Characterizing groundwater seepscapes: Variable hydrologic and biogeochemical fluxes through space and time

Abstract:

Groundwater (GW) discharges along river banks connect local hillslope and regional GW flow paths with surface waters. GW flow paths vary in length and residence time and converge in focused zones along the river corridor, creating complex GW ‘seepscapes’ that are windows into GW quality. Our research aims to quantify the variability of hydrologic and biogeochemical fluxes within clusters of observed river bank seeps over both space and time. We collected water samples from 40 GW seep points, located using thermal infrared cameras along two reaches (1 and 1.5 km) in the Farmington River, CT, USA. Each reach contains two seepage zones consisting of 4-5 seepage facies, (i.e. areas of seepage that extend 10’s of m along the river bank). Water chemistry was measured at 4 to 5 points within each facie in each zone (40 total points) on three sampling dates between August and November 2019 to capture varying river flow conditions. Hourly GW discharge temperature signals were also collected from July to November with temperature profilers to model vertical GW flux. Preliminary chemistry data show varying degrees of spatial and temporal stability within and among facies. For example, within a single facie, the total nitrogen (TN) range of one sampling period was 3.99 - 15.06 mg-N/L (n= 9 points), while an adjacent facie (68 m upstream) ranged from 1.30 - 4.26 mg-N/L (n = 9 points) for the same sample period. Throughout sampling periods, the TN concentration ranged from 2.51-15.06 mg-N/L for a single point within a seep facie, while an adjacent point within the same facie (5 m upstream) ranged from 3.41-3.99 mg-N/L. Preliminary data are being paired with GW flux signals and suggest that seep facies potentially have dynamic hydrologic and biogeochemical behaviors which can be used to better categorize seepscapes across spatial and temporal scales.