Turbulence and velocity barriers to upstream emerald shiner (Notropis atherinoides) movement: A field study at Broderick Park, Buffalo - NY.

摘要

Physical modifications near the head of the upper Niagara River in the form of river dredging and construction of vertical seawalls are assumed to have resulted in the channelization of the river leading to increased water velocities and modified turbulence conditions along the shorelines. These changes have presumably impacted the emerald shiners (Notropis atherinoides), a small pelagic minnow that is a key forage species in the local ecosystem. Emerald shiners have been observed to congregate downstream of a shoreline recess at Broderick Park and the goal of this study was to identify if the Broderick Park shoreline posed a substantial impediment to their upstream movement. Water velocity measurements were collected along the Broderick Park Seawall and the Bird Island Pier using an Acoustic Doppler Velocimeter and an Acoustic Doppler Current Profiler to quantify the existing hydrodynamic conditions along the shoreline. The results indicate that the vertical seawall located upstream of the recess is characterized by water velocities that exceed 1 m s-1 and are beyond the known emerald shiner critical swimming speed of ∼ 0.59 m s -1 (Jones et al. 1974; Young 2001). Also, flow turbulence, quantified in terms of turbulent kinetic energy (TKE) and Reynolds shear stress, is the largest upstream of the shoreline recess. The large turbulence values suggest that the emerald shiners may experience disorientation and body damage while moving upstream past this region. Finally, the vertical seawall upstream of the shoreline recess is also characterized by a large number of eddies within a problematic size range for emerald shiners (55 -- 400 mm) that could potentially cause a reduction in their critical swimming speed due to overturn and imbalance. In contrast, the regions downstream of the recess and along the Bird Island Pier are characterized by (a) water velocities that are mostly within the emerald shiner critical swimming speed of ∼ 0.59 m s-1; (b) smaller magnitudes of TKE and Reynolds shear stress; and (c) sizes of eddies that typically lie outside the problematic size range for the emerald shiners. Therefore, it is concluded from this study that the flows along the Broderick Park Seawall upstream of a shoreline recess are likely to pose a substantial impediment to emerald shiner movement due to the current hydrodynamic conditions.