The influence of floodplain restoration on whole-stream metabolism in an agricultural stream: insights from a 5-year continuous data set

Channelized streams are common in North American agricultural regions, where they minimize water residence time and biological nutrient processing. Floodplain restoration done via the 2-stage-ditch management strategy can improve channel stability and nutrient retention during storms. We examined the influence of floodplain restoration on whole-stream metabolism by measuring gross primary production (GPP) and ecosystem respiration (ER) for 1 y before and 4 y after restoration of an upstream, unaltered control reach and a downstream, restored reach. Both reaches were biologically active and dynamic. GPP ranged from 0.1 to 22.1 g O-2 m(-2) d(-1), and ecosystem respiration (ER) rates ranged from -0.1 to -38.7 g O-2 m(-2) d(-1). We used time-series analysis and found that GPP increased postrestoration during floodplain inundation when expressed per unit length, but not per unit area, of stream. GPP was more resilient post- than prerestoration and returned to prestorm levels more quickly after than before floodplain construction. In contrast, the floodplain restoration had no effect on ER or on any metric of metabolism during base flow. Overall, we showed that floodplain-stream linkages can be important regulators of metabolism in restored agricultural streams.