Interactions between biogeochemistry and hydrologic systems

Here we review the fundamental interactions between hydrology and the cycling of carbon (C) and nitrogen (N) in terrestrial and stream ecosystems. We organize this review around five commonly studied environments: land-atmosphere interface, soil, groundwater, streams, and headwater catchments. Common among all environments is that hydrological transitions, either episodic changes in water availability or hydrologic transport of reactants, result in disproportionately high rates of C and N cycling. Two major research challenges in coupling hydrological and biogeochemical research are (a) effectively scaling reactions at these spatiotemporal transitions and (b) combining the progress made within each of the five environments listed above into an integrated understanding of hydrobiogeochemical cycles. Changes in local-to-regional hydrological cycling are likely to result in unexpected surprises at the landscape scale until progress in these research areas is made.