The Salmon Trout River is the only river on the south shore of Lake Superior known to sustain a reproducing adfluvial coaster brook trout (coaster) population. Previous studies of the Salmon Trout River have characterized the life history and ecology of coasters, but the environmental factors influencing their selection of spawning habitat is unknown. We hypothesize that the spatial distribution of groundwater inflows through river-bottom sediments is strongly related to the distribution of spawning sites. High-resolution data collection methods were implemented to quantify the interaction between the groundwater and surface water in order to verify the presence or absence of groundwater discharge into the river at sites that support a reproducing population of coaster brook trout. A network of 1.5 inch I.D. PVC monitoring wells was installed in two active spawning sites and their associated non-spawning sections located immediately upstream and downstream from the active spawning sites. Each monitoring well was equipped with five temperature loggers placed at incremental depths (up to 4 feet) beneath the riverbed. A portable inflatable packer device was used to isolate discrete intervals within the monitoring wells to acquire differential pressure measurements.
Results/Conclusions
Analysis of temporal temperature and pressure data at multiple substrate depths enabled the exchange of water between the groundwater and surface water to be continuously monitored and quantified at both study sites. By independently inverting temperature and pressure measurements, more precise estimates of subsurface water velocities were obtained. The temperature logger network has been continuously monitoring the interaction between the groundwater and surface water since October 2007, during which time coaster migration, redd building activity, embryonic development, and emergence have taken place. Results of our analysis show a distinct correlation between groundwater discharge and active coaster brook trout spawning sites on the Salmon Trout River.
