Proceedings of the 2007 Georgia Basin Puget Sound Research Conference
Session 1E: Restoration Following Dam and Pier Removal
Chair: Sarah Brace
Evaluating Recovery Endpoints in a Rocky Intertidal System
Determination of recovery following pulse disturbance to marine communities requires that recovery endpoints be defined. This can be especially difficult in marine systems characterized by high spatial and temporal variability. I performed experimental removals in a rocky intertidal community to evaluate the performance of alternative methods of determining recovery. I tested whether 1) disturbed plots would resemble their starting conditions after a recovery period; 2) disturbed plots would converge with undisturbed (control) plots after a recovery period; and 3) the abundance of focal taxa in disturbed plots would fluctuate in parallel with those in undisturbed plots after a recovery period; and 4) recovery of focal taxa would indicate community recovery. Results suggest that 1) recovery to pre-disturbance conditions is not a reasonable recovery endpoint because the systems themselves are dynamic; 2) both convergence and parallelism between disturbed and undisturbed plots is reasonable endpoint at small spatial scales, but their performance declines with increasing spatial scale of comparison; and 3) recovery of focal taxa can occur in the absence of community recovery, suggesting that taxon-specific endpoints are less robust than community-level endpoints.
Tracking Nearshore Habitat Recovery After Removal of Overwater Dock Structures
In February, 2006 the Port of Seattle removed 1.3 acres of an aged dock in the East Waterway of the Duwamish River. The Port of Seattle was interested in documenting the nearshore habitat recovery after removing the existing dock structure. The Port of Seattle hired Taylor Associates, Inc. (TAI) to conduct an assessment of the physical and biological effects of the dock removal. The objectives to support this assessment included:
1. Collect physical habitat data at control and impact sites.
2. Collect biological data at control and impact sites.The impact sites included the newly removed dock area (Dock removal 2006), and a second dock removed in 2000 (Dock removal 2000). A control site was also sampled. Data collection methods were duplicated for each of the three site and included four methods:
1. Substrate and vegetation (macrophyte) monitoring transects
2. Water temperature and light intensity data loggers
3. Epibenthic invertebrate sampling
4. Insect fall-out trapsVisual observations confirm the Dock removal 2000 site has abundant macrophytes and the beginnings of a vegetated backshore. The Dock removal 2006 site had no macrophytes or vegetated backshore. Ironically, initial benthic invertebrate results indicate greater numbers of harpacticoid copepods in the Dock removal 2006 site. The site with more abundant macroalgae did have more corophium amphipods, however.
Nearshore Fish of the Strait of Juan de Fuca- Implications for Removal of Elwha Dams
Removal of two dams along the Elwha River, scheduled to begin in 2009, is expected to help restore natural sediment processes to the estuary and nearshore near the mouth of the river. Understanding the potential effects of increasing sediment in the nearshore is an essential part of evaluating biological responses to dam removal. Since 2006, we have been collecting data on nearshore fish communities at sites in the eastern and central Strait of Juan de Fuca from Discovery Bay to Crescent Bay. Sites were sampled on a monthly basis, as weather and tides permitted, using a 32m Puget Sound beach seine between April and September. Overall 36 species were identified including four species of Pacific salmon, steelhead trout and cutthroat trout. We found wide distribution of several salmon species, juvenile ling cod, and all life stages of surf smelt. Pink salmon were the most abundant of the salmon species. We also found evidence that multiple spawnings of surf smelt were occurring in the same areas. Information collected during this study will provide a baseline to track the effects of dam removal on the distribution and abundance of nearshore fish communities and aid in future dam removal assessments.
Elwha River Dam Removal: An Update on Collaborative Monitoring Efforts
The impending removal of two large dams from the Elwha River on Washington State’s Olympic Peninsula offers a unique opportunity to study ecosystem restoration at a watershed scale. Numerous government and academic agencies have partnered with the Lower Elwha Klallam Tribe to collect critical baseline data prior to dam removal. This multidisciplinary monitoring effort is focused on understanding what impacts the two dams have had on the Elwha River ecosystem and on formulating testable hypotheses regarding river response to dam removal. Above the dams, the absence of anadromous fish has contributed to decreased marine-derived nutrient subsidies and changes to periphyton and benthic invertebrate assemblages. Below the dams, curtailed wood and sediment delivery has led to decreased channel movement, habitat complexity, and diversity of floodplain forest age. Current salmon populations below the dams have been greatly reduced from historical levels and are largely hatchery dominated. Following dam removal, many of these impacts are expected to persist and perhaps even worsen in the near term as sediment stored behind the dams moves through the system. The extended timeline predicted for ecosystem recovery highlights the need for long-term monitoring in the Elwha River Basin.
Eelgrass Mapping of the Elwha Nearshore
The goal of this project was to gather pre-dam removal nearshore habitat data along the “Elwha Shoreline” by mapping the location, extent, depth, and patchiness of eelgrass (Zostera marina) from the west end of Freshwater Bay to the tip of Ediz Hook. Our methods were identical to the underwater videographic methods used by the Washington State Department of Natural Resources Submerged Vegetation Monitoring Project. We observed three eelgrass beds within the study area: one along the north shore of Ediz Hook and two in Freshwater Bay. No eelgrass was observed within 1 nm of the Elwha River mouth. The dominant feature of the nearshore habitat was understory kelp and large schools of juvenile Pacific sand lance (Ammodytes hexapterus). The project, funded by the Clallam Marine Resources Committee (MRC), is part of a multi-disciplinary effort to understand and optimize the nearshore restoration associated with the upcoming dam removals.