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At least 1,063 records · Page 59Linked to original sources

USGS2011

Channel change and bed-material transport in the Umpqua River basin, Oregon

The Umpqua River drains 12,103 square kilometers of western Oregon; with headwaters in the Cascade Range, the river flows through portions of the Klamath Mountains and Oregon Coast Range before entering the Pacific Ocean. Above the head of tide, the Umpqua River, along with its major tributaries, the North and South Umpqua Rivers, flows on a mixed bedrock and alluvium bed, alternating between bedrock rapids and intermittent, shallow gravel bars composed of gravel to cobble-sized clasts. These bars have been a source of commercial aggregate since the mid-twentieth century. Below the head of tide, the Umpqua River contains large bars composed of mud and sand. Motivated by ongoing permitting and aquatic habitat concerns related to in-stream gravel mining on the fluvial reaches, this study evaluated spatial and temporal trends in channel change and bed-material transport for 350 kilometers of river channel along the Umpqua, North Umpqua, and South Umpqua Rivers. The assessment produced (1) detailed mapping of the active channel, using aerial photographs and repeat surveys, and (2) a quantitative estimation of bed-material flux that drew upon detailed measurements of particle size and lithology, equations of transport capacity, and a sediment yield analysis. Bed-material transport capacity estimates at 45 sites throughout the South Umpqua and main stem Umpqua Rivers for the period 1951-2008 result in wide-ranging transport capacity estimates, reflecting the difficulty of applying equations of bed-material transport to a supply-limited river. Median transport capacity values calculated from surface-based equations of bedload transport for each of the study reaches provide indications of maximum possible transport rates and range from 8,000 to 27,000 metric tons per year (tons/yr) for the South Umpqua River and 20,000 to 82,000 metric tons/yr for the main stem Umpqua River upstream of the head of tide; the North Umpqua River probably contributes little bed material. A plausible range of average annual transport rates for the South and main stem Umpqua Rivers, based on bedload transport capacity estimates for bars with reasonable values for reference shear stress, is between 500 and 20,000 metric tons/yr. An empirical bed-material yield analysis predicts 20,000-50,000 metric tons/yr on the South Umpqua River and main stem Umpqua River through the Oregon Coast Range, decreasing to approximately 30,000 metric tons/yr at the head of tide. Surveys of individual mining sites in the South Umpqua River indicate minimum local bed-material flux rates that are typically less than 10,000 metric tons/yr but range up to 30,600 metric tons/yr in high-flow years. On the basis of all of these analyses, actual bedload flux in most years is probably less than 25,000 metric tons/yr in the South Umpqua and main stem Umpqua Rivers, with the North Umpqua River probably contributing negligible amounts. For comparison, the estimated annual volume of commercial gravel extraction from the South Umpqua River between 2001 and 2004 ranged from 610 to 36,570 metric tons, indicating that historical in-stream gravel extraction may have been a substantial fraction of the overall bedload flux.

Oregon↗

USGS2024

First Occurrence of the nonindigenous Asian foraminifera Ammonia confertitesta in the Northeastern Pacific Ocean: Vancouver Island, British Columbia, Canada

Observations in 2022 of intertidal and subtidal foraminiferal faunas at four localities along the central-eastern side of Vancouver Island, British Columbia, Canada, and molecular analyses have documented the first occurrence of the nonindigenous Asian species Ammonia confertitesta Zheng in the northwestern Pacific Ocean. The species was present at three of these localities: Davis Lagoon south of Ladysmith (4% in the lagoon and 49% on the beach) and 0.6% in Nanaimo Harbor. The vector of introduction is thought to be the release of ballast water and associated sediment. These releases probably occurred in the Port of Vancouver, which were then transported by means of the cyclonic circulation across the Strait of Georgia, or from local anchorages close to the sampling sites. The timing of the introduction is impossible to determine because no stratigraphic record is presently available. However, foraminiferal studies in the late 1980s near the Port of Vancouver that recovered calcareous taxa did not report the presence of this species, nor was it found at 33 sites sampled from 1997 to 1999 throughout the Strait of Georgia.

Vancouver Island↗

USGS2011

Host specificity and ecology of infectious hematopoietic necrosis virus (IHNV) in Pacific salmonids

Some circumstances IHNV infection can cause acute disease with mortality ranging from 5-90% in host populations. Genetic typing of IHNV field isolates has shown that three major genetic groups of the virus occur in North America. These groups are designated the U, M, and L virus genogroups because they occur in the upper, middle, and lower portions of the geographic range of IHNV in western North America. Among field isolates there is some indication of host specificity: most IHNV isolated from sockeye salmon ( Oncorhynchus nerka ) is in the U genogroup, and most IHNV isolated from rainbow and steelhead trout ( Oncorhynchus mykiss ) is in the M genogroup. Experimental challenges confirm that U isolates are highly virulent for sockeye salmon, but not rainbow trout. In contrast, M isolates are virulent in rainbow trout but not in sockeye salmon. Studies comparing U and M virus infections show that virulence is associated with more rapid virus replication in the first few days after infection. In addition, high virulence isolates persist at higher viral loads in the host, while low virulence isolates do not persist. These host-specific aspects of the different IHNV genogroups are important for understanding the ecology of IHNV emergence events in the field. The recent emergence of U IHNV in Russian sockeye salmon of the Kamchatka Peninsula, and the emergence of M IHNV in steelhead trout on the Olympic Peninsula in the U.S.A, serve as examples of the relevance of IHNV host specificity.

Conference Paper↗

USGS2012

The challenge of retarding erosion of island biodiversity through phytosanitary measures: An update on the case of Puccinia psidii in Hawai'i

Most rust fungi are highly host specific, but Puccina psidii has an extremely broad host range within Myrtaceae and gained notoriety with a host jump in its native Brazil from common guava ( Psidium guajava ) to commercial Eucalyptus plantations. When detected in Hawaiʻi in April 2005, the first invasion outside the neotropics/subtropics, there was immediate concern for ʻōhiʻa (Metrosideros polymorpha). ʻŌhiʻa composes 80% of native forest statewide, providing stable watersheds and habitat for most Hawaiian forest birds and plants. Within months, rust spores spread statewide on wind currents, but ʻōhiʻa was found to be only a minor host, showing very light damage. The primary host was nonnative rose apple ( Syzygium jambos ), severely affected at a landscape scale, but the epiphytotic subsided as rose apple was largely defoliated or killed within several years. The limited and stable host range in Hawaiʻi (versus elsewhere) led the local conservation community to explore possibilities for excluding new genetic strains of P. psidii . Although national/international phytosanitary standards require strong scientific justification for regulations involving an infraspecific taxonomic level, hopes were buoyed when genetic studies showed no apparent genetic variation/evolution in Hawaiʻi's rust strain. A sophisticated genetic study of P. psidii in its home range is near completion; genetic variation is substantial, and host species strongly influences rust population structure. To prevent introduction of new strains, the Hawaiʻi Department of Agriculture is moving ahead with establishing stringent measures that restrict entry of Myrtaceae into Hawaiʻi. Meanwhile, P. psidii poses a major threat to Myrtaceae biodiversity worldwide.

Hawai'i↗

USGS2006

A new probabilistic seismic hazard assessment for greater Tokyo

Tokyo and its outlying cities are home to one-quarter of Japan's 127 million people. Highly destructive earthquakes struck the capital in 1703, 1855 and 1923, the last of which took 105 000 lives. Fuelled by greater Tokyo's rich seismological record, but challenged by its magnificent complexity, our joint Japanese-US group carried out a new study of the capital's earthquake hazards. We used the prehistoric record of great earthquakes preserved by uplifted marine terraces and tsunami deposits (17 M???8 shocks in the past 7000 years), a newly digitized dataset of historical shaking (10 000 observations in the past 400 years), the dense modern seismic network (300 000 earthquakes in the past 30 years), and Japan's GeoNet array (150 GPS vectors in the past 10 years) to reinterpret the tectonic structure, identify active faults and their slip rates and estimate their earthquake frequency. We propose that a dislodged fragment of the Pacific plate is jammed between the Pacific, Philippine Sea and Eurasian plates beneath the Kanto plain on which Tokyo sits. We suggest that the Kanto fragment controls much of Tokyo's seismic behaviour for large earthquakes, including the damaging 1855 M???7.3 Ansei-Edo shock. On the basis of the frequency of earthquakes beneath greater Tokyo, events with magnitude and location similar to the M??? 7.3 Ansei-Edo event have a ca 20% likelihood in an average 30 year period. In contrast, our renewal (time-dependent) probability for the great M??? 7.9 plate boundary shocks such as struck in 1923 and 1703 is 0.5% for the next 30 years, with a time-averaged 30 year probability of ca 10%. The resulting net likelihood for severe shaking (ca 0.9g peak ground acceleration (PGA)) in Tokyo, Kawasaki and Yokohama for the next 30 years is ca 30%. The long historical record in Kanto also affords a rare opportunity to calculate the probability of shaking in an alternative manner exclusively from intensity observations. This approach permits robust estimates for the spatial distribution of expected shaking, even for sites with few observations. The resulting probability of severe shaking is ca 35% in Tokyo, Kawasaki and Yokohama and ca 10% in Chiba for an average 30 year period, in good agreement with our independent estimate, and thus bolstering our view that Tokyo's hazard looms large. Given $1 trillion estimates for the cost of an M???7.3 shock beneath Tokyo, our probability implies a $13 billion annual probable loss. ?? 2006 The Royal Society.

Philosophical Transactions of the Royal Society A:↗

USGS2001

Analysis of late Quaternary faulting in San Diego Bay and hazard to the Coronado Bridge

Southern California is transected by numerous pervasive northwest-trending Quaternary fault zones. Together they form the broad transform-fault boundary along which the Pacific and North America crustal plates move irregularly past one another in a right-lateral sense at a rate of about 5 centimeters (cm)/year. The city of San Diego, which lies adjacent to the Pacific Ocean in the southwestern-most corner of California, is cut by one such fault zone -- the Rose Canyon Fault Zone. Oblique movement on faults within the Rose Canyon Fault Zone has, over time, led to the development of San Diego Bay, which separates the metropolitan area of San Diego from Coronado and North Island. The Coronado Bridge spans San Diego Bay and connects the cities of San Diego and Coronado. A principal concern regarding the bridge's earthquake safety involves its proximity, especially of its foundation piers, to potential shallow fault rupture. The objectives of this study were (1) to identify and accurately locate Holocene faults (those younger than about 12,000 years) and (2) to determine the time of the most recent movement on these faults and, therefore, their potential hazard to the Coronado Bridge.

California Geology↗

USGS2021

Synthesis of habitat availability and carrying capacity research to support water management decisions and enhance conditions for Pacific salmon in the Willamette River, Oregon

Flow management is complex in the Willamette River Basin where the U.S. Army Corps of Engineers owns and operates a system of 13 dams and reservoirs (hereinafter Willamette Project), which are spread throughout three large tributaries including the Middle Fork Willamette, McKenzie, and Santiam Rivers. The primary purpose of the Willamette Project is flood-risk management, which provides critical protection to the Willamette Valley, but flow managers must also consider factors such as power generation, water-quality improvement, irrigation, recreation, and protection for aquatic species such as U.S. Endangered Species Act-listed Chinook salmon ( Oncorhynchus tshawytscha ) and steelhead ( O. mykiss ). Flow-management decision-making in the basin can benefit from models that allow for flow-scenario comparisons and a wide range of modeling methods are available. For this study, we examined existing datasets and modeling efforts in the basin and provided an overview of available options. Most previous studies used Physical Habitat Simulation System, habitat data were collected from a series of transects within modeled reaches, and habitat suitability indices were obtained from the literature, or using expert opinion. These studies provide information for specific reaches of the Willamette River Basin, which limits their ability to provide broad-scale predictive capability. Recent efforts to develop a two-dimensional hydraulic model in the mainstem Willamette River, and in specific reaches of primary tributaries downstream from Project dams, have bolstered modeling capabilities in the basin. This work has developed spatially continuous water depth and velocity data in more than 250 kilometers (km) of river downstream from Project dams and has predictive capability throughout the year at flows up to normal peak levels. Additionally, other methods are described for estimating habitat availability, which include habitat suitability criteria, logistic regression, occupancy and abundance modeling, and energetic based approaches. There are strengths and weaknesses to each approach and selection of the preferred approach in the Willamette River Basin will depend on the desired metrics of interest and the risk tolerance of managers and stakeholders in the basin.

Oregon↗

USGS2020

Integrating broad‐scale data to assess demographic and climatic contributions to population change in a declining songbird

Climate variation and trends affect species distribution and abundance across large spatial extents. However, most studies that predict species response to climate are implemented at small spatial scales or are based on occurrence‐environment relationships that lack mechanistic detail. Here, we develop an integrated population model (IPM) for multi‐site count and capture‐recapture data for a declining migratory songbird, Wilson's warbler ( Cardellina pusilla ), in three genetically distinct breeding populations in western North America. We include climate covariates of vital rates, including spring temperatures on the breeding grounds, drought on the wintering range in northwest Mexico, and wind conditions during spring migration. Spring temperatures were positively related to productivity in Sierra Nevada and Pacific Northwest genetic groups, and annual changes in productivity were important predictors of changes in growth rate in these populations. Drought condition on the wintering grounds was a strong predictor of adult survival for coastal California and Sierra Nevada populations; however, adult survival played a relatively minor role in explaining annual variation in population change. A latent parameter representing a mixture of first‐year survival and immigration was the largest contributor to variation in population change; however, this parameter was estimated imprecisely, and its importance likely reflects, in part, differences in spatio‐temporal distribution of samples between count and capture‐recapture data sets. Our modeling approach represents a novel and flexible framework for linking broad‐scale multi‐site monitoring data sets. Our results highlight both the potential of the approach for extension to additional species and systems, as well as needs for additional data and/or model development.

Ecology and Evolution↗

USGS2015

Recent changes in annual area burned in interior Alaska: The impact of fire management

The Alaskan boreal forest is characterized by frequent extensive wildfires whose spatial extent has been mapped for the past 70 years. Simple predictions based on this record indicate that area burned will increase as a response to climate warming in Alaska. However, two additional factors have affected the area burned in this time record: the Pacific decadal oscillation (PDO) switched from cool and moist to warm and dry in the late 1970s and the Alaska Fire Service instituted a fire suppression policy in the late 1980s. In this paper a geographic information system (GIS) is used in combination with statistical analyses to reevaluate the changes in area burned through time in Alaska considering both the influence of the PDO and fire management. The authors found that the area burned has increased since the PDO switch and that fire management drastically decreased the area burned in highly suppressed zones. However, the temporal analysis of this study shows that the area burned is increasing more rapidly in suppressed zones than in the unsuppressed zone since the late 1980s. These results indicate that fire policies as well as regional climate patterns are important as large-scale controls on fires over time and across the Alaskan boreal forest.

Alaska↗

USGS2019

Discovery of an extensive deep-sea fossil serpulid reef associated with a cold seep, Santa Monica Basin, California

Multi-beam mapping of the Santa Monica Basin in the eastern Pacific has revealed the existence of a number of elevated bathymetric features, or mounds, harboring cold seep communities. During 2013-2014, mounds at ~600 m water depth were observed for the first time and sampled by Monterey Bay Aquarium Research Institute’s ROV Doc Ricketts. Active cold seeps were found, but surprisingly one of these mounds was characterized by massive deposits composed of fossil serpulid worm tubes (Annelida: Serpulidae) exhibiting various states of mineralization by authigenic carbonate. No living serpulids with equivalent tube morphologies were found at the site; hence the mound was termed ‘Fossil Hill’. In the present study, the identity of the fossil serpulids and associated fossil community, the ages of fossils and authigenic carbonates, the formation of the fossil serpulid aggregation, and the geological structure of the mound are explored. Results indicate that the tubes were most likely made by a deep-sea serpulid lineage, with radiocarbon dating suggesting that they have a very recent origin during the Late Pleistocene, specifically to the Last Glacial Maximum ~20,000 years ago. Additional U-Th analyses of authigenic carbonates mostly corroborate the radiocarbon dates, and also indicate that seepage was occurring while the tubes were being formed. We also document similar, older deposits along the approximate trajectory of the San Pedro Basin Fault. We suggest that the serpulid tube facies formed in situ, and that the vast aggregation of these tubes at Fossil Hill is likely due to a combination of optimal physical environmental conditions and chemosynthetic production, which may have been particularly intense as a result of sea-level lowstand during the Last Glacial Maximum.

California↗

USGS2010

Supraslab earthquake clusters above the subduction plate boundary offshore Sanriku, northeastern Japan: Seismogenesis in a graveyard of detached seamounts?

Thousands of offshore repeating earthquakes with low‐angle thrust focal mechanisms occur along the subduction plate boundary of NE Japan. Double‐difference relocation methods using P ‐ and S ‐wave arrivals reveal clusters of events above these repeating events. To assure good depth control we restrict our study to events that are close to seismic stations. These “supraslab” earthquake clusters are regional features at depths of 25 to 50 km, and most of these clusters are below the depth of the forearc Moho, which we determined from converted waves. Seismicity over this depth range does not occur under the inland area of NE Japan except just below the vicinity of the arc volcanoes. Re‐entrants in the inner trench slope indicate that repeated collisions of seamounts have occurred in the past. Our preliminary interpretation of supraslab clusters is that they represent seismicity in seamounts detached from the Pacific plate during slab descent, driven by the resistance of seamounts to subduction. Detachment during slab descent probably occurs on the sedimented and hydrothermally altered seafloor on which seamounts were originally constructed since these are known as zones of weakness during active island growth. High fluid pressure produced during dehydration of clay minerals and other low‐temperature hydrous minerals could enable detachment at depths. Seamount crust is thus accreted to forearcs, possibly leading to a long‐term component of near‐coastal uplift. Supraslab earthquake clusters may be our most direct evidence of the fates of seamounts and suggest that tectonic underplating is actively occurring in this subduction system.

Northeastern Japan↗

USGS1990

The importance of subarctic intertidal habitats to shorebirds: A study of the central Yukon-Kuskokwim Delta, Alaska

A 6-year study of shorebird use of intertidal habitats of the Yukon-Kuskokwim Delta revealed this area to be one of the premiere sites for shorebirds throughout the Holarctic and worthy of designation as a Hemispheric Shorebird Reserve in the Western Hemisphere Shorebird Reserve Network. The study area, which covered 10% (300 km 2 ) of the delta's intertidal flats, regularly hosted 17 species of shorebirds between late April and mid-October. The greatest use was during the postbreeding period (late June-October), when Dunlins ( Calidris alpina ), Western Sandpipers ( C. mauri ), and Rock Sandpipers ( C. ptilocnemis ), each with large local nesting populations, accounted for 95% of the shorebirds recorded. Peak counts during autumn approached 300,000 birds. Considering the seasonal occurrence and turnover of populations, we estimate 1-2 million shorebirds use the central delta each year. The delta supports large fractions of the Pacific Rim or world populations of Bar-tailed Godwits ( Limosa lapponica ), Black Turnstones ( Arenaria melanocephala ), Red Knots ( C. canutus ), Western Sandpipers, Dunlins, and Rock Sandpipers. Densities of shorebirds using the central delta's four major bays and connecting coastal areas peaked at 950 shorebirds/km 2 in early September. Hazen Bay frequently hosted more than 1,200 shorebirds/km 2 . Postbreeding shorebirds used intertidal habitats in three distinct patterns according to age class. For most species (n = 7), there was a period when adults appeared first, followed by a brief interval when adults and juveniles mixed, then by a prolonged period when only juveniles remained. In the second pattern (n = 3 species), adults moved onto the intertidal flats first, were later joined by juveniles for a prolonged staging period, then migrated with them. In the third pattern (n = 3 species), only juveniles used the delta's intertidal habitat. Temporal segregation among species and age groups may minimize competition for food and thereby allow the delta to support high diversity and numbers of shorebirds.

Alaska↗

USGS2014

Predicting spatial and temporal distribution of Indo-Pacific lionfish ( Pterois volitans ) in Biscayne Bay through habitat suitability modeling

Invasive species may exhibit higher levels of growth and reproduction when environmental conditions are most suitable, and thus their effects on native fauna may be intensified. Understanding potential impacts of these species, especially in the nascent stages of a biological invasion, requires critical information concerning spatial and temporal distributions of habitat suitability. Using empirically supported environmental variables (e.g., temperature, salinity, dissolved oxygen, rugosity, and benthic substrate), our models predicted habitat suitability for the invasive lionfish ( Pterois volitans ) in Biscayne Bay, Florida. The use of Geographic Information Systems (GIS) as a platform for the modeling process allowed us to quantify correlations between temporal (seasonal) fluctuations in the above variables and the spatial distribution of five discrete habitat quality classes, whose ranges are supported by statistical deviations from the apparent best conditions described in prior studies. Analysis of the resulting models revealed little fluctuation in spatial extent of the five habitat classes on a monthly basis. Class 5, which represented the area with environmental variables closest to the best conditions for lionfish, occupied approximately one-third of Biscayne Bay, with subsequent habitats declining in area. A key finding from this study was that habitat suitability increased eastward from the coastline, where higher quality habitats were adjacent to the Atlantic Ocean and displayed marine levels of ambient water quality. Corroboration of the models with sightings from the USGS-NAS database appeared to support our findings by nesting 79 % of values within habitat class 5; however, field testing (i.e., lionfish surveys) is necessary to confirm the relationship between habitat classes and lionfish distribution.

Florida↗

USGS1998

Geohydrology of Storage Unit III and a combined flow model of the Santa Barbara and foothill ground-water basins, Santa Barbara County, California

The city of Santa Barbara pumps most of its ground water from the Santa Barbara and Foothill ground-water basins. The Santa Barbara basin is subdivided into two storage units: Storage Unit I and Storage Unit III. The Foothill basin and Storage Unit I of the Santa Barbara basin have been studied extensively and ground-water flow models have been developed for them. In this report, the geohydrology of the Santa Barbara ground- water basin is described with a special emphasis on Storage Unit III in the southwestern part of the basin. The purposes of this study were to summarize and evaluate the geohydrology of Storage Unit III and to develop an areawide model of the Santa Barbara and Foothill basins that includes the previously unmodeled Storage Unit III. Storage Unit III is in the southwestern part of the city of Santa Barbara. It is approximately 3.5 miles long and varies in width from about 2,000 feet in the southeast to 4,000 feet in the north-west. Storage Unit III is composed of the Santa Barbara Formation and overlying alluvium. The Santa Barbara Formation (the principal aquifer) consists of Pleistocene and Pliocene(?) unconsolidated marine sand, silt, and clay, and it has a maximum saturated thickness of about 160 feet. The alluvium that overlies the Santa Barbara Formation has a maximum saturated thickness of about 140 feet. The storage unit is bounded areally by faults and low-permeability deposits and is underlain by rocks of Tertiary age. The main sources of recharge to Storage Unit III are seepage from Arroyo Burro and infiltration of precipitation. Most of the recharge occurs in the northwest part of the storage unit, and ground water flows toward the southeast along the unit's long axis. Lesser amounts of recharge may occur as subsurface flow from the Hope Ranch subbasin and as upwelling from the underlying Tertiary rocks. Discharge from Storage Unit III occurs as pumpage, flow to underground drains, underflow through alluvium in the vicinity of Arroyo Burro across the Lavigia Fault, evapotranspiration, and underflow to the Pacific Ocean. The faults that bound Storage Unit III generally are considered to be effective barriers to the flow of ground water. Interbasin ground-water flow occurs where deposits of younger alluvium along stream channels cross faults. Ground-water quality in Storage Unit III deposits varies with location and depth. Upward leakage of poor-quality water from the underlying Tertiary rocks occurs in the storage unit, and such leakage can be influenced by poor well construction or by heavy localized pumping. The highest dissolved-solids concentration (4,710 milligrams per liter) in ground water resulting from this upward leakage is found in the coastal part of the storage unit. The ground-water system was modeled as two horizontal layers. In the Foothill basin and Storage Unit I the layers are separated by a confining bed. The upper layer represents the upper producing zone and the shallow zone near the coast. The lower layer represents the lower producing zone. In general, the faults in the study area were assumed to be no-flow boundaries, except for the offshore fault that forms the southeast boundary; the southeast boundary was simulated as a general-head boundary. The Storage Unit III model was combined with the preexisting Storage Unit I and Foothill basin models, using horizontal flow barriers, to form an areawide model. The areawide model was calibrated by simulating steady-state predevelopment conditions and transient conditions for 1978-92. The nonpumping steady- state simulation was used to verify that the calibrated model yielded physically reasonable results for predevelopment conditions. The calibrated areawide model calculates water levels in Storage Unit III that are within 10 feet of measured water levels at all sites of comparison. In addition, the model adequately simulates water levels in the Storage Unit I and Foothill basin areas. A total of 33,430 acre-feet of water was pumped from the study area during the simulation period. Model results indicate that 2,833 acre-feet came from storage and 5, 332 acre-feet crossed the general-head boundary from the ocean, thus indicating that seawater intrusion could occur. A sensitivity analysis indicates that, in general, the model is most sensitive to changes in transmissivity and total recharge.

California↗

USGS2016

Reconstruction of far-field tsunami amplitude distributions from earthquake sources

The probability distribution of far-field tsunami amplitudes is explained in relation to the distribution of seismic moment at subduction zones. Tsunami amplitude distributions at tide gauge stations follow a similar functional form, well described by a tapered Pareto distribution that is parameterized by a power-law exponent and a corner amplitude. Distribution parameters are first established for eight tide gauge stations in the Pacific, using maximum likelihood estimation. A procedure is then developed to reconstruct the tsunami amplitude distribution that consists of four steps: (1) define the distribution of seismic moment at subduction zones; (2) establish a source-station scaling relation from regression analysis; (3) transform the seismic moment distribution to a tsunami amplitude distribution for each subduction zone; and (4) mix the transformed distribution for all subduction zones to an aggregate tsunami amplitude distribution specific to the tide gauge station. The tsunami amplitude distribution is adequately reconstructed for four tide gauge stations using globally constant seismic moment distribution parameters established in previous studies. In comparisons to empirical tsunami amplitude distributions from maximum likelihood estimation, the reconstructed distributions consistently exhibit higher corner amplitude values, implying that in most cases, the empirical catalogs are too short to include the largest amplitudes. Because the reconstructed distribution is based on a catalog of earthquakes that is much larger than the tsunami catalog, it is less susceptible to the effects of record-breaking events and more indicative of the actual distribution of tsunami amplitudes.

Hawaii↗

USGS2002

Performance of a satellite-linked GPS on Pacific walruses (Odobenus rosmarus divergens)

We evaluated the utility of a satellite-linked GPS in obtaining location data from Pacific walruses ( Odobenus rosmarus divergens ). A unit was attached to one of the tusks of each of three adult male walruses in Bristol Bay, Alaska. The units were designed to relay GPS positions through the Argos Data Collection and Location System. The GPS was only minimally effective in obtaining location data. An average of only 5% of the attempts yielded a position, and only a small number of these were locations at sea. The paucity of successful attempts was probably due to infrequent and brief surfacings of the GPS, the proximity of cliffs to predominant haul-out sites in the study region, and the packing of animals when they were hauled out in herds. Argos was effective in relaying GPS positions in this study, but as GPS technology advances, and its application to marine mammal studies becomes more prevalent, it seems that the greatest challenge to the study of many species will be in data retrieval.

Polar Biology↗

USGS2003

Kelp forest ecosystems: Biodiversity, stability, resilience and future

Kelp forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which kelp forests develop globally and where, why and at what rate they become deforested. The ecology and long archaeological history of kelp forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in kelp forest biodiversity. Global distribution of kelp forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed kelp forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread kelp deforestation. Such deforestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deforestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and kelp forests have returned in some locations but, for the first time, these forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of kelp forests were examined to determine their long history with humans and project the status of future kelp forests to the year 2025. Fishing impacts on kelp forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited kelp forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deforestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of kelp forests over vast areas. Despite southern California having one of the longest known associations with coastal kelp forests, widespread deforestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse kelp forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on kelp forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to kelp forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.

Environmental Conservation↗

USGS1992

40 Ar/ 39 Ar dating of Quaternary feldspar: Examples from the Taupo Volcanic Zone, New Zealand

Using a continuous laser and resistance furnace, we have measured ages on Quaternary plagioclase with an absolute precision of about ±30 ka and on Quaternary sanidine with a relative precision of better than 1%. Such precision was achieved by using low-temperature heating steps to remove much of the nonradiogenic argon contamination. Plagioclase is one of the most common mineral phases in volcanic rocks; thus, these procedures will be widely applicable to many problems for which precise radiometric age control has not been available. We studied plagioclase and plagioclase-sanidine concentrates from the oldest and the three largest silicic ash-flow deposits of the Taupo Volcanic Zone, New Zealand, one of the world's largest and most active volcanic systems. The results are in close agreement with new magnetostratigraphic data, suggest that existing fission-track age determinations significantly underestimate the age of older units, and shift the inception of Taupo Volcanic Zone volcanism back to at least 1600 ka. The improved precision has permitted the first correlations between proximal and distal units; previous correlations with deep-sea ash flows in the western Pacific require major revision.

Geology↗