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?, and 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?