New Tools for Characterizing Carbon Cycling in Aquatic Ecosystems

Climate change is rapidly altering our planet as a result of anthropogenic emissions of greenhouse gasses (IPCC 2007). To quantify and forecast future changes in climate, we must understand the sources and sinks of organic carbon and how carbon is transformed and transported through the Earth’s biosphere. Terrestrial landscapes generally act as sinks of atmospheric CO2, but this carbon is usually exported to and through rivers and lakes. These freshwaters are hot spots of carbon cycling. Recent research demonstrates that while lakes and other freshwater resources make up less than 3% of Earth’s landscape, they bury more carbon than the world’s oceans (Dean and Gorham 1998, Cole et al. 2007). In addition, supported by terrestrial inputs of carbon, lakes are net sources of CO2 to the atmosphere similar in magnitude to the CO2 update of the world’s oceans (Tranvik et al. 2009). Despite the important role that lakes play in carbon cycling globally, few tools exist to quantify the carbon flux from the terrestrial landscape into these freshwater resources.

Here, we highlight the potential of emerging technologies to quantify carbon fluxes to and through freshwater ecosystems. We test the utility of naturally occurring stable hydrogen isotopes, fluorescence of fulvic acids, and carbon to chlorophyll ratios as indicators of terrestrial carbon flux into freshwater ecosystems. In addition, we develop two novel indicators of carbon cycling based on optical properties of organic carbon. These new technologies will provide new understanding into global carbon fluxes as well as important properties of aquatic ecosystems.