GLERL Publications Abstracts: FY 1991

ASSEL, R.A. An ice-cover climatology for Lake Erie and Lake Superior for the winter seasons 1897-1898 to 1982-1983. International Journal of Climatology 10:731-748 (1990). http://www.glerl.noaa.gov/pubs/fulltext/1990/19900009.pdf

Observations of mid-lake Great Lakes ice cover are sparse prior to the decade of the 1960s. In an effort to provide an historical perspective of mid-lake ice cover back to the turn of the century, daily averagae ice cover for Lakes Erie and Superior over 86 winters (1897-1898 to 1982-1983) was reconstructed using empirical-statistical ice-cover models developed in an earlier study. Long-term avaerage maximal monthly ice cover occurs in February and is 68 percent for Lake Erie and 40 percent for Lake Superior. Mid-lake ice formation occurs about 1 month earlier on both lakes during several winters. Average maximal monthly ice cover during severe and during mild winters is 95 percent and 14 percent for Lake Erie, 87 percent and 17 percent for Lake Superior. Severe winters are associated with lower 700 mbar heights over the eartern USA compared with mild ice-cover winters. Analysis of total winter ice cover indicates three ice cover regimes: (i) a high ice-cover regime from the late 1890s to early 1920s; (ii) a low ice-cover regime from the early 1920s to late 1950s; and (iii) a high ice-cover regime from the late 1950s to the early 1980s. Ice-cover climatologies developed during the 1960s and 1908s are not representative of ice covers in the low ice-cover regime of the 1920s to late 1950s. Spectral analysis of the reconstructed total winter ice cover suggests interannual variations in ice cycles that correspond with the 2-3 year interannual variation in atmospheric variables known as the quasi-biennial oscillation.

Statistical ice cover models were used to project daily mean basin ice cover and annual ice cover duration for Lakes Superior and Erie. Models were applied to a 1951-80 base period and to three 30-year steady double carbon dioxide (2xCO₂) scenarios produced by the Geophysical Fluid Dynamics Laboratory (GFDL), the Goddard Institute of Space Studies (GISS), and the Oregon State University (OSU) general circulation models. Ice cover estimates were made for the West, Central, and East basins of Lake Erie and for the West, East, and Whitefish Bay basins of Lake Superior. Average ice cover duration for the 1951-80 base period ranged from 13 to 16 weeks for individual lake basins. Reductions in average ice cover duration under the three 2xCO₂ scenarios for individual lake basins ranged from 5 to 12 weeks for the OSU scenario, 8 to 13 weeks for the GISS scenario, and 11 to 13 weeks for GFDL scenario. Winter without ice formation become common for Lake Superior under the GFDL scenario and under all three 2xCO2 scenarios for the Central and East Basins of Lake Erie. During an average 2xCO₂ winter, ice cover would be limited to the shallow areas of Lakes Erie and Superior. Because of uncertainties in the ice cover models, the results given here represent only a first approximation and are likely to represent an upper limit of the extent and duration of ice cover under the climate change projected by the three 2xCO₂ scenarios. Notwithstanding these limitations, ice cover projected by the 2xCO₂ scenarios provides a preliminary assessment of the Statistical ice cover models were used to project daily mean basin ice cover and annual ice cover duration for Lakes Superior and Erie. Models were applied to a 1951-80 base period and to three 30-year steady double carbon dioxide (2xCO₂) scenarios produced by the Geophysical Fluid Dynamics Laboratory (GFDL), the Goddard Institute of Space Studies (GISS), and the Oregon State University (OSU) general circulation models. Ice cover estimates were made for the West, Central, and East basins of Lake Erie and for the West, East, and Whitefish Bay basins of Lake Superior. Average ice cover duration for the 1951-80 base period ranged from 13 to 16 weeks for individual lake basins. Reductions in average ice cover duration under the three 2xCO₂ scenarios for individual lake basins ranged from 5 to 12 weeks for the OSU scenario, 8 to 13 weeks for the GISS scenario, and 11 to 13 weeks for GFDL scenario. Winter without ice formation become common for Lake Superior under the GFDL scenario and under all three 2xCO₂ scenarios for the Central and East Basins of Lake Erie. During an average 2xCO₂ winter, ice cover would be limited to the shallow areas of Lakes Erie and Superior. Because of uncertainties in the ice cover models, the results given here represent only a first approximation and are likely to represent an upper limit of the extent and duration of ice cover under the climate change projected by the three 2xCO₂ scenarios. Notwithstanding these limitations, ice cover projected by the 2xCO₂ scenarios provides a preliminary assessment of the potential environmental and socioeconomic impacts of a 2xCO₂ warming include year-round navigation, change in abundance of some fish species in the Great Lakes, discontinuation or reduction of winter recreational activities, and an increase in winter lake evaporation.

ASSEL, R.A., and D.C. NORTON. A comparison of Great Lakes winter severity and ice cover--winter 1990 vs. the historical record. Proceedings, 1990 Annual Meeting of the Eastern Snow Conference, Guelph, Ontario, Canada, June 6, 1990. 143-154 (1990). http://www.glerl.noaa.gov/pubs/fulltext/1990/19900010.pdf

The large temperature anomaly reversal from December 1989 to January 1990 is described along with its associated impact on early winter snowfall and ice formation. Winter temperature severity is evaluated in terms of magnitude and date of occurrence of the annual maximal freezing degree-day accumulations at several locations on the perimeter of the Great Lakes. Winter severity from the turn of the century to the early 1980s is compared with the 1990 winter severity. The extent and date of occurrence of maximal ice cover for the 1990 winter is placed in a historical perspective by comparing it with the annual maximal ice covers of the preceding three decades.

ASSEL, R.A., and J.M. RATKOS. Animation of the normal ice cycle of the Laurentian Great Lakes of North America. Preprint Volume, Seventh International Conference on Interactive Information and Processing Systems for Meteorology, Hydrology and Oceanography, New Orleans, LA, January 14-18, 1991. American Meteorology Society, Boston, MA, 331-335 (1991). http://www.glerl.noaa.gov/pubs/fulltext/1991/19910008.pdf

An interactive, menu-driven computer tutorial was developed to provide an overview of the annual Great Lakes ice cycle. The tutorial includes an animation to aid in visualizing the seasonal progression and the spatial patterns of ice cover for the base period 1960-1979. The computer algorithm was developed from data contained in the NOAA Great Lakes Ice Atlas. This material is presented as a government technical memorandum to make the tutorial available to the public at large for educational purposes. A computer diskette needed to load and run the tutorial (on a Macintosh Plus with at least 2 megabytes of memory) is included as an appendix. Background information on the ice cover data and methods used to create the tutorial is followed by a description of the spatial and seasonal ice cover distribution patterns as related to lake bathymetry.

Baker, J.E., S.J. Eisenreich, and B.J. EADIE. Sediment trap fluxes and benthic recycling of organic carbon, polycyclic aromatic hydrocarbons, and polychlorobiphenyl congeners in Lake Superior. Environmental Science & Technology 25(3):500-509 (1991).

Sediment trap fluxes of solids, organic carbon, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyl (PCBs) were measured in Lake Superior in 1984 and 1985. Mass fluxes from surface waters ranged from 0.14 to 1.1 g/m2lday and increased near the lake floor due to resuspension of surficial sediment and horizontal transport in the benthic nepheloid layer. Organic matter fluxes from surface waters ranged from 60 to 90 mg of C/m2lday, with ~5% of organic carbon settling from surface waters accumulating in bottom sediments. Concentrations of PCBs and PAHs are enriched 10-100 times on settling particles relative to those on suspended particles. Resultant settling fluxes are 10-100 times greater for several PCB and PAH compounds than net accumulation rates in bottom sediments, indicating the effective and rapid recycling in the benthic region. Biological packaging of organic pollutants into rapidly settling particles is an efficient pathway for the transport of contaminants from surface waters to benthic regions of large lakes.

BEETON, A.M. Limnology of the Nam Ngum Reservoir, Laos. Verhandlugen-Internationale Vereinigung Fur Theoretische und Angewandte Limnologie 24(24):1436-1444 (1991).

No abstract.

BEETON, A.M. Virtual elimination of toxic substances in the changing Great Lakes. Proceedings, 1990 Annual Meeting of the Universities Council on Water Resources (UCOWR), Water Issues in an Environmental Era, West Point, NY, August 2, 1990. 60-61 (1991).

No abstract.

BEETON, A.M., and J.E. Gannon. Effect of environment on reproduction and growth of Mysis relicta. American Fisheries Society Symposium 9:114-148 (1991).

Published and unpublished data were examined to determine whether the time to first reproduction, brood size, and growth rate of Mysis relicta are related to environmental conditions. Time to first reproduction ranged from 1 year in eutrophic lakes to 4 years in an ultraoligotrophic lake. Mysids in nutrient-rich lakes may have 45 eggs per brood, whereas those in less productive lakes had 10-12 eggs per brood. Growth rates ranged from 1.0 to 1.5 mm/month in productive lakes to only 0.2 mm/month in ultraoligotraphic Lake Tahoe. Some differences in reproduction and growth rate consistent with the above observations occurred between areas of Lakes Tahoe and Michigan that differed in trophic conditions.

BRATKOVICH, A.W., R.L. Berstein, D.B. Chelton, and P.M. Kosro. Central California coastal circulation study: Program overview and representative results. Proceedings, Workshop on South California Bight Physical Oceanography. OSC Study MS 91-0033, LaJolla, CA, November 1990. U.S. Dept. of Interior, Minerals Management Service, 91-109 (1991).

No abstract.

CARRICK, H.J., G.L. FAHNENSTIEL, E.F. Stoermer, and R.G. Wetzel. The importance of zooplankton-protozoan trophic couplings in Lake Michigan. Limnology and Oceanography 36(7):1335-1345 (1991). http://www.glerl.noaa.gov/pubs/fulltext/1991/19910005.pdf

The importance of the zooplankton-protozoan trophic coupling was determined experimentally by measured changes in protozoan growth rates with increasing zooplankton biomass. In five of six experiments conducted in Lake Michigan, a significant inverse relationship between protozoan growth and zooplankton biomass was observed (avg r² = 70%). Zooplankton clearance rates on protozoan assemblages [range, 1.0-6.2 ml (mg dry wt)-1 d-1] were comparable to those previously measured for phytoplankton which suggested that protozoa are important prey for zooplankton. Clearance rates on individual protozoan taxa [0-15.6 ml (mg dry wt)-1 d-1] were size-dependent. Rates were greatest for taxa < 20 mm in size (mainly nanoflagellates and small ciliates). In contrast to findings for phytoplankton, no evidence emerged for grazer resistance nor growth enhancement by planktonic protozoa in response to grazing. The high flux rates for macrozooplankton on heterotrophic nanoflagellates observed in all experiments (0.2-6.0 mg C liter-1 d-1) provided evidence that a large fraction of picoplankton C may be directly transferred to higher trophic levels via a picoplankton-flagellate-zooplankton coupling.

CONLEY, D.J., and D. SCAVIA. Size structure of particulate biogenic silica in Lake Michigan. Journal of Great Lakes Research 17(1):18-24 (1991). http://www.glerl.noaa.gov/pubs/fulltext/1991/19910001.pdf

Recent data suggest that chemical estimates of biogenic silica in the Laurentian Great Lakes include large fractions of non-living fragmented diatoms. Therefore, measurements of particulate biogenic silica (BSi) in different size classes (0.2-0.4 mm, 0.4-10 mm, 10-20 mm, and >20 mm) were made from April through July 1987 in southeastern Lake Michigan to assess the importance of diatom fragments to chemical estimates of BSi. During the spring diatom bloom, the period of maximum BSi concentrations, the greatest percentage of BSi (86%) was found in the microplankton size fraction (>10 mm) associated with living diatoms. By contrast, following thermal stratification, when dissolved silica was depleted from epilimnetic waters, particles <10 mm in size dominated and averaged 52% of total BSi. This fraction contained mostly fragmented diatom frustules. Our estimate of non-living diatoms is consistent with previous studies showing that, following the spring diatom bloom, 40% to 60% of total diatom abundance is non-living. Seasonal decreases in epilimnetic BSi, declining from 11.3 mmol L-1 in lake April to an average of 1.96 mmol L-1 during the stratified period, were due primarily to lass of the largest size fraction (>20 mm) which decreased from 76% of total BSi in April to 36% in July. BSi <10% mm varied by less than a factor of two throughout the study period, averaging 3.23 +- 2.79 mmol L-1. Particles 0.2-0.4 mm averaged 0.277+-0.178 mmol L-1. These particles are probably produced through frustule dissolution, settle slowly, and may lead to enhanced BSi recycling rates.

Coordinating Committee on the Great Lakes Basic Hydraulic and Hydrologic Data. Great Lakes Hydromet Database Directory. NOAA Technical Memorandum ERL GLERL-74, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (PB91-201327/GAR) 49 pp. (1991).

No abstract.

CROLEY, T.E.II. Laurentian Great Lakes double-CO₂ climate change hydrological impacts. Climatic Change 17:27-47 (1990).

The Great Lakes Environmental Research Laboratory has developed conceptual daily models for simulating moisture storages in and runoff from the 121 watersheds draining into the Laurentian Great Lakes, over-lake precipitation into each lake, and the heat storages in and evaporation from each lake. We combine these components as net basin supplies for each lake to consider climate change scenarios developed from atmospheric general circulation models n(GCMs). Recent scenarios of a doubling of atmospheric CO, available from the Goddard Institute for Space Studies, the Geophysical Fluid Dynamics Laboratory, and Oregon State University are considered by making changes in historical meteorological data similar to the changes observed in the GCMS, observing the impact of the changed data in the model outputs, and comparing outputs to model results using unchanged data, representing comparison to an unchanged atmosphere. This study indicates a 23 to 51% reduction in net basin supplies to all the Great Lakes; there is significant variation in the components of these supplies among the three GCMS. The basins various moisture storages become dryer and the lakes are warmer with associated hydrological impacts.

CROLEY, T.E.II. Use of general circulation model simulations in regional hydrological climate change impact studies. Proceedings, A Symposium on Climate Scenarios, M. Sanderson (ed.), University of Waterloo, Waterloo, Ontario, Canada, June 12, 1991. (1991).

No abstract.

CROLEY, T.E.II, and S.V. Ferronsky. Climate change impacts on the hydrology of the Caspian Sea, Issue 1: Building digital maps of the hydrological basins. Academy of Sciences of the USSR, Soviet Geophysical Committee and DOC/Great Lakes Environmental Research Laboratory (1990).

No abstract.

CROLEY, T.E.II, and S.V. Ferronsky. Climate change impacts on the hydrology of the Caspian Sea, Issue 2: Areal averaging of point meteorological measurements. Academy of Sciences of the USSR, Soviet Geophysical Committee and DOC/Great Lakes Environmental Research Laboratory (1990).

No abstract.

DERECKI, J.A., and F.H. QUINN. Comparison of measured and simulated flows during the 15 December 1987 Detroit River flow reversal. Journal of Great Lakes Research 16(3):426-435 (1990). http://www.glerl.noaa.gov/pubs/fulltext/1990/19900007.pdf

Flow reversals in the Detroit River are unique hydraulic phenomena which disturb the normal flow patterns and which may cause high concentrations of waterborne pollutant-5 b-v temporarily blocking their downstream transport and dilution. Until recently, flow reversals: in the river have been implied from water level relationships and unsteady numerical flow models, but not directly measured. An acoustic Doppler current profiler deployed on the river bottom at Ft. Wayne, in Detroit, has provided the first opportunity to directly measure a flow reversal, which occurred for about 3 hours on 15 December 1987. The meter provided continuous measurements of the vertical velocity distribution for approximately 1-m depth segments in the overhead water column at quarter-hour intervals. These measurements provided an ideal data set to analyze river dynamics associated with flow reversals and to evaluate the importance of major factors necessary for the occurrence of flow reversals in the river. It was found that reasonably accurate simulation of flow reversals with the unsteady flow models require the inclusion of surface wind shear and the use of small time increments that are much shorter than the standard hourly water level data. Model simulation with specially obtained 5 and 15 minute water level and wind data produced generally similar model flows that are reasonably close to the measured values. Because short-period (15 minute or less) wind and water level data are not readily available, river flow reversals simulated using hourly data may he significantly underestimated.

Donelan, M., M. Skafel, H. Graber, P.C. LIU, D.J. SCHWAB, and S. Venkatesh. On the growth rate of wind-generated waves. NWRI Contri. 91-117. National Water Research Institute, Burlington, Ontario, Canada, 32 pp. (1990).

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.

EADIE, B.J., J.A. ROBBINS, W.R. FAUST, and P.F. LANDRUM. Polycyclic aromatic hydrocarbons in sediments and pore waters of the lower Great Lakes: Reconstruction of a regional benzo(a)pyrene source function. In Organic Substances and Sediment in Water: Volume 2, Processes and Analytical, R. Baker (ed.). Lewis Publishers, Chelsea, MI, Chapter 9, 171-189 (1991).

No abstract.

Edgington, D.N., J. Val Klump, J.A. ROBBINS, Y.S. Kusner, V.D. Pampura, and I.V. Sandimirov. Sedimentation rates, residence times and radionuclide inventories in Lake Baikal from 137-Cs and 210-Pb in sediment cores. Nature 350:601-604 (1991).

Radionuclides in lake sediments may act as indicators of the sedimentation rate of particles on which they are adsorbed; these rates in turn provide a direct indication of the residence times of particles in the water column. The radionuclide 137Cs is anthropogenic (an atomic-bomb product), so that its concentration in sediments also reveals the input history of this species and thus a record of atmospheric contamination by this nuclide in the lake's watershed. Here we report measurements of 137Cs and the natural radionuclide 210Pb in cores from several stations throughout the three basins of Lake Baikal. The results confirm earlier indirect estimates of the mean sedimentation rate, and show that the effective settling rate of these radionuclides is the same as that in the Great Lakes; the longer residence times for Lake Baikal are therefore simply a consequence of its greater depth. As well as allowing estimates of fluxes at the sediment-water interface, our results provide information on the timing of paleolimnological events, on the existence of different depositional zones throughout the lake, on the long-term (decadal) diffusion of nuclides in sediments, and for the development of mass balance models for sediments and contaminants.

Evans, M.S., M.A. QUIGLEY, and J.A. WOJCIK. Comparative ecology of Pontoporeia hoyi populations in southern Lake Michigan: The profundal region versus the slope and shelf regions. Journal of Great Lakes Research 16(1):27-40 (1990). http://www.glerl.noaa.gov/pubs/fulltext/1990/19900003.pdf

This study investigates Pontoporeia hoyi ecology in the profundal region(approximated by a 97-m station) of southern Lake Michigan and compares these results with previous investigations conducted in the slope and shelf regions of the lake. Pontoporeia typically attains its maximum abundance in the slope region, suggesting that this region of the lake is the most favorable for amphipod growth and survival. Profundal and slope P. hoyi exhibited little seasonal variation in mean size while shelf-region populations exhibited strong seasonal variation in mean size. Deepwater sculpins, a major predator on profundal populations of P. hoyi, selectively consumed the largest amphipods: mean size consumed was 6-7 mm. The relative sparsity of larger (> 5 mm) P. hoyi in the profundal, slope, and shelf-regions of the lake may arise from intense size-selective fish predation on this size class of amphipods. Gut content studies revealed that profundal P. hoyi populations feed intermittently. Such feeding behavior was subtly different from that previously observed for slope P. hoyi populations: profundal populations feed more continuously but less intensively than slope populations. Regional differences in feeding behavior may be related to differences in food regime and to predation avoidance strategies. Pontoporeia hoyi apparently is capable of inhabiting a broad range of depth regimes by modifying its physiology (reproductive cycles, generation time) and behavior (feeding, motility) to adjust to spatial variations in temperature, food level, and predation.

FAHNENSTIEL, G.L., H.J. CARRICK, and R. Iturriaga. Physiological characteristics and food-web dynamics of Synechococcus in Lakes Huron and Michigan. Limnology and Oceanography 36(2):219-234 (1991). http://www.glerl.noaa.gov/pubs/fulltext/1991/19910006.pdf

Single Synechococcus cells accounted for an average of 10% (range 1-26%) of surface mixed-layer primary production in Lakes Huron and Michigan in 1986-1988. Maximal photosynthetic rates (Pmax) were relatively low (range = 1.9-6.0 fg C cell-1 h-1) and no significant photoinhibition was found at irradiances as high as 3.0 Einst m-2 h-1. Synechococcus growth rates estimated by four techniques (ampicillin, 14C uptake, dilution, and small inocula) ranged from 0.1 to 0.9 d-1 with a mean of 0.37. Although substantial variability was noted among techniques on any one date, on average all estimates were in reasonable agreement with the exception of the dilution estimates which were significantly lower (P < 0.01). Three techniques for estimating grazing loss rates (ampicillin, dilution, and 14C-labeling of Synechococcus) provided similar estimates ranging from 0.1 to 0.7 d-1. On specific dates, grazing loss rates were 33-120% of growth rates, suggesting that grazing was the major loss for Synechococcus populations in these lakes. Most of the grazing loss (68%) was attributable to small (4-10 mm), heterotrophic flagellates and ciliates. Crustaceans and rotifers accounted for only a small percentage of total grazing loss (5-21%) even when Daphnia accounted for 40% of crustacean biomass.

FAHNENSTIEL, G.L., H.J. CARRICK, C.E. Rogers, and L. Sicko-Goad. Red fluorescing phototrophic picoplankton in the Laurentian Great Lakes: What are they and what are they doing? International Revue Ges. Hydrobiol. 76(4):603-616 (1991).

Epifluoresence microscopy, flow cytometry, and transmission electron microscopy were used to characterize the community of red fluorescing (emission > 665 nm when excited with blue light) phototrophic picoplankton (RFPP) in Lakes Huron and Michigan. A population of coccoid to ovate eukaryotic cells with a mean sixe of 1.2 mm dominated the TFPP community in both surface and deep water samples. Abundant prochlorophyte populations were not found in any samples. Comparisons of counts with epifluorescence microscopy and flow cytometry, revealed that RFPP were adequately enumerated with standard epifluorescence microscopy. These RFPP were significant contributors to total phototrophic picoplankton abundance in both Lakes Michigan (24%) and Huron (18%), with maximum seasonal abundance during the May-June period (surface mixing layer temperatures, 3-9 oC). During thermal stratification, maximum vertical abundance was found in the metalimnion/hypolimnion at the 1-5% isolumes. RFPP were only minor contributors (17%) to total primary production. Growth rates of RFPP measured with dilution and small inocula growth experiments ranged from 0.05-1.0 d-1. Microzooplankton grazing rates on RFPP measured with dilution experiments were similar to estimated growth rates, accounting for 52-280% of growth on any given date.

FAHNENSTIEL, G.L., T.R. PATTON, H.J. CARRICK, and M.J. McCORMICK. Diel division cycle and growth rates of Synechococcus in Lakes Huron and Michigan. Int. Revue Ges. Hydrobiol. 76(4):657-664 (1991).

A clone of Synechococcus isolated from Lake Huron and natural populations of Synechococcus from Lakes Huron and Michigan were studied in 1989 to examine the diel division cycle and to provide estimates of the in situ growth rate based on the frequency of dividing cells (FDC) method. Cultured populations of Synechococcus exhibited a consistent diel division pattern with a midday/afternoon (1100-1800 h) peak in the percent of dividing cells. The maximum percent of dividing cells varied among cultures (8-27%) and was related to the growth rate. A small fraction of dividing cells (3-5%) remained throughout the dark period, suggesting that some cells were arrested in the doublet stage prior to division. The duration of division (td) ranged from 2.6-4.9 h, with a 3.7 h mean for cultures with growth rates > 0.34 d-1 but increased to 8 h at a lower growth rate of 0.20 d-1. The diel division pattern for natural populations was very similar to the laboratory clone; an afternoon peak (1400-2100 h) individing cells and a small fraction of dividing cells (2-5%) remained during the dark period. The maximum percent of dividing cells for natural populations ranged from 6-10%. In situ growth rates, determined from the FDC and assuming a constant td of 3.7 h, ranged from 0.30-0.42 d-1. The FDC method may provide accurate estimates of in situ growth, particularly in environments where the growth rate is > 0.34 d-1, but in Lakes Huron and Michigan where growth rates can be lower and td values may increase, FDC-growth rates must be viewed with caution.

GARDNER, W.S., L.R. HERCHE, St. John, and S.P. Seitzinger. High-performance liquid chromatographic determination of 15NH4:14NH4+15NH4 ion ratios in seawater for isotope dilution experiments. Analytical Chemistry 63(17):1838-43 (1991).

A liquid chromatographic method with fluorometric detection, after postcolumn labeling with o-phthalaldehyde/2-mercaptoethanol reagent, was developed to directly quantify 15NH4:[14NH4 + 15NH4] ion ratios in aqueous samples that had been enriched with 15NH4 for isotope dilution experiments. Cation-exchange chromatography, with a sodium borate buffer mobile phase, was selected as the separation mode because the two isotopes have slightly different constants in the equilibrium reaction between ammonium ion and ammonia. When the two forms of ammonium were passed separately through a high-performance cation-exchange column under precisely controlled chromatographic conditions, the retention time (RT) of 15NH4 was 1.012 times the RT of 14NH4. The two isotopic forms of ammonium ion were not resolved into separate peaks when they were injected together, but the retention time of the combined peak, as defined by an integrator, increased with increasing percentages of 15NH4 in the mixture. The relationship of RT shift vs percentage of 15NH4 relative to total ammonium followed a sigmoid-shaped curve with the maximum RT shifts per change in isotopic composition occurring between 25 and 75% 15NH4. Using a calibration curve based on this relationship and a solution of separately injected 14NH4 in mobile-phase buffer as an "internal standard," we were able to directly determine the concentrations and ratios of the two isotopes in enriched seawater.

GARDNER, W.S., S.P. Seitzinger, and J.M. MALCZYK. The effects of sea salts on the forms of nitrogen released from estuarine and freshwater sediments: Does ion pairing affect ammonium flux? Estuaries 14(2):157-166 (1991).

In sediments with oxidized surface layers, the percentage of mineralized nitrogen that is nitrified/ denitrified, compared with that released directly as ammonium, appears to be affected by the presence of sea salts. In estuarine systems, a significant portion of the nitrogen is released as ammonium, whereas in freshwater systems, most of the mineralized nitrogen is often released from the sediments as nitrogen gas. We hypothesized that this discrepancy is caused by differential competition between physical diffusion and nitrification/denitrification in the two systems. The vertical migration (by Fickian diffusion) of ammonium out of the oxic layer may be hindered by cation exchange (or sorption) interactions with sediment particles to a greater extent in fresh water than in estuarine systems. The resulting relatively long residence time, and potentially high levels of particle-bound ammonium in the freshwater sediments, would favor nitrification as the major ammonium removal process. By contrast, ion pair formation of ammonium with seawater anions and blockage of sediment cation exchange sites with seawater cations may allow a sizable fraction of the ammonium to diffuse out of estuarine sediments before it is nitrified. A salt effect, consistent with this hypothesis, has been demonstrated in experimental systems by changing the ionic composition of water flowing above intact cores of freshwater and estuarine sediments. Steady-state ammonium release from Lake Michigan sediments was substantially enhanced in the presence of 30% seawater over that in the presence of lake water alone. Likewise, steady-state ammonium release, from Ochlockonee River and Bay sediments (Florida) and from Toms River and Barnegat Bay sediments (New jersey), was usually higher in the presence of diluted synthetic seawater than it was in the presence of fresh water.

GARDNER, W.S., and P.A. St. John. High-performance liquid chromatographic method to determine ammonium ion and primary amines in seawater. Analytical Chemistry 63:537-540 (1991).

No abstract.

GOTTLIEB, E.S., J.H. SAYLOR, and G.S. MILLER. Currents and water temperatures observed in Green Bay, Lake Michigan, Part I: Winter 1988-1989. NOAA Technical Memorandum ERL GLERL-73, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (PB91-129072/XAB) 90 pp. (1991).

To help monitor the transport of water within Green Bay and the exchange of waters between the bay and Lake Michigan, current meter moorings were deployed in the bay and in the passages separating the bay and Lake Michigan, from September 1988 to April 1989 (Part I: Winter) and again from May to September 1989 (Part II: Summer). The winter deployment involved 8 current meter moorings, whereas summer included 21 moorings, 3 thermistor chains, and 7 loran-C-tracked drifters (July only). Each mooring held two or three current meters, usually placed at 12 and 20 m depth and 5 m above the bottom. To aid in understanding the winter data, maps of ice concentration and thickness are included in Part 1. Although currents under the ice are surprisingly energetic at the lunar semi-diurnal tide and Lake Michigan surface seiche periods, monthly-averaged currents reveal a very weak and poorly defined mean circulation pattern in the bay. Despite partial ice cover, bidaily-averaged currents are strong, burstlike, and mostly outward through Death's Door Passage, and weaker, steadily inward, and slightly warmer through Rock Island Passage. Monthly-averaged summer cur-rents (Part H) show a somewhat anticyclonic circulation pattern in the southern half of the bay, and a persistent inflow below 20 m depth through all four major passages. Above 20 m however, outflow is notable only through Death's Door Passage. Comparison of bidaily-averaged currents and observed wind patterns indicates that north to northeast winds create a single cyclonic circulation cell in the bay, and south to southwest winds create a two-celled pattern that has an anticyclonic cell in the south half of the bay and a cyclonic cell in the north. Low-pass-filtered cur-rents and temperatures during July and August reveal a strong, persistent, well-defined, 8-day-long oscillation associated with seiching of the thermocline in Green Bay. Thermistor chain data indicate an amplitude of about 6 to 10 m for the internal seiche.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Annual Report for the Great Lakes Environmental Research Laboratory, FY 1990. Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 60 pp. (1991).

No abstract.

HARTMANN, H.C. Climate change impacts on Laurentian Great Lakes levels. Climatic Change 17:49-67 (1990).

Scenarios of water supplies reflecting CO₂-induced climatic change are used to determine potential impacts on levels of the Laurentian Great Lakes and likely water management policy implications. The water supplies are based on conceptual models that link climate change scenarios from general circulation models to estimates of basin runoff, overlake precipitation, and lake evaporation. The water supply components are used in conjunction with operational regulation plans and hydraulic routing models of outlet and connecting channel flows to estimate water levels on Lakes Superior, Michigan, Huron, St. Clair, Erie, and Ontario. Three steady-state climate change scenarios, corresponding to modeling a doubling of atmospheric CO₂, are compared to a steady-state simulation obtained with historical data representing an unchanged atmosphere. One transient climate change scenario, representing a modeled transition from present conditions to doubled CO₂ concentrations, is compared to a transient simulation with historical data. The environmental, socioeconomic, and policy implications of the climate change effects modeled herein suggest that new paradigms in water management will be required to address the prospective increased allocation conflicts between users of the Great Lakes.

HARTMANN, H.C., and T.E. CROLEY. An evaluation of GLERL's hydrological outlook package. Proceedings, Great Lakes Water Level Forecasting and Statistics Symposium, Windsor, Ontario, Canada, May 17-18, 1990. Great Lakes Commission, Ann Arbor, MI, 177-194 (1990).

The Great Lakes Environmental Research Laboratory developed a series of physically-based conceptual models for making deterministic or probabilistic outlooks of large lake hydrology, including net basin supplies and lake levels, which consider existing basin moisture and lake heat storages and National Weather Service forecast meteorology. The performance of GLERL's Hydrological Outlook Package, used in a simulated operational application, is evaluated for the period from August 1982 through December 1988. Two subperiods, which have extreme and extremely different net basin supplies, are evaluated as well. Considering all 3 evaluation periods, deterministic outlooks of net basin supplies are best on Lake Superior. Deterministic outlooks, however, have inherent limitations, since they provide only a single forecast time series. Alternatively, probabilistic outlooks explicitly communicate the uncertainty and potential diversity of future hydrometeorologic conditions. Our probabilistic net basin supply outlooks are most informative for 1-month forecasts for Lakes Michigan, Superior, and St. Clair. Improvements in forecasting depend on better National Weather Service monthly and seasonal weather outlooks, and better selection of historic meteorologic sequences to use as forecast scenarios.

HERCHE, L.R., and H.C. HARTMANN. Estimation of Great Lakes water level statistics: Conditioning via "The Bootstrap". Proceedings, Great Lakes Water Level Statistics Symposium, Windsor, Ontario, Canada, May 17-18, 1990. Great Lakes Commission, Ann Arbor, MI, 291-309 (1990).

Reliable lake level frequency distributions are a critical component of any comprehensive strategy for coping with Great Lakes water level fluctuations. However, statistical techniques commonly used on riverine systems are inappropriate for large lake systems, due to the levels' long-term persistence and dependence on the prevailing climatic regime. To illustrate an alternative methodology, we present a series of resampling analyses modeled after well-known bootstrap techniques, applied to 130 years of monthly Lake Erie water level records. The analyses show that lake level exceedance probabilities should be conditioned on 1) length of planning horizon, 2) starting month of planning horizon, 3) initial lake level, and 4) climatic regime. Our methodology can be extended to additionally consider storm and wind effects on levels, to incorporate levels data available for discontinuous periods prior to 1860, and to develop other types of lake level statistics useful to decision makers, such as duration and time-to-exceedance probabilities.

LANDRUM, P.F., and W.S. DUPUIS. Toxicity and toxicokinetics of pentachlorophenol and carbaryl to Pontoporeia hoyi and Mysis relicta. In Aquatic Toxicology and Risk Assessment: Thirteenth Volume, ASTM STP 1096, W.G. Landis, and W. H. van der Schalie (eds.). American Society for Testing and Materials, Philadelphia, PA, 278-289 (1990).

Two Great Lakes invertebrates, the amphipod Pontoporeia hoyi and the mysid shrimp Mysis relicta, were exposed to pentachlorophenol (PCP) and carbaryl to determine acute mortality. At pH 8, the LC50 for P. hoyi after 96 h was 0.6 ± 0.3 mg mL-1 for PCP while that for carbaryl was 0.23 ± 0.04 mg mL-1. The LC50 for M. relicta at pH 8 and 96 h was 54.1 ± 10.3 mg mL-1 for PCP and for carbaryl 0.23 mg mL-1 (0.103 - 0.356, n=2). The differences in the LC50 values between P. hoyi and M. relicta for PCP result in part from differences in the uptake clearances of the two animals, 3.1 ± 0.9 mL g-1 h-1 for P. hoyi compared to 0.4 ± 0.1 mL g-1 h-1 for M. relicta. A similar difference occurred in the respective carbaryl uptake clearances for the two organisms, 3.74 ± 0.63 mL g-1 h-1 for P. hoyi and 0.134 mL g-1 h-1 (0.135 - 0.133, n=2) for M. relicta. The cumulative toxicant concentrations in the organisms that result in 50% mortality, LD50, were estimated from a toxicokinetics model that was parameterized with the measured uptake and elimination constants and the LC50 values. The M. relicta LD50 for PCP was approximately ten times larger than that for P. hoyi and confirmed the relative sensitivities of the organisms as described by their respective LC50 values. For carbaryl, the LD50 for P. hoyi was greater than that for M. relicta. Thus M. relicta is apparently more sensitive to accumulated carbaryl than P. hoyi despite the similar LC50 values for the two organisms.

LANDRUM, P.F., B.J. EADIE, and W.R. FAUST. Toxicokinetics and toxicity of a mixture of sediment-associated polycyclic aromatic hydrocarbons to the amphipod Diporeia sp. Environmental Toxicology and Chemistry 10:35-46 (1991).

Amphipods, Diporeia sp., were exposed to a reference sediment dosed with two radiolabeled polycyclic aromatic hydrocarbons (PAHs) and sediments dosed with a mixture of PAHs at four concentrations: 21.4, 41.0, 119.6, and 327.0 nmol g-1 dry sediment, as the molar sum of the PAH congeners. Diporeia sp. were sampled for mortality and toxicokinetics for up to 26 d. Significant sediment avoidance was observed at the highest dose out to 6 d of exposure. The toxicity for the mixture was 38 ± 3% after 19 d of exposure at the highest dose, 327 nmol g-1 dry sediment as the molar sum of the PAHs. The measured organism concentration required to produce the mortality at day 19 was 2.9 mmol g-1 as the sum of the bioaccumulated PAHs. The uptake clearance (g dry sediment g-1 organism h-1) from sediments for the radiotracers increased with dose to an apparent plateau. Uptake clearance is the conditional constant relating the contaminant flux into the organisms to the contaminant concentration in the referenced environmental compartment, in this case the sediment. This enhanced bioavailability with dose occurred even in the absence of overt effects and in the absence of changes in the measured partition coefficients for phenanthrene (273 ± 98) and pyrene (540 ± 212), between the freely dissolved radiotracers in interstitial water and the sediment particles. These changes in bioavailability with changes in PAH concentration suggest that predictions of bioaccumulation of PAH congeners from sediments under different field concentration conditions will not be possible with standard partitioning relationships.

LANDRUM, P.F., and C.R. Stubblefield. Role of respiration in the accumulation of organic xenobiotics by the amphipod Diporeia sp. Environmental Toxicology and Chemistry 10:1019-1028 (1991).

Accumulation of hydrophobic organic xenobiotics is thought to occur by passive diffusion across the respiratory membrane of aquatic organisms. This route has been confirmed with fish. However, aquatic invertebrates tend to remove organic xenobiotics from water much more efficiently than oxygen based on the relative uptake clearances. Uptake clearance is the rate coefficient that describes the volume of water stripped of analyte per g of organisms per h. For the amphipod Diporeia sp., formerly classified as Pontoporeia hoyi, ratios of the contaminant uptake clearances to oxygen clearances were essentially constant at 3.9 ± 0.4 (X + SE) for benzo(a)pyrene (BaP) 3.8 ± 0.3 for hexachlorobiphenyl (HCBP), and 4.2 ± 0.6 for phenanthrene (Phe). Therefore, based on the membrane transport efficiencies of nonpolar xenobiotics (60-80%) and oxygen (approximately 63%) in fish, and the uptake clearance for organic xenobiotics by Diporeia sp., either xenobiotics are accumulated through routes other than across the respiratory membrane or the accumulation efficiency of oxygen from water is much lower in amphipods that it is in fish. The variability in the uptake clearance for both BaP and HCBP was best described by regressions with the surface area-to-volume ratio, whereas the uptake clearance for the more hydrophilic Phe was best described by a total surface area relationship.

McCarthy, J.F., P.F. LANDRUM, and A.V. Palumbo. Organic contaminants in sediments: Biological processes. In Organic Substances and Sediments in Water, Volume 3, Robert Blake (ed.). Lewis Publishers, Chelsea, MI, 3-21 (1991).

No abstract.

McCORMICK, M.J. Potential changes in thermal structure and cycle of Lake Michigan due to global warming. Transactions of the American Fisheries Society 119:183-194 (1990).

I used a one-dimensional numerical model to estimate the present and possible future temperature structures in Lake Michigan. The estimates were based on model output from simulations of the 1981-1984 offshore temperature field. Once the water temperature climatology was estimated, I examined three scenarios based on general circulation models in which atmospheric CO₂ was doubled. The models were those of the Goddard Institute for Space Studies (GISS), the Geophysical Fluid Dynamics Laboratory (GFDL), and the Oregon State University (OSU). In general, simulations based on these three scenarios suggested that winter and summer heat contents of the lake would be higher than at present; the summer increase would be less than that in winter. The higher winter heat content would cause an earlier onset of full thermal stratification, and the season of stratification would increase by up to two months. The earlier onset of stratification, coupled with little change in the wind stress pattern, would yield stronger stratification and less energy for large-scale vertical mixing. The GISS and GFDL scenarios suggest that the lake may not fully turn over in most winters, so a permanent thermocline may form in the deeper regions of Lake Michigan, below the shallow seasonal thermocline. Should future wind speeds be reduced from those I used here, sensitivity analyses suggest that the true effect on the annual thermal cycle and structure may be underestimated. Furthermore, given all of the uncertainties surrounding estimates of future climate, these results are best viewed as a sensitivity study, wherein the scales selected for the sensitivity tests are based upon the different general circulation model scenarios.

NALEPA, T.F. Status and trends of the Lake Ontario macrobenthos. Canadian Journal of Fisheries and Aquatic Sciences 48(8):1558-1567 (1991).

The benthic macroinvertebrate community of Lake Ontario was examined relative to communities found in the other Great Lakes and also relative to trends over time. In the nearshore, populations are heavily influenced by municipal and industrial inputs. For example, oligochaete abundances in the nearshore are higher than in any of the other Great Lakes (excluding shallow Lake Erie), communities have been altered even to relatively deep depths near the major river mouths, and the pollution-sensitive Pontoporeia hoyi is scarce along the southern shoreline east of the Niagara River mouth. In the profundal, benthic composition is similar to that found in the other Great Lakes, but biomass is less than might be expected given the amount of organic material settling to the bottom. Benthic standing stocks in this region have apparently declined almost threefold since the 1960s. Reasons for this decline do not appear to be related to trends in water column productivity or to predation pressure, but may be related to the accumulation of contaminants. Research needs include studies to assess benthic trends over a much broader area of the lake and studies to examine the impact of sublethal levels of contaminants.

NALEPA, T.F., B.A. Manny, J.C. Roth, S.C. Mozley, and D.W. Schloesser. Long-term decline in freshwater mussels (Bivalvia:Unionidae) of the western basin of Lake Erie. Journal of Great Lakes Research 17(2):214-219 (1991). http://www.glerl.noaa.gov/pubs/fulltext/1991/19910002.pdf

Long-term trends in the abundance of unionids in the western basin of Lake Erie were examined from data collected at 17 stations in 1961, 1972, and 1982. The mean number of unionids at these stations declined over this time period, decreasing from 10 m-2 in 1961, to 6 m-2 in 1972, down to 4 m-2 in 1982. This decline in abundance was reflected in the decrease in the number of stations where mussels were found; unionids were found at 16 of the 17 stations in 1961, but at only 6 stations in 1982. Reasons for the decrease in the unionid population are not generally apparent, but are probably related to the decline in water quality and periods of low oxygen levels over the time period of the surveys,

NORTON, D.C. Digital investigation of Great Lakes regional snowfall, 1951-1980. Proceedings, 48th Annual Eastern Snow Conference, Guelph, Ontario, Canada, June 5-7, 1991. 68-80 (1991).

A snowfall database for the Great Lakes region containing all available station data has been created. These data were previously translated to 240 high resolution (2 minutes Latitude by 2 minutes Longitude) monthly grids and 30 snow season grids of 198,000 cells for the 1951-1980 period. Using these grids, multiple seasonal snowfalls are presented, digitally compared, and computer contours for the Great Lakes region. This paper introduces the concept of geographically-defined normals and new windowing techniques. The potential for incorporation of digital snowfall data into Geographical Information System (GIS) for climate studies, forecasting, and management is presented.

QUINN, F.H. Proposed climate analog scenarios for the IJC Phase II Levels Study Reference. Proceedings, A Symposium on Climate Scenarios, M. Sanderson, Director The Water Network, (ed.), University of Waterloo, Waterloo, Ontario, Canada, June 12, 1991. 59-66 (1991).

No abstract.

ROBBINS, J.A., and B.J. EADIE. Seasonal cycling of trace elements 137Cs, 7Be, and 239+240Pu in Lake Michigan. Journal of Geophysical Research 96(C9):17081-17104 (1991).

Trace elements, fallout 137Cs (t1/2=30.2 years) and cosmogenic 7Be (t1/2=53.4 days) were measured in trap samples collected from two sites in southern Lake Michigan at selected times during the period from 1982 through 1987. Concentrations of 137Cs in trap material were virtually constant from top to bottom during the period when the lake was vertically well-mixed. Fluxes of 137Cs were more than two orders of magnitude higher than atmospheric loading. With the development of the thermocline, concentrations of the isotope diminished to undetectable levels at a rate indicating a 1-month residence time of resuspended components in the epilimnion. Declines in mass flux (10 to 0.2 g m-2 d-1) and trace element concentrations (some by 30 x) also occurred at this time. Epilimnetic concentration of 7Be increased from a prestratification value of about 30 dpm/g to a maximum of about 120 dpm/g in July. During calcite formation in August, the concentration rapidly declined mainly as a result of enhanced particle settling rates. Throughout the period of stratification, a maximum in concentration and flux of 7Be persisted in trap material between 40 and 60 m depth but only about 15% of the atmospheric flux was transferred to the benthic boundary region below 60 m. In near-bottom trap materials, the 137Cs concentration was reduced at the onset of stratification by addition of radiocesium-deficient authigenic materials. By November, concentrations of 137Cs had returned to prestratification levels through remineralization of these materials. A decrease of 22% in the seasonally invariant ratio of 137Cs/40K between 1982 and 1986 indicated a decay-corrected removal time of about 20 years, which is consistent with the rate of decrease of Pu concentrations in the well-mixed water column measured over more than a decade. In benthic trap samples, 7Be concentration decreased exponentially throughout the stratified period, with a time constant comparable to the half-life of the isotope. The resuspendable sediment pool, evidently isolated from atmospheric loading during stratification, was "recharged" with 7Be following late fall overturn. Box and advection-diffusion models describing the storage and vertical distribution of 7Be during the winter-mixing period successfully account for observations, implying an inverse relation between water depth and winter recharging of the resuspendable pool. A plutonium-calibrated box model for the seasonal cycle of tracers in surface waters describes the main features of the variation of Pu isotopes, 137Cs and 7Be.

ROBBINS, J.A., and N.R. MOREHEAD. Rates of accumulation of recent sediments in Lake Ontario as determined by Cs-137 and Pb-210. A Final Report to the U.S. EPA, Interagency Agreement DW13933058-01-0, U.S. EPA, Washington, DC, 66 pp. (1991).

As part of a multi-institutional study of contaminant mass balance and accumulation history in Lake Ontario, sediment cores were collected from 37 sites in August 1987. All cores were analyzed for fallout Cs-137 to obtain focusing factors useful for contaminant inventory determinations. Ten cores were dated using both Cs-137 and Pb-210.
Lake Ontario sediments store most of the Cs-137 which was deposited on the lake surface mainly as a result of atmospheric nuclear testing in the 1960s. The amount stored varies strongly with coring site and is generally focused most intensely in depositional basins. Focusing factors, varying in this study by more than a factor of 40 from site to site, can be used with suitable qualifications to improve the accuracy of lake-wide contaminant mass balances. A constant sedimentation rate model (RSSM) and variable sedimentation rate model (VSR) were applied independently to Cs-137 and Pb-210 distributions to infer mixing scale-lengths, sedimentation rates and chronologies. The VSR model improved the consistency of rates as determined by the two radiotracer methods and showed (1) sedimentation rates vary in nine cores studied by more than an order of magnitude (0.024 to 0.292 g cm-2 yr-1), and (2) that since roughly 1920 there has been a marked increase in rates relative to pre-modern (baseline) values. Changes ranged from 14 to 50% at sites depending on baseline sedimentation rates. By subtracting individual baseline rates, it is shown that all cores have recorded essentially the same time-dependent increase in accumulation rate in the Lake. Age-depth relations based on RSSM and VSR analysis are presented in graphical form as part of the report text while age-depth tables useful in conjunction with contaminant distribution measurements in companion cores can be found in the tables of the Appendix: RSSM (Appendix D), VSR (Appendix F).

SAYLOR, J.H., and G.S. MILLER. Current flow through the Straits of Mackinac. Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 5 pp. (1991).

No abstract.

SCHWAB, D.J., R.E. Jensen, and P.C. LIU. Comparative performance of spectral and parametric numerical wave prediction models in Lake Michigan. In Mechanics Computing in 1990s and Beyond, H. Adeli and R.L. Sierakowski (eds.). American Society of Civil Engineers, New York, NY, 363-367 (1991).

Four different numerical wave prediction models are used to hindcast wave conditions in Lake Michigan for a 10-day case in October, 1988. Results are compared to observed wave height and period measurements from two deep water NOAA weather buoys and from a nearshore Waverider buoy. The results of the comparison show that the accuracy of the interpolated wind fields is probably at least as important as differences in the wave prediction mls in explaining the differences between observed and computed waves.

Seitzinger, S.P., W.S. GARDNER, and A.K. Spratt. The effect of salinity on ammonium sorption in aquatic sediments: Implications for benthic nutrient recycling. Estuaries 14(2):167-174 (1991).

Ambient exchangeable ammonium concentrations in freshwater sediments are generally considerably greater than those reported for marine sediments. Laboratory measurements indicate that competition for cation exchange sites by ions in seawater is a factor responsible for the lower exchangeable ammonium concentrations in marine sediments. Exchangeable ammonium concentrations were 3- to 6-fold higher when river and estuarine sediments were incubated with fresh water relative to the same sediments incubated with salt water (% = 23). A model was developed to explore the implications for benthic nitrogen cycling of this salinity effect on exchangeable ammonium concentrations. Ammonium diffusion, exchangeable and dissolved ammonium concentrations, and nitrification rates were components of the model formulation. The model output suggests that higher exchangeable ammonium concentrations predicted in fresh water relative to marine sediments can markedly increase the fraction of the ammonium produced in sediments that is nitrified (and subsequently denitrified). These results are consistent with field and experimental laboratory data which indicate that a larger percentage of net ammonium production in aerobic fresh water sediments is nitrified and denitrified (80-100%) relative to marine sediments (40-60%).

SELLINGER, C.E. Hydromet Database Source Code. GLERL Open File Report, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (1991).

No abstract.

VANDERPLOEG, H.A. Feeding mechanisms and particle selection in suspension-feeding zooplankton. In The Biology of Particles in Aquatic Systems, R.S. Wotton (ed.). CRC Press, Boca Raton, FL, 183-212 (1990).

No abstract.

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