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At least 1,333 records · Page 74Linked to original sources

USGS2002

Cordilleran-margin quartzites in Baja California – implications for tectonic transport

One of the current controversies in Cordilleran tectonics concerns the position of Baja California prior to ∼300 km of opening of the Gulf of California. Geologic arguments, together with paleomagnetic results from Lower Cretaceous volcanic rocks, suggest that the rocks of the Baja Peninsula formed and evolved along the coast of northwestern Mexico prior to opening of the Gulf. In contrast, paleomagnetic data from Cretaceous–early Tertiary plutonic rocks and clastic strata have been interpreted by some workers to suggest that Baja was located near southern Mexico at approximately 80 Ma. The presence of similar detrital zircon ages in lower Paleozoic quartzites of northeast Baja and in lower Paleozoic strata east of the Gulf, in northwestern Mexico and southwestern US, provides strong support for the northern paleoposition, suggesting that Baja has been transported northward by only ∼300 km

Earth and Planetary Science Letters↗

USGS2013

Geodatabase compilation of hydrogeologic, remote sensing, and water-budget-component data for the High Plains aquifer, 2011

The High Plains aquifer underlies almost 112 million acres in the central United States. It is one of the largest aquifers in the Nation in terms of annual groundwater withdrawals and provides drinking water for 2.3 million people. The High Plains aquifer has gained national and international attention as a highly stressed groundwater supply primarily because it has been appreciably depleted in some areas. The U.S. Geological Survey has an active program to monitor the changes in groundwater levels for the High Plains aquifer and has documented substantial water-level changes since predevelopment: the High Plains Groundwater Availability Study is part of a series of regional groundwater availability studies conducted to evaluate the availability and sustainability of major aquifers across the Nation. The goals of the regional groundwater studies are to quantify current groundwater resources in an aquifer system, evaluate how these resources have changed over time, and provide tools to better understand a systems response to future demands and environmental stresses. The purpose of this report is to present selected data developed and synthesized for the High Plains aquifer as part of the High Plains Groundwater Availability Study. The High Plains Groundwater Availability Study includes the development of a water-budget-component analysis for the High Plains completed in 2011 and development of a groundwater-flow model for the northern High Plains aquifer. Both of these tasks require large amounts of data about the High Plains aquifer. Data pertaining to the High Plains aquifer were collected, synthesized, and then organized into digital data containers called geodatabases. There are 8 geodatabases, 1 file geodatabase and 7 personal geodatabases, that have been grouped in three categories: hydrogeologic data, remote sensing data, and water-budget-component data. The hydrogeologic data pertaining to the northern High Plains aquifer is included in three separate geodatabases: (1) base data from a groundwater-flow model; (2) hydrogeology and hydraulic properties data; and (3) groundwater-flow model data to be used as calibration targets. The remote sensing data for this study were developed by the U. S. Geological Survey Earth Resources Observation and Science Center and include historical and predicted land-use/land-cover data and actual evapotranspiration data by using remotely sensed temperature data. The water-budget-component data contains selected raster data from maps in the “Selected Approaches to Estimate Water-Budget Components of the High Plains, 1940 Through 1949 and 2000 Through 2009” report completed in 2011 ( http://pubs.usgs.gov/sir/2011/5183/ ). Federal Geographic Data Committee compliant metadata were created for each spatial and tabular data layer in the geodatabases.

Colorado, Kansas, Nebraska, New Mexico, Oklahoma, ↗

USGS2015

Community for Data Integration 2013 Annual Report

The U.S. Geological Survey (USGS) conducts earth science to help address complex issues affecting society and the environment. In 2006, the USGS held the first Scientific Information Management Workshop to bring together staff from across the organization to discuss the data and information management issues affecting the integration and delivery of earth science research and investigate the use of “communities of practice” as mechanisms to share expertise about these issues. Out of this effort emerged the Council for Data Integration, which was conceived as an official organizational function that would help guide data integration activities and formalize communities of practice into working groups. However by 2009, it became apparent that many members of the council had an interest in developing data integration solutions and sharing expertise in a less formal grassroots perspective, thus transforming the “Council” into a “Community” for Data Integration (CDI). Today, the CDI represents a dynamic community of practice focused on advancing science data and information management and integration capabilities across the USGS and the CDI community. The CDI fosters an environment for collaboration and sharing by bringing together expertise from external partners and representatives across USGS who are involved in research, data management, and information technology. Membership is voluntary and open to USGS employees and other individuals and organizations willing to contribute to the community (if interested, contact cdi@usgs.gov). The purpose of the CDI is to advance understanding of Earth systems through enhanced use of data and information including associated tools and techniques provide a forum for people doing work with data integration to come together to share ideas as well as learn new skills and techniques, and grow overall USGS capabilities with data and information by increasing visibility of the work of many people throughout the USGS and the CDI community. To achieve these goals, the CDI operates within four applied areas: monthly forums, annual workshop/webinar series, working groups, and projects. The monthly forums, also known as the Opportunity/Challenge of the Month, provide an open dialogue to share and learn about data integration efforts or to present problems that invite the Community to offer solutions, advice, and support. Since 2010, the CDI has also sponsored annual workshops/webinar series to encourage the exchange of ideas, sharing of activities, presentations of current projects, and networking among members. Stemming from common interests, the working groups are focused on efforts to address data management and technical 2 challenges, including the development of standards and tools, improving interoperability and information infrastructure, and data preservation within USGS and its partners. The growing support for the activities of the working groups led to the CDI’s first formal request for proposals (RFP) process in 2013 to fund projects that produced tangible products. Today the CDI continues to hold an annual RFP that create data management tools and practices, collaboration tools, and training in support of data integration and delivery.

Open-File Report↗

USGS1998

Drought-induced shift of a forest-woodland ecotone: Rapid landscape response to climate variation

In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects—particularly those caused by mortality—largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon–juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.

Proceedings of the National Academy of Sciences of↗

USGS2020

Synthesis: A framework for predicting the dark side of ecological subsidies

In this chapter, we synthesize the state of the science regarding ecological subsidies and contaminants at the land-water interface and suggest research and management approaches for linked freshwater-terrestrial ecosystems. Specifically, we focus on movements of animals with complex life histories and the detrital inputs associated with animal and plant matter delivered to freshwaters. We present a framework based on the physicochemical parameters of contaminants and how they shape the relationship between contaminant persistence within resource subsidies (“dark side” of subsidies) and movement of resource subsidies (“bright side” of subsidies) across ecosystem boundaries. This relationship between the “dark side” and “bright side” of subsidies defines an important parameter space that allows researchers and practitioners to predict the potential impacts of aquatic contaminants on resource subsidies and their interaction with other stressors on consumers. Ecological factors such as ecosystem productivity, community composition, and consumer prey preference shape the ecotoxicological outcomes of aquatic contamination on subsidies. Landscape factors such as lithology, hydrogeomorphology, hydroperiod, and land use underlie chemical, toxicological, and ecological patterns and provide the context within which effects of contaminants play out. Finally, effects of contaminants combine with effects of other global stressors on timing, quality, and quantity of subsidies that drive responses to contaminants at the land-water interface. Understanding the “dark side” of ecological subsidies requires expertise from multiple disciplines. We attempt to synthesize current knowledge from those disciplines and generate conceptual models that ecologists can use to guide future research in understanding cross-ecosystem subsidies and contaminant fate and effects.

Book chapter↗

USGS2023

Flushing time variability in a short, low-inflow estuary

Flushing time, the time scale for exchange and mixing between embayed and oceanic waters in an estuary, plays an integral role in determining water quality and aquatic ecosystem health. Here, we investigated the spatiotemporal variability of flushing times throughout Morro Bay, a short, low-inflow estuary (LIE) on the California coast, using a calibrated and validated hydrodynamic model (Delft3D). Morro Bay has historically supported an extensive eelgrass ( Zostera marina ) habitat, which declined substantially from 139 to 5.4 ha during 2007–2017. Eelgrass decline motivated the current research into the role of changing bed roughness and oceanic drivers (i.e., tide and sea-level rise) on estuarine hydrodynamics and flushing times. We found that tidal variability exerts the strongest control on flushing times compared to other effects, i.e., bed roughness or sea-level rise. Additionally, we found that increasing sea level and decreasing bed roughness (associated with declining seagrass coverage) yielded higher rates of mixing (lower flushing times). We detected a strong correspondence between areas having shorter flushing times (e.g., near the estuary mouth) and areas occupied by resilient eelgrass populations in Morro Bay. Our findings further indicated that flushing times in short LIEs are particularly sensitive to several factors (e.g., bed roughness, sea level) that are susceptible to anthropogenic disturbance and future climate change.

California↗

USGS2008

Molecular and morphological analysis of the critically endangered Fijian iguanas reveals cryptic diversity and a complex biogeographic history

The Pacific iguanas of the Fijian and Tongan archipelagos are a biogeographic enigma in that their closest relatives are found only in the New World. They currently comprise two genera and four species of extinct and extant taxa. The two extant species, Brachylophus fasciatus from Fiji, Tonga, and Vanuatu and Brachylophus vitiensis from western Fiji, are of considerable conservation concern with B. vitiensis listed as critically endangered. A recent molecular study has shown that Brachylophus comprised three evolutionarily significant units. To test these conclusions and to reevaluate the phylogenetic and biogeographic relationships within Brachylophus, we generated an mtDNA dataset consisting of 1462 base pairs for 61 individuals from 13 islands, representing both Brachylophus species. Unweighted parsimony analyses and Bayesian analyses produced a well-resolved phylogenetic hypothesis supported by high bootstrap values and posterior probabilities within Brachylophus. Our data reject the monophyly of specimens previously believed to comprise B. fasciatus. Instead, our data demonstrate that living Brachylophus comprise three robust and well-supported clades that do not correspond to current taxonomy. One of these clades comprises B. fasciatus from the Lau group of Fiji and Tonga (type locality for B. fasciatus), while a second comprises putative B. fasciatus from the central regions of Fiji, which we refer to here as B. n. sp. Animals in this clade form the sister group to B. vitiensis rather than other B. fasciatus. We herein describe this clade as a new species of Brachylophus based on molecular and morphological data. With only one exception, every island is home to one or more unique haplotypes. We discuss alternative biogeographic hypotheses to explain their distribution in the Pacific and the difficulties of distinguishing these. Together, our molecular and taxonomic results have important implications for future conservation initiatives for the Pacific iguanas. ?? 2008 The Royal Society.

Philosophical Transactions of the Royal Society B:↗

USGS2015

Community for Data Integration 2014 annual report

The U.S. Geological Survey (USGS) researches Earth science to help address complex issues affecting society and the environment. In 2006, the USGS held the first Scientific Information Management Workshop to bring together staff from across the organization to discuss the data and information management issues affecting the integration and delivery of Earth science research and investigate the use of “communities of practice” as mechanisms to share expertise about these issues. Out of this effort emerged the Council for Data Integration, which was conceived as an official organizational function that would help guide data integration activities and formalize communities of practice into working groups; however, by 2009 it became evident that many members of the Council for Data Integration had an interest in developing data integration solutions and sharing expertise in a less formal, grassroots manner, which transformed the Council into a Community for Data Integration (CDI). As of 2014, the CDI represents a dynamic community of practice focused on advancing science data and information management and integration capabilities across the USGS and the CDI community. The CDI fosters an environment for collaboration and sharing by bringing together expertise from external partners and representatives across the USGS who are involved in research, data management, and information technology. Membership is voluntary and open to USGS employees and other individuals and organizations willing to contribute to the community (if interested, contact cdi@usgs.gov). The purpose of the CDI is to do the following: • advance understanding of Earth systems through enhanced use of data and information including associated tools and techniques, • provide a forum for people doing work with data integration to come together to share ideas and learn new skills and techniques, and • grow overall USGS capabilities with data and information by increasing visibility of the work of many people throughout the USGS and the CDI community. To achieve these goals, the CDI operates within four applied areas: monthly forums, annual workshop/webinar series, working groups, and projects. The monthly forums, also known as the Opportunity/Challenge of the Month, provide an open dialogue to share and learn about data integration efforts or to present problems that invite the community to offer solutions, advice, and support. Since 2010, the CDI has also sponsored annual workshops/webinar series to encourage the exchange of ideas, sharing of activities, presentations of current projects, and networking among members. Stemming from common interests, the working groups are focused on efforts to address data management and technical challenges including the development of standards and tools, improving interoperability and information infrastructure, and data preservation within USGS and its partners. The growing support for the activities of the working groups led to the CDI’s first formal request for proposals (RFP) process in 2013 to fund projects that produced tangible products. As of 2014, the CDI continues to hold an annual RFP that creates data management tools and practices, collaboration tools, and training in support of data integration and delivery.

Open-File Report↗

USGS1991

Pliocene-Pleistocene coastal events and history along the western margin of Australia

Coastal deposits along the western coastal margin of Australia, a region of relative tectonic stability, record Plio-Pleistocene events and processes affecting the inner shelf and adjacent hinterland. Tectonic deformation of these deposits is more apparent in the Carnarvon Basin, and rather less so in the Perth Basin. The most complete record comes from the Perth Basin, where units of Pliocene and Pleistocene ages are well represented. In the Perth Basin, the predominantly siliciclastic Yoganup Formation, Ascot Formation and Bassendean Sand represent a complex of shoreline, inner shelf and regressive-dune facies equivalents, the deposition of which began at an undetermined stage of the Pliocene, through to the Early Pleistocene. The deposition of this sequence closed with a major regression and significant faunal extinction. Bioclastic carbonates characterize the Middle and Late Pleistocene of the Perth and Carnarvon basins. Fossil assemblages include a distinct subtropical element, unknown from the Ascot Formation and suggesting a strengthening of the Leeuwin Current. The estuarine arcoid bivalve Anadara trapezia characterizes assemblages of Oxygen Isotope Stages 5 and 7 in the Perth and Carnarvon basins, where it is now extinct. Deposits of Substage 5e (Perth Basin) also record a southerly expansion of warm-water corals and other fauna consistent with shelf temperatures warmer than present. New uranium-series ages on corals from marine sequences of the Tantabiddi Member, of the Bundera Calcarenite of the western Cape Range are consistent with the ‘double peak’ hypothesis for levels of Substage 5e but the evidence remains less than conclusive. Initial uranium-series dates from the Bibra and Dampier formations of Shark Bay indicate that both derive from the Late Pleistocene. These numerical ages contradict previous interpretations of relative ages obtained from field studies. The age relationship of the units requires further investigation.

Quaternary Science Reviews↗

USGS2005

Bottled water, spas, and early years of water chemistry

Although hot springs have been used and enjoyed for thousands of years, it was not until the late 1700s that they changed the course of world civilization by being the motivation for development of the science of chemistry. The pioneers of chemistry such as Priestley, Cavendish, Lavoisier, and Henry were working to identify and generate gases, in part, to determine their role in carbonated beverages. In the 18th century, spas in America were developed to follow the traditional activities of popular European spas. However, they were to become a dominant political and economic force in American history on three major points: (1) By far the most important was to provide a place for the leaders of individual colonies to meet and discuss the need for separation from England and the necessity for the Revolutionary War; (2) the westward expansion of the United States was facilitated by the presence of hot springs in many locations that provided the economic justification for railroads and settlement; and (3) the desire for the preservation of hot springs led to the establishment of the National Park Service. Although mineral springs have maintained their therapeutic credibility in many parts of the world, they have not done so in the United States. We suggest that the American decline was prompted by: (1) the establishment of The Johns Hopkins School of Medicine in 1893; (2) enactment of the Pure Food and Drug Act of 1907; and (3) the remarkable achievement of providing safe water supplies for American cities by the end of the 1920s. The current expanding market for bottled water is based in part on bottled water being an alternative beverage Ito alcohol and sweetened drinks and the inconsistent palatability and perceived health hazards of some tap waters.

Groundwater↗

USGS2006

Influence of propagule flotation longevity and light availability on establishment of introduced mangrove species in Hawai'i

Although no mangrove species are native to the Hawaiian Archipelago, both Rbizopbora mangle and Bruguiera sexangula were introduced and have become naturalized. Rbizopbora mangle has spread to almost every major Hawaiian island, but B. sexangula has established only on O'ahu, where it was intentionally introduced. To examine the possibility that differences in propagule characteristics maintain these patterns of distribution, we first reviewed the literature on surface currents around the Hawaiian Islands, which suggest that propagules ought to disperse frequently from one island to another within 60. days. We then tested the ability of propagules of the two species to float for periods of up to 63 days and to establish under two light intensities. On average, R. mangle propagules floated for longer periods than those of B. sexangula , but at least some propagules of both species floated for a full 60 days and then rooted and grew for 4 months under relatively dense shade. A large percentage (???83%) of R. mangle propagules would be expected to float beyond 60 days, and approximately 10% of B. sexangula propagules also would have remained afloat. Therefore, it seems likely that factors other than flotation ability are responsible for the failure of B. sexangula to become established on other Hawaiian islands.

Hawaii↗

USGS2018

Geomorphic expression of rapid Holocene silicic magma reservoir growth beneath Laguna del Maule, Chile

Large rhyolitic volcanoes pose a hazard, yet the processes and signals foretelling an eruption are obscure. Satellite geodesy has revealed surface inflation signaling unrest within magma reservoirs underlying a few rhyolitic volcanoes. Although seismic, electrical, and potential field methods may illuminate the current configuration and state of these reservoirs, they cannot fully address the processes by which they grow and evolve on geologic time scales. We combine measurement of a deformed paleoshore surface, isotopic dating of volcanism and surface exposure, and modeling to determine the rate of growth of a rhyolite-producing magma reservoir. The numerical approach builds on a magma intrusion model developed to explain the current, decade-long, surface inflation at >20 cm/year. Assuming that the observed 62-m uplift reflects several non-eruptive intrusions of magma, each similar to the unrest over the past decade, we find that ~13 km 3 of magma recharged the reservoir at a depth of ~7 km during the Holocene, accompanied by the eruption of ~9 km 3 of rhyolite. The long-term rate of magma input is consistent with reservoir freezing and pluton formation. Yet, the unique set of observations considered here implies that large reservoirs can be incubated and grow at shallow depth via episodic high-flux magma injections. These replenishment episodes likely drive rapid inflation, destabilize cooling systems, propel rhyolitic eruptions, and thus should be carefully monitored.

Laguna del Maule↗

USGS2017

Pharmaceuticals and personal care products (PPCPs) are ecological disrupting compounds (EcoDC)

Pharmaceuticals and personal care products (PPCPs) are ubiquitous in freshwater ecosystems worldwide and are recognized as contaminants of concern. Currently, contaminants of concern are classified for their persistence, bioaccumulation, and toxicity (PBT criteria). PPCPs are not classified as persistent organic pollutants (POPs), although some PPCPs share characteristics similar to POPs. For example, PPCPs are known to be pseudopersistent due to constant discharge into the environment, often at low concentrations. At commonly reported environmental concentrations, PPCPs are rarely toxic, but the ability of these compounds to disrupt ecological processes and functions in freshwater ecosystems is often overlooked. Herein we briefly summarize recent studies highlighting the potential ecological effects of PPCPs, including effects on key ecological processes (e.g. primary productivity and community respiration), and we propose that appropriate screening for harmful effects of PPCPs in surface waters should be expanded to include Ecologically Disrupting Compounds (EcoDC) in addition to the established PBT criteria.

Elementa: Science of the Anthropocene↗

USGS2008

Radargrammetry on three planets

Synthetic Aperture Radar (SAR) can provide useful images in situations where passive optical imaging cannot, either because the microwaves used can penetrate atmospheric clouds, because active imaging can "see in the dark," or both. We have participated in the NASA Magellan mission to Venus in the 1990s and the current NASA-ESA Cassini-Huygens mission to Saturn and Titan, which have used SAR to see through the clouds of Venus and Titan, respectively, and have developed software and techniques for the production of digital topographic models (DTMs) from radar stereopairs. We are currently preparing for similar radargrammetric analysis of data from the Mini-RF instrument to be carried to the Moon on both the ISRO Chandrayaan-1 and NASA Lunar Reconnaissance Orbiter (LRO) missions later in 2008. These instruments are intended to image the permanently shadowed areas at the lunar poles and even see below the surface to detect possible water ice deposits. In this paper, we describe our approach to radargrammetric topographic mapping, based on the use of the USGS ISIS software system to ingest and prepare data, and the commercial stereoanalysis software SOCET SET (® BAE Systems), augmented with custom sensor models we have implemented, for DTM production and editing. We describe the commonalities and differences between the various data sets, and some of the lessons learned, both radargrammetric and geoscientific.

The International Archives of the Photogrammetry, ↗

USGS2016

Persistent and novel threats to the biodiversity of Kazakhstan’s steppes and semi-deserts

Temperate grasslands have suffered disproportionally from conversion to cropland, degradation and fragmentation. A large proportion of the world’s remaining near-natural grassland is situated in Kazakhstan. We aimed to assess current and emerging threats to steppe and semi-desert biodiversity in Kazakhstan and evaluate conservation research priorities. We conducted a horizon-scanning exercise among conservationists from academia and practice. We first compiled a list of 45 potential threats. These were then ranked by the survey participants according to their perceived severity, the need for research on them, and their novelty. The highest-ranked threats were related to changes in land use (leading to habitat loss and deterioration), direct persecution of wildlife, and rapid infrastructure development due to economic and population growth. Research needs were identified largely in the same areas, and the mean scores of threat severity and research need were highly correlated. Novel threats comprised habitat loss by photovoltaic and wind power stations, climate change and changes in agriculture such as the introduction of biofuels. However, novelty was not correlated with threat severity or research priority, suggesting that the most severe threats are the established ones. Important goals towards more effective steppe and semi-desert conservation in Kazakhstan include more cross-sector collaboration (e.g. by involving stakeholders in conservation and agriculture), greater allocation of funds to under-staffed areas (e.g. protected area management), better representativeness and complementarity in the protected area system and enhanced data collection for wildlife monitoring and threat assessments (including the use of citizen-science databases).

Biodiversity and Conservation↗

USGS2019

Salt marsh ecosystem restructuring enhances elevation resilience and carbon storage during accelerating relative sea-level rise

Salt marshes respond to sea-level rise through a series of complex and dynamic bio-physical feedbacks. In this study, we found that sea-level rise triggered salt marsh habitat restructuring, with the associated vegetation changes enhancing salt marsh elevation resilience. A continuous record of marsh elevation relative to sea level that includes reconstruction of high-resolution, sub-decadal, marsh elevation over the past century, coupled with a lower-resolution 1500-year record, revealed that relative sea-level rose 1.5 ± 0.4 m, following local glacial isostatic adjustment (1.2 mm/yr). As sea-level rise has rapidly accelerated, the high marsh zone dropped 11 cm within the tidal frame since 1932, leading to greater inundation and a shift to flood- and salt-tolerant low marsh species. Once the marsh platform fell to the elevation favored by low-marsh Spartina alterniflora , the elevation stabilized relative to sea level. Currently low marsh accretion keeps pace with sea-level rise, while present day high marsh zones that have not transitioned to low marsh have a vertical accretion deficit. Greater biomass productivity, and an expanding subsurface accommodation space favorable for salt marsh organic matter preservation, provide a positive feed-back between sea-level rise and marsh platform elevation. Carbon storage was 46 ± 28 g C/m 2 /yr from 550 to 1800 CE, increasing to 129 ± 50 g C/m 2 /yr in the last decade. Enhanced carbon storage is controlled by vertical accretion rates, rather than soil carbon density, and is a direct response to anthropogenic eustatic sea-level rise, ultimately providing a negative feedback on climate warming.

Massachusetts↗

USGS2005

Modern pollen data from North America and Greenland for multi-scale paleoenvironmental applications

The modern pollen network in North America and Greenland is presented as a database for use in quantitative calibration studies and paleoenvironmental reconstructions. The georeferenced database includes 4634 samples from all regions of the continent and 134 pollen taxa that range from ubiquitous to regionally diagnostic taxa. Climate data and vegetation characteristics were assigned to every site. Automated and manual procedures were used to verify the accuracy of geographic coordinates and identify duplicate records among datasets, incomplete pollen sums, and other potential errors. Data are currently available for almost all of North America, with variable density. Pollen taxonomic diversity, as measured by the Shannon-Weiner coefficient, varies as a function of location, as some vegetation regions are dominated by one or two major pollen producers, while other regions have a more even composition of pollen taxa. Squared-chord distances computed between samples show that most modern pollen samples find analogues within their own vegetation zone. Both temperature and precipitation inferred from best analogues are highly correlated with observed values but temperature exhibits the strongest relation. Maps of the contemporary distribution of several pollen types in relation to the range of the plant taxon illustrate the correspondence between plant and pollen ranges. ?? 2005 Elsevier Ltd. All rights reserved.

Quaternary Science Reviews↗

USGS2007

Transient simulations of nitrogen load for a coastal aquifer and embayment, Cape Cod, MA

A time-varying, multispecies, modular, three-dimensional transport model (MT3DMS) was developed to simulate groundwater transport of nitrogen from increasing sources on land to the shore of Nauset Marsh, a coastal embayment of the Cape Cod National Seashore. Simulated time-dependent nitrogen loads at the coast can be used to correlate with current observed coastal eutrophic effects, to predict current and ultimate effects of development, and to predict loads resulting from source remediation. A time-varying nitrogen load, corrected for subsurface loss, was applied to the land subsurface in the transport model based on five land-use coverages documenting increasing development from 1951 to 1999. Simulated nitrogen loads to Nauset Marsh increased from 230 kg/yr before 1930 to 4390 kg/yr in 2001 to 7130 kg/yr in 2100, assuming future nitrogen sources constant at the 1999 land-use rate. The simulated nitrogen load per area of embayment was 5 times greater for Salt Pond, a eutrophic landward extension of Nauset Marsh, than for other Nauset Marsh areas. Sensitivity analysis indicated that load results were little affected by changes in vertical discretization and annual recharge but much affected by the nitrogen loss rate assumed for a kettle lake downgradient from a landfill.

Environmental Science & Technology↗