Contrasting growing season water use efficiency in an abandoned drained peatland pasture and an adjacent natural bog in western Newfoundland

Study region An abandoned drained peatland pasture undergoing natural revegetation and an adjacent natural bog in the Robinsons peatland complex, western Newfoundland, Canada. Study focus Understanding how agricultural drainage affects ecosystem water use efficiency (WUE = gross primary productivity / evapotranspiration) is critical for managing water resources in cultivated peatlands. However, the relative roles of carbon uptake versus hydrological partitioning of water loss remain poorly quantified. This study compared a natural boreal bog with an adjacent drained peatland pasture using chamber-based flux measurements across plant functional types and microtopographic features. New hydrological insights Equal date mixed model estimates of GPP were 0.49 mg CO 2 m −2 s −1 (95% CI 0.43–0.55) at the abandoned pasture and 0.13 (0.07–0.19) at the natural bog. Estimated WUE was 0.03 mg CO 2 mg −1 H 2 O (0.03–0.04) and 0.006 (0.004–0.009), respectively, corresponding to a site ratio of 5.38 (3.58–8.09). Mean adjusted ET did not differ clearly between the named sites (pasture minus bog = −2.02 mg H 2 O m −2 s −1 , 95% CI −5.84–1.79), although ET trajectories differed by date. At the pasture, ET remained positively associated with photosynthetically active radiation. The environmental relationships were supported for a collar-sensitive positive association between deeper water tables and WUE. The chamber measured total water-vapour flux and did not partition evaporation from transpiration. These results provide site-specific, hypothesis generating evidence and require multisite, multiyear confirmation.