Sarah A. Morley

Effectiveness of large woody debris in stream rehabilitation projects in urban basins

Abstract Urban stream rehabilitation projects commonly include log placement to establish the types of habitat features associated with large woody debris (LWD) in undisturbed streams. Six urban in-stream rehabilitation projects were examined in the Puget Sound Lowland of western Washington. Each project used in-stream log placement as the primary strategy for achieving project goals; none included systematic watershed-scale rehabilitation measures. The effectiveness of LWD in these projects was evaluated by characterizing physical stream conditions using common metrics, including LWD frequency and pool spacing, and by sampling benthic macroinvertebrates. In all project reaches where pre-project data existed, pool spacing narrowed after LWD installation. All project sites exhibited fewer pools for a given LWD loading, however, than has been reported for forested streams. In project reaches where the objective was to control downstream sedimentation, only limited success was observed. At none of the sites was there any detectable improvement in biological conditions due to the addition of LWD. Our results indicate that, although LWD projects can modestly improve physical habitat in a stream reach over a time scale of 2–10 years, they apparently do not achieve commensurate improvement in biological conditions.

Benthic Invertebrates and Periphyton in the Elwha River Basin: Current Conditions and Predicted Response to Dam Removal

Abstract The impending removal of two dams on the Elwha River in Washington State offers a unique opportunity to study ecosystem restoration at a watershed scale. We examine how periphyton and benthic invertebrate assemblages vary across regulated and unregulated sections of the Elwha River and across different habitat types, and establish baseline data for tracking future changes following dam removal. We collected multiple years of data on physical habitat, water chemistry, periphyton, and benthic invertebrates from 52 sites on the Elwha River and a reference section on the Quinault River, a neighboring basin. We found that substrate in regulated river sections was coarser and less heterogeneous in size than in unregulated sections, and summer water temperature and specific conductivity higher. Periphyton biomass was also consistently higher in regulated than unregulated sections. Benthic invertebrate assemblage structure at sites above both dams was distinct from sites between and below the dams, due in large part to dominance of mayfly taxa compared to higher relative abundance of midges and non-insect taxa at downstream sites. Following dam removal, we anticipate that both periphyton and benthic invertebrate abundance and diversity will temporarily decrease between and below dams as a result of sediment released from behind the reservoirs. Over the long-term, increased floodplain heterogeneity and recolonization by anadromous fish will alter benthic invertebrate and periphyton assemblages via increases in niche diversity and inputs of marine-derived nutrients. The extended timeline predicted for Elwha River recovery and the complexities of forecasting ecological response highlights the need for more long-term assessments of dam removal and river restoration practices.

Influence of dams on river-floodplain dynamics in the Elwha River, Washington

Abstract The Elwha dam removal project presents an ideal opportunity to study how historic reduction and subsequent restoration of sediment supply alter river-floodplain dynamics in a large, forested river floodplain. We used remote sensing and onsite data collection to establish a historical record of floodplain dynamics and a baseline of current conditions. Analysis was based on four river reaches, three from the Elwha River and the fourth from the East Fork of the Quinault River. We found that the percentage of floodplain surfaces between 25 and 75 years old decreased and the percentage of surfaces >75 years increased in reaches below the Elwha dams. We also found that particle size decreased as downstream distance from dams increased. This trend was evident in both mainstem and side channels. Previous studies have found that removal of the two Elwha dams will initially release fine sediment stored in the reservoirs, then in subsequent decades gravel bed load supply will increase and gradually return to natural levels, aggrading river beds up to 1 m in some areas. We predict the release of fine sediments will initially create bi-modal grain size distributions in reaches downstream of the dams, and eventual recovery of natural sediment supply will significantly increase lateral channel migration and erosion of floodplain surfaces, gradually shifting floodplain age distributions towards younger age classes.

Ecological Effects of Shoreline Armoring on Intertidal Habitats of a Puget Sound Urban Estuary

Shoreline armoring is extensive in urban areas worldwide, but the ecological consequences are poorly documented. We mapped shoreline armoring along the Duwamish River estuary (Washington State, USA) and evaluated differences in temperature, invertebrates, and juvenile salmon (Oncorhynchus spp.) diet between armored and unarmored intertidal habitats. Mean substrate temperatures were significantly warmer at armored sites, but water temperature similar to unarmored habitats. Epibenthic invertebrate densities were over tenfold greater on unarmored shorelines and taxa richness double that of armored locations. Taxa richness of neuston invertebrates was also higher at unarmored sites, but abundance similar. We did not detect differences in Chinook (O. tshawytscha) diet, but observed a higher proportion of benthic prey for chum (O. keta) from unarmored sites. Given that over 66% of the Duwamish shoreline is armored—similar to much of south and central Puget Sound—our results underscore the need for further ecological study to address the impacts of estuary armoring.

Estimating Changes in Coho Salmon and Steelhead Abundance from Watershed Restoration: How Much Restoration is Needed to Measurably Increase Smolt Production?

Abstract Using existing data from evaluations of habitat restoration, we estimated the average change in coho salmon Oncorhynchus kisutch and steelhead O. mykiss parr and smolt densities for common in-channel (culvert removal, large wood placement, boulder placement, and constructed logjams) and floodplain restoration techniques (constructed side channels and reconnected floodplain habitats). We then used these numbers and a Monte Carlo simulation to predict changes in fish numbers in a model watershed for two restoration scenarios: (1) restoration of all accessible habitat within the watershed and (2) restoration of the average amount historically implemented in Puget Sound watersheds (8% of total restorable areas). Mean increases in coho salmon parr or smolt density after restoration ranged from 0.19 to 2.32 parr/m for in-channel techniques and from 0.34 to 1.70 parr/m2 for floodplain techniques. Increases in steelhead parr or smolt density ranged from −0.06 to 0.71 fish/m and from 0.03 to 0.06 fish/m2 ...

Coho Salmon Smolt Production from Constructed and Natural Floodplain Habitats

Abstract We examined existing smolt trapping data from 30 constructed and natural floodplain habitats to determine whether the number (production), density, and length of coho salmon Oncorhynchus kisutch smolts varied by project type and area. At 13 of the 30 sites we conducted detailed physical surveys to examine how morphology (shoreline irregularity), depth, and cover influenced smolt density and length. Mean smolt production for all sites averaged 2,492, density 0.37 smolts/m2, and length 98.9 mm. We found no significant difference in smolt production or density between natural and constructed sites or among project types. Smolt length differed by project type and morphology, excavated ponds (gravel pits and mill ponds) producing significantly larger smolts than constructed groundwater or natural channels. Smolt production was positively correlated with wetted area. Smolt length was negatively correlated with density and distance from salt water, suggesting that sites further inland with cooler water ...

Using Redd Attributes, Fry Density, and Otolith Microchemistry to Distinguish the Presence of Steelhead and Rainbow Trout in the Elwha River Dam Removal Project

AbstractThe removal of impassable dams can affect stream fish communities in many ways, including allowing previously separated anadromous and resident life history types to intermingle. Recolonization of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) into areas that were previously occupied solely by resident conspecifics presents a challenge for monitoring because (1) staging or spawning adults may be difficult to directly observe; and (2) the offspring of the two life history forms are indistinguishable during early life. We evaluated the utility of using redd attributes, fry (age-0) size, and fry density to distinguish the presence of steelhead and Rainbow Trout in the Elwha River, Washington. Redd area and substrate size differed between forms: steelhead redds were significantly larger and had a greater median substrate particle size than Rainbow Trout redds. Fry density was significantly higher in steelhead spawning reaches than in Rainbow Trout reaches during both survey years (2010 and 2...