Factors Controlling Dissolved Oxygen Concentration in the Hyporheic Zone Induced by Fish Egg Nests

Abstract:

There is currently limited research on the effects of bed depressions, such as those associated with fish nests, on hyporheic flow and biogeochemistry. A series of flume experiments are in progress, with the aim of understanding the effects of bed depressions on the hyporheic flow of oxygenated water. This study focuses on fish nests, also called redds, which represent a typical depression or scour feature. Previous research has shown that redd topography induces hyporheic circulation, but experiments regarding the oxygen concentration in and around the redds have not been conducted. We are determining the ways in which redds affect dissolved oxygen distribution and how this is controlled by hyporheic flow. The oxygen concentration across the cross-sectional plane of a fish nest is measured using a planar optode and microsensors. Hydraulic measurements include pressure measurements along the sediment-water interface and dye visualization. The redd design is based on a salmonid redd, which consists of a scour feature and a tailspin. The salmonid eggs are found in the tailspin. We hypothesize that the oxygen concentration will be greatest in close proximity to the gravel base of the redd and concentration will decrease with increasing depth and distance from the redd. Higher oxygen concentrations in the tailspin supports the placement of fish eggs within that area as opposed to a less oxygenated area of the streambed. Thus, fish nests are likely bio-engineered to optimize hyporheic flow and biogeochemistry to improve egg viability.