Fossil fuels are omnipresent along the lower Schuylkill River. Train tracks lead to an oil refinery just north of the confluence with the Delaware. The Schuylkill Expressway hugs the riverbank on the other side. The transformation of fossil fuels into carbon dioxide, however, is not the only energy exchange in action. Everyday processes of life utilize a similar reaction.
Fossil fuel combustion is metabolism on a different scale. Both use organic matter that was initially produced through photosynthesis, in which solar energy fuels the formation of carbon chains out of carbon dioxide and water. These carbon chains can be rearranged into a plethora of different forms, but they ultimately serve as energy caches. Breaking their chemical bonds releases energy and leaves carbon dioxide as a waste product.
In between the synthesis and metabolism of organic compounds, carbon atoms circulate the biosphere. As photosynthesis ramps up each spring, some of the newly fixed carbon atoms may remain in organic molecules for decades, while others will be metabolized by winter. The balance of carbon fixation and combustion determines the amount of carbon dioxide in the atmosphere. Over the course of decades, the processes of life--growth, feeding, reproduction, death--maintain a stable concentration atmospheric carbon.
The combustion of fossil fuels releases carbon back into the atmosphere that has been absent from the system for millions of years. Even as the balance of carbon fixation and emission tips drastically toward the latter, however, the steady cycling of carbon between atmosphere and biosphere continues. The following photos trace the exchange of carbon along the Schuylkill River amidst the continuous combustion of fossil fuels.