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The National Wind Erosion Research Network: Building a standardized long-term data resource for aeolian research, modeling and land management

The National Wind Erosion Research Network was established in 2014 as a collaborative effort led by the United States Department of Agriculture’s Agricultural Research Service and Natural Resources Conservation Service, and the United States Department of the Interior’s Bureau of Land Management, to address the need for a long-term research program to meet critical challenges in wind erosion research and management in the United States. The Network has three aims: (1) provide data to support understanding of basic aeolian processes across land use types, land cover types, and management practices, (2) support development and application of models to assess wind erosion and dust emission and their impacts on human and environmental systems, and (3) encourage collaboration among the aeolian research community and resource managers for the transfer of wind erosion technologies. The Network currently consists of thirteen intensively instrumented sites providing measurements of aeolian sediment transport rates, meteorological conditions, and soil and vegetation properties that influence wind erosion. Network sites are located across rangelands, croplands, and deserts of the western US. In support of Network activities, http://winderosionnetwork.org was developed as a portal for information about the Network, providing site descriptions, measurement protocols, and data visualization tools to facilitate collaboration with scientists and managers interested in the Network and accessing Network products. The Network provides a mechanism for engaging national and international partners in a wind erosion research program that addresses the need for improved understanding and prediction of aeolian processes across complex and diverse land use types and management practices.

Arizona, California, Colorado, Idaho, North Dakota↗

Agencies collaborate, develop a cyanobacteria assessment network

Cyanobacteria are a genetically diverse group of photosynthetic microorganisms that occupy a broad range of habitats on land and water all over the world. They release toxins that can cause lung and skin irritation, alter the taste and odor of potable water, and cause human and animal illness. Cyanobacteria blooms occur worldwide, and climate change may increase the frequency, duration, and extent of these bloom events. Rapid detection of potentially harmful blooms is essential to protect humans and animals from exposure. Information about potential for exposure, such as bloom duration, frequency, and extent, is especially critical for developing environmental management decisions during periods of limited resources and funding. The National Research Council (NRC) report Exposure Science in the 21st Century suggested that effectively assessing and mitigating exposures requires techniques for rapid measurement of a stressor, such as an algal bloom, across diverse geographic, temporal, and biologic scales (e.g., various bloom concentrations) and an enhanced infrastructure to address threats [ NRC , 2012]. The report specifically calls for approaches that use diverse information, such as satellite remote sensing, to identify and understand exposures that may pose a threat to ecosystems or human health. A collaborative effort integrates the work of the U.S. Environmental Protection Agency (EPA), NASA, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Geological Survey (USGS) to provide an approach for using satellite ocean color capabilities in U.S. fresh and brackish water quality management decisions. The overarching goal of this collaborative project is to detect and quantify cyanobacteria blooms using satellite data records in order to support the environmental management and public use of U.S. lakes and reservoirs. Satellite remote sensing tools may enable policy makers and environmental managers to assess the sustainability of watershed ecosystems and the services they provide, now and in the future. Satellite technology allows us to develop early-warning indicators of cyanobacteria blooms at the local scale while maintaining continuous national coverage.

Eos, Earth and Space Science News↗

Opportunities and challenges for incorporating lithium-ion batteries into geophysical power systems

Batteries play a critical role at seismic and other geophysical stations in ensuring that the equipment receives uninterrupted power to make continuous observations of the Earth. Often sited in remote environments under a wide range of environmental conditions, these stations have almost ubiquitously used conventional lead‐acid batteries. However, recent advances in rechargeable lithium‐ion battery technology have led to the development of lithium‐iron phosphate (LFP) batteries that can replace lead‐acid batteries in energy storage systems. In the past three years, LFP battery production has grown over an order of magnitude, reducing their cost and increasing their availability. In this article, we examine the benefits and challenges associated with incorporating several types of LFP batteries into the power systems of geophysical stations. We review how fundamental differences in battery chemistry enable LFP batteries to weigh less than half of comparable lead‐acid batteries and may have longer service lives but have the added complexity of being managed by an integrated battery monitoring system (BMS) microcontroller. Through a controlled heat chamber experiment, we demonstrate that LFP batteries can be ideally suited for use in high‐temperature environments by offering longer service lives than lead‐acid batteries. However, for safety reasons, the BMS prevents most LFP batteries from being charged at temperatures <0°C, which complicates their use in colder regions and can lead to equipment damage if the charging system is not appropriately designed for this battery type. Finally, we address some of the unique challenges associated with adopting lithium batteries, including unexpected substantial (≤14 W) power consumption from the BMS, safety concerns, and shipping restrictions. It is our goal to help inform station operators and geophysicists about potential benefits and issues that can arise from using LFP batteries at seismic and geophysical stations in a range of environments.

Seismological Research Letters↗

In situ soil moisture sensors in undisturbed soils

Soil moisture directly affects operational hydrology, food security, ecosystem services, and the climate system. However, the adoption of soil moisture data has been slow due to inconsistent data collection, poor standardization, and typically short record duration. Soil moisture, or quantitatively volumetric soil water content (SWC), is measured using buried, in situ sensors that infer SWC from an electromagnetic response. This signal can vary considerably with local site conditions such as clay content and mineralogy, soil salinity or bulk electrical conductivity, and soil temperature; each of these can have varying impacts depending on the sensor technology., Furthermore, poor soil contact and sensor degradation can affect the quality of these readings over time. Unlike more traditional environmental sensors, there are no accepted standards, maintenance practices, or quality controls for SWC data. As such, SWC is a challenging measurement for many environmental monitoring networks to implement. Here, we attempt to establish a community-based standard of practice for in situ SWC sensors so that future research and applications have consistent guidance on site selection, sensor installation, data interpretation, and long-term maintenance of monitoring stations., The videography focuses on a multi-agency consensus of best-practices and recommendations for the installation of in situ SWC sensors. This paper presents an overview of this protocol along with the various steps essential for high-quality and long-term SWC data collection. This protocol will be of use to scientists and engineers hoping to deploy a single station or an entire network.

Journal of Visualized Experiments↗

Development of a standard reference material for Cr(vi) in contaminated soil

Over the last several decades, considerable contamination by hexavalent chromium has resulted from the land disposal of Chromite Ore Processing Residue (COPR). COPR contains a number of hexavalent chromium-bearing compounds that were produced in high temperature industrial processes. Concern over the carcinogenic potential of this chromium species, and its environmental mobility, has resulted in efforts to remediate these waste sites. To provide support to analytical measurements of hexavalent chromium, a candidate National Institute of Standards and Technology (NIST) Standard Reference Material?? (SRM 2701), having a hexavalent chromium content of approximately 500 mg kg -1, has been developed using material collected from a waste site in Hudson County, New Jersey, USA. The collection, processing, preparation and preliminary physico-chemical characterization of the material are discussed. A two-phase multi-laboratory testing study was carried out to provide data on material homogeneity and to assess the stability of the material over the duration of the study. The study was designed to incorporate several United States Environmental Protection Agency (USEPA) determinative methods for hexavalent chromium, including Method 6800 which is based on speciated isotope dilution mass spectrometry (SIDMS), an approach which can account for chromium species inter-conversion during the extraction and measurement sequence. This journal is ?? The Royal Society of Chemistry 2008.

Journal of Analytical Atomic Spectrometry↗

Critical mineral resources of the United States—An introduction

Many changes have taken place in the mineral resource sector since the publication by the U.S. Geological Survey of Professional Paper 820, “United States Mineral Resources,” which is a review of the long-term United States resource position for 65 mineral commodities or commodity groups. For example, since 1973, the United States has continued to become increasingly dependent on imports to meet its demands for an increasing number of mineral commodities. The global demand for mineral commodities is at an alltime high and is expected to continue to increase, and the development of new technologies and products has led to the use of a greater number of mineral commodities in increasing quantities to the point that, today, essentially all naturally occurring elements have several significant industrial uses. Although most mineral commodities are present in sufficient amounts in the earth to provide adequate supplies for many years to come, their availability can be affected by such factors as social constraints, politics, laws, environmental regulations, land-use restrictions, economics, and infrastructure. This volume presents updated reviews of 23 mineral commodities and commodity groups viewed as critical to a broad range of existing and emerging technologies, renewable energy, and national security. The commodities or commodity groups included are antimony, barite, beryllium, cobalt, fluorine, gallium, germanium, graphite, hafnium, indium, lithium, manganese, niobium, platinum-group elements, rare-earth elements, rhenium, selenium, tantalum, tellurium, tin, titanium, vanadium, and zirconium. All these commodities have been listed as critical and (or) strategic in one or more of the recent studies based on assessed likelihood of supply interruption and the possible cost of such a disruption to the assessor. For some of the minerals, current production is limited to only one or a few countries. For many, the United States currently has no mine production or any significant identified resources and is largely dependent on imports to meet its needs. As a result, the emphasis in this volume is on the global distribution and availability of each mineral commodity. The environmental issues related to production of each mineral commodity, including current mitigation and remediation approaches to deal with these challenges, are also addressed. This introductory chapter provides an overview of the mineral resource classifications, terms, and definitions used in this volume. A review of the history of the use and meaning of the term “critical” minerals (or materials) is included as an appendix to the chapter.

Professional Paper↗

Toward a scientifically rigorous basis for developing mapped ecological regions.

Despite the wide use of ecological regions in conservation and resource-management evaluations and assessments, a commonly accepted theoretical basis for ecological regionalization does not exist. This fact, along with the paucity of focus on ecological regionalization by professional associations, journals, and faculties, has inhibited the advancement of a broadly acceptable scientific basis for the development, use, and verification of ecological regions. The central contention of this article is that ecological regions should improve our understanding of geographic and ecological phenomena associated with biotic and abiotic processes occurring in individual regions and also of processes characteristic of interactions and dependencies among multiple regions. Research associated with any ecoregional framework should facilitate development of hypotheses about ecological phenomena and dominant landscape elements associated with these phenomena, how these phenomena are structured in space, and how they function in a hierarchy. Success in addressing the research recommendations outlined in this article cannot occur within an ad hoc, largely uncoordinated research environment. Successful implementation of this plan will require activities--coordination, funding, and education--that are both scientific and administrative in nature. Perhaps the most important element of an infrastructure to support the scientific work of ecoregionalization would be a national or international authority similar to the Water and Science Technology Board of the National Academy of Sciences.

Environmental Management↗

Reducing wet ammonium deposition in Rocky Mountain National Park: The development and evaluation of a pilot early warning system for agricultural operations in eastern Colorado

Agricultural emissions are the primary source of ammonia (NH3) deposition in Rocky Mountain National Park (RMNP), a Class I area, that is granted special air quality protections under the Clean Air Act. Between 2014 and 2016, the pilot phase of the Colorado agricultural nitrogen early warning system (CANEWS) was developed for agricultural producers to voluntarily and temporarily minimize emissions of NH3 during periods of upslope winds. The CANEWS was created using trajectory analyses driven by outputs from an ensemble of numerical weather forecasts together with the climatological expertise of human forecasters. Here, we discuss the methods for the CANEWS and offer preliminary analyses of 33 months of the CANEWS based on atmospheric deposition data from two sites in RMNP as well as responses from agricultural producers after warnings were issued. Results showed that the CANEWS accurately predicted 6 of 9 high N deposition weeks at a lower-elevation observation site, but only 4 of 11 high N deposition weeks at a higher-elevation site. Sixty agricultural producers from 39 of Colorado’s agricultural operations volunteered for the CANEWS, and a two-way line of communication between agricultural producers and scientists was formed. For each warning issued, an average of 23 producers responded to a post-warning survey. Over 75% of responding CANEWS participants altered their practices after an alert. While the current effort was insufficient to reduce atmospheric deposition, we were encouraged by the collaborative spirit between agricultural, scientific, and resource management communities. Solving a broad and complex social-ecological problem requires both a technological approach, such as the CANEWS, and collaboration and trust from all participants, including agricultural producers, land managers, university researchers, and environmental agencies.

Colorado↗

Bioremediation of petroleum hydrocarbon-contaminated ground water: The perspectives of history and hydrology

Bioremediation, the use of microbial degradation processes to detoxify environmental contamination, was first applied to petroleum hydrocarbon-contaminated ground water systems in the early 1970s. Since that time, these technologies have evolved in some ways that were clearly anticipated early investigators, and in other ways that were not foreseen. The expectation that adding oxidants and nutrients to contaminated aquifers would enhance biodegradation, for example, has been born out subsequent experience. Many of the technologies now in common use such as air sparging, hydrogen peroxide addition, nitrate addition, and bioslurping, are conceptually similar to the first bioremediation systems put into operation. More unexpected, however, were the considerable technical problems associated with delivering oxidants and nutrients to heterogeneous ground water systems. Experience has shown that the success of engineered bioremediation systems depends largely on how effectively directions and rates of ground water flow can be controlled, and thus how efficiently oxidants and nutrients can be delivered to contaminated aquifer sediments. The early expectation that injecting laboratory-selected or genetically engineered cultures of hydrocarbon-degrading bacteria into aquifers would be a useful bioremediation technology has not been born out subsequent experience. Rather, it appears that petroleum hydrocarbon-degrading bacteria are ubiquitous in ground water systems and that bacterial addition is usually unnecessary. Perhaps the technology that was least anticipated early investigators was the development of intrinsic bioremediation. Experience has shown that natural attenuation mechanisms - biodegradation, dilution, and sorption - limit the migration of contaminants to some degree in all ground water systems. Intrinsic bioremediation is the deliberate use of natural attenuation processes to treat contaminated ground water to specified concentration levels at predetermined points in the aquifer. In current practice, intrinsic bioremediation of petroleum hydrocarbons requires a systematic assessment to show that ambient natural attenuation mechanisms are efficient enough to meet regulatory requirements and a monitoring program to verify that performance requirements are met in the future.

Ground Water↗

Assessment of the potential for biodegradation of petroleum hydrocarbons in the Railroad Industrial Area, Fairbanks, Alaska

Many technologies for the clean-up of petroleum-hydrocarbon contaminated sites depend on microbial degradation of the pollutant. In these technologies the site may be modified to enhance microbial activity, or may simply be monitored for naturally occurring microbial activity. In either case, an important aspect of site assessment for these technologies is to determine if the microorganisms present at the site have the potential to break down contaminants under the prevailing environmental conditions. We examined the numbers and activity of hydrocarbon-degrading microorganisms in ground water collected from petroleum-hydrocarbon contaminated and uncontaminated wells at the Railroad Industrial Area near Fairbanks, Alaska. We found that the population of gasoline-degrading microorganisms in ground water was correlated to the degree of contamination by benzene, toluene, ethylbenzene and xylenes (BTEX). We also found that these organisms could actively mineralize these types of compounds in laboratory mineralization assays. Increasing temperature and adding nutrients both enhanced the rate of mineralization in the laboratory, but measurable degradation still occurred under conditions similar to those found in the field. Dissolved oxygen in ground water at this site ranged from 0 to 3.6 milligrams per liter. Therefore, oxygen may not always be available to microorganisms as a terminal electron acceptor. Preliminary geochemical evidence from the field indicates that alternative electron acceptors such as Fe(III), sulfate, or nitrate may be used, contributing to degradation of contaminants at this site.

Open-File Report↗

Assessment of native fish passage through Brandon Road Lock and Dam, Des Plaines River, Illinois, using fin ray microchemistry

This study examined evidence of native fish passage through Brandon Road Lock and Dam (BRLD) on the Des Plaines River, Illinois, in light of proposed modifications to prevent the upstream passage of invasive carps. Direct evidence of upstream passage by native fishes at BRLD is lacking and could help to inform assessment of the impacts of barrier technology installation. Fin ray microchemistry was used to assess upstream BRLD passage in the native taxa Centrarchidae, Catostomidae, Ictaluridae, and Lepisosteidae. The fin ray edge strontium : calcium ratio (Sr:Ca) of fish sampled from the Des Plaines River upstream of BRLD and in rivers downstream of BRLD was used to characterize ranges of river-specific fin ray Sr:Ca for each taxon. These were applied to Sr:Ca data along a transect from fin ray core to edge to infer the environmental history of individual fish that were captured upstream from BRLD and to estimate the proportion of fish that had passed upstream through BRLD. Depending on the taxon, 6–37% of individuals sampled upstream from BRLD exhibited fin ray Sr:Ca indicating prior residency in rivers downstream of BRLD and therefore upstream passage through BRLD. Upstream passage was indeterminate for 19–91% of individuals in each taxon due to uncertainty in environmental history inferred from fin ray Sr:Ca. These results provide the first definitive evidence of upstream native fish passage at BRLD and suggest that the installation of barrier technology could have an impact on native fish.

Illinois↗

Mineral resources of the U.S. Atlantic continental margin

Most geologic materials may be usable resources in some form and at some time, whether it be for general land fill and aggregate, beach replenishment, construction material, or as a source of metals and fuels. Thus, most natural materials occurring within the Atlantic continental margin are resources, defined as “materials, including those only surmised to exist, that have present or anticipated future value” (U.S.G.S., 1980). Whether a resource becomes a reserve or not (an economically recoverable commodity) depends upon the properties and economic values of that material, which are determined by the following factors: (a) availability, concentration, and occurrence of the material; (b) methods of recovering and processing the commodity; (c) transportation costs of ore and beneficiated products; and (d) environmental setting and costs of permitting and mitigation. Also, the economics of a given mineral resource change dramatically in response to new technological advances, discoveries of new deposits, or as industrial and social demands change through time. An increasingly critical component associated with the economics for development of any mineral commodity, is a good geologic knowledge of the resource base.

Atlantic Continental Margin↗

Wildlife guilds in Arizona desert habitats

This report summarizes information produced from Interagency Agreement No. AA-851-IA1-27 between the Bureau of Land Management (BLM), USDI, and the Fish and Wildlife Service (FWS), USDI. The contract was instrumental in the final development of wildlife guilds for the Hualapai-Aquarius planning area of the BLM in westcentral Arizona, reported herein. The Arizona study area was selected for the application of the guilding technology because a thorough assessment of the floral and faunal resources had recently occurred in conjunction with the development of a grazing Environmental Impact Statement (EIS). Thus, the association of wildlife species with habitat type was well known, which aided in the compilation of the data base necessary for the development of guilds. Some data were also available that described the vegetative structure of habitats. This was useful in the development of a model that evaluated the quality of habitat on the basis of the diversity of cover in those habitats (Short 1982).

Arizona↗

The effects of tissue fixation on sequencing and transcript abundance of nucleic acids from microdissected liver samples of smallmouth bass (Micropterus dolomieu)

There is an increasing emphasis on effects-based monitoring to document responses associated with exposure to complex mixtures of chemicals, climate change, pathogens, parasites and other environmental stressors in fish populations. For decades aquatic monitoring programs have included the collection of tissues preserved for microscopic pathology. Consequently, formalin-fixed, paraffin-embedded (FFPE) tissue can be an important reservoir of nucleic acids as technologies emerge that utilize molecular endpoints. Despite the cross-linking effects of formalin, its impact on nucleic acid quality and concentration, amplification, and sequencing are not well described. While fresh-frozen tissue is optimal for working with nucleic acids, FFPE samples have been shown to be conducive for molecular studies. Laser capture microdissection (LCM) is one technology which allows for collection of specific regions or cell populations from fresh or preserved specimens with pathological alterations, pathogens, or parasites. In this study, smallmouth bass (Micropterus dolomieu) liver was preserved in three different fixatives, including 10% neutral buffered formalin (NBF), Z-Fix® (ZF), and PAXgene® (PG) for four time periods (24 hr, 48 hr, seven days, and 14 days). Controls consisted of pieces of liver preserved in RNALater® or 95% ethanol. Smallmouth bass were chosen as they are an economically important sportfish and have been utilized as indicators of exposure to endocrine disruptors and other environmental stressors. Small liver sections were cut out with laser microdissection and DNA and RNA were purified and analyzed for nucleic acid concentration and quality. Sanger sequencing and the NanoString nCounter® technology were used to assess the suitability of these samples in downstream molecular techniques. The results revealed that of the formalin fixatives, NBF samples fixed for 24 and 48 hr were superior to ZF samples for both Sanger sequencing and the Nanostring nCounter®. The non-formalin PAXgene® samples were equally successful and they showed greater stability in nucleic acid quality and concentration over longer fixation times. This study demonstrated that small quantities of preserved tissue from smallmouth bass can be utilized in downstream molecular techniques; however, future studies will need to optimize the methods presented here for different tissue types, fish species, and pathological conditions.

PLoS ONE↗

National Unmanned Aircraft Systems Project Office

The U.S. Geological Survey (USGS) National Unmanned Aircraft Systems (UAS) Project Office leads the implementation of UAS technology in the Department of the Interior (DOI). Our mission is to support the transition of UAS into DOI as a new cost-effective tool for collecting remote-sensing data to monitor environmental conditions, respond to natural hazards, recognize the consequences and benefits of land and climate change and conduct wildlife inventories. The USGS is teaming with all DOI agencies and academia as well as local, State, and Tribal governments with guidance from the Federal Aviation Administration and the DOI Office of Aviation Services (OAS) to lead the safe, efficient, costeffective and leading-edge adoption of UAS technology into the scientific research and operational activities of the DOI.

Fact Sheet↗

Can you hear me now? Range-testing a submerged passive acoustic receiver array in a Caribbean coral reef habitat

Submerged passive acoustic technology allows researchers to investigate spatial and temporal movement patterns of many marine and freshwater species. The technology uses receivers to detect and record acoustic transmissions emitted from tags attached to an individual. Acoustic signal strength naturally attenuates over distance, but numerous environmental variables also affect the probability a tag is detected. Knowledge of receiver range is crucial for designing acoustic arrays and analyzing telemetry data. Here, we present a method for testing a relatively large-scale receiver array in a dynamic Caribbean coastal environment intended for long-term monitoring of multiple species. The U.S. Geological Survey and several academic institutions in collaboration with resource management at Buck Island Reef National Monument (BIRNM), off the coast of St. Croix, recently deployed a 52 passive acoustic receiver array. We targeted 19 array-representative receivers for range-testing by submersing fixed delay interval range-testing tags at various distance intervals in each cardinal direction from a receiver for a minimum of an hour. Using a generalized linear mixed model (GLMM), we estimated the probability of detection across the array and assessed the effect of water depth, habitat, wind, temperature, and time of day on the probability of detection. The predicted probability of detection across the entire array at 100 m distance from a receiver was 58.2% (95% CI: 44.0&ndash;73.0%) and dropped to 26.0% (95% CI: 11.4&ndash;39.3%) 200 m from a receiver indicating a somewhat constrained effective detection range. Detection probability varied across habitat classes with the greatest effective detection range occurring in homogenous sand substrate and the smallest in high rugosity reef. Predicted probability of detection across BIRNM highlights potential gaps in coverage using the current array as well as limitations of passive acoustic technology within a complex coral reef environment.

Ecology and Evolution↗

A study of topics for distance education-A survey of U.S. Fish and Wildlife Service employees

The purpose of this study was to identify training topics and distance education technologies preferred by U.S. Fish and Wildlife Service employees. This study was conducted on behalf of the National Conservation Training Center to support their distance education strategy planning and implementation. When selecting survey recipients, we focused on employees in positions involving conservation and environmental education and outreach programming. We conducted the study in two phases. First, we surveyed 72 employees to identify useful training topics. The response rate was 61 percent; respondents were from all regions and included supervisors and nonsupervisors. Five topics for training were identified: creating and maintaining partnerships (partnerships), technology, program planning and development (program planning), outreach methods to engage the community (outreach methods), and evaluation methods. In the second phase, we surveyed 1,488 employees to assess preferences for training among the five topics identified in the first survey and preferences among six distance education technologies: satellite television, video conferencing, audio conferencing, computer mediated training, written resources, and audio resources. Two types of instructor-led training were included on the survey to compare to the technology options. Respondents were asked what types of information, such as basic facts or problem solving skills, were needed for each of the five topics. The adjusted response rate was 64 percent; respondents were from all regions and included supervisors and nonsupervisors. The results indicated clear preferences among respondents for certain training topics and technologies. All five training topics were valued, but the topics of partnerships and technology were given equal value and were valued more than the other three topics. Respondents indicated a desire for training on the topics of partnerships, technology, program planning, and outreach methods. For the six distance education technologies, respondents indicated different levels of usability and access. Audio conferencing and written resources were reported to be most usable and accessible. The ratings of technology usability/access differed according to region; respondents in region 9 rated most technologies higher on usability/access. Respondents indicated they would take courses through either onsite or distance education approaches, but they prefer onsite training for most topics and most types of information.

Open-File Report↗

Guidelines for the use of the semipermeable membrane device (SPMD) and the polar organic chemical integrative sampler (POCIS) in environmental monitoring studies

The success of an environmental monitoring study using passive samplers, or any sampling method, begins in the office or laboratory. Regardless of the specific methods used, the general steps include the formulation of a sampling plan, training of personnel, performing the field (sampling) work, processing the collected samples to recover chemicals of interest, analysis of the enriched extracts, and interpretation of the data. Each of these areas will be discussed in the following sections with emphasis on specific considerations with the use of passive samplers. Water is an extremely heterogeneous matrix both spatially and temporally (Keith, 1991). The mixing and distribution of dissolved organic chemicals in a water body are controlled by the hydrodynamics of the water, the sorption partition coefficients of the chemicals, and the amount of organic matter (suspended sediments, colloids, and dissolved organic carbon) present. In lakes and oceans, stratification because of changes in temperature, water movement, and water composition can occur resulting in dramatic changes in chemical concentrations with depth (Keith, 1991). Additional complications related to episodic events, such as surface runoff, spills, and other point source contamination, can result in isolated or short-lived pulses of contaminants in the water. The application of passive sampling technologies for the monitoring of legacy and emerging organic chemicals in the environment is becoming widely accepted worldwide. The primary use of passive sampling methods for environmental studies is in the area of surface-water monitoring; however, these techniques have been applied to air and groundwater monitoring studies. Although these samplers have no mechanical or moving parts, electrical or fuel needs which require regular monitoring, there are still considerations that need to be understood in order to have a successful study. Two of the most commonly used passive samplers for organic contaminants are the semipermeable membrane device (SPMD) and the polar organic chemical integrative sampler (POCIS). The tips given in this document focus on these two samplers but are applicable to most types of passive sampling devices. The information in this guide is heavily weighted towards the sampling of water; however, information specific to the use of SPMDs for air sampling will also be covered.

Techniques and Methods↗