Investigation of water quality in artificial hellbender shelters
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Hellbender salamanders have been facing population decline due to loss of natural habitat. Concrete shelters have been developed to provide additional nesting habitat. The first concrete boot-shaped artificial hellbender nestboxes (Briggler and Ackerson 2012) could be dislodged due to drag forces from large flows. Mohammed et al. (2016) created a hydrodynamically redesigned nestbox to improve stability by reducing drag forces. Even with greater hydraulic stability, many nest boxes were still not being used. A two-part hypothesis is that poor water quality inside the box may be responsible. If circulation of water into the box is limited, then dissolved oxygen (DO) may decrease over time. To test this hypothesis, an experimental plexiglass flume was used. Five pumps provided a range of flow velocities. Two half-scale models of the hydrodynamically redesigned nestbox were constructed, one with potential reaeration holes in the upstream face and one without. To experimentally assess the concentration of DO in the nest boxes, DO sensors were placed in each half-scale model. Results of these experiments show that absent any reaeration holes, DO in the upstream most portion of a shelter is lower than in the downstream location near the entrance. Multiple holes on the upstream face increase the DO, as do placing the holes on either side of the leading edge. Even with the addition of a DO scavenger, the holes were able to reaerate the system. In summary, the addition of one or more reaeration holes in the upstream face of the shelter creates flowthrough, increasing DO, even after the addition of an oxygen scavenger.
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M.S.