Conclusion

Damming streams and rivers is a complex human-environment interaction that is necessary but also has direct impacts on downstream ecosystems. Increasing stream temperatures throughout New England are impacting native brook trout populations (Lessard, 2003) and causing shifts in the timing of macroinvertebrate emergence (Cheney, 2019). Historical sediments that build up behind dams may contain contaminants from upstream land use and industrial practices. Dams also provide positive ecosystem services by increasing water residence times which may reduce nutrient loading to receiving waters (Maavara, 2020). As humans have shifted the natural flow regime by damming the majority of rivers and streams in New England, we are now starting to see the negative downstream ecosystem consequences of dams mentioned above.  Dam removal should be considered on a case-by-case basis taking into account historical upstream practices and downstream ecosystem health to answer this question: do the downstream ecosystem benefits outweigh the consequences of removing the dam?

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Summary

• The United States has an aging dam infrastructure issue and some dams may not be acting as dams anymore.

  • Thus, are some dams worth removing or not? 

  • The New England region holds a significant portion of these dams, with the majority of their dams being small mill dams that can be as old as 200 years.

• Today, dams are currently impacting New England’s native brook trout population and are causing shifts in macroinvertebrate emergence.

• Additionally, removing dams will decrease nutrient processing due to shorter residence times

• Historical/legacy sediments are building up behind the current dams, and depending on inputs can have contrasting outcomes.

  • The release of natural sediment can i improve coastal erosion, as well as streambed dynamics downstream improving these downstream ecosystems 

  • These sediments may also have contaminants from upstream industrial/land practices. Thus, by removing dams, these contaminants may be released into the downstream ecosystem if not properly remediated beforehand.

• Overall, dam removal should be looked at on a case-by-case basis. 

  • If there is no contamination and not a lot of nutrients within the system, a dam should be removed.

  • If there is a lot of contamination and nutrients within the system, remediation should take place before a dam removal OR the dam should not be removed (usually due to the cost analysis)