GROUNDWATER FLUCTUATIONS, STREAM BASEFLOW, AND ION CONCENTRATIONS IN FIRST-ORDER WATERSHEDS ALONG A GRADIENT OF LANDSCAPE POSITION IN THE SOUTHERN PIEDMONT

The Redlair Observatory (RO) is a newly-established, long-term critical zone research site on the southern Piedmont region (Gaston County, NC). This site is located on permanently-preserved agricultural and forest land in the South Fork Catawba River watershed. Redlair’s geology consists of felsic to mafic metavolcanic rocks of the Charlotte Terrane, weathered to a thick saprolite (>21 m b.l.s) and overlain by soils ranging from entisols to ultisols. The objective of RO is to provide long-term ecologic, pedologic, meteorologic and hydrologic data in small zero- and 1st- order watersheds of the Piedmont. The objectives of this study are (1) to determine whether the position of the water table relative to the bedrock-saprolite interface changes seasonally; (2) if the relationship between the water table, weathering profile, and stream chemistry varies with landscape position in the southern Piedmont region. We have instrumented three 1st-order headwater watersheds (total area ~6-16 ha) that have unique landscape positions along a ~1.2 km topographic transect having 60 m of overall relief. One watershed is located at the ridgeline watershed divide of the South Fork Catawba River, one is approximately mid-slope, and one is at the base of a steeper slope proximal to the South Fork Catawba. 17 wells were drilled at 4-25 m depth in the saprolite.

We are measuring continuous, barometrically-compensated groundwater levels and temperatures at 10 min intervals in paired deep-shallow wells located at 8 ridgeline, hillslope, and riparian sites in the first-order watersheds. Weather stations will record microclimate variability: temperature, relative humidity, atmospheric pressure, wind, and storm events. From March to June 2019, depth to groundwater ranged from 1.3 m to 11.4 m b.l.s. in a subset of the wells. Preliminary results indicate groundwater levels in ridgeline wells have risen ~0.8 m within this 3-month period. Riparian groundwater levels appear to have fluctuated by ~0.2 m within the same timeframe. Overall, the initial data and newly deployed sensors record the expected response to an unusually wet winter-spring period in late 2018- early 2019. These instrumented watersheds will continue to record seasonal and inter-annual variability at RO on a long-term basis.