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GLERL Publication Abstracts: FY 2001

ASSEL, R. A. Ice records on Grand Traverse Bay. In Grand Traverse Bay State of the Bay Report 2000, C. Wright and A. Hensen (Eds.), The Watershed Center, Grand Traverse Bay, Traverse City, MI, pp. 18 (2000).

The dates of formation and loss of ice on lakes and rivers were of interest in past centuries in Europe, Asia, and North America because stable ice cover provided a platform for transportation, fishing, and hunting during the winter months. For these reasons, records of freeze-up and break-up have been kept for several centuries at some bays, rivers, and small inland lakes. These records are also of interest to scientists because the extent and duration of ice cover is a sensitive indicator of climate and climate change. Ice cover also affects biological activity in the waters under the ice. Records of freeze-up and break-up dates for Grand Travers Bay (which start in1851) are among the longest available for the Great Lakes. Freeze-up is defined to occur when there is solid ice over West Bay from its southern shoreline to Power Island.

ASSEL, R. A., and D. C. NORTON. Visualizing Laurentian Great Lakes ice cycles. EOS Transactions 82(7):83 (2001).

In 1994, under the auspices of the National Oceanic and Atmospheric Administration's (NOM) Earth System and Data Information Management (ESDIM) Program, a project was initiated to update a 20-winter digital ice concentration database and ice concentration climatology (see Internet at https://www.glerl.noaa.gov/res/Task_rpts/ccassel11-2.html). The data reduction phase of that project is now complete. The National Ice Center (NIC) and the Canadian Ice Service (CIS) contributed the historic ice charts used in this project. The first analysis product from the updated data- base is a set of computer animations of the seasonal progression of ice cover extent and concentration for 23 individual winter seasons. A daily time series of ice concentration grids was produced by interpolating between consecutive ice charts for a given winter season. These data were used to produce color-coded GIF files of daily ice concentration, the percent of a unit of surface area covered by ice, and subsequently, to make computer animations for each winter in AutoCAD Flic (FLC) and Audio Video Interleave (AVI) formats. The animations portray the spatial and temporal patterns of Great Lakes ice cover for each winter season from 1973 to 1995. The interannual variability of ice cover for a given date or period in the winter is portrayed by comparing animations for that date or period to different winters. Interannual and same-season variations in ice cover are of interest for analysis of other lake-related phenomena such as the frequency and extent of lake-effect snowfall, fish recruitment, and the timing of the spring costal processes associated with the loss of ice cover.

BELETSKY, D., and D. J. SCHWAB. Modeling circulation and thermal structure in Lake Michigan: Annual cycle and interannual variability. Journal of Geophysical Research 106(C9):19745-19771 (2001).

A three-dimensional primitive equation numerical model was applied to Lake Michigan for the periods 1982-1983 and 1994-1995 to study seasonal and interannual variability of lake-wide circulation and thermal structure in the lake. The model was able to reproduce all of the basic features of the thermal structure in Lake Michigan: spring thermal bar, full stratification, deepening of the thermocline during the fall cooling, and finally, an overturn in the late fall. Large-scale circulation patterns tend to be cyclonic (counterclockwise), with cyclonic circulation within each subbasin. The largest currents and maximum cyclonic vorticity occur in the fall and winter when temperature gradients are low but wind stresses are strongest. The smallest currents and minimum cyclonic vorticity occur in spring and summer when temperature gradients are strong but wind stresses are weakest. All these facts are in agreement with observations. The main shortcoming of the model was that it tended to predict a more diffuse thermocline than was indicated by observations and explained only up to half of the variance observed in horizontal currents at timescales shorter than a day.

Breneman, D., C. Richards, and S. LOZANO. Environmental influences on benthic community structure in a Great Lakes embayment. Journal of Great Lakes Research26(3):287-304 (2000). https://www.glerl.noaa.gov/pubs/fulltext/2000/20000007.pdf

Biological and chemical measurements of sediment are useful parameters when establishing long-term assessment and monitoring tools for designated areas of concern (AOCs) in the Great Lakes. An intensified Environmental Monitoring and Assessment Program (EMAP) sampling grid in the St. Louis River estuary of western Lake Superior was used to assess the relationship between surficial sediment characteristics and benthic community structure. Ninety sites within two habitat classes (< 5.5 m and >5.5 m depth) were randomly sampled. Sediment for chemical analysis was collected with a cylindrical drop core while benthic macroinvertebrate abundance and composition were determined from petite Ponar grab samples. Taxa richness was variable (1 to 25 taxa) among sites in the St. Louis River AOC. Oligochaeta were the most abundant taxa while Chironomidae larvae provided a majority of the taxa richness with 43 genera. Results from multivariate redundancy analysis (RDA) on 13 environmental parameters revealed that the majority of variation in benthic community structure was attributed to water depth and site distance from the headwaters. Although physical habitat alterations occur over large spatial scales and are more subtle than those conditions associated with chemically impacted sites, only a small portion of the variability in benthic community structure was explained by sediment chemistry variables. Variability in benthic community structure during this survey was best explained by physical habitat features and must first be quantified prior to understanding benthic response to contaminated sediments.

Budd, J. W., T. D. Drummer, T. F. NALEPA, and G. L. FAHNENSTIEL. Remote sensing of biotic effects: Zebra mussels (Dreissena polymorpha) influence on water clarity in Saginaw Bay, Lake Huron. Limnology and Oceanography 46(2):213-223 (2001).

https://www.glerl.noaa.gov/pubs/fulltext/2001/20010014.pdf https://www.aslo.org/lo/toc/vol_46/issue_2/0213.pdf

In this study, Advanced Very High Resolution Radiometer (AVHRR) remote sensing reflectance (Rrs), imagery from 1987-1993 is used to study changes in water clarity before and after zebra mussels (Dreissena polymorpha) were discovered in Saginaw Bay, Lake Huron. Spatial and temporal trends in the data indicate distinct and persistent increases in water clarity in the inner bay after the first large recruitment of zebra mussels in the fall of 1991. The pre-Dreissena imagery show that turbidity in the inner bay was influenced by the Saginaw River discharge in spring, biological production (plankton) in summer, and wind-driven resuspension in fall, with highest turbidity in spring and fall. Spatial patterns in the post Dreissena images were more similar regardless of season, with low reflectances in the shallow regions of the inner bay where zebra mussel densities were highest. A regression model based on point data from 24 sampling stations over the 7-yr period indicates that reflectances varied significantly by site and zebra mussel densities, as well as seasonally. Trends in observed and predicted values of reflectances followed similar patterns at each station-highest values were found during 1991 and lowest during 1992 at all stations, with slightly higher Rrs in 1993 compared to 1992. Whereas AVHRR Rrs highlight the value of historical imagery for reconstructing seasonal and interannual turbidity patterns in near-shore waters, a new generation of operational ocean color satellites, such as SeaWIFS (Sea-viewing Wide Field-of-view Sensor) and the newly launched MODIS (moderate resolution imaging spectroradiometer), now provide for routine monitoring of important biological and physical processes from space.

CROLEY, T. E. II. Climate-biased decisions via partial historical sampling. Proceedings, World Water and Environmental Resources Congress, Bridging the Gap: Meeting the World's Water and Environmental Resources Challenges, D. Phelps and G. Sehlke (Eds.), Orlando, FL, May 20-24, 2001. American Society of Civil Engineers, Washington, DC, pp. 10 (2001). https://www.glerl.noaa.gov/pubs/fulltext/2001/20010001.pdf

A heuristic approach for incorporating probabilistic meteorology outlook, via operational hydrology, into derivative hydrology probability forecasts or storm frequency distributions is described. It constructs a weighted set of future possibilities that agree with selected meteorology outlooks. Many times, calculated weights are zero-valued and a questions arised on how to properly consider them in the biased sample. After exploring the effects of directly using zero-valued weights, an alternative is presented that omits historical observations from the biased sample corresponding to zero-valued weights (partial historical sampling). This requires adjustment of the non-zero weights and redefinition of hydrology forecast statistics that are based on the biased sample. Examples of simple storm frequency estimation, using El Nino conditional probabilities, illustrate the problem with zero-valued weights for some estimators and their negligible effect with other estimators.

CROLEY, T. E. I. Climate-biased storm-frequency estimation. Journal of Hydrologic Engineering 6(4):275-283 (2001). https://www.glerl.noaa.gov/pubs/fulltext/2001/20010002.pdf

Storm frequencies for the future are often estimated directly from past historical records of sufficient length. The estimation requires no detailed knowledge of the areas meteorology, but presumes it is unchanged in the future. However, the climate seldom remains static. Numerous climate forecasts of meteorological probabilities over extended periods are now available. It is possible to use these meteorological forecasts directly in the estimation of storm frequencies from the historical record. A heuristic approach is defined here to estimate storm frequencies that recognize forecasts of extended weather probabilities. Basically, those groups of historical meteorological record segments matching forecast meteorological probabilities are weighted more than others, during the estimation of storm frequencies. (Affiliated groups of hydrologic record segments may be similarly weighted for hydrological estimation; e.g., flood frequency estimation.) An example of frequency estimation is made for maximum annual daily flow, using currently available agency meteorological forecasts in the United States and Canada.

EADIE, B. J., G. S. MILLER, M. B. LANSING, and A. G. WINKELMAN. Chapter 2. Settling particle fluxes and current and temperature profiles in Grand Traverse Bay, Lake Michigan. In Final Report. Trophic Transfer of Atmospheric and Sedimentary Contaminants into Great Lakes Fish: Controls on Ecosystem-Scale Response Time, University of Maryland Center for Environmental Science, Solomons, MD, pp. 25 (2001).

Settling particle fluxes and mass flux profiles are reported for trap samples collected at five stations in Grand Traverse Bay, Lake Michigan during 1997-1999. Trap collection precision is estimated, and 10 cm and 20 cm diameter sequencing traps are inter-calibrated using data from traps deployed in replicate on specially constructed brackets. Temperature data is reported for two stations (during June-September 1997). Acoustic Doppler Current Profilers (ADCP) current meter data and contours of backscatter strength, U and V current components, and water temperature are included for the 95 m station. All data is available online in ASCII and MS Excel formats at https://www.glerl.noaa.gov/pubs/tech_reports/glerl-116.

EADIE, B. J., and D. J. SCHWAB. Episodic Events - Great Lakes Experiment (EEGLE). In Newsletter of Coastal Ocean Processes, Skidaway Institute of Oceanography, Savannah, GA, pp. 8-9 (2001). https://www.glerl.noaa.gov/pubs/fulltext/2001/20010005.pdf

EEGLE PIs met at a three day workshop in late September, after the successful completion of our third and final year of field work, to discuss preliminary findings and foster interdisciplinary activities. The EEGLE program was designed to quantify the impacts of major late winter-early spring storms on sediment-water exchange, nearshore-offshore transport and subsequent influence on the lakes productivity.

FAHNENSTIEL, G. L., R. A. STONE, M. J. McCORMICK, C. L. Schelske, and S. E. Lohrenz. Spring isothermal mixing in the Great Lakes: Evidence of nutrient limitation and nutrient-light interactions in a sub-optimal light environment. Canadian Journal of Fisheries and Aquatic Science 57(9):1901-1910 (2000). https://www.glerl.noaa.gov/pubs/fulltext/2000/20000003.pdf

During the spring isothermal mixing period (April-May) in 1993-1995, photosynthesis-irradiance and growth-irradiance experiments were conducted in Lakes Erie, Huron. Michigan. and Ontario to assess light limitation. Additionally, nutrient enrichment experiments were conducted in Lake Ontario. Results from the photosynthesis-irradiance experiments suggested that phytoplankton communities in all the lakes can be either light limited or light saturated, as the threshold parameter (Ik) was similar to mean water column irradiances (1 wc, ratio = 1.0). Growth-irradiance experiments also suggested the potential for light saturation: mean daily irradiance exceeded the threshold growth irradiance (I k,g) in 95% of cases. Growth rates became light saturated at lower irradiances than photosynthetic rates. Evidence for a nutrient-light interaction in controlling in situ growth rates was also found in the nutrient enrichment experiments at incubation irradiances >= Iwc .Our results suggest that an interaction between nutrients and light is often controlling phytoplankton growth during spring mixing in the Great Lakes. The role of these nutrient-light interactions has increased in the past decade due to increased light availability in the lower lakes caused by phosphorus load reductions and the filtering activities of nonindigenous mussels.

FANSLOW, D. L., T. F. NALEPA, and T. H. JOHENGEN. Seasonal changes in the respiratory electron transport system (ETS) and respiration of the zebra mussel, Dreissena polymorpha in Saginaw Bay, Lake Huron. Hydrobiologia 448:61-70 (2001).

Electron transport system activity (ETS) and respiration rates (R) of the zebra mussel, Dreissena polymorpha, were determined monthly from April to November over 2 years at two sites in Saginaw Bay, Lake Huron. The sites were located in the inner and outer bay and contrasted in food quantity and quality. ETS ranged from 2 to 40 ug 0² mg DW^-1 h^-1 over the study period. Both ETS and respiration were strongly related to temperature, and maximum values were found between June and August. ETS also peaked in June/July when assays were conducted at a constant temperature (25 deg C), indicating other factors besides temperature affected metabolic activity. R:ETS ratios decreased with increased temperature at the inner bay site, but trends were minimal at the outer bay site. In late summer, blooms of the cyanophyte Microcystis occurred in the inner bay, likely depressing filtration rates, and leading to lower respiration rates relative to ETS. ETS activity was consistently higher in the outer bay and was likely a result of higher food quality. Despite these spatial differences, annual mean R:ETS ratios varied only from 0.04 to 0.09 at the two sites over the 2-year period. Based on these values, ETS may be useful as an indicator of long-term metabolic activity in annual energy budgets of D. polymorpha. However, food conditions differentially affect respiration relative to ETS, and variability in this ratio must be considered when interested in shorter time scales.

GARDNER, W. S., L. Yang, J. B. Cotner, T. H. JOHENGEN, and P. J. Lavrentyev. Nitrogen dynamics in sandy freshwater sediments (Saginaw Bay, Lake Huron). Journal of Great Lakes Research 27(1):84-97 (2001). https://www.glerl.noaa.gov/pubs/fulltext/2001/20010006.pdf

Sediment-water nitrogen fluxes and transformations were examined at two sites in Saginaw Bay, Lake Huron, as a model for sandy freshwater sediments. Substantial ammonium release rates (74 to 350 umole NH4+/m2/hl) were observed in flow-through cores and in situ benthic chamber experiments. Sediment-water ammonium fluxes were similar at the inner and outer bay stations even though inner bay waters are enriched with nutrients from the Saginaw River. The high net flux of remineralized ammonium into the overlying water from these sandy sediments resembles typical data for marine systems (11 to 470 umole NH4+/m2/h1) but were higher than those reported for depositional freshwater sediments (0 to 15 umole NH4+/m2/hl; Seitzinger 1988). Addition of montmorillonite clay (ca. 1 kg dry weight/m2) to the top of the sandy cores reduced ammonium flux. Mean "steady-state " ammonium flux following clay addition was 46 +- 2 (SE) % of the initial rates as compared to 81 +- 8% of the initial rates without clay addition. Zebra mussel excretion dominated ammonium regeneration in the inner bay where the bivalve was abundant, but addition of zebra mussel feces/pseudofeces ( 3.0 g dw/m2) to sediments did not increase ammonium or nitrate flux. Partial nitrification of ammonium at the sediment-water interface was suggested by removal of added 15 NH4+ from lake water passing over dark sediment cores. Sediment-water fluxes of nitrogen obtained from flow-through sediment cores resembled those from in situ benthic chambers. However, extended static incubations in gas-tight denitrification chambers caused more of the regenerated nitrogen to be nitrified and denitrified than occurred with the other two measurement systems.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Aquatic Invasive Species and the Great Lakes: GLERL's Program and Action Plan. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2001). https://www.glerl.noaa.gov/pubs/brochures/broch.html

The national awareness of aquatic invasive species and the problems they cause arose from the costly unintentional introduction of the zebra mussel in the Great Lakes in the late 1980s and its subsequent spread throughout the eastern half of the country.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Great Lakes Fish Community Impacted by Diporeia Disappearance? NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2001). https://www.glerl.noaa.gov/pubs/brochures/broch.html

Sport fishing in the Great Lakes is valued at over $4 Billion per year, with common catches consisting of lake trout, salmon, walleye, and yellow perch. With the coincident introduction of the zebra mussel and the disappearance of the important shrimp-like amphipod Diporeia, the Great Lakes fisheries are in jeopardy.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Great Lakes Ice Cover. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2001). https://www.glerl.noaa.gov/pubs/brochures/broch.html

Ice has a deeper connection to the Great Lakes than simply a signal of winter. In fact, the lakes were formed over several thousands of years as mile-thick layers of glacial ice advanced and retreated, scouring and sculpting the basin. In addition, the ebb and flow of glacial meltwaters and rebound of the underlying land from the weight of the massive ice sheets further changed the basin's shape and drainage patterns.

If you wander down the shores of Lake Michigan nowadays, it's difficult not to notice that beaches seem curiously wide. Rocks that were once barely visible now jut from the waves. Marina docks seem built too high for the boats that pull up to them. A glance at the pilings tells why: the dark line marking the lake levels of previous years is three feet about the water. Since 1998, the level of Lakes Michigan and Huron has dropped at the fastest pace ever recorded. Long-time residents have been reminded of the droughts of the 1930s and 1960s, when water levels also fell dramatically. Many more have grown concerned about the impact upon both the shipping industry and the environment.

During the winter of 1990-1991 time series measurements of current velocity, temperature, and attenuation (a measure of water transparency) were made at a site in 91 m of water near Copper Harbor, MI. The observations show that bottom resuspension occurred several times during the unstratified period. The resuspension is the result of the interaction between high bottom current velocities and surface waves generated by strong winds. Transport during the storms was almost entirely alongshore, although some offshore transport of material occurred. Calculations show that suspended material could have been transported eastward several hundred km during the unstratified period.

A numerical model based upon Deardorff (1980) was used to simulate heat transfer between a lake and the atmosphere. The model includes a lake-atmosphere heat exchange sub model, with penetration of solar radiation. Heat and momentum are transferred in the vertical with a one-dimensional model that disregards horizontal processes. Atmospheric forcing to drive the models was taken from NOAA Marobs buoy 45007 in the south central region of Lake Michigan, and from the nearby land based stations at Milwaukee, WI and Muskegon, MI. Three simulations were run and compared to field data collected by NOAA GLERL in 1996. The simulations focused on the formation of the thermocline from June 9 to August 1. The first simulation used land-based atmospheric data as inputs. the second used buoy data supplemented with land data where needed. The results were compared to the field data and showed that using terrestrial data can lead1o results that are plausible, but inaccurate. The third simulation used buoy and land data as before. but adjusted the incoming solar radiation to produce a better fit to the observed data. The adjustment apparently compensated for deficiencies in the land-based data.

Noninvasive species identification remains a longterm goal of fishers, researchers; and resource managers who use sound to locate, map, and count aquatic organisms. Since the first biological applications of underwater acoustics, four approaches have been used singly or in combination to survey marine and freshwater environments: passive sonar; prior knowledge and direct sampling; echo statistics from high-frequency measures; and matching models to low-frequency measures. Echo amplitudes or targets measured using any sonar equipment are variable signals. Variability in reflected sound is influenced by physical factors associated with the transmission of sound through a compressible fluid, and by biological factors associated with the location, reflective properties, and behavior of a target. The current trend in acoustic target identification is to increase the amount of information collected through increases in frequency bandwidth or in the number of acoustic beams. Exclusive use of acoustics to identify aquatic organisms reliably will require a set of statistical metrics that discriminate among a wide range of similar body types at any packing density, and incorporation of these algorithms in routine data processing.

Lavnun Mirogrex terraesanctae have a dual-chambered swim bladder and are the dominant fish species in Lake Kinneret, Israel. Bi-monthly acoustic assessments are used to monitor lavnun abundance but the relation between the amount of reflected sound and organism morphology is not well described. Predictions from Kirchhoff-ray mode (KRM) backscatter models show a sensitivity of echo amplitude to fish length and fish aspect. Predicted mean KRM target strengths matched maximum in situ target strength measurements of eight tethered fish within 2.5 dB at 120 kHz and within 7 dB at 420 kHz. Tilt and roll of lavnun during tethered measurements increased variance of backscatter measurements. Accurate abundance and length frequency distribution estimates cannot be obtained from in situ acoustic measurements without supplementary net samples.

The relationship between the body residue of 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP) and its effects, including 10-d mortality and chronic sublethal effects on the midge, Chironomus riparius, are examined in a partial life cycle assessment. The alga, Chlorella vulgari , was loaded with 14C-Iabeled HCBP and fed to midges as the method for delivery of the toxicant. In a 10-d bioassay, median lethal body residue (LR50) was 0.57 (95% CI: 0.49-0.66) mmol/kg. In the partial life cycle test, midges were fed a mixture of 12C- and 14C-HCBP-Iaden algae and exposed in four separate tests to assess the different developmental stages representing 2nd to 3rd instar, 2nd to 4th, 2nd to pupa, and 2nd to adult stages. A variety of sublethal endpoints were monitored, including developmental time within a stadium, body concentration at the end of each stadium, body weight, and fecundity (the number of ova) for the female pupae and adults. Overall, midge body concentrations of HCBP increased with increasing exposure concentration. Body weight was not significantly affected by HCBP except during the 4th instar. Body residue also increased with each successive stadium. Developmental time increased significantly with increasing body concentration in 2nd to 4th, 2nd to pupa, and 2nd to adult tests, while there was no statistical significance in developmental time for the 2nd to 3rd instar test. The number of ova decreased significantly in adults with increasing body concentration of HCBP, with an average of 345 ova in controls, 289 ova at 0.028 mmol/kg of HCBP, and 258 ova at 0.250 mmol/kg. These data, which relate chronic endpoints to body residues, suggest that sublethal endpoints in invertebrates are useful for defining sublethal hazards of PCBs. These data also suggest that ecological consequences may result from relatively low body burdens of PCBs.

One goal of acoustic-based abundance estimates is to accurately preserve spatial distributions of organism density and size within survey data. We simulated spatially random and spatially auto-correlated fish density and s_bs distributions to quantify variance in density, abundance, and backscattering cross-sectional area estimates, and to examine the sensitivity of abundance estimates to organism spatial distributions and methods of estimating acoustic size. Our results show that it is difficult to simultaneously estimate fish density and maintain accurate s_b-frequency distributions. Among our acoustic backscatter estimation methods, a weighted-mean from a local search window provided optimal estimates of density, abundance and crbs. Other methods tended to bias either crbs or density estimates. This analysis identifies the relative importance of variance sources when estimating organism density using spatially-indexed acoustic data.

The restoration and rehabilitation of the native fish communities is a long-term goal for the Laurentian Great Lakes. In Lake Superior, the ongoing restoration of the native lake trout populations is now regarded as one of the major success stories in fisheries management. However, populations of the deepwater morphotype (siscowet lake trout) have increased much more substantially than those of the nearshore morphotype (lean lake trout), and the ecosystem now contains an assemblage of exotic species such as sea lamprey, rainbow smelt, and Pacific salmon (chinook, coho, and steelhead). Those species play an important role in defining the constraints and opportunities for ecosystem management. We combined an equilibrium mass balance model (Ecopath) with a dynamic food web model (Ecosim) to evaluate the ecological consequences of future alternative management strategies and the interaction of two different sets of life history characteristics for fishes at the top of the food web. Relatively rapid turnover rates occur among the exotic forage fish, rainbow smelt, and its primary predators, exotic Pacific salmonids. Slower turnover rates occur among the native lake trout and burbot and their primary prey-lake herring, smelt, deepwater cisco, and sculpins. The abundance of forage fish is a key constraint for all salmonids in Lake Superior. Smelt and Mysis play a prominent role in sustaining the current trophic structure. Competition between the native lake trout and the exotic salmonids is asymmetric. Reductions in the salmon population yield only a modest benefit for the stocks of lake trout, whereas increased fishing of lake trout produces substantial potential increases in the yields of Pacific salmon to recreational fisheries. The deepwater or siscowet morphotype of lake trout has become very abundant. Although it plays a major role in the structure of the food web it offers little potential for the restoration of a valuable commercial or recreational fishery. Even if a combination of strong management actions is implemented, the populations of lean (nearshore) lake trout cannot be restored to pre-fishery and pre-lamprey levels. Thus, management strategy must accept the ecological constraints due in part to the presence of exotics and choose alternatives that sustain public interest in the resources while continuing the gradual progress toward restoration.

Sediment-associated contaminants are a legacy of the industrial development of the United States. Sediments provide repositories of persistent and highly sorptive contaminants that have found their way into our lakes, rivers, streams, estuaries, and coastal oceans. These contaminated sediments have been found to have substantial effects on the ecosystem ranging from direct effects on benthic communities to substantial contributions to contaminant loads and effects on upper trophic levels through food chain contamination for tree swallows, for Caspian terns, for mink. These effects directly impact human health in that the number of watersheds with fish consumption advisories is directly proportional to the extent of sediment contamination.

The amphipod, Diporeia spp., the dominant benthic macroinvertebrate in the Great Lakes offshore waters, has exhibited a substantial decline in recent years. This decline occurred after the invasion and colonization of the lakes by the zebra mussel, Dreissena polymorpha. It has been hypothesized that the decline is a direct result of the competition by the zebra mussel decreasing the amount of food available. This study examined the potential of other stressors, e.g., the presence of toxic materials, as the contributing or main cause of the decline. Bioassays were performed with sediments from stations currently devoid of Diporeia (St. Joseph, MI) and with those still having Diporeia populations. In 28-d mortality bioassays, no mortality was observed with any of the sediments tested. However, in avoidance/preference tests, sediments from St. Joseph, that are now devoid of Diporeia, were avoided compared to sediments from Saugatuck, Grand Haven, and Muskegon, which still have a population. This avoidance was not changed by the addition of either Spirulina Plus@ or Tetramin@ flakes to the sediment as a food source but was reversed by a fresh layer of the diatom, Fragillaria crotonensi, on the sediment. These studies suggest that despite the high carbon content of the St. Joseph sediment, the nutritional content of the sediment was limited.

 

The toxicokinetics of four polychlorinated biphenyl (PCB) congeners were determined for the amphipod Diporeia spp. exposed to selected PCB congeners through both water and sediment to determine the effect of temperature and organism size (mass). For compounds with log K_ow 6 or greater, the water-only uptake coefficient (k_u) was inversely proportional to the size of the organism at all temperatures. For monochlorobiphenyl, k_u was directly proportional to organism mass only at 16 deg C. Increasing temperature resulted in increasing uptake rate coefficients for all compounds except hexachlorobiphenyl (HCBP) where k_u did not appear to depend on temperature. The hydrophobicity of the contaminants did not contribute significantly to changes in uptake rate from water. The elimination rate constant (k_e) was inversely proportional to organism size but was not significantly affected by temperature. The elimination rate constant declined exponentially with increasing log K_ow As log K_ow increased, the effect of organism mass on k_e was greatly reduced. The uptake from sediment was affected by temperature and the congener log K_ow. At lower temperatures, the uptake coefficient from sediment (k_s) declined with increasing log K_ow, while at higher temperatures, it exhibited a slight upward trend. Smaller animals had much higher uptake rates from sediment than large or medium size animals. Small animals exhibited very high biota-sediment accumulation factors (5.4 to 20.8) over 4 to 16 deg C for HCBP (BSAF, concentration in the organism normalized to the lipid content divided by the concentration in the sediment normalized to the organic carbon content ). The relationship between BSAF and log K_ow was exponential for both laboratory and field data.

Two models, a S polycyclic aromatic hydrocarbon (PAR) model based on equilibrium partitioning theory and a logistic regression model, were developed and evaluated to predict sediment-associated PAR toxicity to Hyalella azteca. A SPAR model was applied to freshwater sediments. This study is the first attempt to use a IPAR model based on water-only, median lethal concentration (LC50) toxic unit (TU) values for sediment-associated PAR mixtures and its application to freshwater sediments. To predict the toxicity (i.e., mortality) from contaminated sediments to H. azteca, an interstitial water TU, calculated as the ambient interstitial water concentration divided by the water-only LC50 in which the interstitial water concentrations were predicted by equilibrium partitioning theory, was used. Assuming additive toxicity for PAR, the sum of TUs was calculated to predict the total toxicity of PAR mixtures in sediments. The SPAR model was developed from 10- and 14-d H. azteca water-only LC50 values. To obtain estimates of LC50 values for a wide range of PARs, a quantitative structure-activity relationship (QSAR) model (log LC50 - log Kow) with a constant slope was derived using the time-variable LC50 values for four PAR congeners. The logistic, regression model was derived to assess the concentration-response relationship for field sediments, which showed that 1.3 (0.63,9) TU were required for a 50% probability that a sediment was toxic. The logistic-regression model reflects both the effects of co-occurring contaminants (i .e., no measured PAR and unknown pollutants) and the overestimation of exposure to sediment-associated PAR. An apparent site-specific bioavailability limitation of sediment-associated PAR was found for a site contaminated by creosote. At this site, no toxic samples were less than 3.9 TU. Finally ,the predictability of the !PAR model can be affected by species-specific responses (Hyalella vs Rhepoxynius) chemical specific (PAH vs DDT in H. azteca) biases, which are not incorporated in the equilibrium partitioning model, and the uncertainty from site-specific effects (creosote vs other sources of PAR contamination) on the bioavailability of sediment-associated PAR mixtures.

This article uses a comparison of four different numerical wave prediction models for hind-cast wave conditions in Lake Michigan during a 10-day episode in October 1998 to illustrate that typical wave prediction models based on the concept of a wave energy spectrum may have reached a limit in the accuracy with which they can simulate realistic wave generation and growth conditions. In the hindcast study we compared the model results to observed waveheight and period measurements from two deep water NOAA/NDBC weather buoys and from a nearshore Waverider buoy. Hourly wind fields interpolated from a large number of coastal and overlake observations were used to drive the models. The same numerical grid was used for all the models. The results show that while the individual model predictions deviate from the measurements by various amounts, they all tend to reflect the general trend and patterns of the wave measurements. The differences between the model results are often similar in magnitude to differences between model results and observations. Although the four models tested represent a wide range of sophistication in their treatment of wave growth dynamics--they are all based on the assumption that the sea state can be represented by a wave energy spectrum. Because there are more similarities among the model results than significant differ-ences, we believe that this assumption may be the limiting factor for substantial improvements in wave modeling.

The Great Lakes/St. Lawrence Seaway is used for transportation, hydropower generation, and recreation. Hydropower facilities are located on the St. Marys, Niagara, and St. Lawrence Rivers and at DeCew Falls off the Welland Canal. The Great Lakes are also one of the prime recreational boating areas in the country. The three-county area around Detroit has more boating registrations than any other similar-sized area in the U.S. The Great Lakes system contains one of the nation's prime sport fisheries as well as a smaller commercial fishery, representing billions of dollars to the economy. Because the Great Lakes basin is an internationally shared resource, there are numerous state, provincial, county, and municipal authorities, leading to a complex jurisdictional structure.

Accurate estimates of surface energy exchange components are critical for understanding many physical processes of large lakes and their atmospheric environment. In this paper, the seasonal cycle of latent, sensible, and total heat flux from the surface of the Great Lakes is estimated. Lake surface temperatures derived from the NOAA AVHRR satellite, along with meteorological data from surface station observations are incorporated in order to estimate spatial distributions of fluxes. Several well-known features are evident. Among these are the very high outgoing fluxes of latent and sensible heat during the late fall and early winter, which drive strong cooling of the lake surface and consequent convective mixing within the lake column. Another is greater seasonal variation of surface temperature and fluxes in shallower waters than in deeper waters. Due to strong static stability of the overlying atmospheric boundary layer during the spring, both the magnitude and the spatial variations of latent and sensible heat fluxes are small during the spring and, to a lesser degree, during the summer. The annual cycles of latent and sensible heat flux over the Great Lakes are roughly opposite in phase to the same fluxes over land, indicating a large exchange of energy via atmospheric advection between the lake and land surfaces. A major weakness of the method used here is that heat fluxes are calculated on the basis of an ice-free surface, making the derived fluxes for January through March roughly estimated.

The amphipods Hyalella azteca and Diporeia spp. were exposed to sediments dosed with dichlorodiphenyltrichloroethane (DDT), and the toxicity and toxicokinetics were determined. The toxicity was evaluated with the equilibrium partitioning (EqP) and critical body residue approaches, The DDT in the sediments degraded during the equilibration period prior to organism exposure. Thus, the toxicity using EqPpore-water toxic units (TUs) was evaluated for DDT and its degradation product, dichlorodiphenyldichloroethane (DDD), as the ratio of the predicted interstitial water concentration divided by the water-only LC50 values. The sum of TUs (STU) was assumed to best represent the toxicity of the mixture. For H. azteca, the 10-d LC50 was 0.98 and 0.33 STU for two experiments. For Diporeia spp., no toxicity was found in the first experiment with up to 3 STU predicted in the interstitial water. However, in the second experiment, the 28-d LC50 was 0.67 STU. These data suggest that the EqP approach approximately predicts the toxicity for the combination of DDT and DDD in sediment, provided a toxic unit approach is employed. The critical body residue approach also used TUs because DDT is biotransformed by H. azteca and because of the dual exposure to DDT and DDD. Because biotransformation was only determined in the second experiment, the critical body residue approach could only be evaluated for that case. The TUs were calculated as the ratio of the concentration in the live amphipods divided by the respective LR50 (residue concentration required to produce 50% mortality) values. The LR50 was 1.1 STU for H. azteca for the 10-d exposure and 0.53 for Diporeia spp. after a 28-d exposure. Thus, this approach was also quite successful in predicting the toxicity. The accumulation and loss rates for H. azteca were much greater than for Diporeia spp. Thus, 10-d exposures represent steady-state conditions for H. azteca, while even at 28-d, the Diporeia spp. are not at steady state.

Surveys of benthic macroinvertebrates conducted in Lake Ontario during 1994 and 1997 revealed recent declines in populations of three major taxonomic groups: Oligochaeta, Sphaeriidae, and Diporeia spp. (Amphipoda), with the most drastic reductions occurring in the latter. Results from sediment measurements were used to classify deepwater sediments into three habitat zones. Densities of all three taxa declined in the shallowest (12-88 m) of the sediment zones between 1994 and 1997; the greatest changes in density were observed for Diporeia, which declined from 3011 to 145 individuals x m^-2, and for total benthic macroinvertebrates, which declined from 5831 to 1376 individuals x m^-2. Mean densities of Dreissena spp. In 1997 were highest in the shallowest zone, and the areas of greatest densities corresponded to areas of largest reductions in Diporeia populations. We believe that dreissenids are competing with Diporeia by intercepting the supply of fresh algae essential for Diporeia survival. A decline in macroinvertebrate densities, especially populations of an important food item such as Diporeia, in Lake Ontario sediments at depths of 12-88 m may have a detrimental impact on the benthic food web.

A spatially-explicit methodology was developed for estimating system carrying capacities of fish stocks, and used to estimate the seasonal and spatial patterns of carrying capacity of Chesapeake Bay for Atlantic menhaden (Brevoortia tyrannus). We used a spatially-explicit three-dimensional (3-D) model that divided the heterogeneous habitat of Chesapeake Bay into over 4,000 cubes. Each cube represented a volume of water that was characterized by a specific set of environmental variables (phytoplankton biomass, temperature, and dissolved oxygen) driven by the 3-D water quality model. Foraging and bioenergetics models transformed the environmental variables into measures of potential growth rates of menhaden. Potential carrying capacity of menhaden was estimated as a function of phytoplankton production, menhaden consumption rate, and potential growth rate, combining phytoplankton production, thermal habitat, and menhaden physiology into one ecological value that is a measure of habitat quality from the perspective of the fish. Seasonal analysis of the Chesapeake Bay carrying capacity for Atlantic menhaden suggested two bottleneck periods: one in early June and a second during the fall. The fall bottleneck in carrying capacity was at about 10 billion age-0 fish. Annual recruitment of age-0 menhaden for the entire Atlantic coast of the U.S. ranged from 1.2-18.6 billion fish between 1955 and 1986. It appears that carrying capacity of Chesapeake Bay does not limit the coastwide production of young menhaden. Any conditions such as nutrient reduction strategies, further eutrophication, or global climatic warming, that may influence the carrying capacity during the fall or early June periods, may ultimately alter coastwide abundance of menhaden through changes in Chesapeake Bay carrying capacity.

Freeze and breakup dates of ice on lakes and rivers provide consistent evidence of later freezing and earlier breakup around the Northern Hemisphere from 1846-1995. Over these 150 years, changes in freeze dates averaged 5.8 days per 100 years later, and changes in breakup dates averaged 6.5 days per 100 years earlier; these translate to increasing air temperatures of about 1.2 C per 100 years. Interannual variability on both freeze and breakup dates has increased since 1950. A few longer time series reveal reduced ice cover (a warming trend) beginning as early as the 16th century, with increasing rates of change after about 1850.

Applications of underwater acoustics in the Great Lakes can be traced back to the1960s. These early studies focused on fish distributions at power plant thermal plumes (Spigarelli et al., 1973; Stuntz, 1973), and on estimating zooplankton distribution and biomass (McNaught, 1968). During these early years, data assimilation consisted of a paper chart recorder and an analog recording of output voltages on magnetic tape. Even with limited technology, McNaught (1969) was one of the first researchers, in marine or freshwater environments, to propose and develop a multi-frequency sonar system for size-class discrimination of zooplankton. Due to data storage and analysis limitations, these early studies were completed on a localized scale. With technological improvements in electronic and computer technology, larger scale surveys were conducted on Lakes Michigan (Brandt, 1975, 1978, 1980; Brandt et al., 1980; Janssen and Brandt, 1980), Huron (Argyle, 1982), and Superior (Heist and Swenson, 1983) and provided the first quantitative estimates of fish abundance, density, and spatial distribution. Using a 50 kHz single beam scientific echo sounder and deconvolution techniques (Peterson et al., 1976), Brandt (1980) studied the diel vertical migration, thermal ecology, and spatial segregation of various life stages of alewives in Lake Michigan. He found that alewife migrate to the thermocline at night and disperse, and that adult and young-of-the year (YOY) alewives thermally segregate. This information was the foundation for nighttime assessment of alewives in the Great Lakes. Heist and Swenson (1983) estimated rainbow smelt abundance in the western basin of Lake Superior during 1978-1980 to provide prey fish numbers used in reestablishing the native piscivore community and for assessing the impact of an expanding commercial fisheries. Their acoustics application was one of the first in the Great Lakes that focused on direct management applications.

 

Long-term changes in benthic macroinvertebrate populations have long been used to assess trends in environmental conditions and trophic status in the Great Lakes (for summary see Cook and Johnson 1974). Until the late 1960s/early 1970s, although some sensitive forms declined, the general trend was particularly in the bays and nearshore areas. These increases reflected increasing nutrient loads (phosphorus) and greater system productivity, allowing greater inputs of organic materials to the benthic region. This material served as food for the taxa most able to utilize this resource. To reverse atrophic trends, phosphorus control measures were implemented in the mid-1970s. By the early 1970s, overall productivity declined in many areas and water quality improved as indicated by decreased macroinvertebrate densities and a return of more sensitive taxa.

The first finding of the amphipod Echinogammarus ischnus and the mussel Dreissena bugensis in Lake Michigan is documented. These two species are widespread and abundant in the lower lakes, but had not yet been reported from Lake Michigan. E. ischnus is generally considered a warm-water form that is typically associated with hard substrates and Dreissena clusters in the nearshore zone. Along the eastern shoreline of Lake Michigan, this species was present at rocky, breakwall habitats along the entire north-south axis of the lake. Although not abundant, this species was also found at soft-bottomed sites as deep as 94 m in the southern basin. The finding of this species in deep offshore waters apparently extends the known habitat range for this species in the Great Lakes, but it is found in deep water areas within its native range (Caspian Sea). D. bugensis was not abundant, but was present in both the southern and northern portions of the lake. Individuals of up to 36 mm in length were collected, indicating that it had probably been present in the lake for 2 or more years. Also presented are depth-defined densities of D. polymorpha at 37 sites in the Straits of Mackinac in 1997, and densities at up to 55 sites in the southern basin in 1992/93 and 1998/99. Mean densities decreased with increased water depth in both regions. Maximum mean density in the Straits in 1997 was 13,700/m² (<=10 m), and maximum density in the southern basin in 1999 was 2,100/m² (<=30 m). Mean densities at the <=30-m interval in the southern basin remained relatively unchanged between 1993 and 1999, but increased from 25/m² to 1,100/m² at the 31 to 50 m interval over the same time period. D. polymorpha was rare at sites > 50 m. The presence of E. ischnus and the expected population expansion of D. bugensis will likely contribute to further food-web changes in the lake.

NOAA in partnership with the National Ice Center has constructed a near real-time data delivery system for SAR imagery. One of the principal applications of this imagery is to support the mission of the NOAA CoastWatch program; i.e., to provide near real-tie satellite data to environmental resource managers, fishery scientists, and environmental analysts. There are two CoastWatch applications of SAR imagery that are approaching operational status: (1) remote sensing of ice on the Great lakes and in Alaska coastal waters, and (2) monitoring of the spring ice break-u on Alaskan rivers. The status of these applications will be presented. Also, the development status of other potential applications of SAR data will be summarized, including (1) high-resolution wind measurements, (2) mapping of oil spills, and (3) fisheries management.

The abundance and life history characteristics of Mysis relicta were evaluated at an offshore (110-m) and a nearshore (40 to 45-m) station during 1995, 1996, and 1998. Data were collected to monitor mysids relative to ongoing ecological changes in Lake Michigan and as a comparison to studies from the 1970s and 1980s. Mean densities of M. relicta during May through September each year were higher offshore (210/m² to 373/m²) compared to nearshore (41/m² to 168/m²). Growth rates ranged between 0.026 to 0.041 mm/day and did not differ between stations or with age. Juvenile mysids (< 10 mm) dominated the population, and accounted for 30 to 90% of the catch. The size distribution of M. relicta suggested that reproduction occurred year-round with the most consistent influxes of juveniles in the spring (April through June) each year; winter (February and March) and summer (July through September) influxes of juveniles did not occur consistently each year. Mean length of females with broods differed between nearshore (14 mm) and offshore (16 mm). Brood size and the proportion of females with broods did not differ between stations. Abundance estimates were equal or higher and life history characteristics were similar to reported data from the 1970s and 1980s. However, ongoing declines in the benthic macroinvertebrate Diporeia may result in higher fish predation pressure on M. relicta in the near future.

Recent, unmixed sediments from mud banks of central Florida Bay were dated using ²¹⁰Pb/²²⁶Ra, and chronologies were verified by comparing sediment lead temporal records with Pb/Ca ratios in annual layers of coral (Montastrea annulari) located on the ocean side of the Florida Keys. Dates of sediment lead peaks (1978 +- 2) accord with prior observations of a 6 year lag between the occurrence of maximum atmospheric lead in 1972 and peak coral lead in 1978. Smaller lags of 1-2 years occur between the maximum atmospheric radionuclide fallout and peaks in sediment temporal records of ¹³⁷CS and Pu. Such lags are consequences of system time averaging (STA) in which atmospherically delivered particle-associated constituents accumulate and mix in a (sedimentary?) reservoir before transferring to permanent sediments and coral STA model calculations. using time-dependent atmospheric inputs. produced optimized profiles in excellent accord with measured sediment ¹³⁷CS, Pu, lead, and coral lead distributions. Derived residence times of these particle tracers (16 +- 1,15.7 +-; 0.7, 19 +- 3, and 16 +- 2 years, respectively) are comparable despite differences in sampling locations, in accumulating media, and in element loading histories and geochemical properties For a 16 year weighted mean residence time, STA generates the observed 6 year lead peak lag. Evidently, significant levels of nondegradable, particle-associated contaminants can persist in Florida Bay for many decades following elimination of external inputs. Present results, in combination with STA model analysis of previously reported radionuclide profiles, suggest that decade-scale time averaging may occur widely in recent coastal marine sedimentary environments.

We analyzed the relationship between an index of Great Lakes winter severity (winters 1950-1998) and atmospheric circulation characteristics. Classification and Regression Tree analysis methods allowed us to develop a simple characterization of warm, normal and cold winters in terms of teleconnection indices and their combinations. Results are presented in the form of decision trees. The single most important classifier for warm winters was the Polar/Eurasian index (POL). A majority of warm winters (12 out of 15) occurred when this index was substantially positive (POL > 0.23 ). There were no cold winters when this condition was in place. Warm winters are associated with a positive phase of the Western Pacific pattern and El Nino events in the equatorial Pacific. The association between cold winters and La Nina events was much weaker. Thus, the effect of the El Nino/Southern Oscillation (ENSO ) on severity of winters in the Great Lakes basin is not symmetric. The structure of the relationship between the index of winter severity and teleconnection indices is more complex for cold winters than for warm winters. It takes two or more indices to successfully classify cold winters. In general, warm winters are characterized by a predominantly zonal type of atmospheric circulation over the Northern Hemisphere (type W1). Within this type of circulation it is possible to distinguish two sub-types, W2 and W3, Sub-type W2 is characterized by a high-pressure cell over North America, which is accompanied by enhanced cyclonic activity over the eastern North Pacific. Due to a broad southerly "anomalous" flow, surface air temperatures (SATs) are above normal almost everywhere over the continent. During the W3 sub-type, the polar jet stream over North America, instead of forming a typical ridge-trough pattern, is almost entirely zonal, thus effectively blocking an advection of cold Arctic air to the south. Cold winters tend to occur when the atmospheric circulation is more meridional (type C1). As with warm winters, there are two sub-types of circulation, C2 and C3. In the case of C2, the jet stream loops southward over the western part of North America, but its northern excursion over the eastern part is suppressed. In this situation, the probability of a cold winter is higher for Lake Superior than for the lower Great Lakes. Sub-type C3 is characterized by an amplification of the climatological ridge over the Rockies and the trough over the East coast. The strongest negative SAT anomalies are located south of the Great Lakes basin so that the probability of a cold winter is higher for the lower Great lakes than for Lake Superior.

This study examines inconsistencies in the Pacific/North American (PNA) index relative to atmospheric circulation over North America. Two types of atmospheric circulation were found to be associated with high PNA values. The first type is the true PNA pattern characterized by an amplified ridge-trough system. It appears to be related to the leading mode of sea surface temperature variability in the North Pacific. The second type is observed during El Nino events It is characterized by a flattening of the polar jet stream and southward shift of the subtropical jet stream The recognition of these two types of the PNA index improves our understanding of the relative role of to El Nino /Southern Oscillation events and sea surface temperatures in the North Pacific in affecting winter atmospheric circulation over North America.

After an absence of 40 years, mayfly nymphs of the genus Hexagenia were found in sediments of western Lake Erie of the Laurentian Great Lakes in 1993 and, by 1997, were abundant enough to meet a mayfly-density management goal (ca. 350 nymphs m²) based on pollution-abatement programs. We sampled nymphs in western Lake Erie and Lake St. Clair, located upstream of western Lake Erie, to determine the importance of seasonal abundance and life-history characteristics of nymphs (e.g., emergence and recruitment) on density estimates relative to the mayfly-density management goal. Two types of density patterns were observed (1) densities were relatively high in spring and gradually decreased through late summer (observed in Lake Erie and Lake St Clair in 1997 and Lake St Clair in 1999), and (2) densities were relatively high in spring, gradually decreased to mid summer, abruptly decreased in mid summer, and then increased between summer and late fall (Lake Erie and Lake St. Clair in 1998 and Lake Erie in 1999). Length-frequency distributions of nymphs and observations of adults indicate that the primary cause for the two density patterns was attributed to failed (first pattern) and successful (second pattern) reproduction and emergence of nymphs into adults in mid summer. Gradual declines in densities were attributed to mortality of nymphs. Our results indicate that caution should be used when evaluating progress of pollution-abatement programs based on mayfly densities because recruitment success is variable both between and within years. Additionally, the interpretation of progress toward management goals, relative to the restoration of Hexagenia populations in the Great Lakes and possibly other water bodies throughout the world, is influenced by the number of years in which consecutive collections are made.

Detroit River flows are important to the Great Lakes water resources. Changes in these flows affect hydropower usage, navigational activities, and shoreline profiles to name a few. The spread of zebra mussels into the Great Lakes system led to increased clarity of the water in Lakes St. Clair and Erie and the Detroit River due to their filter feeding habits. This increased clarity could amplify aquatic weed growth since light is able to penetrate deeper into the water column and increase the photosynthetic process. Increased weed growth acts to increase the hydraulic roughness of the Detroit River during the growing season, thus changing the river's hydraulic properties. As Detroit River flows are used in a wide variety of water resource studies, it is important to quantify both the amount and the seasonal distribution of the weeds and the increase in roughness due to the impact of the zebra mussel.

Perylene, a polycyclic aromatic hydrocarbon (PAH) that is common in sediments is believed to originate principally from anaerobic diagenesis of organic matter, but its precursor material remains enigmatic. We have investigated the formation of perylene in a dated sediment core from Green Bay, WI. Comparisons of sedimentary profiles of perylene, anthropogenic PAHs, land-plant-derived hydrocarbons, and aquatic contributions of organic matter rule out a specific industrial, terrigenous, or aquatic precursor for perylene. Instead, perylene seems to be formed from any kind of organic matter as a consequence of a specific type of microbial activity in sub-bottom sediments. Despite an abundance of organic matter, the amount of perylene is low in Green Bay and in other organic-carbon-rich lake sediments. The abundant availability of organic matter that stimulates microbial activity in Green Bay sediments would seem to favor perylene formation in such sediments. We therefore hypothesize that the microorganisms responsible for perylene formation do not compete successfully with those that flourish in sediments rich in organic matter. Perylene formation consequently does not become significant until deeper in sediments after the more-reactive types of organic matter have been consumed.

Perylene is an abundant and common polycyclic aromatic hydrocarbon in sedimentary settings, yet its origin remains puzzling. We have investigated the relation of perylene to the amount and type of organic matter in the sediments of Saanich Inlet, a coastal marine anoxic basin. Organic matter is predominantly marine in origin, but the proportions of marine and land-derived components have varied. Perylene concentrations generally increase with sediment depth, relative to TOC, which indicates continued formation of this compound by microbially mediated diagenesis. Perylene d^l3C values range between -27.7 and -23.6 0/00, whereas TOC d^l3C values vary narrowly from -21.7 to -21.2 0/00 over the same sediment depth interval. The variation in isotopic difference suggests that perylene originates from more than one precursor material, both aquatic and continental organic matter, different microbial processes, or some combination of these possibilities.

We developed a mean field, metapopulation model to study the consequences of habitat destruction on a predator-prey interaction. The model complements and extends earlier work published by Bascompte and Sole (1998, J. Theor. Biol. 195, 383-393) in that it also permits use of alternative prey (i.e., resource supplementation) by predators. The current model is stable whenever coexistence occurs, whereas the earlier model is not stable over the entire domain of coexistence. More importantly, the current model permits an assessment of the effect of a generalist predator on the trophic interaction. Habitat destruction negatively affects the equilibrium fraction of patches occupied by predators, but the effect is most pronounced for specialists. The effect of habitat destruction on prey coexisting with predators is dependent on the ratio of extinction risk due to predation and prey colonization rate. When this ratio is less than unity, equihbrial prey occupancy of patches declines as habitat destruction increases. When the ratio exceeds one, equihbrial prey occupancy increases even as habitat destruction increases; i.e., prey "escape" from predation is facilitated by habitat loss. Resource supplementation reduces the threshold colonization rate of predators necessary for their regional persistence, and the benefit derived from resource supplementation increases in a nonlinear fashion as habitat destruction increases. We also compared the analytical results to those from a stochastic, spatially explicit simulation model. The simulation model was a discrete time analog of our analytical model, with one exception. Colonization was restricted locally in the simulation, whereas colonization was a global process in the analytical model. After correcting for differences between nominal and effective colonization rates, most of the main conclusions of the two types of models were similar. Some important differences did emerge, however, and we discuss these in relation to the need to develop fully spatially explicit analytical models. Finally, we comment on the implications of our results for community structure and for the conservation of prey species interacting with generalist predators.

Spatial models of fish growth rate potential have been used to characterize a variety of environments including estuaries, the North American Great Lakes, small lakes and rivers. Growth rate potential models capture a snapshot of the environment but do not include the effects of habitat selection or competition for food in their measures of environment quality. Here, we test the ability of spatial models of fish growth rate potential to describe the quality of an environment for a fish population in which individual fish may select habitats and local competition may affect per capita intake. We compare growth rate potential measurements to simulated fish growth and distributions of model fish from a spatially explicit individual-based model offish foraging in the same model environment. We base the model environment on data from Lake Ontario and base the model fish population on alewife in the lake. The results from a simulation experiment show that changes in the model environment that caused changes in the average growth rate potential correlated extremely highly (r2>=0.97) with changes in simulated fish growth. Unfortunately, growth rate potential was not a reliable quantitative predictor of simulated fish growth nor of the fish spatial distribution. The inability of the growth rate potential model to quantitatively predict simulated fish growth and fish distributions results from the fact that growth rate potential does not consider the effects of habitat selection or of competition on fish growth or distribution, processes that operate in our individual-based model and presumably also operate in nature. The results, however, do support the use of growth rate potential models to describe the relative quality of habitats and environments for fish populations.

The accumulation kinetics of polycyclic aromatic hydrocarbons (PAHs) by the freshwater oligochaete Lumbriculus variegatus were measured for field-contaminated and laboratory-dosed sediment. In addition, sediment manipulations typically used for homogenization and dosing in bioaccumulation assays were compared. Rather than an asymptotic approach to steady state, both resident and dosed PAH accumulation exhibited a peak during the 14-d assays, with steeper declines being noted for the lower molecular-weight compounds. Lack of evidence of a peak for higher-molecular-weight PAHs may be due to slower kinetics and the short length of the assay. Relative to minimally mixed sediment, slurried sediment enhanced the accumulation of less-soluble resident PAHs, did not affect moderately soluble PAHs, and reduced the uptake of the more-soluble PAHs, fluorene and phenanthrene. Aging sediment after mixing reduced the availability of highly to moderately soluble resident PAHs but had no effect on less soluble PAHs. A similar effect was noted for dosed PAHs, though a larger reduction in bioavailability was observed. Dosed PAH uptake clearance coefficients (ks) exceeded those of minimally mixed resident PAHs by factors of 3 to 4 for pyrene and 26 for benzo[a]pyrene. These results demonstrate that sediment manipulations and contamination history need to be considered when measuring PAH bioaccumulation.

Microcystis aeruginosa, a planktonic colonial cyanobacterium, was not abundant in the 2-year period before zebra mussel (Dreissena polymorpha) establishment in Saginaw Bay (Lake Huron) but became abundant in three of five summers subsequent of mussel establishment. Using novel methods, we determined clearance, capture, and assimilation rates for zebra mussels feeding on natural and laboratory M. aeruginosa strains offered alone or in combination with other algae. Results were consistent with the hypothesis that zebra mussels promoted blooms of toxic M. aeruginosa in Saginaw Bay, western Lake Erie, and other lakes through selective rejection in pseudofeces. Mussels exhibited high feeding rates similar to those seen for a highly desirable food alga (Cryptomonas) with both large (>53 um) and small 53 um) colonies of a nontoxic and a toxic laboratory strain of M. aeruginosa known to cause blockage of feeding in zooplankton. In experiments with naturally occurring toxic M. aeruginosa from Saginaw Bay and Lake Erie and a toxic isolate from Lake Erie, mussels exhibited lowered or normal filtering rates with rejection of M. aeruginosa in pseudofeces. Selective rejection depended on "unpalatable" toxic strains of M. aeruginosa occurring as large colonies that could be rejected efficiently while small desirable algae were ingested.

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