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In situ lecture


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Short course lecture on in situ sediment assessment and biogeochemical behaviour of contaminants

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In situ lecture

  1. 1. In Situ Benthic Observation Tools in Sediment Risk Assessments - and- The Need for Biogeochemistry in Characterizing In-situ Exposure and Effects Sabine E. Apitz, Ph.D. SEA Environmental Decisions, Ltd 1 South Cottages, The Ford Little Hadham, Hertfordshire SG11 2AT, UK 01279 771890 [email_address] … Linking science and applications
  2. 2. How we assess and manage sediment systems depends in part on how we conceptualise them In this conceptual model we view sediments and benthic organisms merely as pathways of contaminant transfer up a food chain
  3. 3. This shows a similar conceptual model in cartoon form
  4. 4. <ul><li>Changes in chemical and physical state (and thus mobility) often result in changes in bioavailability </li></ul><ul><li>Thus, to understand exposure (and predict effects) one must understand mechanisms of transport </li></ul>This conceptual model breaks down some of the chemical and physical processes that drive the transfers described above
  5. 5. With our focus on contaminant transfer, we sometimes forget that the sediments themselves are also ecologically important <ul><li>Coastal marine ecosystems </li></ul><ul><ul><li>represent an important reservoir for biodiversity </li></ul></ul><ul><ul><li>play a major role in regulating carbon and nutrient biogeochemical cycles </li></ul></ul><ul><ul><li>particularly vulnerable to anthropogenic perturbations ( including, but not limited to, contamination ) </li></ul></ul><ul><li>However, due to the complexity , remoteness and spatio-temporal variability of this environment, the relationships between tightly coupled biological and geochemical processes are poorly understood </li></ul><ul><li>In contrast with blind, synoptic sampling and laboratory studies, in situ studies provide rigorous scientific insight into the complex interactions between the biota (function and diversity) and their chemical environment and the processes regulating this unique and fragile habitat </li></ul><ul><ul><li>Such studies are the focus of the Coastal Ocean Benthic Observatories ( COBO ) program </li></ul></ul><ul><li>In situ and on site physical, chemical, biological and optical studies provide insight into site conditions and interactions, putting measurements in context and refining our conceptual understanding of the system </li></ul>
  6. 6. What ecosystem functions do marine benthic systems provide? <ul><li>organic material supplied to benthos </li></ul><ul><li>broken down by microbes </li></ul><ul><li>releases nutrients ( NH 4 , NO 2 /NO 3 , PO 4 ) </li></ul><ul><li>nutrients fuel primary production </li></ul><ul><li>important role in carbon cycling </li></ul><ul><li>“ seed bed” for biodiversity </li></ul><ul><li>affect contaminant transport, sequestration, degradation and accumulation in sediment systems </li></ul>(CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 53 SO 4 2- + 14 H + 106 HCO 3 - + 16 NH 4 + + HPO 4 2- + 53 H 2 S adapted from M. Solan
  7. 7. Basic Goals of a Sediment Manager <ul><li>Risk managers and decision makers must evaluate how to balance ecological and socioeconomic objectives for sediments </li></ul><ul><ul><li>How these questions are addressed is often controlled by the scale of the decision makers’ remit (hotspot, stream, river basin, harbor, catchment…), as well as what he/she is mandated to protect (water, fisheries, human health, navigation, global change…) </li></ul></ul><ul><li>Risk managers often have two parallel (but possibly competing) drivers: </li></ul><ul><ul><li>minimizing risk (to the environment and human health, socioeconomic goals, etc) and </li></ul></ul><ul><ul><li>minimizing cost </li></ul></ul>
  8. 8. <ul><li>Absolute Ecorisk </li></ul><ul><ul><li>Does sediment x put species y at risk? </li></ul></ul><ul><li>Site-specific risk </li></ul><ul><ul><li>What is the risk of sediment x relative to regional or background risk? </li></ul></ul><ul><li>Manageable risk </li></ul><ul><ul><li>Can this risk be controlled? </li></ul></ul><ul><li>Management option risk </li></ul><ul><ul><li>What is the risk of leaving sediments in place vs. disturbing them? </li></ul></ul><ul><li>Socioeconomic risk </li></ul><ul><ul><li>Can we afford it? </li></ul></ul><ul><ul><li>How will it impact other goals? </li></ul></ul>An ecologist’s (scientific) definition of risk: But…there are many types of risk, and what you evaluate depends upon your management goals. Each of these types of risk has very different scientific assumptions. However, often managers and decision makers use the same terms for these very different things Risk means different things to different people
  9. 9. Approaches to Contaminated Sediments are in Flux <ul><li>Ten years ago, most people thought that removal and treatment of contaminated sediments would be the remedy of choice </li></ul><ul><ul><li>“ Chemical engineering” approach to management </li></ul></ul><ul><li>Based upon potential volumes and projected costs, some estimate that such an approach would cost in excess of $5 trillion in the United States alone </li></ul><ul><ul><li>Thus, many groups predict or advocate that large volumes of contaminated sediments will be managed in place </li></ul></ul><ul><ul><li>Source control is a major component of such management as well </li></ul></ul><ul><ul><li>The goal is thus to determine the least invasive, but sufficiently protective, management strategy for a given contaminated site </li></ul></ul><ul><ul><li>This can be called “sustainable sediment management” </li></ul></ul><ul><li>There are large gaps in our knowledge of the fate of contaminants in-place, and the effects of in-place remedial strategies, which must be filled if in-place management is to be used wisely </li></ul>
  10. 10. The Problem – Contaminated Sediment Management <ul><li>Currently, there are four groups of remedial strategies for contaminated sediments, to be selected based upon an evaluation of site-specific risks and benefits of management strategies </li></ul><ul><ul><li>monitored natural recovery </li></ul></ul><ul><ul><li>in situ treatment </li></ul></ul><ul><ul><li>in situ containment </li></ul></ul><ul><ul><li>dredging or excavation (followed by treatment and/or disposal) </li></ul></ul><ul><li>However, technology-specific and site-specific data on risks or impacts of sediment remedial strategies (especially in-place strategies) are sparse </li></ul><ul><li>As a result, while there is no presumptive remedy for a contaminated sediment site, expensive removal and disposal actions are being carried out at sites for which in situ management may be a cost effective and viable option </li></ul>
  11. 11. Understanding Contaminant Behavior In Situ <ul><li>Many of the contaminated marine sediment sites currently under investigation are in shallow, coastal areas </li></ul><ul><li>These are much more likely than traditionally studied offshore sediments to be impacted by advective processes such as groundwater flow, tidal pumping, wave pumping and by resuspension via ship and storm activity </li></ul><ul><li>These processes are recognized in the oceanographic community as having significance to chemical fluxes, but are largely unstudied in contaminated systems </li></ul><ul><li>Currently, there is no demonstrated, systematic process for measuring and evaluating contaminant transport pathways within sediment systems in support of in-place management </li></ul>
  12. 12. Managing Contaminants in Sediments <ul><li>Where are they? </li></ul><ul><ul><li>Site assessment, field screening, historical documents </li></ul></ul><ul><li>What are they? What form? </li></ul><ul><ul><li>Analytics, fingerprinting, sediment/contaminant biogeochemical interactions </li></ul></ul><ul><li>Are they a problem? </li></ul><ul><ul><li>Biomarkers, bioassays, bioavailability, community analysis, risk assessment </li></ul></ul><ul><li>Are they mobile? </li></ul><ul><ul><li>hydrodymamics, flux and porewater </li></ul></ul><ul><li>Where do they come from? </li></ul><ul><ul><li>Forensics, geochemistry </li></ul></ul><ul><li>What do we do about them? </li></ul><ul><ul><li>Management, monitoring, remediation </li></ul></ul><ul><li>How do we prevent it in the future? </li></ul>
  13. 13. Contaminated sediments are heterogeneous in space and time <ul><li>We collect discrete samples of sediment in order to establish contaminant levels, and their correlations with toxicity, mobility, behaviour and fate </li></ul><ul><li>However, ultimately, management decisions are not made for grab samples, but for large areas </li></ul><ul><li>This heterogeneity can make it difficult to correlate chemical and biological assessments </li></ul>Cr in surface sediments by a creek mouth and piers, San Diego Bay Pb vs depth in cores from site
  14. 14. When one surveys a site, there can be a range of contaminant concentrations. How one uses the data depends upon the goals and assumptions – what is relevant to the in situ assay? Focus of public Focus of models Cu in sediments Range of Cu in case study sediments from different sites max median mean min
  15. 15. Where are the Contaminants? - Macro Scale In situ and on site chemical screening tools can provide rapid maps of sediment contaminant levels, guiding sampling and the placement of biological studies, and providing insight into heterogeneity Example: Field-portable XRF for rapid screening and mapping of metals
  16. 16. Field Screening vs. Lab Analysis <ul><li>Benefits </li></ul><ul><ul><li>rapid results can guide sampling locations </li></ul></ul><ul><ul><li>potential for high data density for mapping </li></ul></ul><ul><li>Limitations </li></ul><ul><ul><li>often non-specific </li></ul></ul><ul><ul><li>semi-quantitative </li></ul></ul><ul><ul><li>matrix sensitive </li></ul></ul><ul><li>Benefits </li></ul><ul><ul><li>standard methods that are very quantitative </li></ul></ul><ul><ul><li>can often remove interferences </li></ul></ul><ul><li>Limitations </li></ul><ul><ul><li>often blind sampling </li></ul></ul><ul><ul><li>long delays to results </li></ul></ul><ul><ul><li>expensive ($K/sample) </li></ul></ul>Field Screening for Sediments Where are the Contaminants?
  17. 17. How contaminants behave In sediments, and how organisms interact with them, and how particles move is largely dependent upon the nature of the sediments Scanning Electron Microscope Imaging Provides Insight into Sediment Grain Size and Texture Light Microscopy Can Lend Insight into Sediment Grain Type, Mineralogy and Source Where are the contaminants? Micro-Scale
  18. 18. Sediments can bind contaminants in different ways, depending upon sediment characteristics, geochemical conditions and even degree of aging. This can affect contaminant mobility, bioavailability, degradability, fate and risk Chemo- and bio-availability Other organisms Sediment Particle Sediment micelle Cu PCB TPH Zn Pb PAH bacterial cell cell wall
  19. 19. In situ tools for assessing grain size – each has strengths and weaknesses <ul><li>Acoustics </li></ul><ul><ul><li>Can be used to map sediment stratigraphy, topography </li></ul></ul><ul><li>Laser in situ scattering transmissometry (LISST) </li></ul><ul><ul><li>In situ units can to continuously measure grain size spectrum in suspension </li></ul></ul><ul><ul><li>With imaging or sensors, can record sediment changes, responses to events </li></ul></ul><ul><li>In situ imaging </li></ul><ul><ul><li>In situ cameras (eg SPI, see later) can provide gross grain size and stratigraphy information as well as direct imaging of organism/sediment interactions </li></ul></ul><ul><li>Traps </li></ul><ul><ul><li>Provide samples for later analysis </li></ul></ul><ul><ul><li>Sensors can allow for event-triggered sampling </li></ul></ul>
  20. 20. PAH signature TPH signature PCB signature Cu vs. background signatures Cu/ grain size signatures Using Contaminant Concentrations Alone Does Not Provide Enough Information It is important to know what form your contaminants are in to understand and predict exposure, effects, fate and management
  21. 21. PAHs are a class of compounds. Although there are countless congeners with varying degree of substitution, most research and regulation focuses on the unsubstituted “parent” compounds Phenanthrene Pyrene Chrysene Benzo(a)pyrene Fluoranthene
  22. 22. Science – a search of citations for (PAHname* AND sediment AND biodeg*) yielded: Once you get to the substituted PAHs, there are almost no references 23 fluorene 17 chrysene 38 fluoranthene 66 Pyrene 151 Phenanthrene 157 Naphthalene Number of citations PAH
  23. 23. Whether one examines all PAHs over time in the sample, or just a subset, dramatically affects the degree of attenuation one predicts. What you examine depends on whether you want to track regulatory compliance or the reduction of PAH toxicity What is regulated and tracked (and what many lab organisms see) What is actually in sediments (and what in situ organisms see)
  24. 24. Integrating Regional and Historical Data Puts Site Data in Perspective However, if data sets are to be plotted together to look at regional trends, care should be taken to ensure equivalent data sets. In these Bay area results for Cr in sediments, the 1997 samples were prepared by total digestion and the 1998 samples were prepared by acid leach. Merging of data sets results in an offset – data are not comparable.
  25. 25. Sediment Quality Guidelines <ul><li>An important tool in many sediment assessment frameworks is the use of sediment quality guidelines (SQGs) </li></ul><ul><ul><li>also known as action levels, criteria, standards, trigger values or screening values </li></ul></ul><ul><li>The goal of SQGs is to provide a screening-level indication of whether contaminants at a given level in sediments are likely to be non-toxic, possibly toxic, probably toxic or extremely toxic. </li></ul><ul><li>Implicit in their use is an assumption that we can predict, from bulk chemistry, the probability of impact, based upon the scientific understanding of dose-response of organisms to contaminants in sediments </li></ul>In all cases, actual effects should be evaluated
  26. 26. Stacked hazard quotients for case study sediment In all cases, actual effects should be evaluated
  27. 27. “ pristine” sites urbanized and lightly industrialized sites heavily industrialized sites Stacked hazard quotients for international case study sediments In all cases, actual effects should be evaluated
  28. 28. San Diego Bay Risk Assessment: Sediment Contaminant Dispersal and Fate Modeling <ul><li>It is important to know about contaminant – sediment - water interactions, and their potential mobility in order to make decisions about potentially disturbing sediments or leaving them in place </li></ul><ul><li>It also provides insight into what caged organisms and resident organisms are “seeing” in time and space </li></ul>Mixing in San Diego Bay. Where will Contaminants Go? Meaningful models require data from in situ measurements of particle load, contaminant load, hydrodynamics, etc.
  29. 29. <ul><li>An understanding of physical, chemical and biological pathways of contaminant transport (mode, media and mechanism) is critical to inform CSMs, put biological observations in context and design management strategies </li></ul><ul><li>While models and laboratory measurements abound, there are few field studies that assess these issues in an integrated way </li></ul><ul><li>While these mobility pathways represent potential pathways of biological exposure , it is essential that actual exposure be evaluated with biological measurements </li></ul>Are Contaminants Mobile? from SMWG
  30. 30. Risk and Fate of Contaminants in In Place sediments: Pathway Ranking for In-Place Sediment Management ( PRISM ) Project <ul><li>Field-based assessment on a common scale helps evaluate risks and mechanisms of recovery or exposure to aid in management strategies </li></ul><ul><li>Measurement framework is tied to a classical 1D vertical mass balance model of contaminated sediments </li></ul><ul><li>Mobility is quantified as a net flux from the “active” surface layer </li></ul><ul><li>Changes in this layer result from the balance of fluxes through the defined pathways of mobility </li></ul>After Reible, D and Thibideaux, L (1999) &quot;Using Natural Processes to Define Exposure From Sediments&quot; in Sediment Management Work Group; Contaminated Sediment Management Technical Papers, Sediment Management Work Group, There are a number of potential pathways for contaminant transport in sediments. The magnitude and direction of these fluxes controls both risk and recovery potential
  31. 31. PRISM Program Integrates Field-Measurable Flux Parameters into Adapted Theoretical Models Age-dated cores BFSD Degradation Assays SPI Seep meter Microprofiler Sediment Traps Multicores In-situ flume Current Meters
  32. 32. Bioturbation Depth - PRISM <ul><li>Approach </li></ul><ul><ul><li>Uses Sediment Profile Imager (SPI) to take in-place images throughout area, and at high density in study sites </li></ul></ul><ul><ul><li>Used standard methods (Rhodes and Germano, 1982) to estimate the “bio-active” layer depth based on on-site analysis of feeding void depth </li></ul></ul><ul><ul><li>This depth scale is the common depth (H) for sampling and data synthesis for most processes </li></ul></ul><ul><li>Assumptions </li></ul><ul><ul><li>Bio-active mixing depth scale (H) is represented by the depth of visible feeding voids in replicate images at the site </li></ul></ul><ul><ul><li>High density images provide a means of quantifying variability and heterogeneity at the site </li></ul></ul><ul><ul><li>Effects of bioturbation on contaminant fluxes are embedded in other field measurements </li></ul></ul>
  33. 33. <ul><li>Within PRISM, identified the active depth and insight into heterogeneity </li></ul><ul><li>Results </li></ul><ul><ul><li>Images analyzed on-site to provide estimates of “active” mixing depths, P04 ~6-11 cm, P17 ~4-7 cm </li></ul></ul><ul><ul><li>Redox Penetration Depth (RPD) and bioturbation depth both deeper at P04 </li></ul></ul><ul><ul><li>Additional analyses for indicators of redox penetration, successional stage and physical disturbance are consistent with geochemical and microbial observations </li></ul></ul>Bioturbation Depth – PRISM P04 P17
  34. 34. Scale bars = 2cm Other in situ imaging applications: Infaunal functional groups from Joe Germano
  35. 35. In situ imaging provides mechanistic insight into particle/contaminant transport mechanisms and spatiotemporal scaling issue that no model can replicate <ul><li>Bioturbation will: </li></ul><ul><ul><li>Dramatically increase porewater flux rates </li></ul></ul><ul><ul><li>Change oxidation state of sediments </li></ul></ul><ul><ul><li>Alter chemical & mass properties of sediments through burrowing, ingestion, egestion, & mucopolysaccharide production </li></ul></ul><ul><ul><li>Particle, Nutrient (& Contaminant) Flux </li></ul></ul><ul><ul><li>Sediment Aeration (contaminant degradation and sorption) </li></ul></ul><ul><ul><li>Puts in situ biological measures (bioassays, toxicity tests, etc) in context </li></ul></ul><ul><ul><li>Help define sediment stability </li></ul></ul><ul><ul><li>Aids in cap/barrier design </li></ul></ul>Adapted from J. Germano
  36. 36. Organisms alter the sediment structure, and thus the fluid and chemical fluxes from Joe Germano Flow-induced Advection: biogenically induced topography induces fluid flow, and thus localized redox states and chemical fluxes In situ microelectrodes can map small-scale chemical gradients, elucidating these processes
  37. 37. In situ microelectodes, chambers and sensors <ul><li>In situ microelectrodes are available to measure a number of physical and chemical parameters at the mm to cm scale (conductance, oxygen, nutrients, metals) </li></ul><ul><li>In situ chambers have been designed to measure diffusive or advective fluxes, either under natural or altered conditions </li></ul><ul><ul><li>These systems have integrated sensors, samplers, stirrers, cameras, etc. </li></ul></ul><ul><li>When combined with imaging capability, both biological and geochemical responses to various perturbations can be evaluated in situ – simultaneous, integrated observations provide unprecedented insight </li></ul><ul><li>These tools have a growing place in sediment studies, helping us predict the effect of anthropogenic perturbations (contamination, trawling, dredging, fish farms, global change) on benthic ecosystem functioning </li></ul>
  38. 38. Integration of in situ observation technologies <ul><li>The overall objective of the European Community-funded Coastal Ocean Benthic Observatory (COBO) program is to integrate emerging and innovative technologies from different disciplines (physics, chemistry, biology, imagery) to provide in situ monitoring of sediment habitats and ecosystems </li></ul><ul><li>In situ experimental systems will investigate ecosystem response to a variety of natural and anthropogenic perturbations </li></ul>Biogeochemical lander (MPIMM) (AWI) Lander with microprofiler and conceptual drawing (LCSE) In situ image of organism effects on oxygen dynamics (U-COP)
  39. 39. Sensors added to images: In situ planar oxygen optode module provides insight into the spatial and temporal dynamics of oxygen in sediments UCOP CCD camera LED trigger board lens LED array + emission filter dichroic mirror mirror planar optode excitation filter glass 8 mm silicon 40 µm dye 10 µm
  40. 40. Time-lapse 2-D images of O 2 distribution from planar Optodes – over a 24 hour period, much of this “reduced” sediment is oxic UCOP How does this affect chemical fluxes? Should we treat sediments as reduced or oxic?
  41. 41. <ul><li>Approach </li></ul><ul><ul><li>Direct measurement of surface fluxes using the Benthic Flux Sampling Device (BFSD) </li></ul></ul><ul><ul><li>Field variability assessed by triplicate deployments in each area </li></ul></ul><ul><li>Assumptions </li></ul><ul><ul><li>Benthic flux measurement incorporates both diffusive and bioirrigation/bioturbation components </li></ul></ul><ul><ul><li>Diffusion below the “active” layer assumed to be negligible </li></ul></ul>Diffusive Fluxes: PRISM
  42. 42. Flux and Geochemistry Case study: Cu in Pearl Harbor Sediment Two sites at Pearl Harbor with very different grain size, geochemistry and use were examined (Site 2) (Site 4)
  43. 43. Pearl Harbor – Summary of Results <ul><li>Zinc and Copper fluxes were highest at these sites </li></ul><ul><li>Differences between copper fluxes at the two sites appeared to be controlled by differences in background geochemistry and source </li></ul>Note: All fluxes are ug/m 2 /d Coarse-grain associated Cu did not correlate with iron, and was more mobile and toxic (antifouling paint chips)
  44. 44. Flux and geochemical information are important: At other sites (in San Diego Bay), coarse-grained Cu-rich particles contained Cu which was less mobile than that sorbed to fine-grained particles Electron Dispersive X-Ray Scanning Electron Micrograph The Cu sulfides in these sediments were the result of ore spills from ship loading
  45. 45. Motivation for Flux Measurements <ul><li>Mobile contaminants are generally more likely to be bioavailable than immobile ones. Flux measurements help in: </li></ul><ul><ul><li>Understanding and quantifying pathways of biological exposure </li></ul></ul><ul><ul><li>Evaluating the influence of sediment contamination on water quality </li></ul></ul><ul><ul><li>Assessing the potential for de-contamination of sediments </li></ul></ul><ul><ul><li>Quantifying the effectiveness of chemical containment actions such as capping </li></ul></ul><ul><ul><li>Establishing background vs. anthropogenic metal input </li></ul></ul>Flux contribution to Water Column can be modeled Fluxes can be compared to tissue (and sediment) levels from Bart Chadwick
  46. 46. <ul><li>Approach </li></ul><ul><ul><li>Direct measurement of seepage rates using ultrasonic seepage meters </li></ul></ul><ul><ul><li>Concentrations at H determined from porewater samples collected by multicore </li></ul></ul><ul><ul><li>Field variability assessed by replicate seepage meter deployments and porewater sampling in each area </li></ul></ul><ul><ul><li>Samples can be collected and analyzed </li></ul></ul><ul><li>Results </li></ul><ul><ul><li>Advective flow has tidal component </li></ul></ul><ul><ul><li>Mean and tidal seepage rates at each site determined from harmonic analysis of 2-4 day time series deployment </li></ul></ul><ul><ul><li>Oxygen and nutrients are affected as well </li></ul></ul>Advective Fluxes - PRISM
  47. 47. <ul><ul><li>Direct measurement of sediment bed erosion properties using an in-situ flume </li></ul></ul><ul><ul><li>Bed stresses determined over two one-month periods using near-bottom deployed current meters </li></ul></ul><ul><ul><li>Solid phase concentrations at H and H- determined from samples collected by multicore and deep cores </li></ul></ul><ul><ul><li>Field variability assessed by replicate flume deployments and coring in each area </li></ul></ul><ul><ul><li>Tidal currents at sites are generally weak compared to critical shear stress </li></ul></ul><ul><ul><li>Evidence of erosive potential during short periods (<1 h) associated with ship movements </li></ul></ul><ul><ul><li>Resuspension potential is critical to determine sediment stability and to predict when in situ organisms may be exposed to contaminated particles </li></ul></ul>Erosive Fluxes - PRISM
  48. 48. <ul><li>Characterized background settling rates using sediment traps and age-dated cores </li></ul><ul><li>Characterized background settling concentrations using sediment traps </li></ul><ul><li>Characterized storm settling using recent stormwater survey data from Creek and storm drains </li></ul><ul><ul><li>Settling rates appear to be typical for coastal areas </li></ul></ul><ul><ul><li>Deposition remains a source for many chemicals </li></ul></ul><ul><ul><li>High COPC levels in surface vs. depth of cores reflects ongoing sources </li></ul></ul>Settling Fluxes - PRISM
  49. 49. <ul><li>Directly characterized mineralization using instantaneous assay with labelled PAHs </li></ul><ul><li>Assumed instantaneous assays reflect in situ rates and mineralization rates for labeled PAHs reflect rates in sediments </li></ul><ul><li>Rates generally stronger and extend deeper in more bioturbated sediment </li></ul><ul><li>Results correlated with geochemical profiling, SPI observations </li></ul><ul><li>This suggests active attenuation of PAHs moving through surface sediments, possibly attenuating risk </li></ul><ul><li>Evidence that macrobenthic biological activity is affecting contaminant fate </li></ul>Degradation Rates (Naphthalene, Phenanthrene, Fluoranthene)
  50. 50. <ul><li>Approach </li></ul><ul><ul><li>Applied surface mineralization rates measured by NRL for N, P, F </li></ul></ul><ul><ul><li>Applied derived rates for other PAHs </li></ul></ul><ul><ul><li>Applied rates to depth of oxygen penetration based upon microelectrode measurements </li></ul></ul><ul><ul><li>Investigated the impact of other approaches </li></ul></ul><ul><li>Assumptions </li></ul><ul><ul><li>High mineralization rates observed on low PAH sediments the result of entrainment of fresh material during bioturbation </li></ul></ul><ul><ul><li>Bioturbation and other disturbance events can introduce population and conditions for active removal of mobile PAHs </li></ul></ul>Degradation Fluxes microelectrode measurements show oxygen profiles at the mm scale
  51. 51. <ul><li>Approach </li></ul><ul><ul><li>Active sediment layer of depth H is treated as a box from which contaminants can flux in or out </li></ul></ul><ul><ul><li>All pathway study results converted to fluxes, all fluxes calculated in common units </li></ul></ul><ul><ul><li>For each contaminant (16 PAHs, 9 metals), fluxes are compared </li></ul></ul><ul><ul><li>Based upon results, dominant pathways can be determined, and the most sensitive or critical measures can be further evaluated </li></ul></ul><ul><li>Assumptions </li></ul><ul><ul><li>In spite of spatial and temporal variability, field measures, even if “noisy” provide insight no theoretical model can </li></ul></ul><ul><ul><li>“ Intelligent users” of data will apply insights into strengths and weaknesses of this and other approaches and can strike a balance between models, field data and controlled studies </li></ul></ul><ul><ul><li>It is the relative rates and directions of fluxes, and the management question that is applied, that determines to what extent any flux represents risk and/or recovery potential (proper normalization) </li></ul></ul>Comparing flux pathways
  52. 52. Inserting field measurements into models – PAHs Flux into sediments Flux out of sediments
  53. 53. <ul><li>Site: P17 </li></ul><ul><li>COPCs: Copper and Lead </li></ul><ul><li>Results: measurable fluxes by all pathways, loss by advection, diffusion, and erosion is minimal. Significant input by background and/or storm settling </li></ul><ul><li>Management Insight: Source dominated metals. Recovery is unlikely until sources (in-bay and upstream) are controlled </li></ul><ul><li>Sensitivity: These conclusions are sensitive to data on trap and stormwater particle and COPC input. </li></ul>Note uncertainties that result from heterogeneous measurements. Nonetheless, the relative importance of processes can be evaluated Understanding the pathways, directions and forms of contaminant transport will put in situ bioassays and CSMs in context
  54. 54. Variability and Uncertainty <ul><li>variability: “true” variability such as that which results from heterogeneity </li></ul><ul><ul><li>until we have a clear idea of the drivers of spatiotemporal variability, it is impossible to extrapolate from a single point to a site </li></ul></ul><ul><li>uncertainty: “ignorance” based upon gaps in our knowledge and model parameters. </li></ul><ul><ul><li>until we reduce uncertainty, our predictions will not be as good as they should be </li></ul></ul><ul><li>In situ measurements provide insight driving mechanisms and the real heterogeneity of natural systems </li></ul><ul><ul><li>They also provide realistic conditions that our ignorance may preclude in the lab, possibly leading to poor conclusions based upon poor lab design </li></ul></ul><ul><ul><li>On the other hand, field work lacks some of the control of the lab, so it is more difficult to tease out cause-effect relationships </li></ul></ul>
  55. 55. Addressing Issues of Variability and Uncertainty <ul><li>Integration and synthesis of field-based measures forces an acknowledgement of the variability present in natural sediment systems </li></ul><ul><ul><li>Integrating information from multiple field measurements makes clear the variability and heterogeneity of sediment systems in a way that no theoretical model can </li></ul></ul><ul><ul><li>While unsettling, this is not a problem with the measurements, but an accurate reflection of the reality environmental managers face </li></ul></ul><ul><ul><li>The more we accept that real systems are noisy, and that certainty is a myth, the more intelligently we can inform the decision making process </li></ul></ul><ul><ul><li>The better we understand what drives various biogeochemical processes, the better we can make decisions even if variability is high </li></ul></ul>
  56. 56. <ul><li>The Whole is Greater Than the Sum of the Parts </li></ul><ul><li>Individual tools can map the distribution of individual analytes or parameters </li></ul><ul><li>Risk assessment, hazard ranking and site management are generally driven by multiple parameters </li></ul><ul><li>When data are integrated, one obtains insight into the “whole system” - how contaminants co-associate with each other, sediment characteristics, geography and biological indicators. </li></ul><ul><li>Understanding the biogeochemistry of contaminant behavior and fate provides the conceptual link between contamination, exposure and effects </li></ul>
  57. 57. What some decision makers want <ul><li>Clear criteria, “bright lines” </li></ul><ul><ul><li>Since many decisions are controversial, uncertainty can be exploited by those with agendas </li></ul></ul><ul><li>Flowcharts, “cookbooks” </li></ul><ul><li>A defensible and consistent approach to making decisions </li></ul><ul><li>Not to “research a site to death” </li></ul><ul><li>Ecological risk assessment is one input to environmental management decisions. Other inputs include stakeholder concerns, availability of technical solutions, benefits, equity, costs, legal mandates, and political issues. </li></ul><ul><ul><li>Society of Environmental Toxicology and Chemistry (SETAC). 1997. Ecological Risk Assessment Technical Issue Paper. </li></ul></ul>
  58. 58. Some final thoughts (mine and others’) <ul><li>“ Management decisions must be made, even when information is imperfect” </li></ul><ul><ul><li>National Research Council (NRC) (2001): A Risk-Management Strategy for PCB-Contaminated Sediments. </li></ul></ul><ul><li>As scientists, we must become better at understanding how our research is applied, clarifying the assumptions and limitations of our work, and bridging the gap between science and applications </li></ul><ul><li>This is often neglected, in what is called the “valley of death” – few people and little funding are dedicated to the huge gap between discovery and standardisation in environmental work </li></ul><ul><li>When we fail to understand these needs, or consider such base applications beneath us, scientists cease to have a voice in the decision process </li></ul><ul><li>The power of well-considered in situ studies, backed up with an honest assessment of uncertainty cannot be understated. When images are added, we can really help decision makers understand the links between the data and the ecosystem </li></ul>
  59. 59. Acknowledgements <ul><li>Prism Team: SPAWAR Systems Center, San Diego (SSC); SEA Environmental Decisions (SEA); Germano and Associates, Inc. (SPI); Scripps Institution of Oceanography (SIO); Virginia Institute of Marine Sciences, College of William and Mary (VIMS); Naval Research Laboratory (NRL); Cornell University </li></ul><ul><li>Funding provided by the Strategic Environmental Research & Development Program (SERDP) </li></ul>Scottish Association for Marine Science Commissariat à l'Energie Atomique University of Copenhagen, Marine Biological Laboratory Potsdam University University Court of the University of Aberdeen - UK Centre for Environment, Fisheries & Aquaculture Science Stiftung Alfred Wegener Institut für Polar- und Meeresforschung - Max Planck Institute for Marine Microbiology Goeteborg University Consiglio Nazionale delle Ricerche Centre National de la Recherche Scientifique Unisense A/S COBO partners… Funded by…