The objective of this study was to assess whether total dissolved gas (TDG) concentrations are elevated in chum salmon redds during spring spill operations at Bonneville Dam. Two chum salmon spawning locations downstream from the dam were monitored to measure TDG levels both at egg pocket depth and in the river. The concern was that dissolved atmospheric gas supersaturation resulting from spill operations might adversely affect the survival of chum salmon sac fry in the gravel downstream from the dam. However, no prior research had investigated whether TDG levels were indeed elevated in the incubation habitats during spring spill operations.
To gather data, water quality sensors were installed at both spawning areas near Ives Island and Multnomah Falls on the Columbia River. These sensors measured TDG levels, dissolved oxygen, temperature, specific conductance, and water depth, providing valuable information for interpreting the TDG results. The researchers compensated for depth to determine when TDG levels could potentially impact sac fry. The study observed significant differences in water quality responses to river stage fluctuations between the Ives Island and Multnomah Falls sites. At Multnomah Falls, hyporheic responses remained relatively stable despite daily variations in river concentrations of TDG, dissolved oxygen, and temperature. Conversely, during the early spring before the start of spill operations on April 10, the Ives hyporheic values fluctuated widely in response to changes in river TDG, dissolved oxygen, temperature, and specific conductance. Both locations showed indications of groundwater influence, which is not surprising considering chum salmon prefer spawning areas with relatively warm upwelling water.
To assess TDG levels during different spill conditions, the researchers compared hourly data from Ives pair 3 to Bonneville Dam operations, considering voluntary and involuntary spill events. Voluntary spill occurred according to predetermined target spills provided by the US Army Corps of Engineers (USACE), while involuntary spill happened when the actual spill exceeded the target. The study found no statistical difference between TDG levels during voluntary and involuntary spill events.
Although TDG levels exceeding allowable criteria might be expected during involuntary spill, the findings suggest that potentially toxic conditions for incubating chum salmon sac fry could also occur during voluntary spill periods, especially during low water years when depth compensation is limited. In such cases, pre-emergent sac fry could be negatively impacted by sustained elevated TDG levels in the hyporheic zone, as observed in this study. However, whether these elevated TDG levels will indeed lead to negative impacts remains speculative, as no specific studies on elevated levels were available at the time of the research.
The objective of this study was to assess whether total dissolved gas (TDG) concentrations are elevated in chum salmon redds during spring spill operations at Bonneville Dam. Two chum salmon spawning locations downstream from the dam were monitored to measure TDG levels both at egg pocket depth and in the river. The concern was that dissolved atmospheric gas supersaturation resulting from spill operations might adversely affect the survival of chum salmon sac fry in the gravel downstream from the dam. However, no prior research had investigated whether TDG levels were indeed elevated in the incubation habitats during spring spill operations. To gather data, water quality sensors were installed at both spawning areas near Ives Island and Multnomah Falls on the Columbia River. These sensors measured TDG levels, dissolved oxygen, temperature, specific conductance, and water depth, providing valuable information for interpreting the TDG results. The researchers compensated for depth to determine when TDG levels could potentially impact sac fry. The study observed significant differences in water quality responses to river stage fluctuations between the Ives Island and Multnomah Falls sites. At Multnomah Falls, hyporheic responses remained relatively stable despite daily variations in river concentrations of TDG, dissolved oxygen, and temperature. Conversely, during the early spring before the start of spill operations on April 10, the Ives hyporheic values fluctuated widely in response to changes in river TDG, dissolved oxygen, temperature, and specific conductance. Both locations showed indications of groundwater influence, which is not surprising considering chum salmon prefer spawning areas with relatively warm upwelling water. To assess TDG levels during different spill conditions, the researchers compared hourly data from Ives pair 3 to Bonneville Dam operations, considering voluntary and involuntary spill events. Voluntary spill occurred according to predetermined target spills provided by the US Army Corps of Engineers (USACE), while involuntary spill happened when the actual spill exceeded the target. The study found no statistical difference between TDG levels during voluntary and involuntary spill events. Although TDG levels exceeding allowable criteria might be expected during involuntary spill, the findings suggest that potentially toxic conditions for incubating chum salmon sac fry could also occur during voluntary spill periods, especially during low water years when depth compensation is limited. In such cases, pre-emergent sac fry could be negatively impacted by sustained elevated TDG levels in the hyporheic zone, as observed in this study. However, whether these elevated TDG levels will indeed lead to negative impacts remains speculative, as no specific studies on elevated levels were available at the time of the research.