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Presentation Abstracts
Title: Ecosystem Responses to Changed Mercury Loads: Results from the METAALICUS Study
Author:Cynthia Gilmour
Senior Scientist for the METAALICUS Team
Smithsonian Environmental Research Center
647 Contees Wharf Rd. Edgewater, MD 21037
Email: gilmourc@si.edu
Lab website: www.serc.si.edu/labs/microbial/index.jsp
Abstract: The Mercury Experiment to Assess Atmospheric Loading in Canada and the United States (METAALICUS) project is a whole-watershed Mercury loading experiment being conducted in the Lake 658 watershed at the Experimental Lakes Area (ELA) in northwestern Ontario. The goal of the study is to understand how ecosystems respond to changing mercury loads. Key questions include how fast lakes and watersheds respond to a changing load (given the large pools of historical Hg accumulation in sediments and soils) and whether the response is proportional to the change. The mercury load to a small lake and its watershed was increased by a factor of about 4X, beginning in 2001 and ending in 2007. The mercury additions were made using enriched stable mercury isotopes. The use of Hg isotopes allowed the team to distinguish between experimentally applied mercury and mercury already present in the ecosystem, and also to examine bioaccumulation of mercury deposited to different parts of the watershed. Results from seven years of the METAALICUS project will be presented, and considered in the context of potential insights for related restoration efforts for Onondaga Lake.
Title: A Retrospective Analysis of Sediment Phosphorus Release in Onondaga Lake, NY: Regulating Mechanisms and Implications for Recovery
Authors:
David A. Matthews and Steven W. Effler
Upstate Freshwater Institute, Syracuse, NY
Abstract: Long-term changes in phosphorus (P) release from the hypolimnetic sediments of Onondaga Lake, NY were assessed for a 23-year interval, 1986 - 2008. This analysis was supported by a weekly monitoring program that included vertically detailed (2m resolution) measurements of multiple forms of P and ancillary parameters, including dissolved oxygen (DO), nitrate (NO3-), total ammonia (T-NH3), dissolved inorganic carbon (DIC), methane (CH4), ferrous iron (Fe2+), and total sulfide (H2ST). The flux of P from the sediments was estimated from the rate of accumulation in the hypolimnion during the summer stratification period. The range of areal release rate estimates for the 1986 - 2008 interval was 18-39 mg m-2 d-1, which is within the range reported for eutrophic-hypereutrophic lakes. Recent decreases in sediment P release were associated with an increase in NO3- loading from the Metropolitan Syracuse Wastewater Treatment Plant (Metro), which increased the redox potential and binding capacity of the sediments. This observation is consistent with the Einsele/Mortimer model of P release, whereby P is bound to ferric oxyhydroxides (FeOOH) in an oxidized microzone and liberated under iron reducing conditions. The effect of internal P loading on primary production is mediated by diffusive transport to the epilimnion. Sediment release contributed approximately 20% of the summer P load to the upper productive layer during 1995-2000 and 1% during 2007. This is a particularly timely issue for Onondaga Lake because internal P loading has slowed or prevented the recovery of certain culturally eutrophic lakes following major decreases in external P loading.
Title: Partitioning Phosphorus Concentrations and Loads in Tributaries of Onondaga Lake
Authors:
Steven W. Effler, Anthony R. Prestigiacomo and David A. Matthews
Upstate Freshwater Institute, Syracuse, NY
Edward M. Michalenko and Donald J. Hughes
Onondaga Environmental Institute, Syracuse, NY
Abstract: The partitioning of P loading to culturally eutrophic lakes is fundamental information for development of related rehabilitation programs and supporting mathematical models. Spatial and temporal patterns of concentrations and loading rates of forms of phosphorus (P) are documented for the major tributaries of Onondaga Lake, NY, an urban lake that has recently demonstrated marked recovery from extreme cultural eutrophy as a result of decreased P loading from a domestic wastewater treatment plant (WWTP). This analysis is based on long-term (19 years) fixed-frequency and shorter-term higher frequency monitoring of total (TP), dissolved (TDP) and soluble reactive (SRP) forms of P. The three largest tributaries, Onondaga Creek, Ninemile Creek, and Ley Creek, were sampled at their mouths, and at upstream sites of Onondaga Creek and Ninemile Creek, to delineate P contributions from watershed areas dominated by rural, urban, and industrial land uses. Signatures of an unusually robust array of anthropogenic drivers emerged from the patterns, including: (1) combined sewer overflows, (2) leaky sewers or other dry weather discharges, (3) residual industrial waste deposits, (4) hydrogeologic sediment sources, and (5) perhaps domestic waste effluent. Under prevailing conditions, on an annual average basis, the tributary and WWTP contributions to the total P load are approximately 70 and 30%, respectively. However, in terms of effective P loading, that which can be used to support primary production during the critical summer months, the tributaries contributed substantially less (~ 35%) of the P load. Under the prevailing WWTP loading rate, reductions in tributary loading from aggressive tributary loading management efforts (e.g., 10 - 20% decrease) would not be expected to yield conspicuous improvements in related features of lake water quality. However, noteworthy improvements are a reasonable expectation from such tributary management efforts following the mandated further reductions in WWTP loading.
Title: Plunging of Onondaga Creek in Onondaga Lake: Dynamics in Drivers, Signatures, and Implications
Authors:
Steven W. Effler, Susan M. O'Donnell, Anthony R. Prestigiacomo, David M. O'Donnell, David A. Matthews and Adam J.P. Effler
Upstate Freshwater Institute, Syracuse, NY
Abstract: The effective depths of entry tributaries into the water columns of lakes are an important determinant of the impacts of these inflows. A combination of long-term fixed-frequency and robotic monitoring information for a polluted urban lake, Onondaga Lake, NY, and two of its tributaries (Onondaga Creek and Ninemile Creek) is used to resolve the propensity for, and occurrences of, tributary plunging. Cooler temperatures (T) and higher salinity (S) are primarily responsible for the elevated density and plunging of Onondaga Creek for the summer through early fall interval that receives inputs from combined sewer overflows (CSOs). The transport of this plunging tributary is tracked by its high S during dry weather, by its high turbidity following major runoff events and by the ionic composition within the interflow pattern formed in the lake. These signatures are documented extending from the creek mouth, through a connecting navigation channel, through the inflow zone of the lake, and into metalimnetic depths of pelagic portions of the lake. The entry of this polluted tributary below the depth interval(s) of primary production and contact recreation has important implications for the underway major rehabilitation program for this system. This phenomenon diminishes the benefits previously expected for related features of the lake's water quality from on-going management efforts to abate CSO inputs and reduce non-point nutrient loading from the tributary. Previously this tributary tended to instead enter the upper layers of the lake during the operation of an adjoining soda ash manufacturing facility (closure in 1986), as a result of high lake S caused by the industry's ionic waste discharge.
Title: Variations in the Stratification Regime of Onondaga Lake: Patterns, Modeling, and Implications
Authors:
Susan M. O'Donnell, David M. O'Donnell, Emmet M. Owens, Steven W. Effler, Anthony Prestigiacomo and Daniele M. Baker
Upstate Freshwater Institute, Syracuse, NY
Abstract: Density stratification is an important regulator of lake metabolism, including the oxygen resources of hypolimnia. Substantial year-to-year variations in this regime, and coupled features of water quality, can occur in response to natural variations in meteorological and hydrologic drivers. These interactions are investigated for polluted Onondaga Lake, NY, based on the results of long-term monitoring of the lake and its tributaries and the validation and application of a dynamic one-dimensional stratification/transport and water quality model. The substantial variations in the lake's stratification regime observed over the 1987-2007 period are documented and responsible drivers are identified from empirical analyses. The mechanistic stratification/transport model is a mixed-layer, or integral, framework that represents components of the heat budget, the depths of entry of plunging inflows, mixing in the epilimnion and deeper stratified layers, and the dynamics of ice cover. The model is validated through a continuous 21 year simulation, based on long-term driver information that included tributary flow, temperature and salinity and meteorological conditions. The model performs well in simulating interannual variations in features of the stratification regime. The model, with simple oxygen depletion kinetics added, is used to project the substantial effects interannual variations in the stratification regime will have under prevailing conditions on the timing of anoxia in the hypolimnion.
Title: Temporal Dynamic of Mercury Species in the Upper Waters and Zooplankton of Onondaga Lake, NY
Authors:
Svetloslava Todorova and Charles T. Driscoll
Syracuse University, Syracuse NY
David Matthews, Steven Effler and Michael Spada
Upstate Freshwater Institute, Syracuse, NY
Abstract: Historical industrial inputs coupled with eutrophic conditions have resulted in a legacy of mercury (Hg) contamination in Onondaga Lake. The lake sediments are an important zone of methyl mercury production, and fish in the lake have exhibited concentrations of mercury in excess of the U.S. Environmental Protection Agency consumption guidance value (0.3 ug/g ww) for at least 30 years. An important linkage between sediment supply of mercury and accumulation in fish is the interplay of mercury species in the upper mixed waters with the base of the aquatic food chain. A detailed study of the seasonal dynamics of mercury species was conducted in water and zooplankton of the epilimnion of Onondaga Lake during the open water period of 2006. These observations were compared with results obtained from previous studies in the lake.
Volume-weighted concentrations of total mercury in the epilimnion ranged from 1.0 to 7.7 ng/L, with concentrations of methyl mercury ranging from 0.06 to 0.54 ng/L. Water column mercury was largely in the form of ionic mercury, as the fraction of methyl mercury ranged between 2 and 21 % of total mercury. Dissolved methyl mercury in the epilimnion comprised between 15 and 88% of total methyl mercury, while dissolved mercury was between 7 and 39% of total mercury. Concentrations of total mercury were variable in the epilimnion without a distinct seasonal pattern. A peak in total mercury concentrations occurred in late June associated with a major runoff event and persisted for two weeks. In contrast, epilimnetic concentrations of methyl mercury were low and variable during spring and early summer. Concentrations of methyl mercury increased in August associated with wind-driven mixing events, peaking in October during fall turnover. Epilimnetic concentrations of mercury have decreased markedly in recent years in Onondaga Lake.
Zooplankton concentrations of total mercury were moderate in April, decreased in May and increased through the end of June possibly associated with the high epilimnion concentrations during the elevated runoff event. Zooplankton mercury decreased in later summer before increasing during fall turnover. Methyl mercury concentrations in zooplankton followed a similar seasonal pattern, except there was a much more pronounced increase during the late summer/turnover period. The fraction of methyl mercury in zooplankton was highly variable, ranging between 10 to nearly 100% over the open water season. The logarithm of the bioconcentration factor of MeHg in zooplankton ranged from 5.4 to 6.4. Current concentrations of mercury in zooplankton are much lower than historical values. We observed a positive relationship between concentrations of methyl mercury in zooplankton and total Daphnia biomass. Although the current concentrations of mercury in zooplankton are much lower than historical values, the unit increase in mercury concentration per unit biomass has increased. This pattern suggests that the assimilation efficiency of methyl mercury by Daphnia spp. has increased in recent years. Our observation may help explain the persistence of high concentrations of Hg in fish in the lake.
Title: Predicting the Transport and Fate of a Contaminated Sediment Layer in a Lake
Authors:
Steven C. Chapra
Tufts University, Medford, MA
Martin T. Auer
Michigan Technological Univ., Houghton, MI
Abstract: Lake sediments are the repository for many of the contaminants discharged to lakes. Once resident in the sediment, those contaminants may undergo transformations (diagenesis) and then are subject to burial and recycle (release) to the overlying water. The role of this process in mediating the extent and time course of lake restoration has been recognized for a suite of chemicals including phosphorus, PCBs and mercury. The ultimate fate of a contaminant, i.e. burial, transformation and/or recycle is influenced by characteristics of both the chemical itself (e.g. biodegradability and propensity for partitioning to solids) and the lake environment (e.g. sediment porosity, sediment deposition rate).
Here, the transport and fate of a contaminated layer is modeled for a one-dimensional lake sediment. Relationships are developed to determine the sediment release rate as a function of the porosity, solid partitioning, the sediment deposition rate, and the initial depth of the buried layer. A simple procedure based on dimensionless numbers and nomographs is developed to rapidly assess whether sediment feedback is significant. The approach is illustrated by applying it to several contaminants in Onondaga Lake.
Title: Enhanced Natural Recovery of Mercury-Contaminated Lake Sediments by Electron Acceptor Augmentation
Authors:
Martin T. Auer and G. Albert Galicinao
Michigan Technological Univ., Houghton, MI
David A. Matthews
Upstate Freshwater Institute, Syracuse, NY
Svetoslava Todorova and Charles T. Driscoll
Syracuse University, Syracuse NY
Steven C. Chapra
Tufts University, Medford, MA
Abstract: From 1946-1970, a chlor-alkali facility discharged, at peak operation, 10 kg/d of mercury to Onondaga Lake. The water and sediments of the lake are contaminated with mercury and fishing bans/consumption advisories have been issued. The majority of the lake's profundal sediments have mercury concentrations exceeding 2.2 ppm total Hg and 'hotspots' have been identified in the littoral where levels exceed 7 ppm total Hg. A $435 million remediation plan calls for dredging and capping of hotspots (20% of the sediment area) with a program of monitored natural recovery planned for the balance of the lake area. It is expected that source reductions (dredge and cap measures) in the littoral zone will lead to the eventual elimination of mercury release from the deep littoral sediments, i.e. natural recovery.
It is desirable to identify a means to control the release of methylmercury from the profundal sediments (80% of the lake bottom) for the period over which the systems proceeds to steady state with post-remediation conditions (i.e. enhanced natural recovery). An approach, chemical augmentation with electron acceptors (oxygen and nitrate), has been proposed to achieve this objective. This novel technology has been tested in the laboratory by measuring methylmercury flux in flow-through sediment microcosms exposed to various levels of oxygen and nitrate. This paper reports the results of those measurements and compares laboratory fluxes to those observed in the field. The role of organic matter deposition and legacy deposits of labile organic carbon in governing the magnitude and duration of chemical amendment is discussed.
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