Dissolved oxygen and dissolved inorganic carbon cycling in small order rivers: a stable isotope study.

Small order river systems dominate the continental landmass, draining 90% of the land and providing the most common landscape for transport of runoff and constituents. Here, we present measurements of δ13C of dissolved inorganic carbon and δ18O of dissolved oxygen from a small order river system draining a peatland catchment i.e. at the terrestrial-aquatic interface. We chose stable isotope analyses as an analytical tool to identify processes important in shaping the fluvial inorganic carbon load. Diurnal sample collection, undertaken to consider the influence of changing dominance of photosynthesis and respiration, was carried out almost monthly, for a 14-month period. Additionally, the field sampling programme used a nested-catchment matrix, with sample collection at the 1km2, 40km2 and 90km2 catchment scale. This extensive data base allows consideration of both temporal and spatial controls on DIC and DO cycling (as expressed through isotopic composition). Our data shows the TIC and DO pools to be dynamic in behaviour, but to respond in a predictable manner to significant environmental influences, such as changing in discharge profile. Catchment scale appears to have little influence on the cycling of these pools.