10 - Surface and Subsurface Dissolved Organic Carbon

Abstract

This chapter reviews dissolved organic carbon (DOC) concentration in stream waters, ground waters, and hyporheic zone waters, processes involving DOC in hyporheic zones, and the impact of hyporheic zone processes involving DOC on energy flow and carbon cycling in streams. All subsurface waters are ground water; it is useful for purposes of description and modeling to distinguish between different subsurface water zones. These include water in unsaturated soils (vadose zone water), water in the portion of the phreatic zone that is above the regolith (shallow ground water or saturated soil water), and deep ground water that is in the geologic aquifer (bedrock zone water). Data for DOC concentration within hyporheic zones are limited and variable, including instances of higher, lower, and equivalent concentrations compared to surface waters and ground waters. If surface water is enriched with DOC relative to the hyporheic zone water, downwelling surface waters can fuel hyporheic zone metabolism and the hyporheic zone will function as a DOC sink. Similarly, when surface water downwells into the hyporheic zone and flows downstream supporting metabolism before resurfacing, or moves from the stream into the riparian zone, the hyporheic zone functions as a DOC sink.