Lake Michigan Mass Balance Study Research Articles

The Stratification Analysis of Sediment Data for Lake Michigan

Accurately understanding the distribution of sediment measurements within large water bodies such as Lake Michigan is critical for modeling and understanding of carbon, nitrogen, silica, and phosphorus dynamics. Several water quality models have been formulated and applied to the Great Lakes to investigate the fate and transport of nutrients and other constituents, as well as plankton dynamics.This paper summarizes the development of spatial statistical tools to study and assess the spatial trends of the sediment data sets, which were collected from Lake Michigan, as part of Lake Michigan Mass Balance Study. Several new spatial measurements were developed to quantify the spatial variation and continuity of sediment data sets under concern. The applications of the newly designed spatial measurements on the sediment data, in conjunction with descriptive statistics, clearly reveal the existence of the intrinsic structure of strata, which is hypothesized based on linear wave theory. Furthermore, a new concept of strata consisting of two components defined based on depth is proposed and justified. The findings presented in this paper may impact the future studies of sediment within Lake Michigan and all of the Great Lakes as well.

The Stratification Analysis of Sediment Data for Lake Michigan

Accurately understanding the distribution of sediment measurements within large water bodies such as Lake Michigan is critical for modeling and understanding of carbon, nitrogen, silica, and phosphorus dynamics. Several water quality models have been formulated and applied to the Great Lakes to investigate the fate and transport of nutrients and other constituents, as well as plankton dynamics. This paper summarizes the development of spatial statistical tools to study and assess the spatial trends of the sediment data sets, which were collected from Lake Michigan, as part of Lake Michigan Mass Balance Study. Several new spatial measurements were developed to quantify the spatial variation and continuity of sediment data sets under concern. The applications of the newly designed spatial measurements on the sediment data, in conjunction with descriptive statistics, clearly reveal the existence of the intrinsic structure of strata, which is hypothesized based on linear wave theory. Furthermore, a new concept of strata consisting of two components defined based on depth is proposed and justified. The findings presented in this paper may impact the future studies of sediment within Lake Michigan and all of the Great Lakes as well.

A reactive nitrogen budget for Lake Michigan

The reactive (fixed) nitrogen (Nr) budget for Lake Michigan was estimated, making use of recent estimates of watershed and atmospheric nitrogen loads. Reactive N is considered to include nitrate, nitrite, ammonium, and organic N. The updated Nr load to Lake Michigan was approximately double the previous estimate from the Lake Michigan Mass Balance study for two reasons: 1) recent estimates of watershed loads were greater than previous estimates and 2) estimated atmospheric dry deposition and deposition of organic N were included in our budget. Atmospheric and watershed Nr loads were nearly equal. The estimated loss due to denitrification at the sediment surface was at least equal to, and possibly much greater than, the combined loss due to outflow and net sediment accumulation. Within the considerable uncertainty of the denitrification estimate, the budget was nearly balanced, which was consistent with the slow rate of accumulation of nitrate in Lake Michigan (~1%/yr). The updated loads were used to force the LM3-PP biogeochemical water quality model. Simulated water column concentrations of nitrate and organic nitrogen in the calibrated model were consistent with available observational data when denitrification was included at the sediment surface at a rate that is consistent with literature values. The model simulation confirmed that the estimated denitrification rate does not exceed the availability of settling organic N mass. Simulated increase (decrease) in nitrate concentration was sensitive to model parameters controlling supply of sediment organic N, highlighting the importance of internal processes, not only loads, in controlling accumulation of N.

Application of a lower food web ecosystem productivity model for investigating dynamics of the invasive species Bythotrephes longimanus in Lake Michigan

A Lake Michigan Ecosystem Model (LM-Eco) that includes a detailed description of trophic levels and their interactions was developed for Lake Michigan. The LM-Eco model constitutes a first step toward a comprehensive Lake Michigan ecosystem productivity model to investigate ecosystem-level responses and effects within the lower food web of the lake. The effect of the invasive species Bythotrephes longimanus on individual zooplankton species was investigated based upon extensive field data collected at multiple locations in Lake Michigan during the 1994–1995 Lake Michigan Mass Balance Study. Field data collected at 15 sampling stations within Lake Michigan over a series of 8 sampling cruises throughout a 2 year period demonstrated that over 65% of zooplankton species exhibited a decline with the occurrence of Bythotrephes in the sample. The LM-Eco model was successfully applied to simulate the trends of Bythotrephes and zooplankton abundance as observed in the collected field data. Model simulations allowed for examination of interactions between the invader Bythotrephes and native zooplankton groups on a 5 km by 5 km resolution throughout Lake Michigan. Analysis was completed as a time series specific to individual field sampling locations within the lake, and also on a lake-wide scale.

IDENTIFICATION OF POSSIBLE MERCURY SOURCES AND ESTIMATION OF MERCURY WET DEPOSITION FLUX IN LAKE ONTARIO FROM LAKE ONTARIO ATMOSPHERIC DEPOSITION STUDY (LOADS)

Total gas phase mercury (TGM) concentrations and event wet-only precipitation for Hg were collected for nine months (from April, 2002 to Dec., 2002) at Sterling, NY on the shoreline of Lake Ontario. TGM concentrations measured in this study () were in somewhat high range compared to other background sites. Using simplified quantitative transport bias analysis (SQTBA) possible sources affecting high Hg concentration in Sterling was identified, and they are coal-fired power plants located in southern NY and Pennsylvania. Wet deposition measured at Mercury Deposition Network (MDN) sites including Pt. Petre and Egbert, ON were compared with data obtained at the Sterling to estimate the total mercury wet deposition flux to Lake Ontario. The wet deposition flux was calculated to be the highest at the Sterling site ( from April, 2002 to Dec. 2002) and the lowest at the Egbert (), due to the both the difference in precipitation depth and Hg concentration in the precipitation. The deposition measured at the Sterling site is similar to Lake Michigan deposition of (converted for ninth months) measured for Lake Michigan Mass Balance Study (LMMBS).

Atmospheric mercury deposition to Lake Michigan during the Lake Michigan Mass Balance Study.

Wet and dry mercury (Hg) deposition were calculated to Lake Michigan using a hybrid receptor modeling framework. The model utilized mercury monitoring data collected during the Lake Michigan Mass Balance Study and the Atmospheric Exchange Over Lakes and Oceans Studytogether with high-resolution over-water meteorological date provided by the National Oceanic and Atmospheric Administration (July, 1994-October, 1995). Atmospheric deposition was determined to be the primary pathway for mercury inputto Lake Michigan, contributing approximately 84% of the estimated 1403 kg total annual input (atmospheric deposition + tributary input). Wet (10.6 microg m(-2)) and dry deposition (9.7 microg m(-2)) contributed almost equally to the annual atmospheric Hg deposition of 20.3 microg m(-2) (1173 kg). Re-emission of dissolved gaseous Hg from the lake was also significant (7.8 microg m(-2)), reducing the net atmospheric deposition to 12.5 microg m(-2) (720 kg). A strong urban influence was observed in the over-water mercury deposition estimates in the southern portion of the lake. The Chicago/Gary urban area was estimated to contribute approximately 20% (127 kg) of the annual atmospheric mercury deposition to Lake Michigan. The magnitude of local anthropogenic mercury sources in the Chicago/Gary urban area suggests that emission reductions could significantly reduce atmospheric mercury deposition into Lake Michigan.

Deposition and emission of gaseous mercury to and from Lake Michigan during the Lake Michigan Mass Balance Study (July, 1994-October, 1995).

This paper presents measurements of dissolved gaseous mercury (DGM) concentrations in Lake Michigan and the application of a mechanistic approach to estimate deposition and emission fluxes of gaseous mercury (Hg2+ and Hg0) to and from Lake Michigan. Measurements of DGM concentrations made during May and July, 1994 and January, 1995 indicate that Lake Michigan was supersaturated with DGM suggesting that transfer of Hg0 occurs from the water to the atmosphere. Over-water concentrations of gaseous Hg2+ were estimated from total gaseous Hg (TGM) concentrations measured at five sites in the basin and used to model dry deposition fluxes of Hg2+. The modeling approach combines estimates of dry deposited Hg2+ with known photochemical and biotic reduction rates to form Hg0, which is available for re-emission. The model accounts for temporal and spatial variations in the deposition velocity of gaseous Hg2+ and the transfer velocity of Hg0 using high temporal and spatial resolution meteorological data. The modeled DGM concentrations agree well with the observed DGM concentrations in Lake Michigan. The modeled dry deposition fluxes of Hg2+ (286-797 kg yr(-1)) are very similar to the emission fluxes of Hg0 (320-959 kg yr(-1)), depending on the gaseous Hg2+ concentration used in the model.

Atmospheric mercury in the Lake Michigan basin: influence of the Chicago/Gary urban area.

The relative importance of the Chicago/Gay urban area was investigated to determine its impact on atmospheric mercury (Hg) concentrations and wet deposition in the Lake Michigan basin. Event wet-only precipitation, total particulate, and vapor phase samples were collected for Hg, and trace element determinations from five sites around Lake Michigan from July 1994 through October 1995 as part of the Lake Michigan Mass Balance Study (LMMBS). In addition, intensive over-water measurements were conducted aboard the EPA research vessel Lake Guardian during the summer of 1994 and the winter of 1995 as part of the Atmospheric Exchange Over Lakes and Oceans Study. Atmospheric Hg concentrations were found to be significantly higher in the Chicago/Gary urban area than surrounding sites: Hg in precipitation was a factor of 2 and particulate Hg was a factor of 6 times higher. Overwater measurements found elevated Hg concentrations 19 km off shore of Chicago/Gary suggesting an enhanced near field atmospheric deposition to Lake Michigan. Meteorological transport analyses also determined that local sources in the Chicago/Gary urban area significantly impacted all of the LMMBS sites indicating a broad impact to the entire Lake Michigan basin.

Quantifying uncertainty: calculating interval estimates using quality control results.

EPA's Great Lakes National Program Office (GLNPO) is leading one of the most extensive studies of a lake ecosystem ever undertaken. The Lake Michigan Mass Balance Study (LMMB Study) is a coordinated effort among state, federal, and academic scientists to monitor tributary and atmospheric pollutant loads, develop source inventories of toxic substances, and evaluate the fate and effects of these pollutants in Lake Michigan. A key objective of the LMMB Study is to construct a mass balance model for several important contaminants in the environment: PCBs, atrazine, mercury, and trans-nonachlor. The mathematical mass balance models will provide a state-of-the-art tool for evaluating management scenarios and options for control of toxics in Lake Michigan. At the outset of the LMMB Study, managers recognized that the data gathered and the model developed from the study would be used extensively by data users responsible for making environmental, economic, and policy decisions. Environmental measurements are never true values and always contain some level of uncertainty. Decision makers, therefore, must recognize and be sufficiently comfortable with the uncertainty associated with data on which their decisions are based. The quality of data gathered in the LMMB was defined, controlled, and assessed through a variety of quality assurance (QA) activities, including QA program planning, development of QA project plans, implementation of a QA workgroup, training, data verification, and implementation of a standardized data reporting format. As part of this QA program, GLNPO has been developing quantitative assessments that define data quality at the data set level. GLNPO also is developing approaches to derive estimated concentration ranges (interval estimates) for specific field sample results (single study results) based on uncertainty. The interval estimates must be used with consideration to their derivation and the types of variability that are and are not included in the interval.

Overall elemental dry deposition velocities measured around Lake Michigan

Overall dry deposition velocities of several elements were determined by dividing measured fluxes by measured airborne concentrations in different particle size ranges. The dry deposition measurements were made with a smooth surrogate surface on an automated dry deposition sampler (Eagle II) and the ambient particle concentrations were measured with a dichotomous sampler. These long-term measurements were made in Chicago, IL, South Haven, MI, and Sleeping Bear Dunes, MI, from December 1993 through October 1995 as part of the Lake Michigan Mass Balance Study. In general, the dry deposition fluxes of elements were highly correlated with coarse particle concentrations, slightly less well correlated with total particle concentrations, and least well correlated with fine particle concentrations. The calculated overall dry deposition velocities obtained using coarse particle concentrations varied from approximately 12 cm s −1 for Mg in Chicago to 0.2 cm s −1 for some primarily anthropogenic metals at the more remote sites. The velocities calculated using total particle concentrations were slightly lower. The crustal elements (Mg, Al, and Mn) had higher deposition velocities than anthropogenic elements (V, Cr, Cu, Zn, Mo, Ba and Pb). For crustal elements, overall dry deposition velocities were higher in Chicago than at the other sites.

Results from the Lake Michigan Mass Balance study: concentrations and fluxes of atmospheric polychlorinated biphenyls and trans-nonachlor.

In this paper, we summarize the data and methods used to estimate atmospheric exchange of polychlorinated biphenyls (PCBs) and trans-nonachlor with Lake Michigan. This work was conducted as part of the Lake Michigan Mass Balance (LMMB) study. For the atmospheric component of the LMMB, more than 400 gas- and particulate-phase samples were collected at eight sites on the shore around the lake (shoreline) and at 14 sites on the lake (over-water). We review the quality of the data set; describe the concentrations in atmospheric gas and particulate phases; report local, instantaneous, net gas fluxes; and estimate annual deposition of the particle-associated compounds. The quality of the data set is high except for a subset of over-water samples where PCB contamination is suspected. Gas-phase trans-nonachlor concentrations (although not the resulting gas fluxes) are inversely correlated with latitude and positively correlated with temperature. Gas-phase sigmaPCBs (sum of 98 congener groups) are highest in concentration at the Chicago site and lowest at the Sleeping Bear Dunes site. The resulting sigmaPCB gas fluxes exhibit a seasonality that reflects elevated summertime gas-phase concentrations not compensated by temperature-corrected Henry's law coefficients. Particulate-phase deposition is much smaller in magnitude than gas fluxes, for either compound. Gas and particulate fluxes are comparable only at the Chicago site and only when large (> 10 microm) particulates are considered.

Atrazine and Nutrients in Precipitation: Results from the Lake Michigan Mass Balance Study

Atmospheric deposition of anthropogenic air pollutants contributes to degradation of water quality in the Great Lakes and other water bodies and is indicative of atmospheric pollution. In this paper, we discuss deposition of three air pollutants: atrazine; total phosphorus; and nitrogen (total Kjeldahl nitrogen and nitrate) to Lake Michigan. Throughout 18 months in 1994-1995, over 600 atmospheric samples (gas, particulate, and precipitation combined) were collected and analyzed for persistent organic pollutants and nutrients. Here the measurements and modeled deposition estimates are presented for atrazine, phosphorus, and nitrogen. Results indicate that concentrations of atrazine in precipitation have remained constant over 5 years (0.10-0.40 μg L -1 ), consistent with the nearly constant sales rate of the herbicide over that time period. Actual loading of atrazine to the lake was less in 1994-1995 (1.04 × 103 kg y -1 ) than in 1990-1991 (2.6 × 10 3 kg yr -1 ). This difference in loading is due to lower overall precipitation in 1994-1995. Phosphorus concentrations in precipitation, on the other hand, have decreased from an average of 57 μg as P L -1 in 1976 to an average of 6.36 μg as P L -1 for 1994-1995. Nitrate deposition has decreased by a small, but not statistically significant, amount since the late 1970s.

Source Apportionment of Dry Deposited and Airborne Coarse Particles Collected in the Chicago Area

Long-term dry deposition and dichotomous coarse particle samples were collected between November 1993 and October 1995 in Chicago, IL, as part of the Lake Michigan Mass Balance Study (LMMBS). In addition, short-term dry deposition and airborne coarse particle (Noll Rotary Impactor) samples were collected during the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS). These samples were analyzed for trace metals and modeled using the U.S. EPA's Chemical Mass Balance (CMB) Model (Version 7) to determine the sources of these particles. The modeled source contributions were similar. The results indicate that light duty unleaded vehicles, soil dust, and heavy duty diesel vehicles were the major sources of ambient coarse and dry deposited particles in Chicago. The other sources found were lime kilns, coke dust, aluminum foundryreverberatory furnace, coal-fired power plant, paint spray booth, and municipal incineration. The results from this study indicate that the CMB approach can be used to determine the source of deposited particles.

Dry Deposition of Particulate Polychlorinated Biphenyls and Polycyclic Aromatic Hydrocarbons to Lake Michigan

Dry deposition was collected from November 1993 to October 1995 at multiple sites within the Lake Michigan basin to estimate fluxes of particulate polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) as part of the Lake Michigan Mass Balance Study (LMMBS). Samples were also collected during the Atmospheric Exchange over Lakes and Oceans (AEOLOS) project to estimate fluxes to coastal waters adjacent to the Chicago urban area. Fluxes of particulate PCBs and PAHs were higher in Chicago than <15 km offshore and at rural sites. Geometric mean dry deposition fluxes across the Lake Michigan basin ranged from 3.6 to 65 mg/m2-day for particle mass, 0.06 to 0.21 μg/m2-day for Σ-PCBs, and 0.25 to 18 μg/m2-day for Σ-PAHs. Similarities in both the distribution pattern of PCB congeners and PAHs and the magnitude of their fluxes between dry deposition and surficial sediment suggest that dry deposition may dominate loadings to the lake. Conservative estimates of loadings to Lake Michigan through particle dry deposition are estimated to be 1100 kg/yr for PCBs and 5000 kg/yr for PAHs. These loadings are more than 3× greater than loadings by wet deposition and, for PCBs, are similar to inputs by air/water exchange.