Discussion: Should the Dams Be Removed to Save the Pacific Northwestern Salmon Population?

From 1885 till now, dams keep played an important role in Pacific Northwest. However, despite providing transportation convenience and electricity affecting the salmon population, they greatly impacted the salmon population. Nowadays, people standing for different parties are arguing whether the dams should be removed to restore the salmon population. Currently, a solid plan for dam removal has been proposed by Congressman Simpson. And it’s barely a start, further discussions will become more intensified and require an urgent environmental political response.

Reconnecting the Elwha River: Spatial Patterns of Fish Response to Dam Removal

The removal of two large dams on the Elwha River was completed in 2014 with a goal of restoring anadromous salmonid populations. Using observations from ongoing field studies, we compiled a timeline of migratory fish passage upstream of each dam. We also used spatially continuous snorkeling surveys in consecutive years before (2007, 2008) and after (2018, 2019) dam removal during summer baseflow to assess changes in fish distribution and density over 65 km of the mainstem Elwha River. Before dam removal, anadromous fishes were limited to the 7.9 km section of river downstream of Elwha Dam, potamodromous species could not migrate throughout the river system, and resident trout were the most abundant species. After dam removal, there was rapid passage into areas upstream of Elwha Dam, with 8 anadromous species (Chinook, Coho, Sockeye, Pink, Chum, Winter Steelhead, Summer Steelhead, Pacific Lamprey, and Bull Trout) observed within 2.5 years. All of these runs except Chum Salmon were also observed in upper Elwha upstream of Glines Canyon Dam within 5 years. The spatial extent of fish passage by adult Chinook Salmon and Summer Steelhead increased by 50 km and 60 km, respectively, after dam removal. Adult Chinook Salmon densities in some previously inaccessible reaches in the middle section of the river exceeded the highest densities observed in the lower section of the river prior to dam removal. The large number (>100) of adult Summer Steelhead in the upper river after dam removal was notable because it was among the rarest anadromous species in the Elwha River prior to dam removal. The spatial extent of trout and Bull Trout remained unchanged after dam removal, but their total abundance increased and their highest densities shifted from the lower 25 km of the river to the upper 40 km. Our results show that reconnecting the Elwha River through dam removal provided fish access to portions of the watershed that had been blocked for nearly a century.

Carbon, Nutrients and Methylmercury in Water from Small Catchments Affected by Various Forest Management Operations

Forest management activities in boreal and hemiboreal environments have been found to increase the concentration of carbon, nutrients, and methylmercury (MeHg) in runoff water, thus contributing to environmental quality issues. We evaluated carbon, nutrient, and MeHg concentrations in water at eight small, forested catchments on organic soils in Latvia, subject to ditch cleaning and beaver dam removal. These management-induced disturbances were classified into a major, minor, or no disturbance classes. The concentrations of dissolved organic carbon and total nitrogen were elevated in disturbed catchments (both major and minor) compared to the catchments with no disturbance. The concentrations of MeHg in the water displayed a clear seasonal variation with higher concentrations in spring and summer, but there were no significant differences in MeHg concentrations between catchments with major, minor, and no disturbances. However, the higher concentrations of SO42− in the disturbed catchments compared to those undisturbed may promote MeHg formation if the conditions become more reduced further downstream. While most former studies of forest management effects on water quality have focused on forest harvest, our research contributes to the currently rather scarce pool of data on the impact of less-studied management operations, such as ditch cleaning and beaver dam removal, on carbon, nutrient, and MeHg concentrations in runoff water.

A Simulation-Optimization System to Assess Dam Removal With a Focus on Environmental Degradations at Downstream

The present study proposes and evaluates an integrated framework to assess dam removal in which downstream river habitats and reservoir operation were simulated in three different statuses including conventional reservoir operation optimization, optimal release considering environmental aspects in the structure of the optimization model and natural flow. Fuzzy physical habitat simulation was used to assess physical habitats. Moreover, ANFIS based model was utilized to simulate thermal tension and dissolved oxygen tension at downstream habitats. Particle swarm optimization was applied in the optimization models. Results of the optimization models and habitat suitability in the natural flow were compared by applying different measurement indices including reliability index, vulnerability index, The Nash–Sutcliffe model efficiency coefficient (NSE) and root mean square error (RMSE). Based on the results in the case study, reliability of water supply might be reduced in the optimal release for environment and demand. Furthermore, optimal release for environment is not able to protect downstream aquatics habitats properly. Thus, if protecting downstream habitats is aimed, dam removal might be logic in the case study. The main limitation of the proposed method is high computational complexities.