Long-term trends in carbon and color signal uneven browning and terrestrialization of northern lakes

Abstract

The widespread browning of northern lakes has been associated with long-term increases in dissolved organic carbon and color and should be linked to changes in surface water carbon dioxide, yet the long-term covariation in these three key carbon components of lake functioning remains to be assessed. We present long-term trends in dissolved organic carbon, color, and carbon dioxide from lakes, with generally positive but highly variable trends in organic carbon and a large degree of uncoupling with color and carbon dioxide. The highest rates of change in color and carbon dioxide were in lakes with greatest increasing dissolved organic carbon trends. Lakes with the lowest water retention times had greater increases and stronger coupling between all three parameters, coinciding with dominance of terrestrially derived carbon. These results suggest an uneven terrestrialization of northern lakes, where the increases and coupling in the three carbon components depends on hydrology and watershed connectivity.