Evidence of Buried Particulate Organic Carbon as Foundation for Heterotrophic Carbon Metabolism in the Hyporheic Zone of a Montane Headwater Stream in the H. J. Andrews Experimental Forest, Oregon, USA

Streams and rivers play a critical role in global carbon (C) cycling by processing, storing, and transporting C. Headwater streams which make up more than 95% of the length of streams and rivers worldwide have disproportionate influence on fluvial C dynamics. The hyporheic zone (HZ) of headwater streams is a critical site where organic C is processed and the hyporheic exchange flow (HEF) plays crucial role in cycling of C. This study investigated the metabolism of stream-source dissolved organic carbon (DOCst) and buried particulate organic carbon (POCb) in the hyporheic zone of a small mountain headwater stream. We designed hyporheic mesocosms to stimulate near-stream hyporheic flow paths located in the HZ of Watershed 1 located in the H. J. Andrews Experimental Forest. We then investigated the metabolism of C in the hyporheic mesocosm and compared the results from the mesocosm to those from a hyporheic well network located in the riparian zone of Watershed 1. We examined three questions:
1. What is the source of metabolic C substrate for hyporheic metabolism in the hyporheic zone?; 2. What factors influence metabolism in the hyporheic zone?; 3. How do the rate coefficients from hyporheic mesocosm compare to rate coefficients from the near-stream hyporheic flow paths measured in the well network?