1999 OMSAP Workshop Questions & Answers

Post-workshop comments are included in brackets

Effluent quality

OMSAP: annual metals discharged between 1989 and 1990 declined which may have been due to industrial pretreatment in the MWRA system, but after about 1990, it looks like metals reflect simply what is happening with the solids. Does Boston have an ongoing pretreatment program for metals in their wastewater stream?

S. Rhode: yes, the Toxics Reduction and Control department have collected approximately 10,000 samples for metals and continue to strongly enforce metals and other regulated materials. Perhaps the decreases in 1989 and 1990 were the more easily obtained reductions, and now we are dealing with sources which are more difficult to reduce.

A. Rex added that households also contribute to these numbers.

S. Rhode agreed and pointed out that there was an educational campaign during that time period [which may have also led to the decrease in metals loading].

OMSAP: so metals entering the treatment plant have also decreased steadily?

S. Rhode: yes, but a lot more slowly than when the pretreatment program first began.

R. Trubiano: corrosion control has also decreased metal concentrations entering the MWRA system.

S. Rhode agreed. Corrosion control [which increased drinking water pH] was implemented about two years ago for drinking water and is expected to decrease lead and copper loading in wastewater.

OMSAP: do you measure the fingerprint of the PCBs which enters the Deer Island Treatment Plant (DITP) so that changing PCB inputs can be monitored over time?

S. Rhode: yes, but it has been difficult to make conclusions from the results. There is no consistent pattern in the 20 congeners that are routinely monitored. MWRA recently upgraded to a newer gas chromatograph which has about a 10-fold improved sensitivity, hopefully measuring more consistent detects, and possibly providing a more consistent and understandable pattern.

OMSAP: do the PCBs in the sludge end up in the pellets and back in the environment?

S. Rhode: yes, to some extent. This is why MWRA monitors the sludge extensively and must comply with many regulations.

OMSAP: is the use of the MWRA pellets supplying the PCB loading which is measured at the DITP?

S. Rhode: no because most of the pellets are sold out-of-state.

J. Shine pointed out that if we are interested in human or ecological risk, even though only a small fraction of the total concentration of PCBs are being measured, a large percentage of the potential risk may be captured if the most harmful congeners are being measured.

S. Rhode agreed and pointed out that the NOAA 20 congener list includes several of the toxic or co-planar congeners. MWRA's proposed 67 congener list includes all of the "toxic" congeners.

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Changes in Harbor Water Quality
in Response to Transfer of Nut Island Flows

OMSAP: is the high increase in chlorophyll in the Mystic River due to the dredging activities there?

D. Taylor: it could be that, but it also could be an exportation of nutrients from the Mystic River itself. Dredging increases the nutrient availability to phytoplankton but it also reduces water clarity [low water clarity impedes phytoplankton growth by reducing available light for photosynthesis].

Audience: do you know how big of an effect secondary start-up in 1997 might have had on the clarity in the northern harbor?

D. Taylor: MWRA has that data and can examine that question. This presentation focused on the latest change which was the transfer of MWRA south system flows to the DITP.

Audience: maybe the reason why a decrease in clarity was not measured is because the transfer occurred while there were improvements occurring at the same time in the harbor.

D. Taylor: yes, exactly.

Audience: does the dissolved inorganic nitrogen behave conservatively, and if so, could that parameter be used to calculate dilution?

D. Taylor: I have used the average salinity as a surrogate for river inputs to the system. When rainfall amounts are low, there is less nitrogen entering the harbor and thus concentrations are lower. However, in the south harbor there has been a decrease in dissolved inorganic nitrogen (DIN) which is not due to less rainfall or less freshwater input in the area, which would imply a response to the transfer. Thus, though it appears that the transfer had a positive impact in water quality in the southern harbor, there may be other factors that contributed to the water quality improvements also.

OMSAP: how much nitrogen is removed from the wastewater stream by sludge removal?

D. Taylor: less than 10%. Long-term nitrogen loading to the harbor has remained about the same, about 35 metric tons per day. Secondary treatment also does not remove very much nitrogen.

Audience: what kind of pattern is seen when dissolved organic and dissolved inorganic nitrogen are compared?

D. Taylor: MWRA has not observed a significant increase in total nitrogen in the north harbor. However, there appears to be an increase in the DIN which makes sense for two reasons: the Nut Island effluent was relatively enriched in ammonium and secondary treatment transforms more nitrogen to its dissolved inorganic form. However, MWRA has not detected changes in the dissolved organic nitrogen (DON) or particulate nitrogen concentrations in the north harbor.

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Why the outfall?

Audience: will MWRA have to dechlorinate treated effluent?

A. Rex: yes, dechlorination will occur seasonally. Bacterial loading in the effluent varies according to the season. In the summer, bacteria concentrations in the effluent are higher, which means that more chlorine is needed. Thus dechlorination will occur so that the maximum chlorine permit limit (0.456 mg/L for the receiving water) is met. The outfall tunnel will help dechlorinate by increasing effluent residence time. In the winter, MWRA will be adding less chlorine and will meet permit limits without dechlorination.

Audience: will MWRA be testing for chlorine at the outfall site? If so, how frequently?

A. Rex: as part of the initial plume tracking plan MWRA will sample at the diffuser port using a diver as the effluent is discharged. MWRA monitors chlorine every half hour at the DITP and the chlorine residual limit must be met at the treatment plant.

OMSAP: what are the dissolved oxygen levels in the effluent? Will the concentration change with the new outfall?

S. Rhode: dissolved oxygen levels are relatively high after secondary treatment because the process adds oxygen. I would expect the oxygen to drop substantially over the length of the tunnel.

OMSAP: what if effluent in the tunnel becomes anaerobic? Do you expect denitrification to occur in the tunnel?

A. Rex: the effluent will not become anaerobic because of the high flow rates and denitrification will probably not occur.

J. Fitzpatrick added that though dissolved oxygen will decrease, most of the organic carbon will be removed by the treatment plant. There will not be significant impacts to dissolved oxygen in the tunnel due to the high effluent flow rates.

J. Shine pointed out that dissolved oxygen depleting organisms would not survive chlorination and thus would not cause a problem.

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Monitoring Plan

OMSAP: what are the monitoring and reporting costs and how do they compare to the operating costs of the treatment plant (not including construction)?

M. Mickelson, K. Keay, S. Rhode: the receiving monitoring budget (water column, benthos, and fish/shellfish) is typically $2.5 million a year. Effluent monitoring is about $0.5 million a year. The annual operating budget is on the order of $45 million. The construction is on the order of $6 billion.

Audience: does MWRA have to report to the court?

M. Mickelson: yes, MWRA reports to the court through its law division.

Audience: is it possible that EPA/MADEP could respond to an exceedance before obtaining advice from OMSAP?

R. Manfredonia: EPA/MADEP have created OMSAP to secure independent scientific advice. If there is a violation of any effluent requirements, EPA/MADEP will take immediate action. In terms of the ambient monitoring program, it depends on the severity of what happens. But EPA/MADEP will certainly look to OMSAP for scientific advice on these matters.

OMSAP: I would like to see further discussion of thresholds at future OMSAP meetings.

J. Shine suggested dedicating an entire OMSAP meeting to thresholds.

M. Moore suggested MWRA work with the New England Aquarium and their whale watch staff to survey the comeback of harbor porpoise in Boston Harbor.

OMSAP: will the MWRA reports be available on the Internet as ".pdf" Acrobat Reader files?

M. Mickelson: yes, MWRA has already begun making reports available in this format.

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The Physical Environment: Circulation and Water Properties in Massachusetts Bay

Audience: how long did it take for drifters to travel from the new outfall site to Cape Cod Bay?

R. Geyer: typically 1-2 weeks. Though some of the drifters lingered in Cape Cod Bay, water would not collect in the same manner since it is incompressible [drifters accumulate at convergences but water does not].

OMSAP: are the northeasterly wind conditions which appear to be favorable for Alexandrium blooms, also favorable for transport towards Cape Cod Bay?

R. Geyer: northeasterly winds are favorable for transport of Alexandrium blooms towards Cape Cod Bay. These winds cause higher concentration of cells, not necessarily more cells, since the cells are packed closer to the coast where there is sampling.

OMSAP: what kind of study would resolve the question of whether low dissolved oxygen is the result of advection from the Gulf of Maine or a local phenomenon effect?

R. Geyer: the first step would be a more detailed statistical analysis of the data that has already been collected. It would be useful to look at whether there is a high correlation between the dissolved oxygen concentrations in bottom waters at the outfall site and in Stellwagen Basin (though I am not sure we have a long enough time series to distinguish this). Water mass characteristics can also be examined but the time series is still too short for evaluating interannual variability. We could also run the Bays Eutrophication Model. We should also keep monitoring currents and make drifter measurements. Interannual questions such as this are difficult to answer because it takes a long time to collect enough data to attain statistical significance.

OMSAP: to what extent are extreme, but rare, meteorological events (e.g. tropical storms) responsible for a large fraction of the transport processes? To what extent are these events actually dominating the annual transport or biological processes as opposed to the day-to-day transport?

R. Geyer: day-to-day processes influence the water column the most. The mean wind stress correlates with an annual progression of temperature, which correlates with dissolved oxygen. This simple linear connection implies a day-to-day influence not associated with any kind of extreme event. However, sediment and particle-bound contaminant transport relies more on resuspension events such as large storms and will be discussed by B. Butman.

OMSAP: is there any correlation between the "upwelling index" and chlorophyll or primary production values?

R. Geyer: this "upwelling index" is a new variable which has not been compared to the biology yet.

B. Beardsley: the slight decreasing trend in salinity measured by this program over the past few years has been observed on Georges Bank over approximately the same time frame. One of the things that this long time series will allow you to do is compare with other long time series in the Gulf of Maine. The decrease in salinity on Georges Bank seems to be due to a change in the upstream sources of water entering the Gulf of Maine from the Scotian Shelf. This emphasizes the point that R. Geyer made about the connection between Massachusetts Bay and the rest of the Gulf of Maine.

R. Geyer: as we collect a longer time series of data, we can begin to discern locally driven verses more regionally forced processes.

Audience: is there any data within those straight lines between sampling seasons? [Annual Salinity Cycle figure]

R. Geyer: no because the monitoring program does not have any surveys between early December and early February. The scope of the monitoring program is to look for ecological responses and not to generate a long time series of salinity measurements.

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Water Quality Monitoring Program and Baseline Results

Audience: does MWRA make baseline measurements of trash in the surface water (e.g. as plastics or tar balls)? Because if people find trash after outfall goes on-line, they may blame the outfall.

C. Hunt: MWRA makes a note of trash on surveys but does not record amounts. However, the plume tracking survey will be sampling for plastics which may be related to the discharge and the DITP measures amounts of captured floatables. Obviously plastics in Massachusetts Bay come from many sources such as poor waste management on boats.

J. Fitzpatrick: the DITP removes much of the plastics in primary screening. Combined sewer overflows (CSOs) are another source of floatables and the outfall will increase the ability of the DITP to reduce CSOs.

Audience: why do silicate and dissolved inorganic nitrogen behave differently from one another?

C. Hunt: it depends on the dominant phytoplankton species and whether they are silicate-users (e.g. diatoms) or other species.

A. Giblin added that the silicate behavior tends to be temperature and pH driven. Warmer temperatures tend to re-solublize silicate faster. This abiotic dissolution process tends to offset silicate from nitrogen, which is more biologically driven.

Audience: is there a relationship between the amount of carbon production and how long the dissolved oxygen decreases based on direct loading of carbon? Has the actual sediment-oxygen demand (SOD) been measured?

C. Hunt: we have not looked at that relationship, but others have. We now have the data and can study this linkage. A. Giblin will discuss the SOD when she presents results from the benthic flux program.

OMSAP: will the freshwater effluent discharge at the new outfall site increase stratification during the summer which would in turn further decrease dissolved oxygen by "sealing" off more of the bottom waters?

J. Fitzpatrick: there does not seem to be an intensification of stratification in the vicinity of the outfall based on preliminary hydrodynamic calculations.

C. Hunt added that the plume tracking survey will measure stratification after the outfall goes on-line.

M. Mickelson pointed out that adding freshwater at the sea floor may even tend to destabilize/destratify the water column.

OMSAP: is the diatom abundance, on a carbon basis, equal to or less than the microflagellate abundance?

C. Hunt: the draft data suggests that diatoms have the dominant carbon abundance, but this needs to be examined further.

OMSAP: how is it possible to have a 1999 standard deviation of 55,381 for zooplankton abundance on the draft threshold [zooplankton species figure]?

[This was a typographical error, corrected in the figures on this CD.]

A. Solow: OMSAP will discuss this threshold further at its next meeting.

OMSAP: how will you use this zooplankton threshold information?

C. Hunt: this threshold was developed to observe if there is a major shift in the zooplankton abundance of key species which may be food resources to the right whales during the late winter and early spring. We can debate whether we should use the 50th or the 95th percentiles, however, no one has determined what numbers of these zooplankton species are ecologically significant.

OMSAP: so there will be concern if the monitoring program measures a lower number than this threshold, but operations at the DITP would not be changed, correct?

C. Hunt: a lower abundance of these zooplankton species would not be healthy for a part of the ecosystem and so if this happens, we have to evaluate why the decrease in abundance has occurred.

Audience: if long-term zooplankton mean abundance steadily increases, then the variance will also increase. Would the threshold still be valid?

C. Hunt: we need to examine that.

OMSAP: there could be appreciable change that is not meaningful. Any thought on meaningful verses appreciable change?

C. Hunt: our state of thinking has not advanced enough to truly say what is meaningful change [relative to the zooplankton] for this system.

Audience: do the nearfield data provide any link to the farfield patches that are important feeding sources for whales? Is there any information that could be added to Stormy Mayo's [Center for Coastal Studies] feeding threshold?

M. Mickelson: we will work on this issue with OMSAP.

Audience: the physical data seems to be relatively reproducible from year to year, but the chemical and biological data are less predictable, proving the complexity of the system. How much is due to the sampling scheme? Or is it a modeling issue (grid cell sizes)? I have an uneasy feeling about the variability.

C. Hunt: we sample zooplankton using a net tow from the surface to 25 m. Even though the zooplankton data uses information integrated for 0-25m, there is still spatial variability.

OMSAP: is the spatial and temporal variability of the zooplankton understood with confidence?

C. Hunt: temporal variability is roughly two weeks. Spatially, the statistics comparing different regions such as nearfield and coastal still need to be calculated.

OMSAP: if sampling was done over only a small area but at high resolution, would that miss the big picture?

C. Hunt: probably. When MWRA added the two new zooplankton sampling stations in Cape Cod Bay, the range of zooplankton abundance increased so we knew that we had not been sampling the full variability. There have been some high resolution studies in 1998 and 1999 which address some of the spatial scale issues.

OMSAP: one fear is that because there is so much variability in so many of these biological parameters, if we use a statistical model to calculate a percentile, we could have meaningful change which is not statistically appreciable because of the variability.

C. Hunt: I agree. MWRA and the Outfall Monitoring Task Force (OMTF) chose to calculate mean values so that thresholds are not triggered either too often or not often enough. I would like people to lay out these statistical questions so that we can address them in a very systematic manner. MWRA/OMTF have spent the last six years trying to determine meaningful change.

J. Fitzpatrick agreed that choosing a middle value for a threshold is probably the best approach so that thresholds are not triggered by false alarms.

Audience: chlorophyll concentrations in the nearfield area just offshore from Boston Harbor seem to be the highest. When analyzing the data, have you tried to divide the nearfield into sections? In other words are we looking at the right spatial, and/or temporal detail?

C. Hunt: we do not parse out the nearfield. We examine the nearfield as a whole since it is the area of concern. The projections state that this area will not shift, and that there will be a gradient. The nearfield "box" was determined based on projections of where the plume would be located.

Audience: I am not suggesting changing the sampling locations, only to calculate the average of a different area "box" to see if the mean calculated is the same. There seems to be an optimal area just west of the nearfield where phytoplankton are the least light limited but still have the most nutrients available from the harbor. These chlorophyll concentrations seem to have been enhanced due to the diversion of the Nut Island flows to the DITP.

C. Hunt: that area of enhancement seems to be encompassing the western third to half of the nearfield and runs to the south along the coast which is included in the coastal sampling transect.

Audience: is there any evidence that the high chlorophyll measured near the outfall site is due to mixing events when the wind changes?

M. Mickelson: this was observed in July 1995 when we measured increased productivity in response to a mixing event.

Audience: in terms of reproducibility of the biological data, are the trends in production and respiration more consistent as compared to phytoplankton and zooplankton data?

C. Hunt: I can partially answer that. The productivity data vary quite a bit, but the respiration data are somewhat more consistent because the results integrate a larger set of processes.

Audience: will here be a hydroacoustic study to examine fish movements when the new outfall goes on-line?

MWRA: there are no plans for that type of study.

D. Tomey: I suggest customizing the zooplankton thresholds to right whale feeding behavior. The food web model is coming together conceptually, but I think relative to the monitoring, we need to compare the nearfield verses the farfield, and decide what thresholds are useful so that we may determine meaningful change.

M. Mickelson: there are two different approaches in developing the zooplankton threshold. Should we focus on effects of the outfall ["bottom-up" on the food web] or factors that affect whales ["top-down" on the food web]?

D. Tomey: we need to determine if changes in the nearfield reflect changes in the farfield. [Physical water] convergences dominate zooplankton patch formation in Cape Cod Bay. I suggest examining whether there are enough stations in Cape Cod Bay for us to be able to make any decisions. We should also examine results of a recently funded NSF grant which will examine zooplankton patch formation in Cape Cod Bay. Additional high-resolution information could also be gathered.

C. Hunt: there were two high-resolution Video Plankton Recorder surveys in 1998 and 1999. The 1999 results will provide very useful information.

M. Moore: right whales are more successful at finding patches than scientists. Keep this in mind when developing thresholds.

OMSAP: we need to take a broader view with this zooplankton issue. This is an ecosystem/zoological problem, not a number, and we can not collect zooplankton in any kind of a meaningful way at the present time. Thus no zooplankton threshold can be considered meaningful and so we need to find some other way. I think we should look at some of the other work that has been in other places in terms of how they evaluate ecosystems and try to apply that here. To some extent, zooplankton dynamics seem to be beyond our control. If we develop a threshold that does not take that into account, we would be doing ourselves a disservice.

J. Turner: I agree that there is too much emphasis on numbers, and am also concerned about the taxa included in the new zooplankton threshold. If the emphasis is to be on right whales in the late winter/early spring, then the species establishing the threshold should be important to right whales. Data from Stormy Mayo shows that Oithona is too small and will screen through baleen, yet the vast majority of zooplankton captured by the sampling program and considered in threshold calculations is Oithona. The zooplankton threshold was originally developed as part of the eutrophication thresholds, has that emphasis shifted to whales?

Audience: are there any new findings presented at this workshop that would change our thinking over the last few years?

S. Testaverde: a recent right whale study [Caswell H, Fujiwara M, Brault S. 1999. Declining survival probability threatens the North Atlantic right whale. PNAS 96: 3308-3313] concluded that the right whales will go extinct in 191 years.

OMSAP: but that does not change our way of thinking about the effects of the outfall on right whales.

S. Testaverde: it does in terms of the number of stations in Cape Cod Bay. There is not enough sensitivity to determine if MWRA is having an effect on right whales. The extinction calculation is a new piece of information that the federal government should be concerned about.

M. Moore: right whale feeding has a lot to do with physical oceanography [which affects patch formation]. Climate change also affects patch formation.

OMSAP: we often talk about the importance physical oceanography. Part of the reason why the stations in Cape Cod Bay may be sufficient is that it is difficult to describe a process by which the relocation will affect the physical oceanography in Cape Cod Bay. We have some scientific understanding of these processes and we need to use that in allocating the scarce resources we have to monitoring.

S. Testaverde: I am only suggesting additional monitoring when right whales are in this area (March-April).

OMSAP: we should revisit this.

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The Utility of the Bays Eutrophication Model in the
Harbor Outfall Monitoring Program

Audience: how does the model reproduce changes in water quality with the transfer of sewage from Nut Island to Deer Island?

J. Fitzpatrick: we have only run the model for 1992-4 but may do additional runs in the future.

OMSAP: one of the issues early on in the monitoring program is that spring blooms are often missed in terms of the sampling cycle. To what extent do those spring blooms contribute to carbon loading, which in turn affects bottom dissolved oxygen concentrations in the summer? What about the fall Asterionellopsis bloom in 1993 and its contribution to the low dissolved oxygen event in 1994?

J. Fitzpatrick: the model captured the 1994 summer particulate organic carbon and chlorophyll relatively well and the results do not suggest that there was unusual primary production in 1994. Increases in bottom temperature, as well as what appears to be influxes of low bottom dissolved oxygen from the Gulf of Maine, may have been responsible for the low bottom water dissolved oxygen.

OMSAP: do you have time series of the dissolved oxygen at the boundaries, and if so, any idea of what kind of variability there is?

J. Fitzpatrick: 1994 boundary data suggest that much of the low dissolved oxygen values entering from the Gulf of Maine were about 7 mg/L. The model calculated an additional 1 mg/L drop due to oxygen consumption, deposition of organic matter, and increase in bottom temperature. 1995 also was a low dissolved oxygen year, 1996 and 1997 were higher and these years would be worth examining further. However, there are only two cruises during the late summer and the time series is relatively short. It might be useful to increase boundary sampling for better definition, at least with respect to dissolved oxygen.

OMSAP: how many zooplankton species are included in the model?

J. Fitzpatrick: none. Predation pressure in the model takes temperature into account, i.e. warmer temperatures, more predation.

OMSAP: is it a parameterized grazing pressure?

J. Fitzpatrick: yes.

Audience: does the model catch upwelling?

J. Fitzpatrick: yes, reasonably well.

Audience: should there be additional model runs using data after 1994?

K. Keay: as recommended by the Outfall Monitoring Task Force several years ago, MWRA/HydroQual ran the model for the additional years of 1993 and 1994 to see how it captured some of the events that were noted in the monitoring program. MWRA is requesting guidance in terms of whether to proceed with the model as it is currently formulated and run additional years and so the OMSAP agreed to form a model evaluation group (MEG). Some questions we would like to ask are: Should additional baseline years be run, and if so, which years? Is the model evaluation adequate, or should additional model development be looked at before running the model again?

B. Beardsley asked that people submit any questions about the model, model data, model revisions or ideas about whether the model should be run in the future.

OMSAP: the model zooplankton grazing rate and benthic community interactions do not use real data. How important is it to use real data, or can parameterization be used for some of these issues?

A. Solow: the model does parameterize zooplankton grazing.

K. Keay: the model does have sediment regeneration as temperature-dependent functions, also in relation to loadings.

J. Fitzpatrick: yes, it is parameterized in terms of the particle mixing which attempts to represent the benthic fauna. Grazing is basically 10% constant temperature-corrected.

OMSAP: is that sufficient enough, or do you need to add real data?

J. Fitzpatrick: there is a limitation using zooplankton data because the variability measured at the monitoring stations cannot be extended over the entire bay.

OMSAP: can you use any of the data being collected to test the parameterization?

J. Fitzpatrick: yes, at least to find out grazing percentages.

Audience: one of the real strengths of the model for which you may be able to use it in the future is to look at processes which are going on once the outfall goes on-line. Which are the boundary conditions that would make the model easy to run in real time in the future? What would it take to make the model easier to run in the future?

M. Mickelson: [We have been using the BEM model for long-term hindcasting rather than in real-time mode. Real-time modeling (e.g., http://deas.harvard.edu/~robinson/
has different objectives and requires adaptive sampling.]

B. Beardsley: I think the present monitoring program probably does not do a good enough job monitoring the boundary conditions. MEG will address this.

C. Hunt: in 1998-1999 more ammonia was measured in the harbor after the transfer of flows from Nut Island to Deer Island. Would BEM predict the observed response? Though this is not an outer boundary issue, it is a testable event.

B. Butman: models seem to have been used to date as "climatological" tools, but we have not used them to examine particular events. There may be several events that have occurred during the baseline period that you could apply the model to.

C. Hunt: we have used the model to examine things such as the effect of changes in total nitrogen loading.

B. Beardsley: during the summer when the water is stratified, there are a lot of short, spatial phenomena occurring, and the model was able to reproduce the "climate" correctly, but not the "weather". However, during the winter, the water column is more homogeneous and the physics are simpler, so the model does better predicting the "weather". The model could be used to examine winter storm events in greater detail.

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Predicting the Fate of Sediments and Associated Contaminants
in Massachusetts Coastal Waters

OMSAP: what is the tidal excursion at the outfall site?

B. Butman: about 2-3 km.

Audience: is that slide enhanced? [backscatter picture showing the diffusers]

B. Butman: the patterns on either side of the new outfall line are artifacts that could be cleaned up, but the pattern along the outfall is the true image.

Audience: how deep did the sediment core sample? [silver data figure]

B. Butman: roughly a 50cm core was sampled. The results shown are just the upper half centimeter.

Audience: are these results [lead in surface sediments] from the top half centimeter of core?

M. Bothner: possibly the top 1 cm.

OMSAP: is burial in these areas important?

B. Butman: it could be a combination of burial and mixing. Profiles of cores show a subsurface maximum concentration decreasing towards the surface. This implies that newer, cleaner material is being deposited.

Audience: is anyone using a core to reconstruct the history of contamination?

B. Butman: yes, we are in the process of doing that. The pre-industrial levels occur at 50-100 cm below the surface in most of areas. Using lead-210 and cesium dating one can examine the depositional histories of these areas. However, sediment profiles can be complicated by mixing/bioturbation so a mixing model needs to be used to take that into account.

M. Bothner: we have a good core from one location in Boston Harbor where the cesium and lead-210 agree and the lead profile mirrors what has been found in a pond in Central Park in New York City. The lead seems to be more controlled by the practice of incineration in the 1940's rather than the use of lead in gasoline.

Audience: are methylated and bioavailable forms differentiated from total sediment inorganic contaminants?

M. Bothner: we look at total metals but the next phase of this study will use new techniques developed at WHOI to examine speciation (but may not measure methylated forms).

OMSAP: any idea of the relative sources of fine-grained sediments - are they land-based verses relict mud deposits on the shelf?

B. Butman: silver was our first attempt at a mass balance, and we have not calculated a mass balance for fine-grained sediments. However, the sources of natural sediments are pretty small. Existing sediments are mainly moved around and input from rivers is not large.

OMSAP: is the outfall sufficiently offshore and away from the wave resuspension zone?

B. Butman: the outfall is 30m deep, in the midrange of the wave resuspension zone. At 30m, large waves from the northeast will resuspend and move bottom sediments.

OMSAP: are some of these storms strong enough to resuspend sediments even in Stellwagen Basin? Especially in the area containing dredge spoil?

B. Butman: on occasion, but only with very long, low period swell or large amplitude internal waves that occur in the summer. Winter storms cause resuspension in the shallow inner shelf but in the deeper basin, it appears to be summer internal waves that cause resuspension.

OMSAP: is there active dredging in Boston Harbor? If so, where is the dredge spoil disposal site relative to areas of resuspension?

B. Butman: currently, there is dredging in the inner harbor and some dredge spoil is being deposited in the Massachusetts Bay disposal site in 85m of water, out of the wave resuspension zone. This does not appear to be a major source of sediments to the system.

T. Fredette: material from the current deepening project in Boston Harbor is primarily Boston blue clay. Contaminated material is stored within the harbor in sub-channel disposal pits. The entire project is moving about three million cubic yards of material.

OMSAP: is there any possibility that the relocation of the outfall site outside of the harbor will facilitate the transport of contaminated sediments into Cape Cod Bay by wave resuspension and southerly transport?

B. Butman: it was estimated that greater than 75% of particles entering the system were exported from Boston Harbor with the present outfall situation, thus approximately 25% were sequestered in Boston Harbor. I believe that almost anything discharged from the outfall will not be sequestered locally. However, total particle and contaminant loading will be reduced by a factor of 3 or 4.

Audience: with regard to the silver mass balance, nice work, but it might be a little premature to say that all of the silver is from Boston Harbor since there quite a bit of industrialization along the entire coast. Two examples of industrialized areas include Plymouth (outfall present and no sampling station) and the Merrimack River (manufacturing) which could be sources of contaminants in Cape Cod Bay.

M. Bothner: the authors of the study would agree completely and have the same concerns about sources. However silver correlates very well with Clostridium perfringens which is an anaerobic bacteria spore present in sewage. Since Boston is the biggest local source of Clostridium, it makes us believe that most silver in Massachusetts Bay could be coming from Boston Harbor.

B. Butman: we have not made measurements at Plymouth, but we could. However, in terms of sludge and contaminants, Boston is the largest source by about 1-2 orders of magnitude. Another possible source of silver is a glass blowing plant in Sandwich but M. Bothner sampled in nearby marshes and did not find high concentrations of silver.

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Soft-bottom Benthic Community Monitoring in the
Boston Harbor-Massachusetts Bay System

Audience: are all benthic samples taken at the same time of year?

K. Keay: yes, MWRA has conducted soft-sediment sampling mid-summer throughout the baseline period.

OMSAP: are the data rarefied? Do you correct for the number of individuals? [species diversity data]

K. Keay: the graph of "increased Harbor species richness" shows the average species per grab. It is the average number of species collected in the sampled region. Three samples are collected per station at 8 sites and this is the average of the 24 samples. This measure is blind to differences in species composition.

Audience: are units in milligrams of carbon? [HydroQual model results "Bay outfall with secondary treatment"]

K. Keay: correct.

Audience: how deep is the sediment profile? [sediment profile image on page 17]

K. Keay: the entire view is 20 cm and the sediment is 12-14 cm deep.

OMSAP: please define "pollution-tolerant" species?

K. Keay: we examine enrichment-tolerance as opposed to contaminant-tolerance for benthic communities.

Audience: with regard to the community parameters for Massachusetts Bay, you indicated that [evenness] was significantly statistically different in 1998 compared to all the previous years.

K. Keay: that was a one-way ANOVA with two groups. All 1992-1997 replicates were in one group, and 1998 replicates were in the other.

Audience: were you calculating that station by station or averages for each station? Is there any pattern?

K. Keay: individual replicates. In the nearfield, a fraction of the stations have replication whereas a larger number of them only have a single sample. In terms of how best to treat those in analyses, using them as individual replicates is the best we can do. The changes in diversity and evenness are occurring primarily at the sand and silt sites. Stations characterized mostly by medium sands like NF17, have little trend in diversity, richness, and evenness through time. It is mostly the softer sediment stations which drive the pattern. Between 1992 and 1993, we went through a major redesign of the nearfield sampling design and went back again to a design similar to 1992 for 1994 on. Looking at the western Massachusetts Bay farfield sites (FF10, FF12, FF13), the pattern of richness matches the entire western Massachusetts Bay.

Audience: is 1993 is a sampling artifact?

K. Keay: our data review did not indicate that.

OMSAP: are you suggesting that the decreasing trend in species is due to re-setting of the sediment by storms?

K. Keay: the decreasing species diversity trend in 1992-3 was restricted in the nearfield. The farfield sediments outside of western Massachusetts Bay do not show the same pattern. The increase over the last 3-4 years is an exciting finding that we do not have an explanation for but it is similar to some of the cyclical patterns that have been seen in fauna in the Gulf of St. Lawrence as well as the West Coast. Thus this pattern is difficult to ascribe to any sort of recovery due to sediment transport because we did not see large changes in the community from 1993-4 except for a few sites which were highly influenced by storms. Similar fauna were found in the muddy sites in 1993 as 1992 and 1995. So there is increasing species richness. There are additional relatively rare species showing up which appears to be a physical disturbance/recovery from a storm event. This pattern here [showed figure] might be a response to regional Gulf of Maine-scale events. We do not see a trend in, for example, chlorophyll that might suggest some response to the eutrophication on a Bays-wide scale and there is no corresponding trend in the hydrographic data.

OMSAP: could this be natural variability on longer time scales?

K. Keay: I suspect we may have caught part of a long-term cycle. It may be simple variability but seeing it in both in the nearfield and farfield suggests it is variability on a large scale.

Audience: would there be a difference if you separated the mud stations from the sand stations in that average?

K. Keay: most of the muddy sites sampled in the nearfield would show this pattern of increasing richness through time but not the sandy sites.

B. Diaz: it appears that by looking at the images from nearfield and Boston Harbor that 1999 will probably be another "high species year". Ampelisca continues to decline in the harbor which makes sense since species richness is increasing as the community succession advances. Biological processes are dominating in the nearfield and there are practically no bedforms remaining at our sandy sites (have been reworked from 1998-1999).

OMSAP: the coastal area near U. Mass Boston is highly contaminated. Do you see the import of sandy material from outside the harbor into the harbor with high storm surge, i.e. what happens in the harbor in terms of transport during large storms?

K. Keay: northeast winds blow from Deer Island flats across Dorchester Bay near U. Mass Boston. Nearby, material in the highly polluted Savin Hill Cove site is resuspended and settles out. Research by Gordon Wallace on lead-210 and other tracers suggests that the deposition rates are approximately 4-6 cm per year. Is the harbor a net importer or exporter of sediments?

M. Bothner: the harbor could be both an importer and an exporter.

B. Beardsley added that there also could be a lot of resuspension and movement of sediments which remains within the harbor.

OMSAP: the Ampelisca mats have the potential of greatly changing the chemistry of the sediments. Has anyone looked at the sediment contaminant levels at these sites, versus sites that were not colonized for any changes? Is there at least enough data to take a preliminary look?

K. Keay: the Combined Sewer Overflow (CSO) sampling surveys have sampled a lot of sites in Dorchester Bay in 1990, 1994 and 1998. Several of those sites are the same as or close to sediment camera and/or bottom sampling stations. Dorchester Bay is one site where there was a large expansion of Ampelisca mats between 1991-1994. Thus there might be data to examine this.

Audience: does commercial dragging impact areas sampled by this program?

K. Keay: commercial dragging does not occur in Boston Harbor. Dragging does occur in Massachusetts Bay and in the western nearfield, especially in an area called Rosie's Hole. Trawling effects on benthic communities have not been very well studied, however it certainly is a tremendous disturbance. Many of the nearfield depositional sites sampled are too small to be dragged by fishermen (i.e. surrounded by boulders). However, dragging could be affecting the farfield stations that coincide with fishing grounds.

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Benthic Nutrient Cycling in Boston Harbor and Massachusetts Bay

Audience: is there any sediment chlorophyll data from Massachusetts Bay sites to suggest enrichment in May 1999?

A. Giblin: we have the data, but it has not been analyzed yet.

Audience: the sediment oxygen demand data in Massachusetts Bay increases throughout the summer and remains high even in October, whereas in Boston Harbor the data peaked in July and then decreased. What is causing this decrease in Boston Harbor, are animals running out of a food source, or is there a decrease in temperature?

A. Giblin: the sediment oxygen demand follows temperature relatively closely in Massachusetts Bay and the temperature continues to increase until the fall overturn. This relationship is not as evident in Boston Harbor because of the biological influence of amphipod mats. Without the mats, the sediment oxygen demand would correlate with the seasonal cycle of temperature.

OMSAP: within Boston Harbor, it looks as though the sediments are an important source of nutrients to the water column, mostly near the sewage outfall. With the outfall relocation, will there be enough of a reservoir of nitrogen such that sediment fluxes will be driving some of the nutrient productivity dynamics in the harbor?

A. Giblin: I suspect that it will take somewhere between 1-2 years for the system to re-equilibrate, after which we should see a typical coastal environment. Long-term productivity will be driven by new inputs from the outside and the sediments will provide a buffer. In systems with limited tidal exchange it is possible to recycle nutrients many times. But this will not play a large role in Boston Harbor because of the large tidal fluxes and short water residence time.

OMSAP: do you think the presence of toxic contaminants in sediments are having some effects on the regeneration dynamics and if so, will some of those dynamics change as the sediments become cleaner?

A. Giblin: given the high respiration rates, there is no indication that the microbes are having any problems. In 1992 the Savin Hill Cove station was so polluted that hydrocarbons were leaching out of the sediment and yet the respiration rates were still very high, although no macrofauna were visible. Based upon the high densities of animals measured at the other stations, there do not appear to be any acute toxic effects.

Audience: did you make any attempt to separate macrofaunal from bacterial respiration?

A. Giblin: no because we try not to kill any of the animals and keep the whole system as intact as possible so that we simulate the entire community's respiration which is the oxygen demand for the water column. However, it would be interesting to undertake this.

Audience: regarding your statement about Boston Harbor sediments having the ability to provide 35% of the nitrogen given the published net primary production, is that on an annual basis?

A. Giblin: yes.

Audience: does the work here relate to J. Fitzpatrick's nitrogen mass balance?

A. Giblin: the model estimates a 15% nitrogen loss for denitrification. Inputs are entered into the model and there is a small error term in the model. The remaining nitrogen is assumed exported. I actually measure the loss of nitrogen gas. J. Fitzpatrick models the same nitrogen loss based on parameters of carbon deposition and nitrogen remineralization and both the model and the data agree.

J. Fitzpatrick added that there is a more accurate value specific to Boston Harbor.

Audience: what is the amount of nitrogen being exported from Boston Harbor based on?

A. Giblin: this is a mass balance argument based upon the fact that the harbor stations are not responsible for a large amount of nitrogen removal. Therefore, if it is not being removed in the harbor through burial or denitrification, it must be exported.

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Nearfield Hard-bottom Communities Near the Massachusetts Bay Outfall

OMSAP: would these hardbottom communities survive after a large storm such as a hurricane?

B. Hecker: most of these communities would probably survive.

OMSAP: the northeastern part of Georges Bank has cobble areas which are the preferred substrate for cod and haddock larvae. Are similar nursery habitats found near the new outfall?

B. Hecker: larvae are too small to be seen in the video and photographs.

OMSAP: is there any indication of rocks turned over due to dragging/trawling?

B. Hecker: I have not seen any indication of dragging but do see lobster gear. We could tell if there was dragging because it would cause damage to the upright algae.

Audience: what if sea urchins proliferate near the outfall after it goes on-line and consume Lithothamnion, would the loss of Lithothamnion be blamed on the outfall?

B. Hecker: this would not occur because green urchins prefer high relief on the tops of the drumlins away from the diffusers.

Audience: can you give us a sense, in a semi-quantitative way, what kind of confidence you have in how your observations represent a particular station?

B. Hecker: variance measures of pictures within stations generally show that Lithothamnion was the most variable species with a coefficient of variation of 175% per picture. Other species had coefficients of variation of several hundred per picture but this is to be expected from any epifaunal study since you have to pool over a number of pictures or larger areas because of patchiness. However, I am very confident that we can revisit stations since landmarks such as boulders remain stationary.

OMSAP: how good is your navigation, is it plus or minus 5 m?

B. Hecker: yes, on the surface, then the ROV and tether must to be taken into account.

OMSAP: is that accomplished acoustically?

B. Hecker: it is an electronic ranging system. We can use it successfully to find a specific rock or even diffuser 44, but it takes us about four times longer to search and we can not do that for every station.

Audience: do you sample in the summer?

B. Hecker: we sample in June (in 1996 sampling occurred in July).

Audience: I would have thought that the sediment drape would be blown away in the winter, and that the shallow stations would be the cleanest.

B. Hecker: not true because stations found at similar depths have been found to have completely different thicknesses of drape. Most likely, sediment drape is carried away in the winter, and redeposited during the warmer months, but that this process is not stable throughout the year.

Audience: what is the light requirement of Lithothamnion?

B. Hecker: Gulf of Maine Lithothamnion peaked at 40m, and was found down to 63m. In terms of its actual light requirements, kelp is approximately 1% of surface light in terms of extinction depth, the red algae is 0.1%, and the coralline [Lithothamnion] is 0.01% of surface illumination.

Audience: would an increase in turbidity due to the outfall affect Lithothamnion?

B. Hecker: yes, if the increase in turbidity decreased light transmission, I would expect to see a decrease in the percent cover of Lithothamnion. Another negative effect could be particulates settling out of the effluent increasing sediment drape which is detrimental to Lithothamnion.

Audience: do you have any idea how the hardbottom communities around Deer Island may recover? Would Lithothamnion colonize the area?

B. Hecker: a type of coralline algae, possibly Lithothamnion, has been observed around Deer Island.

B. Beardsley: B. Hecker is monitoring communities within one tidal cycle of the outfall pipe at a depth below the thermocline. There might be an increase of particles from the new outfall which affect Lithothamnion.

B. Butman: the suspended solid concentrations in the effluent are about 30 mg/l. Dilution past the zone of initial dilution is 100:1 to 300:1 diluting the suspended solids concentrations to 0.03 - 0.3 mg/l. Background concentrations of suspended solids are about 1 mg/l.

B. Hecker: I am more interested in changes in productivity that might affect light transmission and increase particle deposition thus negatively affecting Lithothamnion. There has not been any work done on how long Lithothamnion can survive buried.

B. Butman: there are no measurements in this monitoring program of the flux of sediments to the hard bottom because of the difficulty in obtaining measurements.

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Caged Mussel Bioaccumulation Monitoring in Massachusetts and Cape Cod Bays

Audience: are the mussels from Sandwich high in organic contaminants?

L. Lefkovitz: they are relatively high in DDT, but not at dangerous levels.

Audience: are these units in wet weight?

L. Lefkovitz: yes, units on all of our tissue thresholds are calculated using wet weight so that we can compare to FDA limits.

OMSAP: is your outfall station in the zone of initial dilution?

C. Hunt: it is near to that. It was set near Buoy B for every baseline year except 1998 when we tried to move it closer to the outfall. However, we had some problems with recovery due to dragging and other fishing activities in that area so we are still working on how to protect deployments. When the outfall goes on-line, we will try to deploy as close as we can to the diffusers.

M. Hall: the intent is to get within the zone of initial dilution that is 60m on either side of the outfall diffusers.

OMSAP: the caution levels are quite close to what is already being measured yet the Massachusetts Bay mussels are not showing nearly as much bioaccumulation as the harbor mussels. If the mussels are within the zone if initial dilution, the original EPA Environmental Impact Statement would allow for some degradation. Isn't the threshold overly conservative?

D. Tomey: yes and we have a mixing zone established. We had discussed using the edge of the mixing zone.

C. Hunt: I do not expect us to see changes that would exceed the threshold.

OMSAP: what are we aiming for with the caution level shown on the graphs of contaminants versus years?

M. Mickelson: the caution level is the doubling of the mean baseline; the warning level is 80% of the FDA advisory level.

OMSAP: but within the zone if initial dilution, you might expect an impact. I think the caution level should apply to samples from the edge of that zone of initial dilution (60m).

C. Hunt: so the physical location of the mooring should be just outside the edge of the ZID (about 60m to the north or south). The caution number here is based on twice the baseline so it is very conservative. The 70:1 dilution of the modeling was met approximately 60m off of the diffuser line.

OMSAP: is that over a tidal cycle?

M. Mickelson: [70:1 was the lowest dilution, which occurs at slack water. Currents perpendicular to the line of diffusers increase the dilution.]

C. Hunt: in the outfall siting studies, we measured water column metals and organics at several stations and Massachusetts Bay water column contaminants are fairly constant and very low, unlike contaminants in the sediments. We can sample anywhere in that area pre-outfall and obtain a representative number. However, when the outfall goes on-line, we have to measure any bioaccumulation within the zone of initial dilution where we meet the permit requirements.

OMSAP: will there be another mussel deployment location further downstream?

C. Hunt: there will be one in Cape Cod Bay.

OMSAP: nothing in between?

C. Hunt: nothing between right now.

K. Keay: we set the baseline caution level at twice the baseline mean as a result of discussions with the Outfall Monitoring Task Force in late 1997 in terms of tissue residues of PCBs. We apply this approach to the entire fish and shellfish program which looks at appreciable change so that we have a consistent approach in setting caution levels. We set the warning level thresholds at 80% the FDA levels for compounds that have FDA consumption advisories. I would be surprised if we see a doubling of the current levels on the edge of the zone of initial dilution.

C. Hunt: we have looked at significant change and based on the baseline data and variability, we should be able to see significant change before we hit that caution level so we can detect change before we get to that level. Thus the detectability is powerful.

Audience: is it the average that is compared to the caution level?

C. Hunt: it is the mean. In the water column thresholds, using the upper confidence interval could trigger a threshold too early and using the lower confidence interval could trigger a threshold too late so using the mean is more conservative.

M. Moore suggested adding an additional mussel deployment once the outfall goes on-line to provide greater spatial coverage.

B. Beardsley: agreed that this would help initially and might answer some of the spatial questions.

L. Lefkovitz: that is possible but it is difficult to successfully deploy caged mussels.

Audience: why does 1996 seem to have more variation than some of the other years?

L. Lefkovitz: we have not identified any particular reasons for that.

Audience: are results lipid normalized for organic contaminants?

L. Lefkovitz: we found that lipid normalizing the data did not reduce any variability or provide additional information or trends. We still examine lipid concentrations but we do not normalize the results.

Audience: have similar studies been done elsewhere which look at interannual variability?

L. Lefkovitz: caged mussels are used routinely for monitoring in other areas.

C. Krahforst: GulfWatch is an ongoing regional program with 6 years of data (using native and caged mussels).

L. Lefkovitz: there are also mussel studies in Boston Harbor.

C. Hunt asked to look at the GulfWatch data.

M. Hall added that MWRA detection limits are lower than GulfWatch.

OMSAP: are there problems when different population of mussels are used from year to year?

L. Lefkovitz: we always collect mussels from the same place every year. Early on, all mussels used were from Gloucester, and we found that the pre-deployment metals values were higher than Sandwich mussels.

OMSAP: what if different strains of mussels are used which have different bioaccumulation potentials or what if there is a diseased population one year which has a different bioaccumulation potential, would that confound the results?

L. Lefkovitz: we try to assess the health of the pre-deployed mussels as soon as we collect them. We collect a certain size class (60-70mm) from the same locations.

OMSAP: would you ever want to use SPMDs (Semi-Permeable Membrane Devices)? A SPMD is a polyethylene bag with a hollow tube pressed flat containing a thin film of synthetic lipid. This device mimics living membrane such as gills, fish skin, or mussels and bioaccumulates organics.

L. Lefkovitz: we may use them in the future, however SPMDs do not accumulate metals. In my opinion, they would be good to use because they are very consistent, and animal health is not an issue. Though the mussels generally survive quite well, there are definitely confounding factors whenever animals are used in monitoring.

Audience: how are PCBs calculated?

L. Lefkovitz: we use a sum of the 20 NOAA congeners but do not multiply by two for comparison to the FDA limits. Results do not come close to the FDA limits.

Audience: it may be useful to measure silver, which is a potentially good tracer of effluent, to assess the impacts of bioaccumulation.

C. Hunt: in general, metals do not bioaccumulate. After they reach some level, they do not continue to increase as with the organic contaminants, and thus are not a good measure of bioaccumulation.

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Flounder Histology and Tissue Chemistry

OMSAP: how old are the flounder which are studied?

M. Moore: they average about 4 years of age and the average age has not changed very much over the duration of this study.

OMSAP: What is the cause for the original decrease [in tumors]?

M. Moore: it precedes much of the MWRA Boston Harbor Project considering that the latency period of tumor development is 5 years. It may be due to the recession in the 1980's during which a lot of the dirty industries in the Boston watershed area were shut down. Certainly the later trend is significantly associated with source reduction and better MWRA effluent quality. USGS has a data series of Deer Island Flats sediment concentration trends over the last 10-15 years that I would like to examine. Organic contaminant data is important since organics drive flounder disease much more than the inorganic contaminants.

OMSAP: what if flounder migratory patterns change, could you see an effect and mistakenly blame the outfall? [i.e. if Boston Harbor flounder migrate to Cape Cod Bay]

M. Moore: that is a problem since there is no genetic distinction between the flounder.

OMSAP: can you tag flounder to study their migration?

M. Moore: yes, there is tagging data from the mid-1970's which we still use to base assumptions on migration today. However, one of the authors expressed reservation about the significance of the data due to bias with regards to fishermen inside the harbor returning more tags than fishermen outside the harbor. It would be useful to conduct acoustic tagging studies.

OMSAP: percent prevalence of centrotubular hydropic vacuolation (CHV) of Cape Cod Bay flounder liver seems to be increasing over time, is this significant?

M. Moore: I do not think so.

OMSAP: what kinds of values would be measured further out?

M. Moore: Georges Bank flounder have zero percent CHV and the entire liver structure is far less complicated.

OMSAP: what kinds of values would be measured east of Stellwagen Bank or the western Gulf of Maine?

M. Moore: I have not looked but suspect results would be more similar to inshore flounder as opposed to Georges Bank.

OMSAP: can you use commercially obtained fish?

M. Moore: if you have accurate information as to where they were fished. I always capture the flounder which I analyze.

Audience: have you examined other species of bottom fish for tumors?

M. Moore: I have not, but there have been no reports of tumors [in this area].

Audience: do you catch other fish?

M. Moore: mainly yellowtail flounder, winter flounder, and many small skates.

Audience: would a decrease in size distribution be a compounding factor when examining trends in CHV over time?

M. Moore: we have age data from NMFS from 1991 onwards and we have not seen a significant reduction in age, but this can be revisited.

OMSAP: assuming tumors have a latency period of five years, if tumors begin to be measured in a population, does that mean that the stress happened five years ago?

M. Moore: yes, for tumors. Vacuolated cells can develop in 2-3 years, and so this is not an acute response indicator.

OMSAP: what happens if you remove the stress at year four, does that mean that you will not see elevated tumors?

M. Moore: it depends on the nature of the tumor, genetic change, and chemical compound causing the stress. If we consider the growth of a pre-existing condition, then removing the stress of the outfall will not change anything. If the stress that is still promoting the growth of that tumor is removed or reduced, the time before the tumor becomes evident is prolonged. However, hydropic lesions are much more sensitive and are predictive of tumor risk. If there is a persistent impact of toxics at the Massachusetts Bay outfall site over three years, it can be measured in about three years.

OMSAP: it was found that fish exposed to contaminated sediments formed lesions, and that the lesions disappeared when the fish were placed in clean sediments.

M. Moore: it depends on the severity of the lesion and the type of fish since various species have different disease processes. The CHV is present in winter flounder, starry flounder, and croaker but not English sole. We do not know whether CHV is reversible since no one has successfully done those kinds of experiments in winter flounder.

Audience: do you have any idea why the metals in flounder fillet are so different from the organics? Results, in particular silver, show higher levels in flounder from the outfall and lower levels in flounder from Boston Harbor and Cape Cod Bay.

M. Moore: it is not clear what the metals data indicate.

J. Fitzpatrick: it is possible that the sediments in Boston Harbor are very reduced producing a lot of sulfides which bind metals and make them not bioavailable but I am not sure if this same process is occurring in Cape Cod Bay.

Audience: any idea of what percentage of these compounds have a strong atmospheric component? Now that we will soon have full secondary, are we still looking at one major source?

M. Moore: if there was a strong atmospheric component, then the consistent between site variability would not be so high.

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