Spatial Heterogeneity in Shallow Streambed Water Temperatures, Copper River Delta, Alaska: Implications for Understanding Landscape-Scale Climate Change Impacts to Pacific Salmon Egg Incubation Rates

Abstract:

Shallow streambed water temperature is a driving factor for Pacific salmon egg incubation. Small (1 to 2 ^oC) increases in incubation period water temperature may accelerate embryo development. We collected year-round water temperature data at 14 salmon spawning areas on the Copper River Delta (CRD), a 100 km wide coastal foreland in Southcentral Alaska. Our data show considerable temporal and spatial heterogeneity in shallow streambed water temperatures. Different water sources (precipitation vs. groundwater) and a spectrum of hydraulic conductivity and pressure head conditions were also observed. Landscape-scale patterns were not adequately characterized by typical watershed metrics including elevation, area, and slope. We found that catchment- and reach- scale geomorphology and surficial geology govern the surface-groundwater interactions that determine shallow streambed water temperature. The observed differences indicate that, across the CRD landscape, shallow streambed water temperature will not respond equally to projected climatic changes. Water temperature sensitivity to atmospheric conditions also varied by season, suggesting that year-round water temperature data are valuable for assessing potential climate change impacts to Pacific salmon in catchments where incubation period air temperatures are projected to exceed the freezing point with increasing frequency.