GENERATION AND IMPLICATIONS OF WINTER DIEL DISCHARGE FLUCTUATIONS IN A HEADWATER CATCHMENT IN WESTERN NC, USA

Diurnal or diel fluctuations in discharge associated with evapotranspiration have been identified in catchments around the world. While several mechanisms have been proposed to explain the generation of these signals, there is not a clear consensus. To investigate diurnal discharge fluctuations in western North Carolina, we examined discharge and groundwater level records from a 43 ha headwater catchment near Cullowhee, NC. Land cover in the catchment has varied significantly over the past 100+ years. Widespread cutting of the forest occurred near the turn of the century, followed by a period where it was primarily pasture, followed by reforestation, cutting again in the 1980/90’s, and finally another period of reforestation. As a result, invasive species dominate parts of the catchment. We found diel fluctuations in discharge in the growing season, as expected, but also in the dormant season. Furthermore, this diel signal increased in amplitude by about 50% during the dormant season. We attribute the increased amplitude winter diel fluctuations to a combination of higher winter groundwater levels and the dominance of Chinese privet, an invasive evergreen species, in riparian areas in the lower portion of the catchment. This suggests an invasive species is altering the water budget for the catchment. Furthermore, the seasonal differences in diel discharge fluctuations paired with groundwater records suggest that diel streamflow variations are generated primarily in the near-stream zone and not from evapotranspiration on hillslopes.