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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><i>The Columbia Basin Bulletin: Weekly Fish and Wildlife News </i><a href="http://www.cbbulletin.com">www.cbbulletin.com</a> January 19, 2018 Issue No. 859<o:p></o:p></p><p class=MsoNormal><b><o:p> </o:p></b></p><p class=MsoNormal><b><span style='font-size:12.0pt'>Study Looks At How Elwha Dam Removals Changed Nearshore Ecosystems Near Mouth<o:p></o:p></span></b></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>In the time since the removal of two dams on Washington’s Elwha River, scientists from University of Washington-based Washington Sea Grant, the U.S. Geological Survey, Washington Department of Natural Resources, the Lower Elwha Klallam Tribe, the Environmental Protection Agency and the UW have sifted through eight years of data collected before and after the dam removal projects to analyze the impacts the resulting sediment load has had on the nearshore ecosystems near the mouth of the Elwha River.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The dams sat on the river for more than 100 years, trapping approximately 30 million tons of sediment behind their concrete walls. As the dams were removed between 2012 and 2014, much of this sediment was released downstream.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>“The main impetus for the dam removal was the salmon reintroduction,” said study co-author Stephen Rubin, a USGS fishery biologist. “But it was also about a whole ecosystem restoration, all the way from above the dams to the strait.”<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>In the short-term, however, some hypothesized that the sediment influx to the nearby coastal marine ecosystem could negatively impact certain species. This study sought to monitor these potential impacts and the ecosystem’s progression as it adjusted to post-dam life.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>They found that how organisms were affected depended on the type of sediment that was deposited in their habitat (for example, whether it was sand or mud) and the local turbidity (how murky suspended sediment had made the water). Still, some organisms were more resilient to the changes than others.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>According to the study, the dam removal projects did not result in significant overall changes in the invertebrate or fish communities. Kelp, however, markedly decreased. Understandably so, since kelp relies on light for photosynthesis, and when more sediment is suspended in the water, there is less light available to them.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>“We viewed this as an opportunity to find out what really happens to the nearshore environment after a dam is removed,” said co-author Ian Miller, coastal hazards specialist at Washington Sea Grant.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Their findings <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0187742">http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0187742</a> were published in the journal PLOS ONE in December 2017.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The researchers used SCUBA surveys and towed video transects to quantify the relative abundances of algae, invertebrate species and benthic fish living along the shore near the river, and then compared these findings to the patterns of sediment influx using data collected by the USGS and the UW School of Oceanography on substrate changes, and MODIS satellite imagery to track changes in the suspended sediment in the water column.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>“We had a huge suite of data we were working with, which is one of the things that made this such a complicated endeavor,” Miller said.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>While the study showed a decrease in kelp, Miller notes that these are still relatively early days on the Elwha’s road to recovery. More recent data suggests that, over the last two years, kelp populations at the mouth of the river have already begun to rebound.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>“Even where we saw a negative consequence for one group of organisms, kelp, in our more recent surveys we’ve already begun to see a rapid recovery,” Miller said. Another proverbial grain of sand to add to the pile of knowledge that could help resource managers elsewhere assess the impacts of events that send large amounts of sediment into the coastal zone – and answer questions such as whether to remove dams on their own local rivers.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='mso-margin-top-alt:20.15pt;margin-right:0in;margin-bottom:13.45pt;margin-left:0in'><span style='font-size:15.0pt;font-family:""","serif";color:#333333'>Abstract<o:p></o:p></span></p><p class=MsoNormal style='margin-bottom:9.7pt;line-height:13.45pt'><a name=article1.front1.article-meta1.abstract1.></a><span style='font-size:9.5pt;font-family:""","serif";color:#333333'>The coastal marine ecosystem near the Elwha River was altered by a massive sediment influx—over 10 million tonnes—during the staged three-year removal of two hydropower dams. We used time series of bathymetry, substrate grain size, remotely sensed turbidity, scuba dive surveys, and towed video observations collected before and during dam removal to assess responses of the nearshore subtidal community (3 m to 17 m depth). Biological changes were primarily driven by sediment deposition and elevated suspended sediment concentrations. Macroalgae, predominantly kelp and foliose red algae, were abundant before dam removal with combined cover levels greater than 50%. Where persistent sediment deposits formed, macroalgae decreased greatly or were eliminated. In areas lacking deposition, macroalgae cover decreased inversely to suspended sediment concentration, suggesting impacts from light reduction or scour. Densities of most invertebrate and fish taxa decreased in areas with persistent sediment deposition; however, bivalve densities increased where mud deposited over sand, and flatfish and Pacific sand lance densities increased where sand deposited over gravel. In areas without sediment deposition, most invertebrate and fish taxa were unaffected by increased suspended sediment or the loss of algae cover associated with it; however, densities of tubeworms and flatfish, and primary cover of sessile invertebrates increased suggesting benefits of increased particulate matter or relaxed competition with macroalgae for space. As dam removal neared completion, we saw evidence of macroalgal recovery that likely owed to water column clearing, indicating that long-term recovery from dam removal effects may be starting. Our results are relevant to future dam removal projects in coastal areas and more generally to understanding effects of increased sedimentation on nearshore subtidal benthic communities.<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>