ASSEL, R.A. The 1997 ENSO event and implications for North American Laurentian Great Lakes winter severity and ice cover. Geophysical Research Letters 25(7):1031-1033 (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980016.pdf
Mild winters and below-average annual maximum ice cover for the Laurentian Great Lakes occur during strong warm ENSO events. During the six strongest warm ENSO events since 1950 a Great Lakes winter severity temperature index and simulated annual maximum ice cover averaged 1.2oC above and 15% below a 1950-1994 average, respectively. The observed differences between the average of the strong ENSO event years and the base period average are statistically significant.
ASSEL, R.A., and L.R. HERCHE. Ice-on dates, ice-off dates, and ice duration for lakes and rivers with long-term records. Proceedings, 14th International Ice Symposium, H.T. Shen, Potsdam, New York, July 27-31, 1998. A.A. Balkema, Rotterdam, Netherlands, p. 147-151 (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980017.pdf
Decadal to century trends in ice event dates and ice duration are summarized from previous studies. The climatology of ice-on dates, ice-off dates, and ice duration are analyzed for several selected lakes and rivers in the northern hemisphere having long-term records. Long-term averages and standard deviations are summarized for each site and comparisons are made among sites to identify climate influence on ice event dates over the northern hemisphere.
ASSEL, R.A., D.C. NORTON, and F.H. QUINN. Early 20th Century Lake Superior Basin Precipitation Estimate. NOAA Technical Memorandum ERL GLERL-107, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (NTIS# PB98-167935INZ) 22 pp. (1998). https://www.glerl.noaa.gov/pubs/tech_reports/glerl-107
A method to provide improved estimates of the annual value of over-land areally weighted Lake Superior basin precipitation is described and compared with the traditional Thiessen method. The method consists of calculating the ratio of areally weighted precipitation to precipitation at individual grid cells in the basin during periods when station density is high. The ratios are used in conjunction with data collected during the late 19th and early 20th centuries to generate improved basin precipitation estimates. The "ratio method" provides precipitation estimates for that period that are more in agreement (relative to the Thiessen method) with trend in flow for the outlet of Lake Superior.
ASSEL, R.A., and S. Rodionov. Atmospheric teleconnections for annual maximum ice cover on the Laurentian Great Lakes. International Journal of Climatology 18:425-442 (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980001.pdf
Great Lake ice cover records for winters 1963-1990 were used to define anomalously high (low) average ice cover based on the seven highest (seven lowest) annual maximum ice covers. Analysis of the maximum ice cover reveals (i) a low (1964-1976); (ii) a high (1977-1982); and (iii) once again a low (1983-1990) ice cover regime. The high ice cover regime corresponded in part with a hiatus in El Nino-Southern Oscillation (ENSO) events and the beginning of an interdecadal change in Northern Hemipshere atmospheric circulation that started in the late 1970s. About 46% of the lowest quartile ice covers occurred during the mature phase (year + one winter) of El Nino. Only 1 year out of seven with the mature phase of El Nino between 1963 and 1990 was not associated with the lowest quartile ice cover, this was 1977, a pivotal year after which a new climatic regime in the Northern Hemiphere was established. Anomaly maps of 700 hPa geopotential height for the lowest quartile ice cover reveal a zonal flow pattern. Highest quartile ice cover was associated with meridonal circulation from the Arctic directed toward the Great Lakes. Significant differences occur for highest minus lowest quartile ice cover composite 700hPa height anomaly maps in the Pacific Ocean, the west coast of North America, north Mexico, eastern North America, north central Siberia, western Europe and the adjacent North Atlantic. Correlations between first differences (year t + 1 minus year t) of annual maximum ice cover and 700 hPa geopotential heights for winters 1963-1990 agrees with these teleconnections and were higher than the absolute time series correlations, indicating strong interannual teleconnections. Annual maximum ice cover was also significantly correlated with the tropical Northern Hemiphere teleconnection index.
BEETON, A.M. NOAA advances and activities in climate prediction. Proceedings, Adapting to Climate Change and Variability in the Great Lakes-St. Lawrence Basin. Toronto, Ontario, Canada, May 13-15, 1997. Environmental Adaptation Research Group, 67-71 pp. (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980021.pdf
The National Oceanic and Atmospheric Administration is a diverse agency, with many different facets, responsibilities, and obligations. NOAA was formed some twenty years ago, in response to the Stratton Commission Report, which recommended that ocean science, ocean operations, weather service, and related agencies be combined as one large agency. Consequently, NOAA houses the National Weather Service (NWS), National Marine Fisheries Service (NMFS), National Ocean Service (NOS), National Environmental Satellite, Data, and Information Service (NESDIS), and a unit called Ocean and Atmospheric Research (OAR). These are separate and distinct units under the umbrella of NOAA.
BELETSKY, D., K.W. Lee, and D.J. SCHWAB. Recent advances in hydrodynamic modeling of the Great Lakes. Proceeding of Theme B, Water for a Changing Global Community, San Francisco, CA, August 10-15, 1997. The 27th Congress of the Int'l Assoc. for Hydraulic Research, p. 925-930 (1997).
This paper reviews the progress in hydrodynamic modeling of the Great Lakes made in recent years, specifically numerical modeling of circulation and thermal structure. We examine three closely related components of lake circulation studies: general circulation modeling, high resolution modeling of the coastal zone, and development of hydrodynamic forecasting systems.
BELETSKY, D., and D.J. SCHWAB. Modeling thermal structure and circulation in Lake Michigan. Estuarine and Coastal Modeling, Proceedings of the Conference of American Society of Civil Engineers, Alexandria, Virginia, October 22-24, 1997. p. 511-522 (1998).
A three-dimensional primitive equation numerical ocean model, the Princeton model of Blumberg and Mellow (1987), was applied to Lake Michgan for the 1982-83 study period. The model has a terrain following (sigma) vertical coordinate and the Mellow-Yamada trubulence closure sheme. This two-year period was chosen because of an extensive set of observational data including suface temperature observations at permanent buoys and current and temperature observations from subsurface moorings. The emphasis of this paper is on the large-scale seasonal variations of thermal structure and circulation in Lake Michigan. The hydrodynamic model of Lake Michigan has 20 vertical levels and a uniform horizontal grid size of 5 km. The model is driven with surface fluxes of heat and momentum derived from observed meteorological conditions at eight land stations and two buoys from April 1982 to November 1983. The model was able to reproduce all of the basic features of the thermal structure in lake Michigan: spring thermal front, full stratification, deepening of the thermocline during the fall cooling, and finally an overturn in the late fall. The largest currents occur in the fall and winter when temperature gradients are lowest and winds strongest. Large-scale circulation patterns tend to be cyclonic (counterclockwise), with cyclonic circualtion within each subbasin. All these facts are in agreement with observations.
Breaker, L., and P.C. LIU. Application of the wavelet transform to the characterization of the intraseasonal oscilliations in sea surface temperature, wind stress, and sea level off Monterey, California. Proceedings, Second Conference on Coastal Atmospheric and Oceanic Prediction Processes, Phoenix, AZ, January 11-16, 1998. American Meterological Society, p. 166-170 (1998).
CROLEY, T.E. Great Lakes advanced hydrologic prediction system. Proceedings, 1st Federal Interagency Hydrologic Modeling Conference, Las Vegas, NV, April 19-23. 1998. 6.1-6.8 (1998).
The Great Lakes Environmental Research Laboratory's hydrology research over the past decade and a half addressed the Great Lakes community's forecasting needs and has culminated in a mature and tested Great Lakes Advanced Hydrologic Prediction System. Recently designed and tested technology properly incorporates multi-agency, multi-area, multi-period climate outlooks of meteorology probabilities into the package. This allows provision of 1- to 12-month (and longer) outlooks of probabilities for 25 hydrology variables over the entire Great Lakes basin, including simultaneous water levels on all lakes. It is important not to confuse probabilistic hydrology outlooks with currently available deterministic forecasts of lake levels, and to realize the much greater utility of the probabilistic hydrology outlooks. Probabilistic outlooks allow decision makers to incorporate some of the uncertainty inherent in forecasts, to properly consider the wide range of possibilities always present, and to consider the risk associated with their decisions, not possible with deterministic forecasts.
CROLEY, T.E. Mixing probabilistic meteorology outlooks in operational hydrology. Journal of Hydrologic Engineering 2(4):161-168 (1997).
There are now several kinds of probabilistic meterology outlooks available to the water resource engineer or hydrologist. These outlooks are defined over different time periods at different lag times, and they forecast either event probabilities or only most-probable events. An existing operational hydrology approach (for making hydrology outlooks) builds a set of hydrological possibilities from past meteorology to match forecast event probabilities, but it does not consider most-probable event forecasts. This approach is extended to mix both types of probabilistic meteorology outlooks in determining weights to apply to the set of hydrological possibilities to make hydrological outlooks. Boundary condition equations for the weights are constrcted corresponding to forecast event probabilities, and boundary condition inequalities are constructed corresponding to forecast most-probable events. The inequalities are converted to equivalent equations through the introduction of additional variables. The resulting set of all boundary condition equations is solved for physically relevant values. The solution is an optimization problem for the general case, similar to earlier consideration of only forecast event probabilities. An example illustrates the concepts and methods.
CROLEY, T.E., F.H. QUINN, K.E. Kunkel, and S.A. Changnon. Great Lakes hydrology under transposed climates. Climatic Change 38:405-433 (1998).
Historical climates, based on 43 years of daily data from areas south and southwest of the Great Lakes, were used to examine the hydrological response of the Great Lakes to warmer climates. The Great Lakes Environmental Research Laboratory used their conceptual models for simulating moisture storages in, and runoff from, the 121 watersheds draining into the Great Lakes, over-lake precipitation into each lake, and the heat storages in, and evaporation from, each lake. This transposition of actual climates incorporates natural changes in variability and timing within the existing climate; this is not true for General Circulation Model-generated corrections applied to existing historical data in many other impact studies. The transposed climates lead to higher and more variable over-land evapotranspiration and lower soil moisture and runoff with earlier runoff peaks since the snow pack is reduced up to 100%. Water temperatures increase and peak earlier. Heat resident in the deep lakes increases throughout the year. Bouyancy-driven water column turnover frequency drops and lake evaporation increases and spreads more throughout the annual cycle. The response of runoff to temperature and precipitation changes is coherent among the lakes and varies quasi-linearly over a wide range of temperature changes, some well beyond the range of current GCM predictions for doubled CO2 conditions.
Fornstrom, C.B., P.F. LANDRUM, C.P. Weisskopf, and T.W. La Point. Effects of terbufos on juvenile Red Swamp Crayfish (Procambarus clarkii): Differential routes of exposure. Environmental Toxicology and Chemistry 16(12):2514-2520 (1997).
During rain events, terbufos may be transported into aquatic ecosystems via agricultrual runoff. Because crayfish are closely associated with sediment, they may be exposed to aqueous terbufos through the gills or by ingesting contaminated sediment, detritus, or plants. Bioavailability of terbufos in food and toxicity of terbufos to crayfish were examined by measuring mortality and acetylcholinesterase (AChE) inhibition and by observing behavior. A 96-h aqueous exposure and a 12-h dietary exposure of juvenile red swamp crayfish, Procambarus clarkii, to terbufos produced median lethal concentrations (LC50s) of 5.9 ug/L (95% CI: 4.4, 8.1) and 4.4 ug/g pellet (95% CI: 2.9, 6.7), respectively. Aberrent behavior, such as loss of motor control and equilibrium, was noted at concentrations almost 50% of the aqueous LC50 and 80% of the dietary LC50. As concentration increased, AChE activity decreased and mortality and aberrant behavior increased. I50s, the percentage of AChE inhibition at which 50% of the crayfish died, for aqueous and dietary exposures were 76.5% (95% CI: 67.4, 85.6) and 86.1% (95% CI: 78.1, 84.1) of control activity, respectively. Based on present study results, terbufos is available for uptake by crayfish through ingestion and causes detrimental effects at concentrations less than expected in agricultural runoff.
GOSSIAUX, D.G., P.F. LANDRUM, and S.W. Fisher. The assimilation of contaminants from suspended sediment and algae by the zebra mussel, Dreissena polymorpha. Chemosphere 36(15):3181-3197 (1998).
Since their invasion into the Great Lakes, zebra mussels, Dreissena polymorpha, have increased the water clarity in Lake St. Clair and Lake Erie due to their extensive particle filtration. Because these particles contain sorbed contaminants, the potential for contaminant accumulation from both suspended sediment and algae were examined. Sediment or algae were dosed with selected radiolabeled polycyclic aromatic hydrocarbon congeners and/or hexachlorobiphenyl (HCBP). Assimilation efficiencies were measured and depended on food quality. Zebra mussels, 17 +/- 2mm long, assimilated 58.3 +/- 13.5% of the pyrene and 44.7+/- 5.8% of the benzo(a)pyrene (BaP) from sediment particles with a particle clearance rate of 493-897 ml/g tissue/h. However, assimilation efficiencies were 91.7 +/- 3.7% for pyrene, 91.9 +/- 1.4% for BaP, 96.6 +/- 1.4% for chrysene, and 97.7 +/- 0.5% for HCBP from suspended algae. Algal particle clearance rates for the mussels ranged from 47-143 ml/g tissue/h. Thus, zebra mussels efficiently accumulated non-polar contaminants sorbed to algae, while a smaller fraction of the sediment-associated contaminant was bioavailable. Furthermore, the contaminants sorbed onto suspended sediment particles were quickly removed from the water and deposited as pseudofeces. The pseudofeces production was positively correlated with filtration rate and suspended particle concentrations.
GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Fish Accoustics at the Great Lakes Environmental Research Lab. Great Lakes Environmental Research Lab, Ann Arbor, MI, 2 pp. (1998). https://www.glerl.noaa.gov/pubs/brochures
Holcombe, T., D.F. REID, L. Taylor, P. VINCENT, J. Warren, and G. Schwartz. Bathymetry of Lake Erie and Lake St. Clair: A color poster with descriptive text and digital data available on CD-ROM (https://www.ngdc.noaa.gov/mgg/greatlakes/erie.html). U.S. Dept of Commerce, National Oceanic and Atmospheric Administration, National Geophysical Data Center, Boulder Colorado, CO. Report MGG-13 (1998).
HORNE, J.K., and C.S. Clay. Sonar systems and aquatic organisms: matching equipment and model parameters. Canadian Journal of Fisheries and Aquatic Sciences 55:1296-1306 (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980003.pdf
Acoustic technology is an accepted and important component of aquatic research and resource management. Despite the widespread use of echosounders, few guidlines aid in the choice of appropriate sonar system parameters for acoustic surveys. Choice of acoustic carrier frequency is analogous to the choice of spotlight color used to illuminate a painting. Three primary biological factors influence the scattering of sound by aquatic organisms: swimbladder presence, organism length, and organisms behavior. We illustrate the influence of these factors on the amplitude of backscattered echoes using a Kirchhoff-ray mode scattering model to quantify fish and zooplankton backscatter as a function of carrier frequency, fish length, and swimbladder aspect. Model results illustrate that echo amplitudes from aquatic organisms are largely dependent on the presence or absence of a swimbladder. Target strengths generally increase with increasing carrier frequency and organism length. Swimbladder angle relative to the incident sound wave affects scattering amplitudes at all frequencies. Measurements of backscatter from swimbladdered fish are relatively robust when the ratio of fish length to acoustic frequency wavelenth ranges between 2 and 10. As fish length to frequency wavelength ratios increase, echo amplitudes become more dependent on aspect and peak when the swimbladder is perpendicular to the acoustic wavefront.
HORNE, J.K., and J.M. JECH. Quantifying intra-species variation in acoustic backscatter models. Proceedings, 135th Meeting of the Accoustical Society of America, Seattle, WA, August 20-26, 1998. 1821-1822 (1998).
Fisheries researchers are increasing the use of acoustic backscatter models in estimates of fish and zooplankton abundance. Target strength models based on measurements from a few fish may be applied to all individuals of the same species at frequency. The choice of carrier frequency combined with morphological and behavioral differences among organisms will influence amplitudes and variability of backscattered echoes. We quantified variability in backscatter of Atlantic cod (Gadus morhua) and brook trout (Salvelinus fontinalis) using data from digitized x-rays and Kirchhoff-ray mode models. Backscatter means and variances were combined to map the probability of discriminating cod from trout backscatter over a range of aspect angles, fish lengths, and acoustic frequencies.
Hunkins, K., T.O. Manley, P. Manley, and J. SAYLOR. Numerical studies of the 4-day oscillation in Lake Champlain. Journal of Geophysical Research 103(C9):18,425-18,436 (1998).
The summer thermocline of Lake Champlain, which is found at depths of 20-30 m, oscillates with typical vertical amplitudes of 20-40 m and periods of ~4 days. Fluctuations at the ends of the lake are opposite in phase and accompanied in the central lake by strong shears across the thermocline. These are basin-wide baroclinic disturbances which are forced by wind. A numerical, one-dimensional, two-layer, shallow-water model incoporating nonlinear and frictional effects in a rectangular basin forced by wind was first tested with idealized wind impulses. The results do not resemble the observed thermocline motion. However, when this simple model is forced with wind data from a nearby shore site, there is reasonable agreement between the model results and observed long-period thermoline motions in Lake Champlain. Dispersion effects appear to be negligible here. This contrasts with other long, narrow lakes where dispersion effects are important and internal surges are followed by wave trains resembing the soliton solutions of the Korteweg-de Vries equation. A possible explanation for the different regime in Lake Champlain may be found in its unique bathymetry with sloping bottom at the ends and numerous embayments on the sides that provide traps to collect wind-driven warm water and then release it slowly during recovery of equilibrium, preventing the formation of steep fronts and soliton wave trains.
JECH, J.M., and J.K. HORNE. Sensitivity of acoustic scattering models to fish morphometry. Proceedings, 135th Meeting of the Acoustical Society of America, Seattle, WA, August 20-26, 1998. 1819-1820 (1998).
Current efforts to model fish backscatter use digitized images of fish anatomy to realistically represent swimbladder shape, volume, and aspect. X-rays images of Atlantic cod (Gadus morhua) were digitzed at high resolution to examine the effects of varying image resolution on predicted backscatter as a function of carrier frequency and swimbladder shape. Backscatter amplitude scattering curves diverge with decreasing image resolution and increasing carrier frequency in the geometric scattering region. Image resolution has less effect on backscatter amplitude variability at/near resonance than in the geometric
KANE-DRISCOLL, S., and P.F. LANDRUM. Comparison of equilibrium partitioning and critical body residue approaches for predicting toxicity of sediment-associated flouranthene to freshwater amphipods. Environmental Toxicology and Chemistry 16(10):2179-2186 (1997).
Equilibrium partitioning (EqP) theory, which has been used to develop sediment quality criteria, predicts that the effects of organic compounds in sediments can be assessed by comparison of organic carbon-normalized sediment concentrations and estimated pore-water concentrations to effects determined in water-only exposures. A complementary approach, the critical body residue (CBR) theory, examines actual body burdens in relation to toxic effects. Critical body residue theory predicts that the narcotic effects of nonpolar compounds should be essentially constant for similar organisms, and narcosis should be observed at body burdens of 2 to 8 umol/g tissue. This study compares these two approaches for predicting toxicity of the polycyclic aromatic hydrocarbon (PAM) fluoranthene. The freshwater amphipods Hyalella acteca and Diporeia spp. were exposed for up to 30 d to sediment spiked with radiolabeled fluoranthene at concentrations of 0.1 (trace) to 3,940 nmol/g dry weight (=346 umol/g organic carbon). Mean survival of Diporeia was generally high (>70%) and not significantly different from that of control animals. This result agrees with EqP predictions, because little mortality was observed for Diporeia in 10-d water-only exposures to fluoranthene in previous studies. After 10-d exposures, mortality of H. acteca was not significantly different from that of controls, even though measured interstitial water concentrations exceeded the previously determined 10-d water-only median lethal concentration (LC50). Equilibrium partitioning overpredicted fluoranthene sediment toxicity in this species. More mortality was observed for H. azteca at later time points, and a 16-d LC50 of 3,550 nmol/g dry weight sediment (291 umol/g organic carbon) was determined. A body burden of 1.10 ~mol fluoranthene-equivalents/g wet weight in H. azteca was associated with 50% mortality after 16-d exposures. Body burdens as high as 5.9 umol/g wet weight resulted in little mortality in Diporeia. Diporeia, which has limited ability to metabolize fluoranthene and a higher lipid content, appears to be less sensitive than H. azteca, which does metabolize fluoranthene. These results demonstrate that the CBR approach is a useful complement to the EqP approach for the prediction and assessment of toxicity associated with contaminated sediments.
Kukkonen, J.V.K., and P.F. LANDRUM. Effect of particle-xenobiotic contact time on bioavailability of sediment-associated benzo(a)pyrene to benthic amphipod, Diporeia spp. Aquatic Toxicology 42:229-242 (1998).
A sample of Lake Michigan sediment was dosed with [14C]benzo(a)pyrene ([14C]BaP) and stored in the dark at 40C. Sets of experiments exposed Diporeia spp. for 28 days to this dosed sediment after 1 week, 6 and 13 months storage. Just prior to the exposures, the sediment was dosed again with [3H]benzo(a)pyrene ([3H]BaP). The accumulation of [14C]BaP with and without [3H]BaP was also examined after 13 months contact time to see whether the dosing with [3H]BaP affected the bioavailability. After 1 week contact time, the uptake clearance (Ks, g sed. g-1 h-1) for [14C]BaP was about 38% lower than the Ks for [3H]BaP. After 6 months and 13 contact time the Ks for [14C]BaP was 46% and 42% lower, respectively, than the Ks for [3H]BaP suggesting that contact time between the compund and sediment particles may affect the bioavailability of BaP. The Ks for [14C]BaP with and without [3H]BaP was the same. The log Koc of BaP varied from 5.25 to 6.18 at different time points but there was no large difference between [3H]BaP and [14C]BaP. The particle size distribution of [14C]BaP did not change during the 13 months storage and it was similar to the distribution of [3H]BaP.
Kunkel, K.E., S.A. Changnon, T.E. CROLEY, and F.H. QUINN. Transposed climates for study of water supply variability on the Laurentian Great Lakes. Climatic Change 38:387-404 (1998).
Hydrological models of the Great Lakes basin were used to study the sensitivity of Great lakes water supplies to climate warming by driving them with meteorological data from four U.S. climate zones that were transposed to the basin. Widely different existing climates were selected for transposition in order to identify thresholds of change where major impacts on water supplies begin to occur and whether there are non-linear responses in the system. The climate zones each consist of 43 years of daily temperature and precipitation data for 1,000 or more stations and daily evaporation-related variables (temperature, wind speed, humidity, cloud cover) for approximately 20-35 stations. A key characteristic of these selected climates was much larger variability in inter-annual precipitation than currently experienced over the Great Lakes. Climate data were adjusted to simulate lake effects; however, a comparison of hydrologic results with and without lake effects showed that there were only minor effects on water supplies.
LANDRUM, P.F. Kinetic models for assessing bioaccumulation. Proceedings, National Sediment Bioaccumulation Conference, February 1998. U.S. Environmental Protection Agency, p. 47-50 (1998).
LANDRUM, P.F., D.C. GOSSIAUX, and J. Kukkonen. Sediment characteristics influencing the bioavailability of nonpolar organic contaminants to Diporeia spp. Chemical Speciation and Bioavailability 9(2):43-55 (1997).
Organic carbon is considered the major variable affecting the bvioavailability of non-polar, sediment-associated contaminants. Previously, variation in bioavailability for some Great lakes sediments compared to a soil material was nearly a factor of 10 after carbon normalization. Because a soil might not truly represent sedimentary materials, sediments and soils were gathered from several locations in the United States, Canada, and Finland. The accumulation kinetics of the amphipod Diporeia spp. were measured for pyrene, benzo[a]pyrene (BaP), 2,4,2',4'-tetrachlorobiphenyl (TCBP), and 2,4,5,2'',4',5'-hexachlorobiphenyl (HCBP) sorbed to sediments and soils. The organic carbon content of the sediments ranged from 0.45-21.2% and 32.2-45.0% for soils. The bioavailability, measured as the uptake clearance (amount of source compartment cleared of contaminant per mass of organism per hour), was controlled by the amount of organic carbon, particualrly for the chlorinated biphenyls. However, for polycyclic aromatic hydrocarbons (PAH), bioavailability was controlled more by the organic carbon polarity represented by the carbon/nitrogen ration of the sediment. PAH bioavailability increased as the ratio increased: thus, the more nonpolar the organic matter, the more availbable the compound. This polarity did not account for any of the chlorinated biphenyl bioavalability. The amount and type of mineral matrix of the sediment did not influence the bioavailabiltiy for either compund class. In addition, the amount of oxygen in the sediment was correlated with the bioavailibility for BaP after carbon normalization.
LANDRUM, P.F., S. Kane-Driscoll, E. Tigue, D. GOSSIAUX, M. GEDEON, and M. Adler. Toxicokinetics of polychlorinated biphenyl congeners by Diporeia spp.: Effects of temperature and organism size. NOAA Technical Memorandum ERL GLERL-106, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (NTIS# PB98-167893INZ) 21 pp. (1998). https://www.glerl.noaa.gov/pubs/tech_reports/glerl-106
This report describes the experimental and quality control methods and data of the toxicokinetics of polychlorinated biphenyl congerner accumulation by the amphipod Diporeia spp. This data was collected as part of the U.S. Environmental Protection Agency's Lake Michigan Mass Balance Program. The work examines the impact of temperature and organism size on the accumulation of these congeners from water and sediment and loss from the Diporeia.
LAVRENTYEV, P.L., H.A. BOOTSMA, T.H. JOHENGEN, J.F. CAVALETTO, and W.S. GARDNER. Microbial plankton response to resource limitation: insights from the community structure and seston stoichiometry in Florida Bay, USA. Marine Ecology Progress Series 165:45-57 (1998).
Concentrations of dissolved and particlulate nutrients, chlorophyll, and microorganisms (0.01 to 200 um) were simultaneously measured during a 1 d survey of 12 stations in Florida Bay, USA, to characterize the microbial plankton community with respect to resource limitation. Three distinct types of trophic conditions, reflected in seston elemental stoichiometry and community structure, were identified within the bay. The first type, characteristic of the isolated eastern region, had low nutrient concentrations, imbalanced stoichiometry, and small microbial biomass with a large proportion of bacteria. The microbial community in this region was characterized by weak relationships between microzooplantion and phytoplankton and the predominance of mixotrophic taxa and the autotrophic ciliate Mesodinium rubrum. The second type, found in the north-central region influenced by Taylor Slough inflow, had elevated nutrient concentrations, elemental stoichiometry skewed toward N, and high turbidity. Under these conditions, the picocyanobacterium Synechococcus formed a dense bloom and coincided with an abundant, multi-step microbial good web. Finally, at the boundary with the Gulf of Mexico, low concentrations of nutrients were balanced at approximately the Redfield ratio and supported nanphytoplankton that were tightly correlated with microzooplankton. These data are consistent with the notion of P limitation in Florida Bay but also demonstrate that Si, light, and N may be co-limiting to phytoplankton in the eastern, north-central, and western boundary regions, respectively. Our findings suggest that multiple resource gradients, in conjunction with microbial food web processes, are important factors determining the plankton community structure in Florida Bay and should be considered in studies on ecological
LAVRENTYEV, P.J., W.S. GARDNER, and J.R. JOHNSON. Cascading trophic effects on aquatic nitrification: experimental evidence and potential implications. Aquatic Microbial Ecology 13:161-175 (1997).
Experiments, using natural plankton collected from a eutrophic site in Saginaw Bay, Lake Huron (USA) and from a hypereutrophic wetland of southern Lake Ene (USA), were conducted to test the hypothesis that bactenvory can control aquatic nitrification rates. The dynamics of nitrogen and protists in these experiments revealed a consistent pattern: an increase in concentrations of nitrates due to oxidation of NH4+ always followed the collapse of bacterivorous nanoplankton populations. This col-lapse was, in turn, caused by predation pressure of larger ciliates and metazooplankton. Experiments, using enrichment batch cultures maintained at near-ambient concentrations of NH4+, indicated that bacterivorous protists can inhibit nitrification directly by reducing bacterial numbers and indirectly by promoting bacterial aggregation. The latter experiments also suggest that feeding strategies of micro-bial grazers, e.g. suspension-feeding Spumella sp. versus surface-feeding Bodo saltans, may determine their grazing impacts on nitrifiers. Finally, ingestion rates of fluorescently labeled nitrifying bactena (FLNB) by the natural planktonic assemblage from Saginaw Bay demonstrated that nanoflagellates were able to efficiently prey on low concentrations of FLNB. Our study suggests that previously neglected trophic factors may be of potential importance for mediating nitrification rates in the pelagic environment.
Lee, C-H., and N. HAWLEY. The response of suspended particulate material to upwelling and downwelling events in southern Lake Michigan. Journal of Sedimentary Research 68(5):819-831 (1998).
Abstract not yet available.
LEE, D.H. Great Lakes water levels. In Michigan's Relative Risk Task Force Report on Hydrology, Surface and Ground Water Hydrology Alteration Task Force. Michigan DEQ, Office of Special Environmental Projects, Lansing, MI, p. 8-19 (1997).
LEE, D.H., C. MORSE, and S. BANDHU. Great Lakes and St. Lawrence River medium resolution vector shoreline data. NOAA Technical Memorandum ERL GLERL-104, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (NTIS# PB98-115843INF) 27 pp. (1998). https://www.glerl.noaa.gov/pubs/tech_reports/glerl-104
Digital medium-resolution vector maps of the Great Lakes and St. Lawrence River shoreline are compiled by the Great Lakes Environmental Research Laboratory (GLERL), and translated into multiple common formats including the Topological Vector Profile of the Spatial Data Transfer Standard (SDTS), to enhance data accessibility. The data were originally produced by the Detroit District, U.S. Army Corps of Engineers and Water Issues Division of Environment Canada-Ontario Region for the International Joint Commission's Levels Reference Study, and used to assess the influence of lake levels on shore erosion. The vector maps include a three tier classification representing the shorline geomorphic nature, the extent ofshoreline protection, and the nearshore subaqueous geomorphic nature. Metadata, documented in accordance with SDTS specifications, accompanies the digital maps. This work was done in conjunction with the National Geophysical Data Center to develop medium resolution vector coastline data for the conterminous United States and was funded by NOAA's Earth System Data and Information Management Program. Potential exists for use of the data in shorline management and environmental and coastal processes studies.
LESHKEVICH, G.A., S.V. Nghiem, and R. Kwok. Algorithm development for satellite synthetic radar (SAR) classification and mapping of Great Lakes ice cover. Proceedings, IEEE International Geoscience and Remote Sensing Symposium (IGARSS '98), Seattle, WA, July 6-10, 1998. 3 pp. (1998).
Computer analysis of ERS-1 and RADARSAT ScanSAR narrow images of Great Lakes ice cover using a supervised (level slicing) classification tecnique indicates that different ice types in the ice cover can be identified and mapped and that wind speed and direction can have a strong influence on the back scatter from open water. During the 1997 winter season, shipborne polarimetric backscatter data using the Jet Propulsion Laboratory (JPL) C-band scatterometer, together with surface-based ice physical characterization measurements and environmental parameters were acquired concurrently with RADARSAT and ERS-2 overpass. This data set was processed to radar cross-section and will establish a library of signatures (look-up table) for different ice types to be used in the machine classification of calibrated satellite SAR data.
LOFGREN, B.M. Simulated effects of idealized Laurentian Great Lakes on regional and large-scale climate. Journal of Climate 10:2847-2858 (1997). https://www.glerl.noaa.gov/pubs/fulltext/1997/19970002.pdf
Comparison is made between general circulation model (GCM) cases with and without the inclusion of idealized Great Lakes, in the form of four rectangular bodies of water, each occupying a single grid cell of the GCM at R30 resolution. The presence of idealized Great Lakes, as opposed to land, results in a phase shift in the annual cycle of latent and sensible heat flux. Very high upward sensible hear flux occurs over these idealized Great Lakes during the early winter. Ont heaverage over a region encompassing these idealized Great Lakes, evaporation and precipitation increase during the autumn and winter and decrease during the late spring and summer due to the lakes. Annual average water vapor flux convergence increases. The Great Lakes also alter the meridional air tempeature gradient. During the autumn and winter, the meridional temperature gradient is intensified to the north of the Great Lakes and diminished to the south. This intensifies the mean jet stream core and displaces it toward the north. This effect is reduced during the winter compared to the autumn because air temperature changes due to the lakes are unable to penetrate as deeply into the strongly stably stratified winter atmosphere. The increase in jet stream speed seems to increase synoptic wave activity to the northeast of the Great Lakes. As an additional experimental case, a swamp suface (saturated surface with no thermal capacity) is used to represent the Great Lakes. In this case there is little effect on the thermal state of the surface and atmosphere and on the fluxes between them. However, there is increased evaporation during the late summer and early autumn and increased precipitation throughout the summer and autumn. Annual water vapor flux convergence in this experimental case is greater than in the case with no lakes.
Lohrenz, S.E., G.L. FAHNENSTIEL, D.G. Redalje, G.A. LANG, X. Chen, and M.J. Dagg. Variations in primary production of northern Gulf of Mexico continental shelf waters linked to nutrient inputs from the Mississippi River. Marine Ecology Progress Series 155:45-54 (1997).
Increases in nutrient concentrations in the Mississippi River over the past 35 yr have led to speculation that primary production of organic carbon has been elevated as a result of increased nutrient fluxes that have occurred in the northern Gulf of Mexico coastal ecosystem. However, studies thus far have not provided direct demonstration of temporal relationships between measured primary production in continental shelf water and river-borne nutrient fluxes. This investigation compared temporal variations in primary production with associated annual and interannual changes in river-borne nutrient inputs. Primary production in shelf water near the river delta were found to be significantly correlated with nitrate (NO3- ) + nitrite (NO2-) concentration and fluxes over a 6 yr period from 1988 to 1994. Although light limitation was probably an important factor during winter months, a positive correlation was demonstrated between river inputs of NO3- + NO2- and promary production for data collected from other times of the year. Peak nutrient inputs generally occurred in the spring. The magnitude of the riverborne NO3- + NO2- inputs averaged 106% of estimated nitrogen requirements for phytoplankton in the river-impacted region, considerably greater than in Amazon shelf waters, which have been less subject to anthropogenic nutient increases. The possibility exists that further increases in anthropogenic nutrients in the Mississippi River could lead to higher and more widespread primary production, and this may intensify and extend the depletion of oxygen that has already been observed in the Louisiana shelf ecosystem. However, such a prediction is difficult because relationships between increasing nutrient inputs and primary production are unlikely to be linear, and a complete understanding of processes intermediate between primary production of organic matter and oxygen depletion in bottom waters on the Louisiana shelf is still lacking.
Mortsch, L.D., and F.H. QUINN (Eds.). Adapting to Climate Change and Variability in the Great Lakes-St. Lawrence Basin. Proceedings of a Binational Symposium, Toronto, Ontario, Canada, May 13-15, 1997. Environmental Adaptation Research Group, 193 pp. (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980019.pdf
Climate change and climate variability have profound implications for both natural processes, and the human socioeconomic systems intrinsically tied to them. Events associated with the 1997-98 El Niño have emphasized the vulnerability of many areas of North America to climate variability. Canada and the United States have a century-long history of cooperative research and shared management of resources in the Great Lakes Region. Extending this successful association to examine the potential impacts of climate change and variability in the Basin and to assess potential adaptive responses of interests was a natural outcome.
Mortsch, L.D., and F.H. QUINN. Great Lakes-St. Lawrence basin project: What have we learned? Proceedings, Adapting to Climate Change and Variability in the Great Lakes-St. Lawrence Basin. Proceedings of a Binational Symposium, Toronto, Ontario, Canada, May 13-15, 1997. Environmental Adaptation Research Group, 52-66 pp. (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980020.pdf
When we were preparing for this talk on what we have learned in the Great Lakes- St. Lawrence Basin (GLSLB) Project, we realized that it was in May 1992 that the first Steering Committee meeting for GLSLB Project was held. Five years later, we are presenting what have we learned. The primary lesson is that the people involved in the Project have made the difference. Although we are the Project Co-Chairs, we are indebted to the Steering Committee members who have contributed their ideas, helped steer and encourage us, as well as to the researchers who have spent a great deal of time, thought, and effort in contributing to the science. The presentation today will focus on some of the key components of the GLSLB Project, including: · project design, · research framework, · scenario development, · climate change and variability impacts, · adaptation, · integration, and · communication.
Nghiem, S.V., G.A. LESHKEVICH, and R. Kwok. C-band polarimetric backscatter observations of Great Lakes ice. Proceedings, IEEE International Geoscience and Remote Sensing Symposium (IGARSS '98), Seattle, WA, July 6-10, 1998. 3 pp. (1998).
Two experiments were carried out during the 1997 winter season across the Staits of Mackinac and Lake Superior. C-band radar backscatter signatures of various ice types and open water were measured from U.S. Coast Guard Ice Breaker vessels together with ground truth data. Polarimetric backscatter data were obtained at incident angels up to 600 for all polarizations. Backscatter signatures of 20 ice types/conditions were collected along the Coast Guard ship tracks in February and March 1997. The backscatter data set with in-situ ice characteristic parameter measurements are to be used in the development of the ice mapping algorithms using satellite SAR data over the Great Lakes. The results at C-band frequency for multiple incident angels and multiple polarizations are applicable to the current ERS and RADARSAT Synthetic Aperture Radars (SAR) and the furture ENVISAT SAR.
Nghiem, S.V., G.A. LESHKEVICH, and R. Kwok. Satellite SAR remote sensing of the Great Lakes ice cover. Assigned Project No. 56, NOAA, NOAA Code E/SP, Washington, DC, 32 pp. (1998). https://www.glerl.noaa.gov/pubs/fulltext/1998/19980012.pdf
The main objective of this project is to map the Great Lakes ice cover using radar data acquired by satellite synthetic Aperture Radar (SAR) data such as RADARSAT or ERS SAR. ERS is a European satellite and RADARSAT is a Canadian satellite on sun-synchronous near-polar orbits. ERS carries a SAR with the vertical polarization and RADARSAT has a SAR with the horizontal polarizaion. Both SARs operate at C-band frequency, which image ice cover on the Great Lakes during winter seasons. ERS SAR Precision Image (PRI) data over the Great lakes were received at the Gatineau station and processed by the German Processing and Archiving Facility (D-PAF). RADARSAT data were acquired in ScanSAR Wide A (SWA) mode and were also received at the Gatineau station. In the SWA mode, the data calibration is more involved because several antenna beams are mosaiced together to form an image covering an area of 500 km by 500 km on the ground.
Pirrone, N., I. Allegrini, G.J. Keeler, J.O. Nriagu, R. Rossmann, and J.A. ROBBINS. Historical atmospheric mercury emissions and depositions in North America compared to mercury accumulations in sedimentary records. Atmospheric Environment 32(5):929-940 (1998).
Gold and silver production in North America (including the United States, Canada and Mexico) released a large amount of mercury to the atmosphere until well into this century when mercury (Hg) amalgamation was replaced by cyanide concentration. Since then, emissions from industries have been the dominant anthropogenic sources of atmospheric Hg in North America as a whole. Past Hg emissions from gold and silver extractions in North America during the 1800s do not show a clear evidence of atmospheric deposition occurred at the coring sites considered in this study. Estimated atmospheric emissions of Hg in North America peaked in 1879 (at about 1708 t yr-1) and 1920 (at about 940 tyr-1), primarily due to Hg emissions from gold and silver mining. After the Great Economic Depression (1929) Hg emissions peaked again in 1947 (274 t yr-1), in 1970 (325 t yr-1) and in 1989 (330 t yr-1) as a result of increased Hg emissions from industrial sources, though improvements in the emissions control technology in United States and Canada have been substantial. Estimates of total atmospheric deposition fluxes of Hg to water and terrestrial receptors were in the range of 14.3-19.8 ug m-2 yr-1 in North America as a whole, and averaged 135 ug m-2 yr-1 (global background + local emissions) in the Great Lakes. These values were in good agreeement with recent estimates reported in literature. The comparison of atmospheric Hg deposition fluxes with Hg accumulation rates in sediment cores suggests that atmospheric deposition was the major source of Hg entering the lakes system at coring sites, however, important contributions to Lake Ontario sediment cores sites from 1940 to 1970 likely originated from local point sources (i.e. direct discharges).
POTHOVEN, S.A., S.B. BRANDT, J.M. JECH, D.W. HONDORP, and K.L. BARRY. Fish abundance, size and speices composition in the G-West and reference areas Near Pooles Island. Final Report, Maryland Environmental Service, Annapolis, Maryland, 199 pp. (1998).
This report summarizes fish community compostition, abundance and size structure near Poole's Island during 1997. Results from 1997 were compared with results from previous years (1992-1996).
QUIGLEY, M.A., and T. NALEPA. Decline in Lake Michigan bottom life. Great Lakes Environmental Research Laboratory, 2 pp. (1997). https://www.glerl.noaa.gov/pubs/brochures
QUINN, F.H. Potential Effects of Climate Change on the Great Lakes Basin. State of the Great Lakes 1997 Annual Report (1998).
QUINN, F.H., T.E. CROLEY, K. Kunkel, and S.J. Changnon. Laurentian Great Lakes hydrology and lake levels under the transposed 1993 Mississippi River flood climate. Journal of Great Lakes Research 23(3):317-327 (1997). https://www.glerl.noaa.gov/pubs/fulltext/1997/19970004.pdf
The Laurentian Great Lakes are North America's largest water resource, and include six large water bodies (Lakes Superior, Michigan, Huron, Erie, Ontario, and Georgian Bay), Lake St. Clair, and their connecting channels. Because of the relatively small historical variability in system Iake levels, there is a need for realistic climate scenarios to develope and test sensitivity and resilience of the system to extreme high lake levels. This is particularly important during the present high lake level regime that has been in place since the late 1960's. In this analysis, we use the unique climate conditions which resulted in the 1993 Mississippi River flooding as an analog to test the sensitivity of Great Lakes hydrology and water levels to a rare but actual climate event. The climate over the Upper Mississippi River basin was computationally shifted, corresponding to a conceptual shift of the Great Lakes basin 10¡ west and 2¡ south. We applied a system of hydrological models to the daily meteorological time series and determined daily runoff, lake evaporation, and net basin water supplies. The accumulated net basin supplies from May through October 1993 for the 1993 Mississippi River flooding scenario ranged from a 1% decrease for Lake Superior to a large increase for Lake Erie. Water levels for each lake were determined from a hydrologic routing model of the system. Lakes Michigan, Huron, and Erie were most affec ted. The simulated rise in Lakes Michigan and Huron water levels far exceeded the historically recorded rise with both lakes either approaching or setting record high levels. This scenario demonstrates that an independent anomalous event, beginning with normal lake levels, could result in record high water levels within a 6- to 9-month period. This has not been demonstrated in the historical records or by other simulation studies.
Schelske, C.L. and G.L. FAHNENSTIEL. Comemorating 50 years of Great Lakes research at the University of Michigan: A tribute to David C. Chandler. Journal of Great Lakes Research 24(3)487-494 (1998). http:www.glerl.noaa.gov/pubs/fulltext/1998/19980006.pdf
This special section includes papers commemorating 50 years of Great Lakes research at the University of Michigan that are dedicated to David C. Chandler who guided the development of Great lakes research. Nine papers were authored or co-authored by: Chandler's students at the University of Michigan (Beeton, Richman, Robertson, and Schelske), students who obtained their degrees under faculty affiliated with various Great Lakes programs (Kerfoot, Fahnenstiel, and Francis), and former or current research scientists and staff in the Great Lakes programs (Evans, Jude, Schneider, and Stoermer). In addition, a version of another paper originally intended for this special section is dedicated to Dr. Chandler (Schelske in press). Each of these contributions is placed in the historical setting that follows and is also summarized in the Appendix to this introductory paper.
Shen, H., S. Nghiem, G.A. LESHKEVICH, and M. Manore. A summary of current remote sensing and modeling capabilities of the Great Lakes ice conditions. Occasional Paper Series: Understanding Great Lakes Issues, 98-11. Great Lakes Program, State University of New York at Buffalo, Buffalo, NY, 10 pp. (1998).
The capability of current remote sensing tools and mathematical models to study the Great Lakes ice conditions is reported. This report is based on a workshop held in October of 1997. In which, the feasibility of studying Great lakes ice conditions from a combined remote sensing and modeling effort was discussed. The participants of the workshop recommended to have this report produced as a document to stimulate future coordinated field-remote sensing-modeling studies in the Great Lakes. It is believed that well-coordinated study can greatly accelerate the progress towards better forecast models.
Tomaszek, J.A., W.S. GARDNER, and T.H. JOHENGEN. Denitrification in sediments of a Lake Erie coastal wetland (Old Woman Creek, Huron, Ohio, USA). Journal of Great Lakes Research 23(4):403-415 (1997). https://www.glerl.noaa.gov/pubs/fulltext/1997/19970005.pdf
Denitrification in Old Woman Creek estuary (Lake Erie) sediments was measured by an in vitro N2-flux method with intact cores and by an in situ chamber method. In both methods, nitrogen gas, the end product of denitrification, was measured directly by gas chromatography. The in situ approach allowed measurement of denitrification directly over short time intervals but its use was limited to shallow depths. Denitrification rates measured with in situ chambers agreed well with those from in vitro intact cores when temperatures in the estuary remained constant. However, the two methods could not be accurately compared during the spring when temperature increased rapidly, because of the 4-day pre-incubation time needed for sparging for the in vitro method. In vitro denitrification rates ranged from ca 40 to 135 umole N2 m-2 h-1 in October 1993 and from 66 to 428 umole N2 m-2 h-1 in May and July 1994. Oxygen consumption rates in these experiments ranged from 0.71 to 3.0 mmole O2 m-2h-1. Denitrification rates tended to decrease along the flow axis but differences among stations were usually not significant. In situ N2 accumulation rates ranged from 45 umole N2 m-2 h-1 in dark chambers during October 1993 up to apparent values of 2,100 umole N2 m-2 h-1 in May 1994, immediately after the water temperature had rapidly increased to 27oC. These calculated values included gas-solubility corrections due to the water-temperature increases. In situ measurements of denitrification rates in transparent chambers were 76-79% higher than rates measured in a similar dark chamber. The results suggest that denitrification is an important sink for nitrogen in Old Woman Creek estuary and that environmental conditions such as temperature, light, and available substrate affect denitrification rates.
VANDERPLOEG, H.A., J.F. CAVALETTO, J.R. LIEBIG, and W.S. Gardner. Limnocalanus macrurus (Copepoda: Calanoida) retains a marine arctic lipid and life-cycle strategy in Lake Michigan. Journal of Plankton Research 20(8):1581-1597 (1998).
Limnocalanus macrurus, an omnivorous copepod with strong carnivorous tendencies that invaded fresh water during the Pleistocene glaciation, retains a marine arctic lipid and life cycle stategy in the hypolimnion of Lake Michigan. Its maximum lipid concentration of 67% of dry mass--consisting largely of wax esters--is the highest reported for freshwater zooplankton and is among the highest reported for marine polar species. The high lipid concentration of L. macrurus runs counter to the pardigm that high wax ester concentrations are found in herbivorous, but not in carnivorous, polar species. Lipids are drawn down to extremely low levels (10% of dry mass) during the reproductive period, November-May. Reproduction in this univoltine species appears to be timed so that the new generation develops during the high abundance of prey (crustacean microzooplankton and net phytoplankton) in spring. A high wax ester content may allow egg production to start in winter when the prey concentration is low. In contrast to many polar species, the new generation moves through all copepodid stages to adult without diapausing. Copepodid 5 females have a low lipid concentration, and lipids are slowly built up in new generation adults during summer and fall before reproduction commences. This lipid and life cycle strategy may have given L. macrurus an advantage over potential freshwater competitors, such as the arctic freshwater cyclopoid copepod Cyclops scutifer, in the hypolimnia of glaciated lakes.
WINKELMAN, A., E. STABENAU, and B.J. EADIE. Particle size distribution and concentration of total suspended matter in Sothern Lake Michigan: January 28-February 10, 1998. NOAA Technical Memorandum ERL GLERL-105, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (NTIS# PB98-167885INZ) 34 pp. (1998). https://www.glerl.noaa.gov/pubs/tech_reports/glerl-105
Profiles of grain size distributions of suspended matter in the water column of southern Lake Michigan are presented from a cruise from January 28 through February 10, 1998. This cruise was prior to the very large sediment resuspension event that began on March 10, 1998. The majority of samples had less than 1 mg/L of Total Suspended Material (TSM), although concentrations were higher off Racine, IL and Saugatuk, MI. An inverse thermal stratification was observed at Racine, all other stations were well-mixed. Although the error was large, the distribution of particle sizes throughout the coastal region of the southern basin were remarkably consistent, with the peak of the mass distribution generally between 20 and 40 um.
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