Using thermal tracers to determine fall-run chinook spawning site selection preferences on the Lower American River, California, USA

Thesis (M.S., Geology)--California State University, Sacramento, 2014.Thermal tracers were used to characterize two adjacent salmonid spawning habitat sites on the Lower American River: a natural spawning feature heavily used by fall-run Chinook salmon and a less utilized site that was enhanced with spawning gravels. A network of monitoring wells were installed at the sites to monitor stream and subsurface water temperatures coupled with pressure to determine subsurface flow characteristics. Data was qualitatively analyzed to investigate differences in subsurface flow paths using temperature gradients. Additionally, hydraulic conductivity and seepage discharge values were estimated at the monitoring wells using 1DTempPro, a recently developed graphical user interface for VS2DH that facilitates the one-dimensional energy transport model.\ud \ud Qualitative and quantitative results show clear differences between the two study sites. The natural spawning site showed more temperature variation with depth from surface water temperature while the enhanced site???s subsurface temperatures closely followed stream temperature variations. Furthermore, estimated hydraulic conductivity and specific discharge values at the natural site were one to two orders of magnitude lower than those estimated at the enhanced spawning site. Specific discharge values also showed a mix of upwelling and downwelling conditions at the natural spawning site while downwelling dominated the enhanced spawning site. \ud \ud Qualitative and quantitative results suggest spawning fall-run Chinook salmon in the Lower American River prefer spawning features that have a mix of downwelling and upwelling flow conditions with relatively lower hydraulic conductivity values which allow adequate mixing of groundwater and surface water in the subsurface. These conditions create a temperature signal in the shallow subsurface that is distinctly different than the surface water temperature signal. \ud \ud This study also shows the utility of employing heat as a tracer to characterize spawning features in streams. Spawning habitat enhancement projects are likely to increase in the future in response to salmonid population vulnerability in rivers. Therefore, qualitative and quantitative evaluation of habitat quality before and after project completion is crucial for improving this restoration technique. Thermal tracers provide a relatively simple, low-cost, low-maintenance method for determining key habitat characteristics over long time scales and at potentially high spatial resolutions.Geolog