A new nationwide study shines a light on something amazing. The aquatic ecosystem in the Hudson River Estuary watershed has completely rebounded since the dam was removed. Originally constructed in the early 1960s, the dam was intended as a water supply reservoir. In September 2016, removing it literally opened the door to life-enhancing ecological restoration. Inspired and directed by Jeremy Dietrich, the researchers designed a rigorous monitoring protocol. This simple protocol helps determine the health of the stream and measure its recovery over time.
Before the dam was removed, Dietrich established baseline data in June 2016. In less than three years after the removal, the stream’s ecology returned to a more natural state. This new study proves in no uncertain terms just how resilient nature can be. It serves as a reminder about the tangible benefits that dam removal has on local ecosystems.
The Impact of Dam Removal
Dams unequivocally change the natural ecology of streams and rivers by halting sediment and nutrient flow. This physical disruption results in undesirable conditions for aquatic organisms, often resulting in a loss of habitat heterogeneity. Even so, with the dam’s removal, migrating fish—especially juvenile American eels—were once again able to reach previously inaccessible upstream rearing habitats.
Dietrich noted, “If you just look at the stream after removal, you wouldn’t even have known there was a dam there.” This comment encapsulates the drastic reversal in the stream’s ecology since the dam was removed. The upstream and downstream habitats were almost indistinguishable after three years, an encouraging sign of recovery.
The study reported that differences in macroinvertebrate species composition between the upper and lower portion of the stream disappeared during this period. Researchers found this dramatic turnaround remarkable. Water quality indices went from poor to excellent. By year three, upland conditions had made significant improvements and downstream concentrations were above pre-removal levels.
Monitoring Recovery and Assessing Success
TPR’s senior scientist, Jeremy Dietrich, collaborated with a team of criminologists and social scientists to design a community-safe monitoring protocol. Their objective was to monitor and assess the stream’s ecological recovery process. To estimate improvements in water quality, the New York State Department of Environmental Conservation (NYS DEC) calculated changes in Biological Assessment Profile scores. This score was found to be closely correlated with the ecological recovery seen in the study areas.
Dietrich remarked on the broader implications of their findings: “The findings suggest that repeating these types of improvements at many sites within a watershed can potentially lead to cumulative benefits on a regional scale.” This promising outlook is an invitation to dig deeper with us on dam removals as an effective tool for improving local ecosystems in communities big and small.
The economic cost of keeping aging dams safe was another key factor in decision-making. According to Dietrich, “It can generally cost about $1.2 million to fix up a small dam, or you could take it out for about $400,000 and not have to worry about it.” This huge cost differential renders dam removal an attractive option for local stakeholders.
A Step Towards Ecological Restoration
The longer small dams remain in place, the more expensive they become to maintain and operate. This research offers strong and clear support for removing dams as a new strategy for developing more self-regulated aquatic ecosystems. The NYS DEC is beginning to realize the tremendous ecological benefits that can come from removing small dams. Those changes have been profound and meaningful to local communities.
Dietrich emphasized the importance of sharing success stories in environmental restoration efforts: “I think increasingly people have a need to show good news in a broader media environment of gloom and doom.” His insights capture the moment with which we’re increasingly recognizing the value of achieving both environmental resilience and community recovery.
