Influence of groundwater on distribution of dwarf wedgemussels (<i>Alasmidonta heterodon</i>) in the upper reaches of the Delaware River, northeastern USA

Abstract

Abstract. The remaining populations of the endangered dwarf wedgemussel (DWM) (Alasmidonta heterodon) in the upper Delaware River, northeastern USA, were hypothesized to be located in areas of greater-than-normal groundwater discharge to the river. We combined physical (seepage meters, monitoring wells and piezometers), thermal (fiber-optic distributed temperature sensing, infrared, vertical bed-temperature profiling), and geophysical (electromagnetic-induction) methods at several spatial scales to characterize known DWM habitat and explore this hypothesis. Numerous springs were observed using visible and infrared imaging along the river banks at all three known DWM-populated areas, but not in adjacent areas where DWM were absent. Vertical and lateral groundwater gradients were toward the river along all three DWM-populated reaches, with median upward gradients 3 to 9 times larger than in adjacent reaches. Point-scale seepage-meter measurements indicated that upward seepage across the riverbed was faster and more consistently upward at DWM-populated areas. Discrete and areally distributed riverbed-temperature measurements indicated numerous cold areas of groundwater discharge during warm summer months; all were within areas populated by DWM. Electromagnetic-induction measurements, which may indicate riverbed geology, showed patterning but little correlation between bulk streambed electromagnetic conductivity and areal distribution of DWM. In spite of complexity introduced by hyporheic exchange, multiple lines of research provide strong evidence that DWM are located within or directly downstream of areas of substantial focused groundwater discharge to the river. Broad scale thermal-reconnaissance methods (e.g., infrared) may be useful in locating and protecting other currently unknown mussel populations.

Identification of groundwater exfiltration, interflow discharge, and hyporheic exchange flows by fibre optic distributed temperature sensing supported by electromagnetic induction geophysics

“…The presence of clays below permeable sands and gravels agrees with the abrupt vertical transition from low to high EC values observed in the EMI profiles at around 1‐m depth. The assimilation of high EC values to fine materials (in the absence of bedrock) is consistent with EMI geophysics observations of Rosenberry et al (). Downstream cores at TR3 and TR4 indicate the absence of fine‐textured materials such as clay or organic deposits.…”

“…The present study applies a multilinear 2D layout of FO-DTS to identify the intensity and spatial distribution of the different HEF In addition, similarly to the works of Rosenberry et al (2016) at coarse-grained fluvial settings, we test the potential of EMI geophysics for exploring the subsurface structures of a heterogeneous sandy stream to support the interpretation of GW-SW exchange based on the thermal footprints observed with FO-DTS.…”

“…In contrast to other geophysical techniques such as electrical resistivity imaging or georadar (Crook et al, ; Day‐Lewis, White, Johnson, Lane, & Belaval, ), there are few electromagnetic induction (EMI) applications in stream sediments (Binley et al, ; Gourry, Vermeersch, Garcin, & Giot, ; Mansoor, Slater, Artigas, & Auken, ; Rosenberry, Briggs, Voytek, & Lane, ) despite its advantages for quick and economic exploration of subsurface structures (Robinson et al, ). Advantages of EMI compared with electrical resistivity imaging are its readiness and flexibility to explore large subsurface areas in detail without requiring much manpower, resources or time.…”

DTSGUI: A Python Program to Process and Visualize Fiber‐Optic Distributed Temperature Sensing Data

“…For wide and complex rivers, it may be desirable to deploy fiber-optic cables in more complicated geometries to better define SWI temperature dynamics in two dimensions. Dwarf wedgemussels have been observed on the south side of a mid-channel island in the Delaware River, so a FO-DTS cable was deployed along the SWI throughout that area from July 25, 2012, to July 27, 2012, as originally reported by Rosenberry et al (2016). Due to the double-ended measurement scheme and the complicated spatial deployment, the complete dataset is difficult to interpret in heat-map view (Figure 3a).…”

Wetland‐Scale Mapping of Preferential Fresh Groundwater Discharge to the Colorado River

“…Airborne applications are fundamentally advancing hydrogeologic characterization at basin scales, but do not yet have the spatial resolution and near‐surface sensitivity applicable to most studies of groundwater/surface water (GW/SW) exchange (Minsley et al ). Along the land surface, EMI instruments are hand carried (Callegary et al ), pulled (Ong et al ), and (or) floated (Rosenberry et al ) while georeferenced data are continuously collected. Depth of investigation depends on the instrument type and configuration, and on subsurface resistivity, where more conductive materials limit the effective depth of penetration.…”