Using SPI can obtain undisturbed in situ images of the sediment profile and observe the effect individual species have on the sediment profile Not all species have same effect on the sediment profile: epifaunal, burrowing polychaetes (diffusive movement of particles), tube worms (advective transport), and deep burrowing fauna. can use this information to inform functional groups
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
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
This shows a similar conceptual model in cartoon form
Changes in chemical and physical state (and thus mobility) often result in changes in bioavailability
Thus, to understand exposure (and predict effects) one must understand mechanisms of transport
This conceptual model breaks down some of the chemical and physical processes that drive the transfers described above
With our focus on contaminant transfer, we sometimes forget that the sediments themselves are also ecologically important
Coastal marine ecosystems
represent an important reservoir for biodiversity
play a major role in regulating carbon and nutrient biogeochemical cycles
particularly vulnerable to anthropogenic perturbations ( including, but not limited to, contamination )
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
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
Such studies are the focus of the Coastal Ocean Benthic Observatories ( COBO ) program
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
What ecosystem functions do marine benthic systems provide?
organic material supplied to benthos
broken down by microbes
releases nutrients ( NH 4 , NO 2 /NO 3 , PO 4 )
nutrients fuel primary production
important role in carbon cycling
“ seed bed” for biodiversity
affect contaminant transport, sequestration, degradation and accumulation in sediment systems
(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
Risk managers and decision makers must evaluate how to balance ecological and socioeconomic objectives for sediments
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…)
Risk managers often have two parallel (but possibly competing) drivers:
minimizing risk (to the environment and human health, socioeconomic goals, etc) and
What is the risk of sediment x relative to regional or background risk?
Can this risk be controlled?
Management option risk
What is the risk of leaving sediments in place vs. disturbing them?
Can we afford it?
How will it impact other goals?
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
Approaches to Contaminated Sediments are in Flux
Ten years ago, most people thought that removal and treatment of contaminated sediments would be the remedy of choice
“ Chemical engineering” approach to management
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
Thus, many groups predict or advocate that large volumes of contaminated sediments will be managed in place
Source control is a major component of such management as well
The goal is thus to determine the least invasive, but sufficiently protective, management strategy for a given contaminated site
This can be called “sustainable sediment management”
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
The Problem – Contaminated Sediment Management
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
monitored natural recovery
in situ treatment
in situ containment
dredging or excavation (followed by treatment and/or disposal)
However, technology-specific and site-specific data on risks or impacts of sediment remedial strategies (especially in-place strategies) are sparse
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
Many of the contaminated marine sediment sites currently under investigation are in shallow, coastal areas
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
These processes are recognized in the oceanographic community as having significance to chemical fluxes, but are largely unstudied in contaminated systems
Currently, there is no demonstrated, systematic process for measuring and evaluating contaminant transport pathways within sediment systems in support of in-place management
Biomarkers, bioassays, bioavailability, community analysis, risk assessment
Are they mobile?
hydrodymamics, flux and porewater
Where do they come from?
What do we do about them?
Management, monitoring, remediation
How do we prevent it in the future?
Contaminated sediments are heterogeneous in space and time
We collect discrete samples of sediment in order to establish contaminant levels, and their correlations with toxicity, mobility, behaviour and fate
However, ultimately, management decisions are not made for grab samples, but for large areas
This heterogeneity can make it difficult to correlate chemical and biological assessments
Cr in surface sediments by a creek mouth and piers, San Diego Bay Pb vs depth in cores from site
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
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
Field Screening for Sediments Where are the Contaminants?
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
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
In situ tools for assessing grain size – each has strengths and weaknesses
Can be used to map sediment stratigraphy, topography
Laser in situ scattering transmissometry (LISST)
In situ units can to continuously measure grain size spectrum in suspension
With imaging or sensors, can record sediment changes, responses to events
In situ imaging
In situ cameras (eg SPI, see later) can provide gross grain size and stratigraphy information as well as direct imaging of organism/sediment interactions
Provide samples for later analysis
Sensors can allow for event-triggered sampling
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
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
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
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)
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.
An important tool in many sediment assessment frameworks is the use of sediment quality guidelines (SQGs)
also known as action levels, criteria, standards, trigger values or screening values
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.
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
In all cases, actual effects should be evaluated
Stacked hazard quotients for case study sediment In all cases, actual effects should be evaluated
“ 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
San Diego Bay Risk Assessment: Sediment Contaminant Dispersal and Fate Modeling
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
It also provides insight into what caged organisms and resident organisms are “seeing” in time and space
Mixing in San Diego Bay. Where will Contaminants Go? Meaningful models require data from in situ measurements of particle load, contaminant load, hydrodynamics, etc.
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
While models and laboratory measurements abound, there are few field studies that assess these issues in an integrated way
While these mobility pathways represent potential pathways of biological exposure , it is essential that actual exposure be evaluated with biological measurements
Are Contaminants Mobile? from SMWG
Risk and Fate of Contaminants in In Place sediments: Pathway Ranking for In-Place Sediment Management ( PRISM ) Project
Field-based assessment on a common scale helps evaluate risks and mechanisms of recovery or exposure to aid in management strategies
Measurement framework is tied to a classical 1D vertical mass balance model of contaminated sediments
Mobility is quantified as a net flux from the “active” surface layer
Changes in this layer result from the balance of fluxes through the defined pathways of mobility
After Reible, D and Thibideaux, L (1999) "Using Natural Processes to Define Exposure From Sediments" in Sediment Management Work Group; Contaminated Sediment Management Technical Papers, Sediment Management Work Group, http://www.smwg.org/index.htm. 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
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
Within PRISM, identified the active depth and insight into heterogeneity
Images analyzed on-site to provide estimates of “active” mixing depths, P04 ~6-11 cm, P17 ~4-7 cm
Redox Penetration Depth (RPD) and bioturbation depth both deeper at P04
Additional analyses for indicators of redox penetration, successional stage and physical disturbance are consistent with geochemical and microbial observations
Bioturbation Depth – PRISM P04 P17
Scale bars = 2cm Other in situ imaging applications: Infaunal functional groups from Joe Germano
In situ imaging provides mechanistic insight into particle/contaminant transport mechanisms and spatiotemporal scaling issue that no model can replicate
Dramatically increase porewater flux rates
Change oxidation state of sediments
Alter chemical & mass properties of sediments through burrowing, ingestion, egestion, & mucopolysaccharide production
Particle, Nutrient (& Contaminant) Flux
Sediment Aeration (contaminant degradation and sorption)
Puts in situ biological measures (bioassays, toxicity tests, etc) in context
Help define sediment stability
Aids in cap/barrier design
Adapted from J. Germano
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
In situ microelectrodes are available to measure a number of physical and chemical parameters at the mm to cm scale (conductance, oxygen, nutrients, metals)
In situ chambers have been designed to measure diffusive or advective fluxes, either under natural or altered conditions
These systems have integrated sensors, samplers, stirrers, cameras, etc.
When combined with imaging capability, both biological and geochemical responses to various perturbations can be evaluated in situ – simultaneous, integrated observations provide unprecedented insight
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
Integration of in situ observation technologies
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
In situ experimental systems will investigate ecosystem response to a variety of natural and anthropogenic perturbations
Biogeochemical lander (MPIMM) (AWI) Lander with microprofiler and conceptual drawing (LCSE) In situ image of organism effects on oxygen dynamics (U-COP)
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
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?
Zinc and Copper fluxes were highest at these sites
Differences between copper fluxes at the two sites appeared to be controlled by differences in background geochemistry and source
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)
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
Results: measurable fluxes by all pathways, loss by advection, diffusion, and erosion is minimal. Significant input by background and/or storm settling
Management Insight: Source dominated metals. Recovery is unlikely until sources (in-bay and upstream) are controlled
Sensitivity: These conclusions are sensitive to data on trap and stormwater particle and COPC input.
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
Since many decisions are controversial, uncertainty can be exploited by those with agendas
A defensible and consistent approach to making decisions
Not to “research a site to death”
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.
Society of Environmental Toxicology and Chemistry (SETAC). 1997. Ecological Risk Assessment Technical Issue Paper.
“ Management decisions must be made, even when information is imperfect”
National Research Council (NRC) (2001): A Risk-Management Strategy for PCB-Contaminated Sediments.
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
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
When we fail to understand these needs, or consider such base applications beneath us, scientists cease to have a voice in the decision process
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
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
Funding provided by the Strategic Environmental Research & Development Program (SERDP)
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…