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.     

Patterns of Surf Smelt, Hypomesus pretiosus, Intertidal Spawning Habitat Use in Puget Sound, Washington State

Surf smelt Hypomesus pretiosus are an important part of the Salish Sea food web and obligate beach spawners, yet little is known about the spatiotemporal distribution of spawning and beach characteristics related to spawning success. We counted smelt eggs at 51 sites around Camano Island, Puget Sound, Washington every 2?weeks for 1?year and at 13 of those 51 sites each month in the following year. At each site, we measured beach characteristics hypothesized to affect spawning habitat suitability as measured by egg abundance and mortality. Eggs were collected at 45 sites and pooled by month for analyses. Few sites (N?=?10, 19.6?%) contributed 87?% of total eggs and 89?% of all live eggs collected. Mean total egg counts at sites were higher (p?<?0.019) in Jul?CSep (1,790.7, SE?=?829.5) than in Jan?CMar (26.1, SE?=?10.2). Principal component and regression analyses suggested that aspect, fetch, solar radiation, and beach temperature predicted egg abundance but not mortality. Because a small proportion of sites appear to support most spawning activity, a conclusion consistent with year?2 egg counts, impacts to relatively few beaches could greatly affect surf smelt production.     

Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA

Episodic, large‐volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late Holocene delta at southern Puget Sound. Multibeam bathymetry, ground‐penetrating radar (GPR) and vibracores were used to investigate the morphologic and stratigraphic evolution of the Nisqually River delta. Two fluvial–deltaic facies are recognized on the basis of GPR data and sedimentary characteristics in cores, which suggest partial emplacement from sediment‐rich floods that originated on Mount Rainier. Facies S consists of stacked, sheet‐like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta. Flat‐lying, highly reflective surfaces separate the sand sheets and comprise important facies boundaries. Beds of massive, pumice‐ and charcoal‐rich sand overlie one of the buried surfaces. Organic‐rich material from that surface, beneath the massive sand, yielded a radiocarbon age that is time‐correlative with a series of known eruptive events that generated lahars in the upper Nisqually River valley. Facies CF consists of linear sandbodies or palaeochannels incised into facies S on the lower delta plain. Radiocarbon ages of wood fragments in the sandy channel‐fill deposits also correlate in time to lahar deposits in upstream areas. Intrusive, sand‐filled dikes and sills indicate liquefaction caused by post‐depositional ground shaking related to earthquakes. Continued progradation of the delta into Puget Sound is currently balanced by tidal‐current reworking, which redistributes sediment into large fields of ebb‐ and flood‐oriented bedforms.     

Circulation in Carr Inlet,Puget Sound,during Spring 2003

The relatively slow flow and exchange of Carr Inlet water with the main basin of Puget Sound, Washington, favor eutrophication. To study Carr Inlet’s circulation, the Model-measurement Integration Experiment in Estuary Dynamics (MIXED) was conducted in March–May 2003, spanning the spring bloom. From observations and numerical simulations the circulation was decomposed into tidal and subtidal components; the former was dominated by the M2 tide, the latter by atmospheric forcing. Near the surface, the subtidal velocity was correlated with wind. At mid depths, the subtidal velocity was organized into vertical bands arising from internal waves excited by wind forcing of the water surface. The tidal flow was more strongly steered by local bathymetry and weaker in peak magnitudes than the subtidal flow, yet it contributed more mechanical energy to the inlet. Tidal eddies reduce exchange of water through the inlet’s entrances. Numerical simulations with the Princeton Ocean Model recreated many observed features, including the three-layer vertical structure of outflow at the surface and bottom and inflow at mid depth, the mid-depth subtidal response to the wind, and characteristics of the tide. While the model produced greater subtidal flow magnitudes at depth and differences in the phase of the M2 tide compared to observations, overall the case study provided support for more comprehensive simulations of Puget Sound in the future.     

Significance of soft-sediment clasts in glacial outwash, Puget Sound, USA

Soft-sediment clasts composed of silt and clay are contained within glacial outwash sands in the Puget Sound, Washington State, USA. The outwash was deposited during ice retreat of the Cordilleran ice sheet around 17 cal kyr BP. The soft-sediment clasts have a distinctive and consistent morphology and disposition within the sand beds. The sedimentology, sedimentary structures and presence of soft-sediment clasts suggest sand was deposited as proglacial outwash with silts and clays deposited in meltwater pools. Following drying-out of the pools and subaerial cracking, lumps of silt and clay were excavated by meltwater and transported distally as soft-sediment clasts within high-density flows. The most likely final depositional setting is as a Salisbury-type ‘delta’ in which subaqueous outwash grades distally into deeper water. This interpretation shows the power of soft-sediment clasts to inform on past processes and palaeogeography for which there is often little evidence in the geologic record.     

Sponge gemmules from lake sediments in the Puget Lowland,Washington

Gemmules of five species of freshwater sponge found in deposits at Cedar Mountain bog in the southeastern Puget Lowland were used to infer that during the late-glacial period the water was calcareous, was not deficient in SiO₂, was aerobic, and had a pH in the range 6.6–8.5. This is consistent with plant fossil data. In view of their paleoenvironmental potential it is worth looking for gemmules when extracting other fossils from lake sediments.     

Organo-sulfur compounds in sediments of the Puget Sound basin

Sediment samples from a variety of different environments were analyzed for organo-sulfur compounds (OSC) to provide the first characterization of the amounts and types of these compounds in sediments of the greater Puget Sound basin. A gas Chromatograph equipped with a sulfur specific flame photometric detector was used to quantify individual OSC. Compositions of OSC mixtures were essentially constant throughout the study area. Dibenzothiophene (DBT), its alkylated homologs, and an unknown compound were the predominant OSC in most samples. Concentrations of total OSC and DBT ranged from 4 to 60 and 0.4 to 2 μg/g organic carbon, respectively. The flux of OSC to the sediments at a station in central Puget Sound west of Seattle was approximately 140 ng/cm²/yr. The profile of total OSC concentration with depth showed three organic sulfur compounds that are apparently created in situ in the vicinity of where hydrogen sulfide production begins. The concentrations of the aromatic OSC were relatively constant with depth. Although several anthropogenic sources of OSC were identified, there was no evidence that OSC from these sources were accumulating in the sediments. The major source of the aromatic OSC in the sediments is apparently atmospheric input from natural sources such as forest fires.     

A record of late Quaternary vegetation from Davis Lake,southern Puget Lowland,Washington

Pollen and macrofossil analyses of a core spanning 26,000 yr from Davis Lake reveal late Pleistocene and Holocene vegetational patterns in the Puget Lowland. The core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units. The late Pleistocene pollen sequence records two intervals of tundra-parkland vegetation. The earlier of these has high percentages of Picea, Gramineae, and Artemisia pollen and represents the vegetation during the Evans Creek Stade (Fraser Glaciation) (ca. 25,000–17,000 yr B.P.). The later parkland interval is dominated by Picea, Tsuga mertensiana, and Gramineae. It corresponds to the maximum ice advance in the Puget Lowland during the Vashon Stade (Fraser Glaciation) (ca. 14,000 yr B.P.). An increase in Pinus ontorta pollen between the two tundra-parkland intervals suggests a temporary rise in treeline during an unnamed interstade. After 13,500 yr B.P., a mixed woodland of subalpine and lowland conifers grew at Davis Lake during a period of rapid climatic amelioration. In the early Holocene, the prolonged expansion of Pseudotsuga and Alnus woodland suggests dry, temperate conditions similar to those of present rainshadow sites in the Puget Lowland. More-mesic forests of Tsuga eterophylla, Thuja plicata, and Pseudotsuga, similar to present lowland vegetation, appeared in the late Holocene (ca. 5500 yr B.P.).     

Ice-Sheet Glaciation of the Puget lowland, Washington, during the Vashon Stade (late pleistocene)

During the Vashon Stade of the Fraser Glaciation, about 15,000–13,000 yr B.P., a lobe of the Cordilleran Ice Sheet occupied the Puget lowland of western Washington. At its maximum extent about 14,000 yr ago, the ice sheet extended across the Puget lowland between the Cascade Range and Olympic Mountains and terminated about 80 km south of Seattle. Meltwater streams drained southwest to the Pacific Ocean and built broad outwash trains south of the ice margin. Reconstructed longitudinal profiles for the Puget lobe at its maximum extent are similar to the modern profile of Malaspina Glacier, Alaska, suggesting that the ice sheet may have been in a near-equilibrium state at the glacial maximum. Progressive northward retreat from the terminal zone was accompanied by the development of ice-marginal streams and proglacial lakes that drained southward during initial retreat, but northward during late Vashon time. Relatively rapid retreat of the Juan de Fuca lobe may have contributed to partial stagnation of the northwestern part of the Puget lobe. Final destruction of the Puget lobe occurred when the ice retreated north of Admiralty Inlet. The sea entered the Puget lowland at this time, allowing the deposition of glacial-marine sediments which now occur as high as 50 m altitude. These deposits, together with ice-marginal meltwater channels presumed to have formed above sea level during deglaciation, suggest that a significant amount of postglacial isostatic and(or) tectonic deformation has occurred in the Puget lowland since deglaciation.     

Lake Tapps tephra: An early Pleistocene stratigraphic marker in the Puget Lowland, Washington

The rhyolitic Lake Tapps tephra was deposited about 1.0 myr ago, shortly after culmination of the early phase of the Salmon Springs Glaciation in the Puget Lowland. It is contained within sediments that were deposited in ponds or lakes in front of the reteating glacier. An herb-dominated tundra existed in the southern Puget Lowland at that time. Lake Tapps tephra is most likely the product of an eruption that in part was phreatomagmatic. It forms an early Pleistocene stratigraphic marker across the southern sector of the Puget Lowland and provides a link between Puget lobe sediments of the Cordilleran Ice Sheet and sediments deposited by Olympic alpine glaciers.     

Nitrogen limitation of phytoplankton in a shallow embayment in northern Puget Sound

The effect of nutrient enrichments on natural phytoplankton assemblages was examined in six experiments conducted from June to October 1992. Short-term (4 d to 7 d) nutrient enrichment bioassays were incubated in situ in Padilla Bay, a slough-fed estuary in northern Puget Sound, Washington. Ammonium additions (15 μM) significantly (p<0.001) stimulated phytoplankton biomass accumulation during all six experiments. In two experiments, nitrate additions (15 μM) significantly stimulated accumulation of phytoplankton biomass during October, but not September. Addition of phosphate (1.0 μM) or silicate (15 μM) alone did not stimulate phytoplankton biomass accumulation during any of the experiments. In most experiments, phytoplankton response was greatest in combination treatments of ammonium and phosphate. Dissolved inorganic nutrient concentrations in the containers decreased during all incubations, but showed the greatest reduction in treatments receiving nitrogen. Dissolved inorganic nitrogen (DIN) to phosphate (PO₄ ^3?) ratios were below 16∶1 during all experiments, suggesting the potential for nitrogen limitation. In three experiments, the response of photosynthetic nanoplankton (<20 μm) to ammonium additions was compared to that of the total phytoplankton assemblages. Accumulation of nanoplankton biomass exceeded that of the total phytoplankton during two experiments in August but showed no significant response to ammonium additions in October. Results from the bioassays, the low DIN∶PO₄ ^3? ratios, and the reduction in nutrient concentrations in the containers provide evidence for potential nitrogen limitation of phytoplankton production during summer in Padilla Bay.     

Seasonal Variation in Guild Structure of the Puget Sound Demersal Fish Community

Identification of food web linkages is a major aim in ecology because it provides basic information on trophic flows and the potential for interspecific interactions. In addition, policy and restoration measures mandated to conform to ecosystem-based management principals can benefit from information on temporal and spatial variability in community-level interactions. Here, we analyzed guild structure of the demersal fish assemblage in Puget Sound, WA, a temperate estuarine system on the US west coast. Using diet information from 2,401 stomachs collected across three seasons (fall, winter, and summer), we identified guild membership for 21 fish species, examined seasonal guild switching, and tested for seasonal shifts in predation and for differences in the degree of diet overlap at the assemblage level. We accounted for ontogenetic variation in diet by dividing species into large (L) and small (S) size classes when appropriate. Using cluster analysis and a permutation approach, we identified seven significant guilds that were typified by predation on benthic invertebrates, pelagic invertebrates, and piscivory. Of the 18 species with more than one season of diet information, six switched guilds (Pacific sanddab L, sturgeon poacher, Pacific tomcod S, speckled sanddab, rex sole, and rock sole S). At the assemblage level, we tested for seasonal differences in prey use between seasons by performing an analysis of similarities based on Bray–Curtis diet similarities and found no significant difference. However, diet overlap was significantly higher in the summer than the fall and winter (with summer > fall > winter) indicating that diets within the assemblage converged in the summer. These results indicate that analyses of guild structure and diet overlap can reveal seasonal variation in community trophic structure and highlight intra-annual food web variation in the Puget Sound demersal fish community.     

Implications of Subfossil Coleoptera for the Evolution of the Mima Mounds of Southwestern Puget Lowland, Washington

The origin of Washington State's Mima Mounds has been debated for over a century, with numerous mechanisms being postulated. Subfossil Coleopteran (beetle) remains recovered from the base of a mound at Mima Prairie consist of species that would be expected in rodent burrows and nests; all but one species are obligate burrow inhabitants. These results suggest the past presence of fossorial rodents (probably pocket gophers,Thomomys mazama) in the mounds, although none live there at present. Whether or not the gophers created the mounds, they may well have been instrumental in maintaining mound geometry until very recently.     

Hydrocarbon geochemistry of the Puget Sound region—I. Sedimentary acyclic hydrocarbons

Hydrocarbon compositions have been determined for ²¹⁰Pb-dated sediment cores collected at 23 sites within the inland marine waters of northwestern Washington State, U.S.A. Concentrations of total aliphatic hydrocarbons (TAH) and an unresolved complex mixture (UCM) are significantly higher in surface sediments near urban areas than at all other locations with a chronology that indicates a predominantly anthropogenic origin. Concentrations of chromatographically resolvable alkanes are comparatively uniform; the major constituents are plant wax n-alkanes and a naturally-occurring suite of fossil isoprenoid and n-alkanes. Pristane concentrations decrease sharply near the sea-sediment interface suggesting rapid degradation of a plankton-derived component. A saturated multibranched, but nonisoprenoid, C₂₀ hydrocarbon and two novel mono-olefinic analogs have been isolated along with a previously unreported suite for four acyclic multibranched C₂₅ polyenes. Structural and distributional similarities between the C₂₀ and C₂₅ multibranched hydrocarbons suggest that they may be structurally homologous and share a common source.     

Mixing and cycling of uranium,thorium and 210Pb in Puget Sound sediments

Activity profiles of excess ²³⁴Th, excess ²¹⁰Pb, ²³²Th, ²³⁰Th, ²³⁴U and ²³⁸U, and ^228/232Th ratios determined in eight box cores of sediment from six sites in central Puget Sound provide new insights into the dynamic nature of solid phase mixing in surface sediments, the exchange of ²²⁸Ra and other soluble species across the sediment-water interface, and the cycling of U, Th and ²¹⁰Pb in this coastal zone.Comparison of excess ²³⁴Th inventories in sediments with its production rate in the overlying water column indicates a mean residence time of at most 14 days for particles in the central Puget Sound water column.Surface sediment horizons with excess ²³⁴Th have no excess ²²⁸Th which might be used to ascertain sediment accumulation rates over the past decade. Instead, deficiencies of ²²⁸Th due to loss of soluble ²²⁸Ra from pore water to the overlying water persist to 20–30 cm, revealing that exchange of soluble chemicals between pore and overlying waters reaches these depths in the extensively bioturbated sediments of Puget Sound.Solid phase U isotope concentrations tend to increase by up to a factor of two with depth in sediments, as a result of dissolved U being biologically pumped down into sediments where it is partially removed when conditions become mildly reducing. ²³²Th and ²³⁰Th activities and ^230/232Th ratios are constant with depth in sediments, indicating constant detrital phase compositions and essentially no authigenic ²³⁰Th. Steady state ²¹⁰Pb depositional activities in and fluxes to Puget Sound sediments average only about onehalf those for sediments of the open Washington coast north of the Columbia River mouth, primarily because of a much lower supply of dissolved ²¹⁰Pb in sea waters adverting into Puget Sound.Excess ²³⁴Th profiles in sediments reveal much more detail about the depth dependency, dynamic nature and recent history of solid phase mixing processes than excess ²¹⁰Pb profiles. At least six of eight ²³⁴Th profiles show that mixing within the ²¹⁰Pb-defined surface mixed layer is depth dependent. In three profiles, ²³⁴Th-derived mixing rates are fastest several centimeters below the sediment-water interface, indicating greater macro-benthic activity at these depths. Depth dependent mixing coefficients derived from the best fit of a four layer, advection-diffusion-decay model to the ²³⁴Th data are consistent with ²¹⁰Pb profiles determined for the same sediments, strongly suggesting that ²³⁴Th and ²¹⁰Pb are mixed equivalently and in a multilayered manner.     

Vented sediments and tsunami deposits in the Puget Lowland,Washington – differentiating sedimentary processes

The sandy deposits produced by tsunamis and liquefaction share many sedimentary features, and distinctions between the two are important in seismically active coastal zones. Both types of deposits are present in the wetlands bordering Puget Sound, where one or more earthquakes about 1100 years ago caused both tsunami flooding and sediment venting. This co‐occurrence allows an examination of the resulting deposits and a comparison with tsunami and liquefaction features of modern events. Vented sediments occur at four of five wetland field localities and tsunami deposits at two. In comparison with tsunami deposits, vented sediments in this study and from other studies tend to be thicker (although they can be thin). Vented sediments also have more variable thickness at both outcrop and map scale, are associated with injected dykes and contain clasts derived from underlying deposits. Further, vented sediments tend to contain a greater variety of sedimentary structures, and these structures vary laterally over metres. Tsunami deposits compared with vented sediments are commonly thinner, fine and thin landward more consistently, have more uniform thickness on outcrop and map scales, and have the potential of containing coarser clasts, up to boulders. For both tsunami deposits and vented sediments, the availability and grain size of source material condition the characteristics of the deposit. In the cases presented in this paper, both foraminifera and diatom assemblages within tsunami deposits and vented sediments consisted of brackish and marine species, and no distinction between processes could be made based on microfossils. In summary, this study indicates a need for more careful analysis and mapping of coastal sediments associated with earthquakes to avoid misidentification of processes and misevaluation of hazards.     

Effects of shoreline modification on a Northern Puget Sound beach: Microclimate and embryo mortality in surt smelt (Hypomesus pretiosus)

Human alteration of Puget Sound shorelines is extensive yet its ecological consequences are largely undocumented. This study evaluates differences between natural and heavily modified beaches in terms of microclimate and one aspect of biological condition. Electronic data laggers were placed at a tidal height of approximately 3.7 m (12 ft) above mean lower low water during July 16–20, 2001, to monitor light intensity, substrate and air temperatures, and humidity. Substrate samples were collected at the end of the monitoring period to evaluate condition and density of eggs from surf smelt (Hypomesus pretiosus), a forage fish species that spawns on gravel-sand beaches in the upper intertidal zone. The modified beach had significantly higher daily mean light intensity, air temperature and substrate temperature, and significantly lower daily mean relative humidity. Particularly striking were the differences in substrate temperature which, on the natural beach, ranged from 12.1°C to 18.2°C (mean=14.1°C) and on the modified beach ranged from 14.4°C to 29.4°C (mean=18.8°C). In addition to these different means and more extreme values, microclimate conditions on the modified beach were more variable, indicative of a less buffered environment. The proportion of smelt eggs containing live embryos on the altered beach was approximately half that of the natural beach.     

Substrate additive studies for the development of hardshell clam habitat in waters of Puget Sound in Washington State: An analysis of effects on recruitment,growth, and survival of the Manila clam,Tapes philippinarum,and on the species diversity and abundance of existing benthic organisms

To meet demands of expanding tribal and recreational hardshell clam fisheries, the Washington State Department of Fish and Wildlife has been developing new hardshell clam habitat. In Oakland Bay, near Shelton, Washington, two artificial substrates were studied to determine the best substrate for use in improving Manila clam (Tapes philippinarum) production. Treatments consisted of a control of natural substrate; a 10 cm layer of nonuniform size gravel ranging from 6 mm to 19 mm in diameter; and a 10 cm layer of a 50∶50 mixture of gravel and crushed oyster shell ranging from 10 mm to 30 mm in diameter. Effects of these substrates on species diversity and relative abundance of existing, benthic organisms were also investigated. Recruitment of Manila clam seed, less than 10 mm shell length, was significantly higher (p<0.05) in the control plots than in the gravel and gravel + shell plots, which showed no significant differences. Recruitment improved in the gravel and gravel + shell plots after a layer of organic debris and fine sediments collected on them. Manila clam survival was significantly higher in gravel and gravel + shell plots compared to control plots. No significant differences in survival were observed between gravel and gravel + shell plots. Manila clam biomass in the gravel and gravel + shell plots was significantly higher than in control plots. Between the gravel and gravel + shell plots there was no significant difference in biomass. Minor differences in species diversity and abundance of existing benthic organisms were observed among treatments. Gammarid amphipods and nemertean worms were enhanced in gravel and gravel + shell plots. Densities of polychaete worms were slightly lower in gravel and gravel + shell plots compared to control plots.     

Exploring the Effects of Shoreline Development on Fringing Salt Marshes Using Nekton,Benthic Invertebrate,and Vegetation Metrics

Fringing marshes are important but often overlooked components of estuarine systems. Due to their relatively small size and large edge to area ratio, they are particularly vulnerable to impacts from adjacent upland development. Because current shoreland zoning policies aim to limit activities in upland buffer zones directly next to coastal habitats, we tested for relationships between the extent of development in a 100-m buffer adjacent to fringing salt marshes and the structure of marsh plants, benthic invertebrates, and nekton communities. We also wanted to determine useful metrics for monitoring fringing marshes that are exposed to shoreline development. We sampled 18 fringing salt marshes in two estuaries along the coast of southern Maine. The percent of shoreline developed in 100-m buffers around each site ranged from 0 to 91 %. Several variables correlated with the percent of shoreline developed, including one plant diversity metric (Evenness), two nekton metrics (Fundulus heteroclitus %biomass and Carcinus maenas %biomass), and several benthic invertebrate metrics (nematode and insect/dipteran larvae densities in the high marsh zone) (p?<?0.05). Carcinus maenas, a recent invader to the area, comprised 30–97 % of the nekton biomass collected at the 18 sites and was inversely correlated with Fundulus %biomass. None of these biotic metrics correlated with the other abiotic marsh attributes we measured, including porewater salinity, marsh site width, and distance of the site to the mouth of the river. In all, between 25 and 48 % of the variance in the individual metrics we identified was accounted for by the extent of development in the 100-m buffer zone. Results from this study add to our understanding of fringing salt marshes and the impacts of shoreline development to these habitats and point to metrics that may be useful in monitoring these impacts.