GLERL Publication Abstracts: 1993

Publications List Key
Capitalized names represent GLERL authors.
* = Not available from GLERL.
** = Available in GLERL Library only.

ASSEL, R.A. Book review of "Climate Change on the Great Lakes Basin". Bulletin of the American Meteorological Society 74(6):1087-1088 (1993).

No abstract.

*BOLSENGA, S.J., and C.E. Herdendorf. Lake Erie and Lake St. Clair Handbook. Wayne State University Press, Detroit, MI, 467 pp. (1993).

No abstract.

BOLSENGA, S.J., and D.C. NORTON. Great Lakes air temperature trends for land stations, 1901-1987. Journal of Great Lakes Research 19(2):379-388 (1993).

An examination of gridded data developed from quality controlled land station temperature data for the 1901-1987 period for the Great Lakes basin reveals temperature trends not previously reported. On an annual basis, from early 1900 through the mid 1950s, a 5-year moving average shows that overall basin temperatures increased. A cooler regime prevailed for the remainder of the period of record. Seasonal 5-year moving averages show that spring temperatures increased throughout the period. Summer temperatures were highly variable, but with an early upward trend through the mid 1940s and a recent downward trend for the remainder of the period. Fall temperatures slowly warmed from the early 1900s until the mid 1960s, but have recently shown a cooling trend. Winter temperatures show an upward trend with intermittent wide swings from the early 1900s through the mid 1950s after which a lower temperature regime has prevailed. Temperature differences between a warm and a cool year and the long term mean show markedly varying patterns.

BOLSENGA, S.J., and H.A. VANDERPLOEG. Estimating photosynthetically available radiation into open and ice-covered freshwater lakes from surface characteristics; a high transmittance case study. Hydrobiologia 243/244:95-104 (1992).

A simple technique, based on several published studies, is presented to estimate photosynthetically available radiation (PAR: 400-700 nm) at the air/water and ice/water interfaces on freshwater lakes. Grand Traverse Bay of Lake Michigan of the Laurentian Great Lakes before, during, and after ice cover is used as a case study. The technique depends on assigning PAR transmittances to air/water or air/ice surfaces from empirically determined relationships. During ice cover, PAR reaching the water column under the ice exceeded 45% of incoming PAR, on the average, due to the amount of clear ice present on the bay.

Breaker, L.C., and A.W. BRATKOVICH. Coastal-ocean processes and their influence on the oil spilled off San Francisco by the M/V Puerto Rican. Marine Environmental Research 36:153-184 (1993).

The oil tanker M/V Puerto Rican exploded on 31 October 1984 and later broke apart to produce a major oil spill in the coastal waters off San Francisco, California, USA. Oil from this spill initially moved to the SSW until 5 November, when it abruptly reversed direction and began moving rapidly to the north and then to the NNW during the following week. The oceanic processes that most likely contributed to the displacement of the oil spilled by the Puerto Rican are examined within the framework of a simple, empirical-hindcasting model. A large-scale flow component, wind drift, and tidal currents are included in the model. Wind drift, inferred by using a simple linear formulation, was the single most important factor in determining the over-all displacement of the oil. Residuals from the model, however, indicate that the winds alone could not fully account for the sudden and dramatic reversal in oil movement that occurred on 5 November 1984. This reversal was surge-like and coincided with an increase in sea level along the central California coast. Finally, the close agreement between the local and advective changes in sea-surface temperature in the Gulf of the Farallones at the time of the Puerto Rican oil spill indicate, although not conclusively, that this reversal could have been related to the onset of the Davidson Current or other larger-scale flow phenomena.

Brown, R.W., W.W. Taylor, and R.A. ASSEL. Factors affecting the recruitment of Lake Whitefish in two areas of Northern Lake Michigan. Journal of Great Lakes Research 19(2):418-428 (1993).

Stock-recruitment and integrated recruitment models incorporating biotic and abiotic factors were developed for lake whitefish populations in northern Green Bay and the North Shore areas of Lake Michigan. Abundance and recruitment indices were calculated for the 1961-1985 year classes based on lake whitefish catch and effort data from the commercial fishery in each area. Previous research indicates that spawning stock abundance, winter ice cover, and spring temperatures are important in determining the egg and larval abundance and survival of lake whitefish. Therefore, spawning stock abundance, ice cover, winter wind velocity, and spring water and air temperature variables were used as model inputs in regression modeling. The biotic/abiotic recruitment model for northern Green Bay hindcasted lake whitefish recruitment as a function of spawning stock abundance and the number of days that ice cover exceeded 40% during egg incubation. This regression model (R2=0.62) demonstrated improved hindcasting ability of historic recruitment when compared to the Beverton-Holt (R2=0.37) or the Ricker (R2=0.33) stock-recruitment models for the 1961-1985 cohorts. The biotic/abiotic recruitment model for the North Shore hindcasted lake whitefish recruitment as a function of average air temperature in May after larval emergence, the number of days that ice concentration exceeded 70% during egg incubation, and spawning stock abundance. The regression model (R2=0.57) also demonstrated improved hindcasting ability of historical recruitment when compared with Beverton-Holt (R2=0.09) or the Ricker (R2=0.13) stock-recruitment models. Results of this study indicate that biotic/abiotic recruitment models were more successful in hindcasting recruitment than solely biologically based stock-recruitment relationships. Consideration of significant abiotic variables will be useful in the management of lake whitefish stocks in the Great Lakes by improving forecasts of recruitment.

Callender, E., and J.A. ROBBINS. Transport and accumulation of radionuclides and stable elements in a Missouri River reservoir. Water Resources Research 29(6):1787-1804 (1993).

Several long sediment cores from the Cheyenne River Embayment of Lake Oahe, a 250-km-long Missouri River reservoir in South Dakota, have been analyzed for radionuclides and stable elements. The combination of fine-scale sampling and rapid sedimentation produces radionuclide distributions that can be used to estimate the detailed chronology of particle transport processes in the Oahe reservoir system. A self-consistent and quantitative treatment of the 137Cs data suggests processes to which characteristic times may be associated. Times that characterize system-wide processes include (1) an integration time of several years reflecting retention of the sediment-bound tracer in regions within or external to the reservoir, (2) a relaxation time of approximately 15 years reflecting a decreasing rate of sediment accumulation ascribed to shoreline stabilization, (3) a time of a few months characterizing the breadth of riverine signatures in cores due to integration effects in the Cheyenne River system and deltaic deposits, and (4) times of a few years associated with propagation of riverine load signatures along the embayment. The distribution of total sedimentary arsenic confirms the validity of the variable sedimentation model. In 1977, a tailings retention facility was built at the Homestake Mine site, and the unrestricted input of As ceased. As a result of this remedial action, the concentration of sedimentary As decreased dramatically. In the upper section of the core, above the depth represented by the year 1976, the concentration of As decreases tenfold. In this same core the distribution of lithologically discriminating chemical elements, calcium and vanadium, relate to major flow events in the Cheyenne River basin. Because there is minimal diagenesis of chemical constituents in these rapidly accumulating sediments, stable element signatures, in addition to radiotracers, may be used to reconstruct hydrologic events in drainage basins that contribute sediment to lakes and reservoirs.

CARRICK, H.J., G.L. FAHNENSTIEL, and W.D. Taylor. Growth and production of planktonic protozoa in Lake Michigan: In situ versus in vitro comparisons and importance to food web dynamics. Limnology and Oceanography 37(6):1221-1235 (1992).

Growth of an entire planktonic protozoan community in Lake Michigan (nanoflagellates, microflagellates, and ciliates) was measured on 10 dates in 1988-1989 in fractionated lake water (<3, <8, <30, and <153 mm) incubated in bottles (in vitro), while in June and July 1989, in vitro growth rate estimates were compared with in situ growth rates derived from the mitotic index. Comparisons of in situ vs. in vitro growth rates for the taxa assayed were similar, indicating that in vitro experiments provide reasonable estimates of protozoan growth, and these rates were similar to those measured from other oligotrophic/mesotrophic habitats. However, containment artifacts in some bottle experiments influenced community growth as some taxa experienced mortality in bottles, thus underscoring the importance of censusing the entire community. Protozoa in Lake Michigan contribute significantly to both heterotrophic and phototrophic carbon pools; phototrophic flagellates represented 24% of primary production, while heterotrophic nanoflagellates and ciliates collectively constituted 40% of bacterial production. The fate of high bacterial production can be accounted for through grazing by both heterotrophic nanoflagellates and ciliates, indicating the trophic importance of protozoa in Lake Michigan.

Chow, K.C.A., D.H. LEE, and D. Fay. Hydrologic impact of regulation scenarios on flood risk levels on the Great Lakes. Proceedings, Stochastic and Statistical Methods in Hydrology and Environmental Engineering. Volume: Environmental Management, Waterloo, Ontario, Canada, June 21-23, 1993. Kluwer Academic Publishers, Dordrecht, The Netherlands, 14 pp. (1993).

As part of the International Joint Commission (IJC) Levels Reference Study, seasonal flood risk levels were developed for selected U.S. and Canadian sites on the shores of the Great Lakes. Flood risk levels were computed through the convolution of frequency distributions which best fit the maximum seasonal monthly static water levels (lake level) for a given regulation scenario and the maximum seasonal historic storm rises (or storm surges) recorded at the site. The Ontario Ministry of Natural Resources computer program HYDSTAT, was used initially for the combined frequency analysis. It was found in HYDSTAT that the selection criteria for the "best-fit" distributions were biased and the refitting procedures were unjustified. The Akaike Information Criterion (AIC) is used to select the "best fit" distribution. At each site, the effect of the proposed regulation schemes on the seasonal flood risk levels are compared with those of the present hydraulic regime.

CLITES, A.H. (Editor). Improved communication of Great Lakes water level information. NOAA Technical Memorandum ERL GLERL-77, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (PB94-156163/XAB) 75 pp. (1993).

This report outlines a strategy for improving the content and communication of Great Lakes water level information. It is hoped that by providing decision-makers with more helpful information, the social and economic disruptions caused by fluctuating lake levels can be mitigated. To define the water level information needs of the decision-makers, an assessment of user needs was conducted by phone-interview. This was not a scientific survey, but an attempt to interview as many informed representatives of different water level information user groups as time allowed. Sixty-five interviews were completed during the fall of 1991. The user needs assessment revealed that unmet needs seem to be concentrated in certain user groups: coastal engineers, emergency government workers, recreational boaters and marina operators, and riparians. Some of the needs expressed included better extreme level statistics, more storm surge information, better access to historical and real-time data, and a more understandable water level bulletin. According to our small sampling, there are many user groups that are satisfied with the water level information they now receive. The water level bulletins prepared monthly by the governments of Canada and the United States proved to be the most widely used decision-making tools. As effective as they are, it was also apparent that, even among frequent users, the bulletins are not completely understood. This suggested strategy for improving the quality and communication of water level information involves (1) developing better extreme level statistical decision-making tools, (2) proposing to the relevant agencies that subtle changes be made to the water level bulletins to increase their understanding, and (3) tailoring existing forecast and statistical information so that users can take better advantage of the wealth of Great Lakes water level information generated by governments. Authors of this report included J. Philip Keillor, Charles F. Southam, Murray Clamen, and Deborah H. Lee.

Coakley, J.P., J.H. Carey, and B.J. EADIE. Specific organic components as tracers of contaminated fine sediment dispersal in Lake Ontario near Toronto. Hydrobiologia 235/236:85-96 (1992).

Bottom sediments around the outfall of the Humber Sewage Treatment Plant (STP), which, with the Humber River, comprises the major contaminant point source emptying into Humber Bay, Lake Ontario, were analyzed for a number of cultural and industrial organic contaminants, including sewage-related compounds such as the faecal sterol coprostanol, a-tocopheryl acetate (a-TA), linear-chain n-alkane hydrocarbons, and carbon and nitrogen isotope ratios of refractory sediment organic matter. The goal was to test these chemical makers as tracers of contaminated fine sediment transport. Although these chemical species are not all conservative (some decompose at fairly rapid rates), they are believed to be good 'natural' tags for fine sediment and should nonetheless exhibit clear dispersal plumes from a presumed source. Their plumes can thus provide an effective way to obtain qualitative, intermediate- and long-term transport pathway indicators for contaminated sediments discharged on a continuing basis. The contoured plots for coprostanol, alpha-tocopheryl acetate, and n-alkane distribution were characterized by high values near the STP outfall, and these tracers were detectable at distances of 1 km or more. Interpretation of the net transport patterns indicates a primary transport toward the south and southwest, with a secondary trend northward, curving eastward. The carbon and nitrogen ratios, while showing a slightly different pattern, served to differentiate STP-source materials from those coming from the river and the open lake. Thus, transport from these sources, sometimes in the opposite direction to that from the main source, were resolved. Systematic variations in the interpreted transport patterns are explained by the presence of different pathways taken by the sediments, i.e. whether bedload or suspended load in a stratified water column.

COTNER, J.B., Jr., and W.S. GARDNER. Heterotrophic bacterial mediation of ammonium and dissolved free amino acid fluxes in the Mississippi River plume. Marine Ecology Progress Series 93:75-87 (1993).

Bacterial nitrogen regeneration processes are an important source of nitrogen in the most productive regions of the Mississippi River plume (Gulf of Mexico). We examined bacterial growth rates, ammonium regeneration rates, and labile dissolved organic carbon/nitrogen fluxes on two cruises in the Mississippi River plume. In summer, surface water bacterial production rates, ammonium regeneration rates, and amino acid turnover rates were higher at intermediate salinities than corresponding rates at the river mouth or in high salinity waters. In winter, surface amino acid turnover rates were highest in the river but growth rates were highest in the plume, and ammonium regeneration rates were similar at all sites. Regeneration rates in the plume were an order of magnitude greater in the summer than in the winter. A significant proportion of the bacterial nitrogen demand may be provided by amino acid fluxes in summer, especially in the plume. Measurements of NH4 regeneration after manipulating bacterial abundances suggest that heterotrophic bacteria contributed a variable proportion (7-50%) of total N-regeneration in summer and that dissolved free amino acids could be a major substrate for ammonium regeneration. Depth profiles, spatial distributions, and seasonal differences in ammonium regeneration rates imply that the fastest regeneration rates occur spatially and temporally where primary production is the greatest.

CROLEY, T.E.II. Climate change impacts on Great Lakes water supplies. Proceedings, Managing Water Resources During Global Change, Reno, NV, November 1-5, 1992. American Water Resources Association, Minneapolis, MN, 241-250 (1992).

The Great Lakes Environmental Research Laboratory (GLERL) and the Canadian Climate Centre (CCC) combined models to estimate net basin supplies for each of the Great Lakes under a changed climate. GLERL used their hydrological models of the 121 watersheds draining into the Great Lakes, over-lake precipitation into each lake, and heat storage in, and evaporation from, each lake. The CCC provided a "present-climate" simulation (1xCO2) and a changed-climate scenario (2xCO2) developed from their atmospheric global circulation model. GLERL used the CCC outputs of air temperature, precipitation, humidity, wind speed, and cloud cover to consider steady-state doubling of atmospheric CO2. They abstracted differences between the 1xCO2 and 2xCO2 atmospheres, made these changes to historical data, and observed the impact of the changed data in the hydrological model outputs. The high air temperatures lead to higher overland evapotranspiration, lower runoff, earlier runoff peaks, reduced snow pack, shortened snow season, and reduction in soil moisture. Water temperatures increase and peak earlier; heat resident in the deep lakes increases throughout the year. Mixing of the water column diminishes and lake evaporation increases. Net basin supplies to each of the Great Lakes drop 20-100 percent.

CROLEY, T.E., II, and D.H. LEE. Evaluation of Great Lakes net basin supply forecasts. Water Resources Bulletin 29(2):267-282 (1993).

Evaluation of the Great Lakes Environmental Research Laboratory's (GLERL's) physically-based monthly net basin supply forecast method reveals component errors and the effects of model improvements for use on the Laurentian Great Lakes. While designed for probabilistic outlooks, it is assessed for giving deterministic outlooks along with other net basin supply forecast methods of the U.S. Army Corps of Engineers and Environment Canada, and with a stochastic approach commissioned by the Corps. The methods are compared to a simple climatological forecast and to actual time series of net basin supplies. Actual net basin supplies are currently determined by estimating all components directly, instead of as water-balance residuals. This is judged more accurate and appropriate for both forecasting and simulation. GLERL's physically-based method forecasts component supplies while the other methods are based on residual supplies. These other methods should be rederived to be based on component supplies. For each of these other methods, differences between their outlooks and residual supplies are used as error estimates for the rederived methods and component supplies. The evaluations are made over a recent period of record high levels followed by a record drought. Net basin supply outlooks are better than climatology, and GLERL's physically-based method performs best with regard to either component or residual net basin supplies. Until advances are made in long-range climate outlooks, deterministic supply outlooks cannot be improved significantly.

Diebel, D., J.F. CAVALETTO, M. Riehl, and W.S. GARDNER. Lipid and lipid class content of the pelagic tunicate Oikopleura vanhoeffeni. Marine Ecology Progress Series 88:297-302 (1992).

Lipid biochemistry of pelagic tunicates is poorly known, despite the fact that the larvae of several flatfish species depend exclusively on oikopleurid appendicularians at time of first feeding. Microgravimetric analysis and thin-layer chromatography with flame ionization detection (TLC-FID) were used to determine the total lipid content and lipid class composition of the pelagic tunicate Oikopleura vanhoeffeni. Our goal was to determine the dominant storage form of lipid in O. vanhoeffeni before and after the spring diatom bloom. Lipid levels and lipid class composition were measured for all 5 ontogenetic stages of O. vanhoeffeni, plus eggs. Levels ranged from 23 to 525 mg ind.-1 over the entire life cycle, increasing exponentially with increasing body size and ontogenetic (i.e. maturity) stage. Regression analyses showed that 84% of the variation in the logarithm of total lipid content was explained by the logarithm of ontogenetic stage. Per unit dry weight, the mean (± SE) lipid concentration was 5 ± 0.3% before the bloom and 7.5 ± 1.2% after the bloom. Lipid class composition provided scant evidence for energy storage by O. vanhoeffeni, with no wax esters before or after the spring bloom and moderate levels of triacylglycerols present in pre-bloom animals only. Individuals collected after the spring bloom were significantly smaller than those from before the bloom, suggesting that a spawning event had occurred sometime during the bloom. Predominant lipid classes before and after the bloom were phospholipids (65 to 90% of total lipid) and acetone-mobile polar lipids (4 to 24%). Thus, although this appendicularian is a suspension feeder inhabiting very cold water, it does not store wax esters as do high-latitude copepods. Rather, O. vanhoeffeni has the lipid characteristics of a gelatinous, opportunistic colonist, i.e. that of an omnivore with the ability to direct ingested food energy into rapid somatic growth or gamete production.

Donelan, M., M. Skafel, H. Graber, P.C. LIU, D.J. SCHWAB, and S. Venkatesh. On the growth rate of wind-generated waves. Atmosphere-Ocean 30(3):457-478 (1992).

A new approach to fetch-limited wave studies is taken in this paper. Using data from five towers arranged along a line from the eastern shore of Lake St. Clair, the differential growth between towers is explored as a function of local wave age. It is argued that this method avoids the usual fetch-limited pitfall of inhomogeneity over long fetches and, in particular, the changes in wind speed downfetch of an abrupt roughness change. It is found that the growth rate decreases uniformly downfetch as the waves approach full development. This differential method leads to a smooth transition from rapidly growing short fetch waves to the asymptotic invariant state of full development. When the variation in wind speed after an abrupt (land to water) roughness change is taken into account, the idea of a universal fetch-limited growth curve is called into question.

DONG, D.Y., A.W. BRATKOVICH, and S.P. Dinnel. Nutrient Enhanced Coastal Ocean Productivity (NECOP) CTD Observations from R/V Longhorn Cruise May 14-21, 1992. NOAA Technical Memorandum ERL GLERL-80, Ann Arbor, MI (PB93-197895/XAB) 109 pp. (1993).

This memorandum describes the hydrographic data set acquired as part of NOAA's Nutrient Enhanced Coastal Ocean Productivity (NECOP) program. The data were collected on a cruise aboard the R/V Longhorn (University of Texas Marine Science Institute) during the period of May 14 to May 21, 1992. The survey spanned a region starting immediately east of the Mississippi River delta and continuing westward to the Texas border.

Fisher, S.W., D.C. GOSSIAUX, K.A. Bruner, and P.F. LANDRUM. Investigations of the toxicokinetics of hydrophobic contaminants in the zebra mussel (Dreissena polymorpha). In Zebra Mussels: Biology, Impacts, and Control, T.F. Nalepa, and D. W. Schloesser (eds.). Lewis Publishers, Chelsea, MI, 465-490 (1993).

Physiological and toxicokinetic parameters for the zebra mussel, Dreissena polymorpha, were examined along with effects of feeding and temperature on selected measurements. Filtration rate for Dreissena was related to the algal concentration and ranged from 352 to 2651 mL/gDW/hr. There was a trend toward higher filtration rates in smaller mussels but the trend was insignificant. Oxygen consumption was inversely proportional to mussel size and directly proportional to temperature. Oxygen consumption ranged from 6.9 mgO2/gDW/day at 4oC to 60.8 mgO2gDW/day at 23oC. Uptake clearance rates for contaminants from water exhibited similar relationships with temperature and mussel size and an additional direct proportionality with the lipophilicity of contaminants as represented by log Kow. At 20oC, mean uptake clearances ranged from 428 to 1073 mL/gDW/hr across a range of compounds with log Kow values of 5.2-6.7. Efficiency for oxygen accumulation was much lower than that for contaminants, while filtration rate for a wide range of particle sizes was similar to uptake clearances for contaminants. Thus, it appears that high filtration rates are not a result of oxygen requirements but rather food requirements, and thus dissolved contaminants are effectively accumulated. Elimination of contaminants was relatively slow with half-lives ranging from 41 to 173 hr for the range of contaminants studied. The presence of food complicates contaminant accumulation by sorbing contaminants and reducing their availability on a whole-water concentration basis while also increasing rates of contaminant elimination. Overall, high filtration rates, relatively high bioconcentration potential, and high fecundity of zebra mussels will probably affect cycling of contaminants in the Great Lakes.

Fisher, S.W., M.J. LYDY, J. Barger, and P.F. LANDRUM. Quantitative structure-activity relationships for predicting the toxicity of pesticides in aquatic systems with sediment. Environmental Toxicology and Chemistry 12:1307-1318 (1993).

The toxicity of a series of organophosphorus (OP) and carbamate insecticides was measured against the midge Chironomus riparius in aquatic systems with and without sediment. Five molecular descriptors (molecular volume, Henry's law constant, n-octanol/water partition coefficient (Kow), molecular connectivity, and linear solvation energy) were used in regression analysis as potential predictors of insecticidal activity. The regressions were conducted for each descriptor against toxicity values for the series of chemicals. Molecular volume and Henry's law constant showed no relationship with toxicity. However, log Kow was moderately successful in describing the effect of sediment on toxicity (r2 - 0.508). Prediction of toxicity was substantially improved when a linear solvation energy (LSE) or molecular connectivity (MC) model was used in regressions. In multiple regressions conducted on carbamates and OPs separately, use of MC or LSE parameters explained up to 95.8% of the variability in toxicity. Based on the results of regressions analyses, sorptive interactions between these insecticides and sediment apparently dominate the processes affecting the toxicity of these compounds when sediment is present. In the absence of sediment, the regressions suggest that the molecular structure of the insecticides is more important than solubility or partitioning for determining toxicity.

FITZGERALD, S.A., and W.S. GARDNER. An algal carbon budget for pelagic/benthic coupling in Lake Michigan. Limnology and Oceanography 38(3):547-560 (1993).

A budget for algal carbon was constructed to quantify the magnitude and major pathways of pelagic-benthic coupling at a site in southeastern Lake Michigan. The flux of algal C to the benthos and the rate of carbon burial were estimated from sediment traps and dated sediment cores, respectively. Assimilation and respiration rates of Diporeia sp., an abundant benthic amphipod, and of sediment microheterotrophs were measured in a microcosm study with 14C-labeled algae (Melosira italica). Melosira (italica and islandica) accounted for 53% of the algal C flux to the sediments. Radionuclide concentrations indicated no net sediment burial of organic C. Of the total C assimilated by Diporeia, 60% was respired, 35% was incorporated into biomass, and 5% was accounted for as soluble dissolved organic compounds. The areal rate of Diporeia respiration (29 nmol C cm-2 d-1) was 23 times greater than that for sediment bacteria (1.3 nmol C cm-2 d-1). Release of radioisotope in the form of dissolved organic compounds was much lower than that incorporated and respired for both Diporeia and sediment bacteria. Of the 61 mmol C m-2 algal C estimated to be deposited during the spring bloom, Diporeia assimilation accounted for 61%, significantly more than the 2% observed for microbially mediated algal decomposition. These observations support the hypothesis of a strong pelagic-benthic energy coupling between the spring diatom bloom and Diporeia in Lake Michigan.

GARDNER, W.S., J.B. COTNER, and L.R. HERCHE. Chromatographic measurement of nitrogen mineralization rates in marine coastal waters with 15N. Marine Ecology Progress Series 93:65-73 (1993).

Isotope ratios for ammonium were determined directly on seawater filtrates by high performance liquid chromatography (HPLC) for isotope dilution and enrichment experiments in the Mississippi River plume region of the Gulf of Mexico. The two isotopic forms could be differentiated by cation exchange chromatography because the ratio of 15NH4+:15 NH3 is slightly greater than the ratio of 14NH4+:14NH3 in aqueous solutions at pH's near the pK for ammonium (ca pH 9). Relatively small (e.g. 60 ml) water samples were fortified in the field with 15N-ammonium or 15N-amino acids and incubated at simulated in situ temperature and light conditions. At 2 to 13 h intervals, subsamples were filtered (0.2 mm pore size) and frozen for later HPLC analysis in the laboratory. Isotope-dilution experiments conducted on water samples collected from different depths in the plume indicated that maximum ammonium regeneration rates occurred in near-surface waters where phytoplankton and bacterial production rates are relatively high. Amino acid and ammonium concentration changes and 15N-NH4 compositonal changes were measured at 4 intervals over 21 h after the addition of an 15N-labeled amino acid mixture (4 µ). Comparison of the amount of 15N recovered at 15NH4 to that removed from solution as 15N-labeled amino acids indicated that the potential conversion of 'assimilated' 15N-labeled amino acids to dissolved ammonium ranged from about 50% in surface water to about 90% in near-bottom (30 m depth) water. These results demonstrate the usefulness of the HPLC approach for measuring nitrogen regeneration rates or conversion efficiencies in small volumes of marine coastal waters.

GOSSIAUX, D.C., P.F. LANDRUM, and V.N. Tsymbal. A survey of Saginaw River and Saginaw Bay, Lake Huron sediments using two bioassays with the amphipod Diporeia spp. Journal of Great Lakes Research 19(2):322-332 (1993).

The Saginaw River and Saginaw Bay ecosystem is identified as an Area of Concern by the International Joint Commission for recognized anthropogenic contamination, which includes sediments. The potential impact of sediment-associated contamination of Saginaw Bay and Saginaw River was evaluated by employing two solid phase bioassays with the amphipod Diporeia spp. (formerly named Pontoporeia hoyi). Two effects examined in the bioassays were mortality after 28 d and avoidance/preference for the sediments after 5 d. Saginaw Bay Station S-61, located off the coast of Tawas Bay, was the only location where bay sediment elicited significant mortality. Although sediment preference tended to increase from the inner bay to the outer bay with S-61 the most preferred, there were no statistical differences among stations. River sediments from all stations collected in December 1989 produced significant mortality, with sediments from Station SR-106, just below the Bay City Waste Water Treatment Plant outfall, producing the greatest response. Sediments from SR-106 were also the most avoided of the river sediments from this first collection. A subsequent collection of sediments in June 1990 from the Saginaw River produced no mortality and no significant avoidance of the sediments. The results from these two bioassay methods suggest the presence of potential contaminant problems in both the bay and river, and indicate that both lethal and sublethal effects may occur.

GOSSIAUX, D.C., P.F. LANDRUM, and V.N. Tsymbal. Response of the amphipod Diporeia sp. to various stressors: cadmium, salinity, and temperature. Journal of Great Lakes Research 18(3):364-371 (1992).

The tolerance of the amphipod Diporeia spp. (formerly Pontoporeia hoyi) to salinity and temperature and the acute toxicity of cadmium were determined by laboratory tests. No mortality occurred during 28 d exposure at a salinity of 20 g sea salt L-1. Slower swimming and mortality occurred when the salinity was increased to 25 g sea salt L-1. In fresh water, Diporeia tolerate a temperature of 26oC but exhibit 82% mortality within 24 h at 28oC. Thus, Diporeia collected from southern Lake Michigan demonstrate a significant salinity and thermal tolerance. Sensitivity to cadmium depends on both the temperature and the salinity of the exposure solution. At 4oC in fresh water, the 96 h LC50 for Cd, administered as CdCl2, was 0.78 mg CdL-1 (95% C.I. 0.40-1.02 mg CdL-1). At 15oC, it decreased to 0.065 mg CdL-1 (95% C.I. 0.051-0.074 mg CdL-1). In salt water, the tolerance to Cd at 4oC [96 h LC50 of 49.4 mg CdL-1 (95% C.I. 45.3-52.7 mg CdL-1)] was much greater than in fresh water and decreased with increasing temperature, 96 h LC50 of 6.02 mg CdL-1 (95% C.I 6.02-7.32 mg CdL-1) at15oC. Overall sensitivity to cadmium increases with increasing temperature and decreases with increasing salinity within the salinity tolerance of the organism. Diporeia are important Great Lakes benthos exposed to a wide range of contaminants. While Diporeia's sensitivity to contaminants has been implied, this work provides supportive data on the sensitivity of Diporeia to selected stressors.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Directory. C.M. Darnell (ed.). Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 42 pp. (1992).

No abstract.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. FY 1992 Yearly Report. C.M. Darnell and S.J. Bolsenga (eds.). Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 68 pp. (1993).

No abstract.

HARKEY, G.A., and S.J. Klaine. Bioconcentration of trans-chlordane by the midge, Chironomus decorus. Chemosphere 24(12):1911-1919 (1992).

The accumulation and transport of the organochlorine pesticide, trans-chlordane, by the midge, Chironomus decorus was examined in a whole life cycle laboratory exposure assay. Larvae were kept in dosed water exposures including food particles from egg stages through adult metamorphosis and were sampled for weight gain and chemical content over the course of the 50 day study. Accumulation of trans-chlordane was related to the amount of contaminant in the larval environment. Concentration of trans-chlordane (ng contaminant/g tissue) in larvae was not significantly different from second through fourth instar states but depended upon the weight of the larvae. Differences in time to metamorphosis, weight gain, and sex ratios occurred among all replicate exposures, including controls, suggesting nongenetic maternal differences, rather than environmental variation caused by chemical exposure. When the larvae metamorphosed, an average of 82.6% of the contaminant was retained in the adults while 11.4% was left behind in the shed exuviae. This study suggests that terrestrial predators feeding on emerging aquatic insects can be exposed to organic pesticides from aquatic environments.

HAWLEY, N., and B.M. Lesht. Sediment resuspension in Lake St. Clair. Limnology and Oceanography 37(8):1720-1737 (1992).

Time-series measurements of water transparency, wave conditions, and current speed were made at several different sites in Lake St. Clair during five different 1-month periods in 1985 and 1986. Observed changes in suspended sediment concentration were modeled with a simple zero-dimensional, spatially averaged, mass balance model in which local bottom erosion was expressed as a linear function of the bottom shear stress. Estimates of the three parameters required by the model (particle settling velocity, resuspension concentration, and background suspended material concentration) are reasonably consistent for the various data sets, suggesting that the properties of the lake bottom do not change significantly through either space or time. The modeled settling velocities agree with the observed suspended particle size data and the erosion rates are comparable to laboratory results for freshwater sediments. The results show that a simple mass flux model can be used to model local sediment resuspension events in Lake St. Clair with reasonable accuracy.

HAWLEY, N., and J. NIESTER. Measurement of horizontal sediment flux in Green Bay, May-October, 1989. Journal of Great Lakes Research 19(2):368-378 (1993).

Time series measurements of water transparency were made at stations located in the passages on either side of Chambers Island from May through October, 1989. These data were combined with the current measurements of Miller and Saylor (1993) to determine the sediment transport into and out of southern Green Bay. The data show that the sediment flux past Chambers Island is driven primarily by the non-tidal circulation in the two channels; both tidal and storm effects are of secondary importance. The cumulative sediment flux is southward through the western channel and northward in the eastern channel with a small net transport of sediment into the southern bay. Since the sediment load from tributaries to the bay is much greater than the transport in the channels, this excess sediment must be stored in the southern bay.

Hill, C., M.A. QUIGLEY, J.F. CAVALETTO, and W.M. GORDON. Seasonal changes in lipid content and composition in the benthic amphipods Monoporeia affinis and Pontoporeia femorata. Limnology and Oceanography 37(6):1280-1289 (1992).

Seasonal variation in lipid content and composition was studied in deposit-feeding amphipods from a Baltic archipelago. In Monoporeia affinis, which is more active and has a higher respiration rate, lipid levels were low in winter and early spring, rose to 27% of the dry mass in late summer, then declined in autumn. In Pontoporeia femorata, which regulates its oxygen consumption, lipid levels were 20-23% of the dry mass. In October, maturing male P. femorata had a significantly lower lipid content than females. Triacylglycerol and phospholipid accounted for ~90% of lipids. Phospholipid dominated in M. affinis in March, but triacylglycerol accumulated and became the main lipid after the spring bloom. Triacylglycerol was always the main lipid in P. femorata, but also accumulated after the spring diatom bloom. Both species seem to assimilate and store food resources from the diatom bloom. The higher feeding rate of M. affinis may explain its greater accumulation of lipid. Lower metabolic costs in P. femorata may allow it to maintain steady lipid levels for most of the year.

LANDRUM, P.F., T.D. FONTAINE, B.J. EADIE, and G.A. LANG. Modeling the accumulation of polycyclic aromatic hydrocarbons by the amphipod Diporeia (spp.). In Chemical Dynamics in Fresh Water Ecosystems, F.A.P.C. Gobas, and J. A. McCorquodale (eds.). Lewis Publishers, Boca Raton, FL, 111-128 (1992).

No abstract.

LANDRUM, P.F., H. Lee, and M.J. LYDY. Toxicokinetics in aquatic systems: Model comparisons and use in hazard assessment. Environmental Toxicology and Chemistry 11:1709-1725 (1992).

Toxicokinetic models are not constrained by assumptions of equilibrium as are thermodynamic (equilibrium-partitioning) models and are more accurate predictors of toxicant accumulation for non-steady-state exposures and multiple uptake routes. Toxicokinetic modelscompartment-based models, physiological-based models, and energetics-based modelsare reviewed and the different mathematical formalisms compared. Additionally, the residue-based toxicity approach is reviewed. Coupling toxicokinetic models with tissue concentrations at which toxicity occurs offers a direct link between exposure and hazard. Basing hazard on tissue rather than environmental concentrations avoids the errors associated with accommodating multiple sources, pulsed exposures, and non-steady-state accumulation.

LEE, D.H. (Editor). Great Lakes water level statistical techniques. NOAA Technical Memorandum ERL GLERL-78, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (PB94-157443/XAB) 63 pp. (1993).

Every day, important decisions are made regarding activities affected by variations in water levels and flows on the Great Lakes. These involve large-scale issues, such as lake level control or land-use regulation, as well as local issues, such as siting and design of structures and protective works. Such decisions can and should make use of statistical models that quantify the variability of levels and flows. To date, the only widespread applications of statistical models have been to estimate the probability distributions of high lake levels for use in shoreline zoning and of waves for use in the design of shoreline facilities and protective works. New statistical models of Great Lakes levels should be able to correctly account for serial correlation in hydrologic levels, provide estimates of the marginal and joint distribution of hydrologic levels and storm surge, provide estimates of the joint distribution of various wave parameters and storm surge, and be readily applied to specific coastal locations. The alternative modeling strategies explored address some of the deficiencies of existing models. To improve Great Lakes water level statistics, a comprehensive, coherent, and unified strategy for modeling Great Lakes hydrology is required. Key elements of such a strategy include user community accessibility, linkage between deterministic and stochastic elements, and validity over a wide range of temporal and spatial scales. With the development of improved hydrologic models, statistics that reflect the level of model sophistication would be derived. These statistics would be conditioned on present levels and existing climate regimes, and incorporate the concept of planning horizon, correctly compute the joint probability of the combined effects of mean levels, surges, and waves, and correct for physical trends such as crustal movement.

LEE, D.H. (Editor). Basis of comparison, Great Lakes-St. Lawrence River system. NOAA Technical Memorandum ERL GLERL-79, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (PB93-197978/XAB) 119 pp. (1993).

A 90-year set of lake levels and flows has been developed that reflects a consistent hydraulic regime in the Great Lakes-St. Lawrence River system. This hydraulic regime is defined by the diversion rates into and out of the system, consumptive use withdrawals from the system, the time series of water supplies to the system, outlet conditions of each lake, flow retardation due to ice or weeds in the connecting channels, initial starting elevations for the simulation, the hydraulic condition of the St. Lawrence River, and tidal levels at its outlet. These levels and flows can be used as a reference for assessing the effects of modified lake regulation and climate change.

LEE, D.H. (Editor). Climate, Climate Change, Water Level Forecasting, and Frequency Analysis. Main Report and Volumes 1-4, Task Group 2, Working Committee 3, International Joint Commission Levels Reference Study (Phase II), International Joint Commission, Ann Arbor, MI, 211 pp. (1993).

No abstract.

LEE, D.H., and F.H. QUINN. Climate change impacts on Great Lakes levels and flows. Proceedings, Managing Water Resources During Global Change, Reno, NV, November 1-5, 1992. American Water Resources Association, 387-396 (1992).

The availability of adequate fresh water supplies is potentially one of the United States most serious long-range problems. The U.S.-Canada International Joint Commission is studying the impact of changing climate on the water levels of the Laurentian Great Lakes. As part of this, the Great Lakes Environmental Research Laboratory and the Canadian Climate Centre combined global circulation model output with hydrological models. This enables them to estimate changes in the net basin water supplies to the Great Lakes under a double-CO2 scenario. GLERL ran these net basin supplies through a hydrologic response (routing) model of the unregulated lakes and used modified regulation plans for Lakes Superior and Ontario to determine resulting changes in lake levels and flows. The anticipated 20 to 100 percent decrease in individual lake net basin supplies substantially lowers water levels by 0.5 to 2 meters. The lower lake levels accompany significant decreases in flows of the connecting channels and St. Lawrence River. These results would have major environmental and socioeconomic implications and would require a change in the present water management strategies for the Great Lakes. The change in levels and flows is also compared with extreme scenarios based upon the present climate to put the results into perspective.

LESHKEVICH, G.A., D.J. SCHWAB, and G.C. MUHR. NOAA's CoastWatch: Satellite Environmental Monitoring of the Great Lakes. Proceedings, First Thematic Conference on Remote Sensing for Marine and Coastal Environments, New Orleans, LA, June 15-17, 1992. American Society for Photogrammetry and Remote Sensing, 575-588 (1992).<

To address critical coastal environmental problems, the National Oceanic and Atmospheric Administration (NOAA) has established the Coastal Ocean Program. Within that program, CoastWatch is designed to provide a rapid supply of up-to-date, coordinated, environmental information, including remotely sensed data, to support Federal and state decision makers and researchers who are responsible for managing the Nation's living marine resources and ecosystems. This Paper describes the NOAA CoastWatch program for the Great Lakes. The initial products of the CoastWatch program, a set of surface water temperature images, are routinely derived from NOAA AVHRR (Advanced Very High Resolution Radiometer) satellite data and made available within hours of acquisition. Preliminary analysis has shown excellent correlation of satellite-derived temperatures with in situ water temperature measurements from mid-lake weather buoys. Other products including turbidity, ocean color, and ice mapping are planned. Components of the CoastWatch system including a wide area communications system, on-line product data bases, an electronically-accessible product archive, and PC software for display and analysis of the satellite imagery are also described.

LESHKEVICH, G.A., D.J. SCHWAB, and G.C. MUHR. Satellite environmental monitoring of the Great Lakes: A review of NOAA's Great Lakes CoastWatch program. Photogrammetric Engineering and Remote Sensing 59(3):371-379 (1993).

To address critical coastal environmental problems, the National Oceanic and Atmospheric Administration (NOAA) has established the Coastal Ocean Program. Within that program, CoastWatch is designed to provide a rapid supply of up-to-date, coordinated, environmental information, including remotely sensed data, to support Federal and state decision makers and researchers who are responsible for managing the Nations living marine resources and ecosystems. This paper describes the NOAA CoastWatch program for the Great Lakes. The initial products of the CoastWatch program, a set of surface water temperature images, are routinely derived from NOAA AVHRR (Advanced Very High Resolution Radiometer) satellite data and made available within hours of acquisition. Preliminary analysis has shown excellent correlation of satellite-derived temperatures with in situ water temperature measurements from mid-lake weather buoys. Other products including turbidity, ocean color, and ice mapping are planned. Components of the CoastWatch system including a wide area communications system, on-line product data bases, an electronically-accessible product archive, and PC software for display and analysis of the satellite imagery are also described.

LYDY, M.J., and P.F. LANDRUM. Assimilation efficiency for sediment sorbed benzo(a)pyrene by Diporeia spp. Aquatic Toxicology 26:209-224 (1993).

Two methods are currently available for determining contaminant assimilation efficiencies (AE) from ingested material in benthic invertebrates. These methods were compared using the Great Lakes amphipod Diporeia spp. and [14C]benzo(a)pyrene (BaP) sorbed to Florissant sediment (<63 mm). The first approach, the direct measurement method, uses total organic carbon as a tracer and yielded AE values ranging from 45.9-60.4%. The second approach, the dual-labeled method, uses 51Cr as a non-assimilated tracer and did not yield AE values for our data. The inability of the dual-labeled approach to estimate AEs was due, in part, to the selective feeding by Diporeia resulting in a failure of the non-assimilated tracer (51Cr) to track with the assimilated tracer ([14C]BaP). The failure of the dual labeled approach was not a result of an uneven distribution of the labels among particle size classes, but more likely resulted from differential sorption of the two isotopically labeled materials to particles of differing composition. The [14C]BaP apparently sorbs to organic particles that are selectively ingested, while the 51Cr apparently sorbs to particles which are selectively excluded by Diporeia. The dual-labeled approach would be a viable and easier experimental approach for determining AE values if the characteristics that govern selective feeding can be determined.

McNaught, D.C. Commentary. IAGLR: Who are we today and how did we evolve? Journal of Great Lakes Research 19(1):183-193 (1993).

No abstract.

Merritt, R.W., D.A. Craig, E.D. Walker, H.A. VANDERPLOEG, and R.S. Wotton. Interfacial feeding behavior and particle flow patterns of Anopheles quandrimaculatus larvae (Dipteria: Culicidae). Journal of Insect Behavior 5(6):741-761 (1992).

The interfacial feeding behavior, mouthpart movements, and particle flow patterns of Anopheles quadrimaculatus larvae were investigated, using videotape recordings, high-speed microcinematography, SEM, and laboratory experiments. While positioned at the water surface, larvae demonstrated 12 behaviors associated with movements of the head. In one of these, a larva rotated its head 180o and directed its mouthparts against the air-water interface. The larva rapidly extended and retracted its lateral palatal brushes (LPBs) at a rate of 5 cycles/s (5 Hz), creating currents and allowing for the collection of particles. Particles moved toward the head at a velocity of 4.31 mm/s, in discrete stops and starts, as the LPBs beat. Our analyses determined that particle movement toward the mouth was governed by the very low Reynolds numbers (0.002-0.009). This finding indicated that viscous forces predominated in Anopheles feeding and no inertial movement of particles occurred. According to this model, the LPBs cannot intercept particles directly, but function as paddles for particle entrainment. We did not observe the pharynx to function in particle filtration but, rather, in food bolus formation. We propose that the maxillary pilose area and midpalatal brush function as interception structures. It appeared that the LPBs do not break the surface film to feed, but collect particles from the surface microlayers. A plume of uningested particles emerged from the sides of the cibarium and descended into the water column. The plume consisted of alternately clear and dark, lenticular laminae formed beneath the larval head during the collecting-filtering feeding mode. A comparison of particle sizes from surface microlayers and gut contents of fourth instars showed that larvae ingested mainly small particles in the range of 1.5 to 4.5 um in diameter. The potential significance of interfacial feeding by anopheline larvae in their aquatic environment is discussed.

Meyers, P.A., and B.J. EADIE. Sources, degradation, and resynthesis of organic matter associated with sinking particles in Lake Michigan. Organic Geochemistry 20(1):47-56 (1993).

Sediment trap material collected at five depths from two locations in Lake Michigan has been studied to determine the sources of particulate organic matter and the early diagenetic changes which occur during sinking of particles. Aquatic material dominates in shallower depths whereas land-derived material is more important in near-bottom depths. Organic carbon concentrations decrease with depth as a result of remineralization of organic matter by microbial activity and dilution by resuspended bottom sediments. Preferential remineralization of algal organic matter and downslope transport of particulate matter from coastal areas create differences in the lipid biomarker characteristics of settling particles found at different depths in the water column. Calculations of apparent decomposition rate constants from lipid distributions at different depths show that shorter chainlength n-alkanoic acids are degraded faster than longer components. Carbon and nitrogen isotopic compositions of total organic matter are nearly unaffected by large-scale amounts of remineralization during sinking.

MILLER, G.S., and J.H. SAYLOR. Low-frequency water volume transport through the midsection of Green Bay, Lake Michigan, calculated from current and temperature observations. Journal of Great Lakes Research 19(2):361-367 (1993).

Moorings with current meters and temperature recorders were deployed along a mid-bay transect on either side of Chambers Island in Green Bay from September 1988 to October 1989. Daily transport estimates calculated from the current, temperature, and wind data, show temporal and spatial variability. Net summer transport during stratification west of Chambers Island was out of the lower bay (350 m3s-1) in the epilimnion, into the lower bay (900 m3s-1) in the hypolimnion, and out of the lower bay (320 m3s-1) through the passage east of the island. The residence time for the lower bay is reduced to less than 1 year using the above transport compared to a water balance estimate of over 3 years. During the mid-September to May isothermal period, a horizontal transport gradient existed. Under the solid ice cover of winter, transport variability was significantly reduced and was uniformly out of the lower bay (500 m3s-1). Fluctuations in daily transport were often large (up to 2x104 m3s-1). The temporal and spatial variability of the water volume transport suggests that material mass fluxes between lower and upper Green Bay will be similarly dependent.

MOLL, R.A., A.W. BRATKOVICH, W.Y.B. Chang, and P. Pu. Physical, chemical, and biological conditions associated with the Lake Michigan vernal thermal front. Estuaries 16(1):92-103 (1993).

An investigation of the thermal front in southeastern Lake Michigan during April 1988 revealed a dynamic physical, chemical, and biological environment. The front was observed approximately 4 km from the coast as a distinct gradient separating cold open-lake waters from warmer nearshore waters. Surface isotherms near the front were generally parallel to one another but skewed with respect to shore. Comparison between April 22 and 29 showed that the surface isotherm pattern was modulated by wind stress. The pattern from April 29 showed signs of flow instabilities with horizontal scales of 1 km to 5 km. Surface drifter trajectories provided estimates of horizontal convergence at the front which varied from 7 x 10-6 s-1 to 20 x 10-6 s-1. Inferred rates of downwelling, which ranged from 9.5 m d-1 to 20.7 m d-1, were sufficient to move a water parcel from the surface to the bottom in 2 d to 6 d at the front. Convergent circulation was observed on both sampling dates despite contrasts in windstress. Concentrations of chloride, soluble silica, and chlorophyll, which were always higher inshore, were 5% to 82% larger than offshore mean values. The aquatic environment just inshore of the thermal front was characterized by chlorophyll concentrations which exceeded 5.0 mg l-1 while concentrations offshore were between 1.0 mg l-1 and 2.0 mg l-1. A relatively uniform vertical structure in chlorophyll concentrations in the frontal zone was consistent with the observed convergence and inferred downwelling near the front.

MOLL, R.A., T.H. JOHENGEN, A.W. BRATKOVICH, J.H. SAYLOR, G. Meadows, L. Meadows, and G.L. PERNIE. Vernal thermal fronts in large lakes: A case study from Lake Michigan. Verhandlugen Internationale Vereinigung Fur Theoretische und Angewandte Limnologie 25:65-68 (1993).

Many temperate large lakes of the world undergo a transition in the spring from fully mixed winter conditions to thermally stratified summer conditions (Rodgers, 1966; Tikhomirov, 1963). That transition often includes the formation of a well-defined front characterized by a nearly vertical, shore-parallel 4oC isotherm (Saylor et al., 1981). This front, which is maintained by a convergent secondary circulation and accompanied by geostrophic currents, induces a significant redistribution of heat and other properties in the coastal waters (Bennett, 1971; Rousar, 1973). Many vernal thermal fronts are characterized by large chemical and biological gradients (Scavia and Bennett, 1980). The current state of knowledge of vernal thermal fronts in large lakes is largely based on theoretical studies that are relatively unconfirmed by field observations. Given this state of knowledge, our study group elected to begin a multidisciplinary, multiyear study of vernal thermal fronts in southeastern Lake Michigan. The point of departure for this study was the theoretical framework of water circulation in the vicinity of vernal fronts developed by Huang (1969; 1972) and Mortimer (1974; 1988). The purpose of this paper is to provide an overview of the results from five field seasons of study (1988 to 1992) of the Lake Michigan vernal thermal front.

**NALEPA, T.F., and D.W. Schlosser. Zebra Mussels: Biology, Impacts, and Control. Lewis Publishers, Chelsea, MI, 810 pp. (1992).

No abstract.

NORTON, D.C., S.J. BOLSENGA, and M. Badarch. Snowdepth mapping in Mongolia. Proceedings, 50th Eastern Snow Conference, M. Ferrick, and T. Pangburn (eds.), Quebec City, Quebec, June 8-10, 1993. Hydro Quebec, Montreal, Quebec, 381-387 (1993).

The Great Lakes Environmental Research Laboratory (GLERL) has a cooperative program with Mongolian scientists to produce snow depth maps for that country. Snow depth data has been provided to GLERL. A raster data set was compiled from these data and preliminary maps produced. Since all stations are currently located inside the country in valleys, the snow depths are not correctly projected across the country's borders or over mountains. This progress report presents the preliminary maps and outlines the future course of the project. Information on locale, climate, people, customs, and problems with the study is also included.

QUIGLEY, M.A., W.S. GARDNER, and W.M. GORDON. Metabolism of the zebra mussel (Dreissena polymorpha) in Lake St. Clair of the Great Lakes. In Zebra Mussels: Biology, Impacts, and Control, T.F. Nalepa, and D. W. Schloesser (eds.). Lewis Publishers, Chelsea, MI, 295-306 (1993).

Laboratory measurements of oxygen consumption and nitrogen (ammonia) excretion rates of zebra mussels, Dreissena polymorpha, were obtained from mussels collected at a 5-m site in southwest Lake St. Clair, April to November 1990. Metabolic activity varied widely between spring and fall. Oxygen to nitrogen ratios approached a value of 50 in spring, declined to a minimum of 16 in summer, and increased moderately in fall. The low O:N ratios observed in summer suggest that higher metabolic rates associated with high temperatures and lower supplies of nutritionally rich food may have a negative impact on the condition of Lake St. Clair mussel populations during summer months. Over this interval, mussel populations may be more vulnerable to eradication measures than in spring and fall, and future control strategies might prove more effective if treatment is timed to coincide with such periods of heightened vulnerability.

ROBBINS, J.A., and L.R. HERCHE. Thirty years of 210Pb dating: successes and problems. Proceedings, Ninth International Conference on Heavy Metals in the Environment, R.J. Allan, and J. O. Nriagu (eds.), Toronto, Ontario, Canada, September 1993. CEP Consultants, Ltd., Great Britain, 202 (1993).

Establishment of a sediment chronology is central to the task of developing historical records of marine and lacustrine heavy metal contamination and modeling diagenetic processes. 210Pb dating, introduced by Goldberg (ref. 1) thirty years ago, is now a method of choice for determining recent sediment ages (<100 years). Today over 2000 published papers have dealt with 210Pb in sediments. But contradictions lie in the method: it is best suited to reconstructing historical records over the period when human impacts may render interpretation of 210Pb profiles problematic; geochronological information originates from the vicinity of the sediment-water interface where diagenetic and redistributive processes are often active; the technique is most urgently needed in circumstances where accurate stratigraphic methods (e.g. varve counting) are ruled out for reasons which may apply to radio-lead as well. If these were not sufficient reasons to approach 210Pb dating with care, additional problems have arisen from inclinations of researchers themselves. Often 210Pb provides the basis for a story, but is not the story itself. Sometimes as a result, insufficient attention has been given to the interpretation and evaluation of 210Pb data. In extreme cases, age-depth relations have been published without reference to primary data at all. Moreover, since the assignment of dates to sediment layers is achievable with minimal computational skill, some researchers have paid little attention to the development of mathematical models. Unfortunately good dates depend on good models (ref. 2). Valid system-specific models may have to include such processes as atmospheric and catchment transport of 210Pb, biological and chemical mediation in the water column, partitioning of the radionuclide to particles, variable deposition processes, focusing effects, post-depositional mobility of lead, mass wasting, biological mixing, and particle sorting. Accurate chronological inferences require mindfulness of the whole system. The quest for mathematical simplicity has led to the improper use of point transformations (ref. 3), to establish age-depth relations. Unlike models, transforms do not yield predicted profiles which may be compared with measurement and carry no intrinsic test of their validity. Absurdities, resulting from misapplication of CRS (and other) transforms to 210Pb data and inappropriate choices of process models, are abundantly illustrated in the literature.

SCHWAB, D.J. Hydrodynamic modeling in the Great Lakes from 1950 to 1990 and prospects for the 1990's. In Chemical Dynamics in Fresh Water Ecosystems, F.A.P.C. Gobas and J.A. McCorquodale (eds.). Lewis Publishers, Boca Raton, FL, 41-62 (1992).

No abstract.

SCHWAB, D.J., G.A. LESHKEVICH, and G.C. MUHR. Satellite measurements of surface water temperature in the Great Lakes: Great Lakes CoastWatch. Journal of Great Lakes Research 18(2):247-258 (1992).

This paper describes the NOAA CoastWatch program for the Great Lakes and discusses the applications and limitations of satellite-measured surface water temperature images received as a result of this program in mapping and analyzing physical features of the Great Lakes environment. The initial product of the CoastWatch program is a set of surface water temperature images derived from NOAA AVHRR (Advanced Very High Resolution Radiometer) data. These temperature maps are produced on a routine basis (usually 2-3 sufficiently cloud-free images per week) and are made available within hours of acquisition. The satellite-derived water temperatures from images acquired during the period May 1990 to May 1991 were compared to temperatures measured at NOAA weather buoys and found to be highly correlated. We found the satellite-derived temperatures were consistently 1-1.5oC cooler than buoy temperatures. Root mean square deviations between buoy and satellite temperatures ranged from 0.8 to 1.6oC. There was also a consistent pattern to the geographic registration errors of the images, ranging from 8.4 km westward for the NOAA 10 nighttime pass to 8.3 km northeast for the NOAA 11 nighttime pass. Potential application of the imagery to detection and location of thermal fronts, analysis of circulation patterns, and ice and snow mapping are also discussed.

Smith, R.E.H., J.F. CAVALETTO, B.J. EADIE, and W.S. GARDNER. Growth and lipid composition of high Arctic ice algae during the spring bloom at Resolute, Northwest-Territories, Canada. Marine Ecology Progress Series 91:1 (1993).

The concentration and composition of particulate organic matter, with special reference to lipids, was measured throughout the spring bloom of bottom ice algae in 1989 at a site in the Canadian high arctic. By comparing areas of differing snow cover, and thus, light history, we showed that light was initially limiting to algal production. Where snow cover was relatively thin (0 to 5 cm), light apparently ceased to be limiting to biomass accumulation in the ice as the bloom neared its peak. Compositional regions, such as C:chlorophyll a and C:N, were consistent with a physiological response of the algae to light-sufficient and, possibly, nutrient-limited conditions following the peak of the bloom. the transition from early to late bloom conditions was accompanied by a shift in lipid composition, from a predominance of polar lipids (glycolipids and phospholipids) and pigments to a predominance of neutral lipids (triacylglycerols and free fatty acids). Neutral lipids varied directly, as a proportion of total lipid, with the light available to the algae under the different snow covers. Similar changes of lipid composition were only partially reproduced in a short-term (approx. 2 weeks) manipulation of light availability to the natural communities, however, indicating that factors other than the immediate availability of light were important to lipid synthesis by the ice algae.

VANDERPLOEG, H.A., S.J. BOLSENGA, G.L. FAHNENSTIEL, J.R. LIEBIG, and W.S. GARDNER. Plankton ecology in an ice-covered bay of Lake Michigan: utilization of a winter phytoplankton bloom by reproducing copepods. Hydrobiologia 243/244:175-183 (1992).

Plankton ecology was examined during the 1986 winter in Grand Traverse Bay, a 190-m deep, fjord-like bay on Lake Michigan. Before ice cover, algal concentration was low and uniformly distributed with depth, as it is in open Lake Michigan. During ice cover (February and March), a bloom of a typical winter-spring phytoplankton developed in the upper 40-m, resulting in a 4-7 fold increase in feeding rate of adult Diaptomus spp. High algal concentration and zooplankton feeding persisted after ice melt (April). During and after ice cover, lipid concentrations of Diaptomus dropped rapidly from 34% of dry weight to 17% because of high egg production. High incident photosynthetically active radiation (PAR), high (45-50%) PAR transmittance of the ice due to little snow on the ice,a nd water column stability were probably responsible for the bloom. High ice transparency may be a common feature of large lakes and bays, where strong winds blow snow cover off the ice, or at low latitudes where snow melt due to occasional rains and warm temperatures is common. Winter reproducing calanoid copepods use these blooms to increase their reproductive output.

VANDERPLOEG, H.A., J.R. LIEBIG, and M. Omair. Bythotrephes predation on Great Lakes zooplankton measured by an in situ method: implications for zooplankton community structure. Archiv f. Hydrobiologie 127(1):1-8 (1993).

A modified in situ method was used to estimate selective predation impacts of Bythotrephes. In Saginaw Bay (Lake Huron) Bythotrephes showed the following prey preference ranking (with clearance rates in liter d-1 indicated in parentheses): Ceriodaphnia (1.7) Eubosmina (1.6) > Bosmina (1.4) Daphnia retrocurva (1.2) > Chydorous (0.8) Asplanchna (0.7) > copepod nauplii (0.17) > Cyclops C1-C5 (0.09). In offshore Lake Huron, where copepod nauplii were the only zooplankton, Bythotrephes cleared them at a relatively high rate (0.55 liter d-1). These results were used to determine if Bythotrephes was responsible for recent changes in the cladoceran assemblage in Lake Michigan. Based on maximum abundance estimates, Bythotrephes induced a maximum mortality of 0.05 d-1. This modest predation rate and the high selectivities for most cladocerans suggest little impact; however, this estimate ignores possible spatial coupling between Bythotrephes and its prey.

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