Influence of groundwater on distribution of dwarf wedgemussels (<i>Alasmidonta heterodon</i>) in the upper reaches of the Delaware River, northeastern USA
The remaining populations of the endangered dwarf wedgemussel (DWM) (<i>Alasmidonta heterodon</i>) 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,...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-10-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/20/4323/2016/hess-20-4323-2016.pdf |
| Summary: | The remaining populations of the endangered dwarf wedgemussel (DWM)
(<i>Alasmidonta heterodon</i>) 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. |
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| ISSN: | 1027-5606 1607-7938 |