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Geology topics

Renee K. Takesue

Publications and source records attributed to Renee K. Takesue.

At least 19 recordsLinked to original sources
USGS2026

Erosion and transport of sediments in watersheds of southwest Puerto Rico determined from strontium isotopes and mixing models

Sediment outflow from streams to coastal regions can adversely affect water quality and the health of ecosystems including Puerto Rico's southwestern carbonate platform with shallow marine communities. Knowledge of sediment provenance and erosional areas would aid effective restoration to reduce excessive sedimentation. Strontium (Sr) isotopic ratios ( 87 Sr/ 86 Sr) can be used to differentiate between sediment eroded into streams from different lithologies, or rock types, and used in mixing models to estimate proportions of source materials in downstream mixtures. The goal of this study was to use Sr isotopes to differentiate between river sediments in drainages with distinct geologies and present a case study where Sr isotope mixing models are used to identify sediment sourcing to Río Loco and Bahía de Guánica, a priority watershed of the U.S. Coral Reefs Task Force. For the Río Loco watershed, model results indicate that serpentinites in the uplands contributed approximately 71 % of sediment to Bahía de Guánica. About 21 % of sediment was from trachy-andesitic basalts in the foothills, and the remaining 8 % originated from sources on the coastal plain. Neither the uppermost headwater region of Río Loco, the Canal Principal De Riego Valle De Lajas, nor the tributary Quebrada Susúa appeared to be significant sources of sediment to Río Loco's mainstem or Bahía de Guánica at the time of the study. Our results demonstrate that sediment from the serpentinite-bearing areas of Río Loco watershed was effectively transported to the lowlands, which then discharge into Guánica Bay, and highlight the potential use of Sr isotopes as tracers of sediment provenance. This will, in turn, enable better science-based restoration efforts aimed at reducing terrestrial sediment erosion and impacts to marine ecosystems.

Puerto Rico↗
USGS2025

Refining PAH and PCB bioavailability predictions in industrial sediments using source-fingerprinting, particle size, and bulk carbon, Puget Sound, Washington

Nearshore marine sediments in a Puget Sound, Washington industrial embayment had elevated levels of PAHs, PCBs and DDTs. Chemical fingerprints implicated nearshore sources including creosote, industrial oil and tar waste, and a landfill. Elevated concentrations were confined to an approximate 300-m shoreline buffer in the industrial waterfront, suggesting high site fidelity and limited along-shore or off-shore transport. Total PAH concentrations approximately doubled when including alkylated compounds. The industrial sediments often exceeded toxicity criteria; however, chemicals were likely less bioavailable than predicted, in part, due to assumed strong sorption to anthropogenic carbon like coal tar. Analyses of separated particle-size fractions showed that approximately half of PAHs were associated with particles greater than 500 μm, suggesting that a wide range of particle sizes are relevant to occurrence and transport. Predicted freely dissolved chemical concentrations in sediment pore water were unrealistically high using a bulk organic carbon sorption coefficient. When reduced to environmentally reasonable levels by applying a high-sorption partition coefficient applicable to contaminated sediments, predicted freely dissolved concentrations in some industrial sediments exceeded sublethal effect levels or surface water quality standards. Chemical assemblages predicted in the freely dissolved aqueous fraction, which is relevant for biotic uptake from water, shifted to predominantly low molecular weight as compared to sediment, highlighting the role of exposure pathways in bioavailability. Insights from chemical fingerprinting coupled with co-analysis of bulk carbon and grain size allowed refinement of bioavailability assessments of complex chemical mixtures in contaminated nearshore environments that are relevant for ecosystem health and restoration.

Washington↗
USGS2023

Fluvial delivery and wave resuspension of sediment in a sheltered, urbanized Pacific Northwest estuary

The sequence and timing of sediment delivery and redistribution in coastal systems is important for shoreline stability, ecosystem services, and remediation planning. In temperate estuaries, understanding the role of fluvial sediment delivery and dispersal relative to wind and wave remobilization processes is particularly important to address the fate of contaminants, many of which adsorb to fine particles, and to assess changes in coastal systems under projected changes in climate. Here we present an integrated analysis of observations at multiple timescales to evaluate sediment dynamics and the sedimentary coupling between fluvial and oceanographic processes within Bellingham Bay, Washington, USA, an urban estuary. Time-series data of currents, waves, and turbidity at four moorings along with geochemical data from grab samples and cores of seabed sediment from across the bay are contrasted with the dynamics of the Nooksack River, its fluvial sediment source. Even during large (5-yr return interval) river-flood events, water-column suspended-sediment concentration (SSC) near the bed on the outer delta topset was not correlated with Nooksack River runoff and was instead closely correlated with local wind-wave height. In contrast, near-surface SSC was strongly correlated with fluvial discharge, suggesting intense water-column suspended-sediment stratification during flood events. Grain-size and geochemical ( 7 "> 7 Be and excess 210 "> 210 Pb) results from seabed-sediment samples and historical bathymetric measurements of the subaqueous Nooksack River delta reveal spatial gradients of fluvial and wave influence and sediment-accumulation rates. Analysis of historical bathymetric surveys of the Nooksack River delta combined with the geochemical data reveal that about 75% of the fluvial sediment load can be accounted for in the Bellingham Bay receiving system. Studies of this type in urbanized coastal settings can help address ecological and geological questions regarding the risks from contaminants associated with fine-grained sediment, predict longer-term delta morphological evolution, and inform managers planning future coastal restoration efforts

Washington↗
USGS2022

Element concentrations and grain size of sediment from the Similkameen River above Enloe Dam (Enloe Reservoir) near Oroville, Washington, 2019

In 2019, the U.S. Geological Survey conducted a reconnaissance survey of concentrations of 41 trace elements present in bed sediment in the reservoir on the Similkameen River upstream from Enloe Dam, near Oroville, Washington. The Similkameen River drains a watershed containing highly mineralized geologic deposits with current (2019) and historical mining activity. Results of this survey indicated that surface and subsurface sediment are substantially enriched in element concentrations of silver (Ag), arsenic (As), gold (Au), bismuth (Bi), cadmium (Cd), copper (Cu), manganese (Mn), antimony (Sb), selenium (Se), tin (Sn), and tellurium (Te) relative to average concentrations found in upper continental-crustal material. Conversely, concentrations of mercury (Hg) and lead (Pb) in sediment above Enloe Dam (Enloe Reservoir) were generally less than average concentrations in upper continental-crustal material (Hg = 0.05 milligrams per kilogram [mg/kg]; Pb =17 mg/kg). Concentrations of most trace elements were higher in the less than 63-micrometer fraction (silt) and tended to be higher in subsurface than in surface sediment. The concentrations of trace elements were compared to consensus-based aquatic toxicity reference concentrations, Washington State Department of Ecology sediment management standards, and average concentrations of upper continental-crustal material. Arsenic concentrations were consistently elevated above these criteria among samples and often exceeded sediment management standards and aquatic toxicity reference values (both threshold effects and probable effects concentrations). High concentrations of As were measured in sediment with proportionally more material in the less than 63-micrometer size fraction; this result may be related to the presence of ore-processing waste material that has entered the aquatic system from approximately 125 years of mining operations in the basin. Elevated concentrations of chromium and copper that exceed the same criteria as arsenic (As) were measured less consistently and predominantly in the fine-grain size fraction.

Washington↗
USGS2021

Marine paleoseismic evidence for seismic and aseismic slip along the Hayward-Rodgers Creek fault system in northern San Pablo Bay

Distinguishing between seismic and aseismic fault slip in the geologic record is difficult, yet fundamental to estimating the seismic potential of faults and the likelihood of multi-fault ruptures. We integrated chirp sub-bottom imaging with targeted cross-fault coring and core analyses of sedimentary proxy data to characterize vertical deformation and slip behavior within an extensional fault bend along the Hayward-Rodgers Creek fault system in northern San Pablo Bay. We identified and traced four key seismic horizons (R1–R4), all younger than approximately 1400 CE, that cross the fault and extend throughout the basin. A stratigraphic age model was developed using detailed down-core radiocarbon and radioisotope dating combined with measurements of anthropogenic metal concentrations. The onset of hydraulic mining within the Sierra Nevada in 1852 CE left a clear geochemical and magnetic signature within core samples. This key time horizon was used to calculate a local reservoir correction and reduce uncertainty in radiocarbon age calibration and models. Vertical fault offset of strata younger than the most recent surface-rupturing earthquake on the Hayward fault in 1868 CE suggest near-surface vertical creep is occurring along the fault in northern San Pablo Bay at a rate of approximately 0.4 mm/yr. In addition, we present evidence of at least one and possibly two coseismic events associated with growth strata above horizons R1 and R2, with median event ages estimated to be 1400 CE and 1800 CE, respectively. The timing of both these events overlaps with paleoseismic events on adjacent fault sections, suggesting the possibility of multi-fault rupture.

California↗
USGS2021

Land-based sediment sources and transport to southwest Puerto Rico coral reefs after Hurricane Maria, May 2017 to June 2018

The effects of runoff from land on nearshore ecosystems, including coral reef communities, are influenced by both sediment supply and removal by coastal processes. Integrated studies across the land-sea interface describing sources and transport of terrestrial sediment and its nearshore fate allow reef protection initiatives to target key onshore and offshore areas. Geochemical signatures in the fine fraction of terrestrial sediment from watersheds in southwest Puerto Rico were determined by multivariate principal component analysis and used to identify terrestrial sources of sediment runoff to nearshore coral reefs. Sediment settling out of suspension at reefs was collected at approximately 2 month-long intervals in bottom-mounted sediment traps from May 2017 to June 2018, a period that included Hurricanes Irma and Maria. Bulk sediment accumulation rates in traps exceeded a 10 mg/cm 2 /d threshold found to stress corals at 5 of 7 reef sites throughout the 13 month-long study. Geochemical signatures showed that watersheds 10s km to the east were a predominant, year-round source of fine sediment to reefs offshore of Guánica Bay and could have introduced sediment-bound contaminants due to a higher degree of industrialization and urbanization than the local watershed. Sediment runoff from the local watershed appeared to be constrained to a narrow band close to shore. During the 2.5 months after Hurricanes Irma and Maria, bulk sediment accumulation rates increased substantially and fine sediment geochemical signatures were indicative of predominantly distal sources, except outside of the mouth of Guánica Bay, which was strongly impacted by local runoff. Mass wasting, sediment runoff, and coastal turbidity persisted for months after Hurricane Maria and could account for the appearance of a small fraction of geochemical variance from a distal sediment source that appeared in reef traps 4 months post-hurricane and persisted through the end of the study 9 months post-hurricane. Sediment geochemical sourcing in temporally resolved records from sediment traps showed how landscape-scale changes after a major hurricane affected both near-term and long-term sediment delivery to reef communities. In addition, the importance of fine sediment advection from distal sources indicates that successful reduction of land-based pressures on nearshore ecosystems will require cross-jurisdictional strategies.

Puerto Rico↗
USGS2020

Legacy and current-use toxic contaminants in Pacific sand lance (Ammodytes personatus) from Puget Sound, Washington

Forage fish are primary prey for seabirds, fish and marine mammals. Elevated levels of pollutants in Puget Sound, Washington salmon and killer whale tissues potentially could be sufficiently high to elicit adverse effects and hamper population recovery efforts. Contaminant transfer and biomagnification of the toxic compounds measured in this study likely contribute to those elevated concentrations. Pacific sand lance tissues from nine locations were analyzed for a suite of legacy and emerging contaminants including polychlorinated biphenyls, polybrominated diphenyl ethers, chlorinated pesticides, polycyclic aromatic hydrocarbons, alkylphenols, and chlorinated paraffins. Chemicals were detected at all sites generally below available health effect levels for the host. However, sub-lethal effects are known to occur and additive effects from exposure to multiple compounds, like this study’s mixture, are not well understood. Biomagnification calculations suggest that, in some locations, concentrations of polychlorinated biphenyls in forage fish could result in predator tissue concentrations that exceed effect levels.

Washington↗
USGS2019

Physicochemical controls on zones of higher coral stress where Black Band Disease occurs at Mākua Reef, Kauaʻi, Hawaiʻi

Pervasive and sustained coral diseases contribute to the systemic degradation of reef ecosystems, however, to date an understanding of the physicochemical controls on a coral disease event is still largely lacking. Water circulation and residence times and submarine groundwater discharge all determine the degree to which reef organisms are exposed to the variable chemistry of overlying waters; understanding these physical controls is thus necessary to interpret spatial patterns in coral health. The recent discovery of coral Black Band Disease at Mākua Reef on Kauaʻi, Hawaiʻi prompted an investigation into the physicochemical drivers and geomorphic controls of reef water circulation, and the temporally variable nutrient fluxes derived from submarine groundwater discharge. Results reveal localized stagnant water parcels at Mākua Reef where groundwater-derived high nutrient loading and low salinities act in concert as stressors to coralline health – and where Black Band Disease was uniquely identified. The observed high nutrient levels during low tide conditions are likely associated with nearby upstream cesspools and drain fields. Information obtained using such a multidisciplinary approach has direct value for successful management of coastal aquifers and the health and sustainability of adjacent nearshore coral reef ecosystems.

Hawaii↗
USGS2019

Polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and metals in ambient sediment at mussel biomonitoring sites, Puget Sound, Washington

Caged mussels used as biomonitors can provide insights about ambient contaminant assemblages and spatial patterns, sources of contaminants, and contaminant exposure risks for consumers of wild and farmed mussels. This study explored the potential role of ambient sediment in the uptake of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and potentially toxic inorganic elements by caged mussels and complements findings from a Puget Sound-wide stormwater-contaminant mussel-monitoring survey in Washington State. In summary, ambient sediment appeared to be related to mussel uptake of lead and possibly copper at all sites, PCBs at industrial sites, and PAHs at Liberty Bay, Eagle Harbor, and, to a lesser extent, Smith Cove. These findings indicate that resuspended bed sediment is one, but not the only, pathway that filter-feeding mussels are exposed to contaminants. Overall, PAHs, PCBs, arsenic, and potentially toxic metals were low in intertidal bed sediment at the nine sites measured in Puget Sound in February 2016 and signify a low risk of sediment-bound contaminant exposure to mussels at those locations.

Washington↗
USGS2019

Stream sediment geochemistry of four small drainages on the north shore of Kauai west of Hanalei

Geochemical compositions of fine-grained stream sediment from four drainages on the north shore of the island of Kauai, Hawaii, west of Hanalei and two back-beach sites were explored to increase understanding about land-based runoff and ecological risk from runoff to nearshore coral communities. Stream and beach sediment were collected between July 30 and August 2, 2016, and major, minor, and trace elements in the less than 63 micrometer-diameter fraction were analyzed by inductively coupled plasma optical emission spectroscopy and mass spectroscopy. The potentially toxic metals Cr, Cu, Ni, and Zn exceeded levels at which adverse biological effects could be observed; however, these metals seemed to be largely mineral-bound and thus were unlikely to harm organisms. Cd and Pb were below levels of ecological concern. Only a small amount of fine-grained sediment was retained on beaches west of Hanalei sampled in summer 2016 (mean=8.8 percent, median=0.4 percent, range=0–92.8 percent, n=41). Although the scarcity of fine-grained sediment precluded land-based runoff sourcing to the nearshore region, it did indicate that fine-grained sediment and associated contaminants did not accumulate over the long term in the sampled intertidal, subtidal, and reef-flat environments, which would reduce sediment-related pressures on coral communities there.

Hawaii↗
USGS2019

Contaminant baselines and sediment provenance along the Puget Sound Energy Transport Corridor, 2015

The transport of coal and oil can result in contaminated soil, water, and organisms from unintended releases. Trains carrying coal and crude oil regularly pass through Puget Sound, Washington, and an increase in the number of coal and oil trains is expected in the future. This study characterized levels of potentially toxic contaminants in sediment in September 2015: arsenic, metals, and polycyclic aromatic hydrocarbons (PAHs) at four sites with fine-grained sediment (Chuckanut Bay, Padilla Bay, Snohomish River Delta, Nisqually River Delta) adjacent to the Burlington Northern Santa Fe (BNSF) rail line in the Puget Sound region. Arsenic (As) and metals levels were compared to those measured at a fifth site, urban Saltwater State Park, which was expected to show contaminants associated with urbanization but not rail transport of coal and oil because it is not adjacent to the BNSF rail line. Knowledge about current properties of soil and sediment is essential for quantifying impacts of spills and other releases, and for setting remediation or restoration targets. For the sampling effort and timing of this study, all five sites had fine sediment contents of cadmium (Cd), mercury (Hg), lead (Pb), and zinc (Zn) below minimal effects levels. Pb and Zn appeared to be urban sourced. Median As, chromium (Cr), copper (Cu), and nickel (Ni) levels were in the range where adverse biological effects would possibly occur; however, Cr and Ni were geologically sourced and unlikely to be bioavailable to organisms. As, Cu, and antimony (Sb) levels were highly correlated, an association that is characteristic of legacy smelting operations; however, total sediment contents of these three elements, along with Hg and As/Sb ratios, were near natural levels and could indicate river-borne inputs. Median total PAH concentrations were highest at Snohomish River Delta, but were below minimal effects levels at all sites. Diagnostic PAH ratios were indicative of PAHs sourced from petroleum combustion and coal/biomass burning, rather than from spilled petroleum or coal. Rare earth element patterns were distinct among watersheds with Cascade volcanoes, granitic rocks, or non-volcanic sediments, making them promising sediment provenance indicators. Knowledge about sediment sources and contaminant distributions could provide unique insights about sediment-bound contaminant sourcing, delivery, and dispersal in nearshore regions.

Washington↗
USGS2019

Geochemical sourcing of runoff from a young volcanic watershed to an impacted coral reef in Pelekane Bay, Hawaii

Runoff of sediment and other contaminants from developed watersheds threatens coastal ecosystems and services. A sediment geochemical sourcing study was undertaken on a sediment-impacted coral reef flat to identify terrestrial sediment sources and how these changed over time. Geochemical signatures were identified for watershed soils that formed on Hawaiian basaltic and alkalic lavas using relatively immobile compatible (Ni, Sc) and incompatible (Nb, REE , Th) elements quantified by ICP-MS in total decompositions of the fine fraction of surface soils. Some soils also contained ash from late-erupting cinder cones that added alkalic geochemical signatures, resulting in distinctive mixed signatures near these geologic features. Sediment was collected in Pelekane Bay using sediment traps during winter 2010–2011 and a sediment core in order to geochemically source runoff entering the bay. Geochemical signatures in trapped sediment showed that runoff predominantly originated from the lower watershed along a highway corridor rather than from the upper watershed or areas with alkalic lavas. Soil in the highway corridor also contained Zn above levels of concern for aquatic organisms and anthropogenic Pb, indications that runoff control measures could reduce the exposure of the reef community to potentially toxic metals and other road-associated contaminants. The upper portion of a 60-yr long sediment record from Pelekane Bay was disturbed by tsunamigenic waves from the Tohoku earthquake , and the remainder was likely subject to mixing by winter waves that averaged out geochemical variations. On average, watershed regions with basaltic soils were the predominant source of runoff to the bay over the past 60 years. By linking sediment runoff to geographic regions or features in watersheds, geochemical sourcing can provide insights that allow resource managers to direct runoff mitigation and soil conservation efforts to areas where they will be most effective.

Hawaii↗
USGS2019

Sources, timing, and fate of sediment and contaminants in the nearshore: insights from geochemistry

Rivers in Cascade watersheds carry sediment with a volcanic composition that is distinct from the plutonic composition of the Puget lowlands. Compositional properties (signatures) allow discrimination of river-sourced Cascade from lowland sediment, and inferences about transport pathways. Surface sediment on land contains atmospheric radionuclides whose known decay rates define monthly (7Be) and decadal (210Pb) timescales of sediment inputs from land to nearshore regions. We used geochemical signatures to source river-borne sediment in two urban embayments in Cascade watersheds: Commencement Bay (CB) and Bellingham Bay (BB). We concurrently determined sediment contaminant levels and, in CB, used geochemical aging to distinguish contaminants in recent winter outflow from those that were pre-existing. Methods are described in Takesue et al. (2017). Geochemical signatures showed that Puyallup River (PU)-sourced fine sediment (<63 µm) accumulated more along the northeast (NE) shore of CB than the southwest: median 91% and 69%, respectively. River-sourced sediment from recent winter storms, containing higher 7Be activities (open circles, Fig. 1A), also accumulated on the NE shore and had lower contents of PAHs, fecal sterols, PCBs, and potentially toxic metals (TM) compared to the south shore; only PBDEs were higher (column graphs, Fig. 1A). Lower 7Be and 210Pb activities in south shore sediment indicated that contaminants there were associated with older sediment. Existing sediment in CB contained higher levels of urban contaminants than new PU material. No PAH, PCB, or TM levels in CB exceeded Washington State marine sediment quality standards (WAMSQS). Geochemical signatures were not distinct in the Nooksack River watershed and lowlands, precluding sediment sourcing in BB. PAH ratios in BB sediments were ubiquitous (open circles, Fig. 1B), suggesting atmospheric rather than riverine transport, and had values indicating biomass/coal combustion sources, except for three sites along the urban waterfront that had values indicative of vehicle emissions (closed circles, Fig. 1B). Elevated TM occurred offshore of Fairhaven (cadmium, Cd; copper, Cu; lead, Pb; zinc, Zn), Whatcom Creek Waterway (Pb, Zn), and the marina (Cu, Zn). No PAH or TM concentrations in BB exceeded WAMSQS. Insights gained from sediment geochemistry about the sources, timing, transport, and fate of riverborne fine sediment and contaminants in nearshore regions are valuable components of monitoring programs that can help guide habitat restoration and resource management decisions toward effective and sustainable outcomes.

Washington↗
USGS2019

Polychlorinated biphenyls (PCBs) in the Pacific sand lance, Puget Sound, Washington

Forage fish are small, abundant, schooling planktivores that form a critical link in marine food webs by transferring energy from plankton up to birds, fishes, and marine mammals. Forage fishes in Puget Sound include the iconic Pacific herring as well as lesser known species such as surf smelt and the Pacific sand lance. There are significant knowledge gaps regarding the basic life history and population status of Pacific sand lance and no information regarding potential stressors such as contaminants.

Washington↗
USGS2017

Tracking riverborne sediment and contaminants in Commencement Bay, Washington, using geochemical signatures

Large rivers carry terrestrial sediment, contaminants, and other materials to the coastal zone where they can affect marine biogeochemical cycles and ecosystems. This U.S. Geological Survey study combined river and marine sediment geochemistry and organic contaminant analyses to identify riverborne sediment and associated contaminants at shoreline sites in Commencement Bay, Puget Sound, Washington, that could be used by adult forage fish and other marine organisms. Geochemical signatures distinguished the fine fraction (<0.063 millimeter, mm) of Puyallup River sediment—which originates from Mount Rainier, a Cascade volcano—from glacial fine sediment in lowland bluffs that supply sediment to beaches. In combination with activities of beryllium-7 ( 7 Be), a short-lived radionuclide, geochemical signatures showed that winter 2013–14 sediment runoff from the Puyallup River was transported to and deposited along the north shore of Commencement Bay, then mixed downward into the sediment column. The three Commencement Bay sites at which organic contaminants were measured in surface sediment did not have measurable 7 Be activities in that layer, so their contaminant assemblages were attributed to sources from previous years. Concentrations of organic contaminants (the most common of which were polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and fecal sterols) were higher in the <0.063-mm fraction compared to the <2-mm fraction, in winter compared to summer, in river suspended sediment compared to river bar and bank sediment, and in marine sediment compared to river sediment. The geochemical property barium/aluminum (Ba/Al) showed that the median percentage of Puyallup River derived fine surface sediment along the shoreline of Commencement Bay was 77 percent. This finding, in combination with higher concentrations of organic contaminants in marine rather than river sediment, indicates that riverborne sediment-bound contaminants are retained in shallow marine habitats of Commencement Bay. The retention of earlier inputs complicates efforts to identify recent inputs and sources. Understanding modern sources and fates of riverborne sediment and contaminants and their potential ecological impacts will therefore require a suite of targeted geochemical studies in such marine depositional environments.

Washington↗
USGS2016

Environmental and eelgrass response to dike removal: Nisqually River Delta (2010–14)

Restoration of tidal flows to formerly diked marshland can alter land-to-sea fluxes and patterns of accumulation of terrestrial sediment and organic matter, and these tidal flows can also affect existing nearshore habitats. Dikes were removed from 308 hectares (ha) of the Nisqually National Wildlife Refuge on the Nisqually River Delta in south Puget Sound, Washington, in fall 2009 to improve habitat for wildlife, such as juvenile salmon. Ecologically important intertidal and subtidal eelgrass ( Zostera marina ) beds grow on the north and west margins of the delta. The goal of this study was to understand long-term changes in eelgrass habitat and their relation to dike removal. Sediment and eelgrass properties were monitored annually in May from 2010 to 2014 at two sites on the west side of the Nisqually River Delta along McAllister Creek, a spring-fed creek near two restored tidal channels. In May 2014, the mean canopy height of eelgrass was the same as in previous years in an 8-ha bed extending to the Nisqually River Delta front, but mean canopy height was 20 percent lower in a 0.3-ha eelgrass bed closer to the restored marsh when compared to mean canopy height of eelgrass in May 2010, 6 months after dike removal was completed. Over 5 years, the amount of eelgrass leaf area per square meter (m 2 ) in the 8-ha bed increased slightly, and surface-sediment grain size became finer. In contrast, in the 0.3-ha bed, eelgrass leaf area per m 2 decreased by 45 percent, and surface sediment coarsened. Other potential stressors, including sediment pore water reduction-oxidation potential (redox) and hydrogen sulfide (H 2 S) concentration in the eelgrass rhizosphere, or root zone, were below levels that negatively affect eelgrass growth and therefore did not appear to be environmental stressors on plants. Eelgrass biomass partitioning, though less favorable in the 8-ha eelgrass bed compared to the 0.3-ha one, was well above the critical above-ground to below-ground biomass ratio of 2:1 for Z. marina , an indication that these plants were not at risk of a carbon deficit during low-light conditions. After 5 years, nearshore changes associated with the restoration of tidal flows to formerly diked marshes of the Nisqually River Delta appeared to have little impact on the large eelgrass bed extending from Luhr Beach to the Nisqually River Delta front; however, restoration appears to be contributing to the decline of a small eelgrass bed closer to the restoration area.

Washington↗
USGS2013

Integration of bed characteristics, geochemical tracers, current measurements, and numerical modeling for assessing the provenance of beach sand in the San Francisco Bay Coastal System

Over 150 million m 3 of sand-sized sediment has disappeared from the central region of the San Francisco Bay Coastal System during the last half century. This enormous loss may reflect numerous anthropogenic influences, such as watershed damming, bay-fill development, aggregate mining, and dredging. The reduction in Bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches, wetlands, and submarine environments. A unique, multi-faceted provenance study was performed to definitively establish the primary sources, sinks, and transport pathways of beach-sized sand in the region, thereby identifying the activities and processes that directly limit supply to the outer coast. This integrative program is based on comprehensive surficial sediment sampling of the San Francisco Bay Coastal System, including the seabed, Bay floor, area beaches, adjacent rock units, and major drainages. Analyses of sample morphometrics and biological composition (e.g., Foraminifera) were then integrated with a suite of tracers including 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopes, rare earth elements, semi-quantitative X-ray diffraction mineralogy, and heavy minerals, and with process-based numerical modeling, in situ current measurements, and bedform asymmetry to robustly determine the provenance of beach-sized sand in the region.

California↗