ecosystems, as well as management implications for fisheries and drinking-water resources
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
