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Bramburger A.J.,St Lawrence River Institute Of Environmental Science | Hamilton P.B.,Canadian Museum of Nature | Haffner G.D.,University of Windsor
Hydrobiologia | Year: 2014

Currently accepted paradigms in ecology dictate that disturbances at all temporal scales exert a significant influence on community structure and ecosystem stability. Microbial community resistance and resilience to perturbations are largely dependent on the physiological flexibility and taxonomic richness of the pre-perturbation community. Can a microbial community dominated by late-successional endemic taxa exhibit resistance and/or functional redundancy? In this study, intact littoral epilithic diatom communities from an ancient, tropical lake were exposed to oxygenated, filtered hypolimnetic water to simulate a lake upwelling event. Filtered lake surface water was used as a control. Discriminant function models based on changes in density and relative abundance of taxa after both treatments assigned samples to their correct treatment groups 100% of the time. A change in relative abundance of taxa between the two treatments indicated that competitive outcomes varied with a shift in the water chemistry, with different taxa exhibiting positive, negative, or neutral numerical responses. These results suggest that highly endemic diatom communities can maintain community function through shifts in competitive dynamics. We conclude that condition-specific competition models can be invoked to explain diatom community dynamics despite the inability of diatoms to use behavior to respond to changes in the abiotic environment. © 2013, Springer Science+Business Media Dordrecht.


Delongchamp T.M.,University of Ottawa | Ridal J.J.,St Lawrence River Institute Of Environmental Science | Lean D.R.S.,University of Ottawa | Poissant L.,Environment Canada | Blais J.M.,University of Ottawa
Environmental Pollution | Year: 2010

Contaminated sediments in the St. Lawrence River remain a difficult problem despite decreases in emissions. Here, sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and diffusion from the sediment to the overlying water was 17.5 ± 10.6 SE ng cm-2 yr-1 for THg and 3.8 ± 1.7 SE ng cm-2 yr-1 for MeHg. These fluxes were very small when compared to the particle-bound mercury flux accumulating in the sediment (183 ± 30 SE ng cm-2 yr-1). Studies have reported that fish from the westernmost site have higher Hg concentrations than fish collected from the other two sites of the Cornwall Area of Concern, which could not be explained by differences in the Hg flux or THg concentrations in sediments, but the highest concentrations of sediment MeHg, and the greatest proportions of MeHg to THg in both sediment and pore water were observed where fish had highest MeHg concentrations. © 2009 Elsevier Ltd.


Avramescu M.-L.,University of Ottawa | Yumvihoze E.,University of Ottawa | Hintelmann H.,Trent University | Ridal J.,St Lawrence River Institute Of Environmental Science | And 2 more authors.
Science of the Total Environment | Year: 2011

The activity of various anaerobic microbes, including sulfate reducers (SRB), iron reducers (FeRP) and methanogens (MPA) has been linked to mercury methylation in aquatic systems, although the relative importance of each microbial group in the overall process is poorly understood in natural sediments. The present study focused on the biogeochemical factors (i.e. the relative importance of various groups of anaerobic microbes (FeRP, SRB, and MPA) that affect net monomethylmercury (MMHg) formation in contaminated sediments of the St. Lawrence River (SRL) near Cornwall (Zone 1), Ontario, Canada. Methylation and demethylation potentials were measured separately by using isotope-enriched mercury species ( 200Hg 2+ and MM 199Hg +) in sediment microcosms treated with specific microbial inhibitors. Sediments were sampled and incubated in the dark at room temperature in an anaerobic chamber for 96h. The potential methylation rate constants (K m) and demethylation rates (K d) were found to differ significantly between microcosms. The MPA-inhibited microcosm had the highest potential methylation rate constant (0.016d -1), whereas the two SRB-inhibited microcosms had comparable potential methylation rate constants (0.003d -1 and 0.002d -1, respectively). The inhibition of methanogens stimulated net methylation by inhibiting demethylationand by stimulating methylation along with SRB activity. The inhibition of both methanogens and SRB was found to enhance the iron reduction rates but did not completely stop MMHg production. The strong positive correlation between K m and Sulfate Reduction Rates (SRR) and between K d and Methane Production Rates (MPR) supports the involvement of SRB in Hg methylation and MPA in MMHg demethylation in the sediments. In contrast, the strong negative correlation between K d and Iron Reduction Rates (FeRR) shows that the increase in FeRR corresponds to a decrease in demethylation, indicating that iron reduction may influence net methylation in the SLR sediments by decreasing demethylation rather than favouring methylation. © 2010 Elsevier B.V.


Razavi N.R.,Queen's University | Ridal J.J.,Queen's University | Ridal J.J.,St Lawrence River Institute Of Environmental Science | de Wit W.,St Lawrence River Institute Of Environmental Science | And 5 more authors.
Environmental Toxicology and Chemistry | Year: 2013

Ebullition, the release of gas from anaerobic decomposition in sediments, was recorded in a mercury-contaminated depositional zone (Zone 1) of the St. Lawrence River Area of Concern in Cornwall, Ontario, Canada. The aim of the present study was to test if this disturbance affected the bioavailability of total mercury (THg) and methylmercury (MeHg) in surficial sediments to a benthic invertebrate (Echinogammarus ischnus). Ebullition rates ranged from <1 to 2,800ml/m2 daily, with methane gas comprising 29 to 84% of the total. No direct effects of ebullition were found on either abiotic (sediment or pore water THg or MeHg concentrations) or biotic (amphipod THg or MeHg concentrations) variables measured. Instead, amphipod MeHg concentrations were best predicted by pore water THg and MeHg concentrations, organic matter of surficial sediments, and water depth and location. Trend surface analyses demonstrated that a shallow, southwestern part of Zone 1 was most contaminated with pore water mercury, which decreased in a gradient toward the northeast. Further study is needed to determine if the amount of sediment resuspended by ebullition affects the spatial distribution of mercury. © 2013 SETAC.


Bramburger A.J.,St Lawrence River Institute Of Environmental Science | Stephen Brown R.,Queen's University | Haley J.,St Lawrence River Institute Of Environmental Science | Ridal J.J.,St Lawrence River Institute Of Environmental Science
Journal of Great Lakes Research | Year: 2015

Membrane filtration/culture techniques have been demonstrated to be reliable and broadly applicable for determination of fecal contamination in recreational waters. The time-consuming nature of culture techniques, however, is viewed as the major disadvantage of this type of analysis, and many authors have asserted the need for improved rapid-detection methods. In this study, we evaluated the performance of the ENDETEC™ TECTA™ B16, an automated fluorometry-based microbial detection system, by comparing its detection time and accuracy to those of two common culture-based methods, which are widely-used for recreational water quality monitoring in Canada. Our results demonstrated that Escherichia coli densities inferred by the TECTA™ method were generally in agreement with those generated by standard culture methods (y=1.19x+0.002, R2=0.89) and under the current calibration regime, TECTA™ tended to slightly overestimate E. coli densities. In addition, TECTA™ was able to detect E. coli densities in exceedance of the Ontario Provincial Water Quality Objective for recreational waters in as little as 4h (mean detection time=7.03h), representing a substantial improvement over traditional culture techniques. Our findings suggest that with improved calibration, TECTA™ may provide a viable, cost-effective, rapid alternative to culture approaches for the detection of fecal contamination in recreational waters. © 2014 International Association for Great Lakes Research.


Gaiser E.E.,Florida International University | Sullivan P.,Florida International University | Tobias F.A.C.,Florida International University | Bramburger A.J.,St Lawrence River Institute Of Environmental Science | Trexler J.C.,Florida International University
Wetlands | Year: 2014

Water flow and flooding duration in wetlands influence the structure and productivity of microbial communities partly through their influence on nutrient loading. The effect of flow-regulated nutrient loads is especially relevant for microbial communities in nutrient-poor settings, where delivery controls nutrient uptake rates and the intensity of microbial interactions. We examined the effect of hydrologic history and proximity to water sources on nutrient enrichment of benthic microbial assemblages (periphyton) and on their diatom species composition, along the artificial boundaries of Taylor Slough, a historically phosphorusdepleted drainage of the Florida Everglades. Concentrations of phosphorus in periphyton declined from the wetland boundary near inflow structures to 100-m interior, with spatial and temporal variability in rates dependent on proximity to and magnitude of water flow. Phosphorus availability influenced the beta diversity of diatom assemblages, with higher values near inflow structures where resources were greatest, while interior sites and reference transects contained assemblages with constant composition of taxa considered endemic to the Everglades. This research shows how hydrologic restoration may have unintended consequences when incoming water quality is not regulated, including a replacement of distinctive microbial assemblages by ubiquitous, cosmopolitan ones. © Society of Wetland Scientists 2013.


Bramburger A.J.,St Lawrence River Institute Of Environmental Science | Munyon J.W.,Florida International University | Gaiser E.E.,Florida International University
Phytotaxa | Year: 2013

A pivotal component of hydrological restoration of the Florida Everglades is the improvement of water conveyance to Everglades National Park by the degradation of the current network of canals, roadways and levees. The Tamiami Trail (L29) road/canal complex represents a major barrier to natural water flows into the park and a variety of modification options for flow improvement are currently being explored, including the installation of spreader swales immediately downstream of culverts conveying water under Tamiami Trail from the L29 canal into Everglades National Park. In this study, we evaluated water column chemistry and wet-season diatom community structure to provide baseline information for use in future monitoring activities related to the proposed Tamiami Trail modifications. Water chemistry showed pronounced fluctuations in response to precipitation and anthropogenically mediated hydrological events. Differences in water quality variables among sites were dampened during periods of inundation, and became more pronounced during periods of low canal stage, suggesting the importance of small-scale mechanisms related to isolation of habitat patches. Diatom assemblages were unexpectedly speciose (127 taxa in 40 samples) compared to typical Everglades assemblages, and spatially heterogeneous in sites associated with concentric areas of dense vegetation immediately downstream of culverts. We also observed significant compositional dissimilarities among transects, indicating that culvert pool and north transect assemblages were substantially influenced by propagule input from the canal and areas to the north, while south transect sites were compositionally similar to typical sawgrass prairie diatom communities. Central transect sites were compositionally intermediate to their north and south counterparts. We propose that the position and spatial extent of this "transitional assemblage" is a sensitive indicator of subtle environmental change related to Tamiami Trail modifications.


Lessard C.R.,University of Ottawa | Poulain A.J.,University of Ottawa | Ridal J.J.,St Lawrence River Institute Of Environmental Science | Blais J.M.,University of Ottawa
Environmental Pollution | Year: 2013

We have developed a local mass balance model for the St. Lawrence River near Cornwall, Ontario that describes the fate and transport of mercury in three forms, elemental, divalent, and methylated, in a five compartment environment (air, water, sediments, periphyton, and benthos). Our objective was to construct a steady-state mass balance model to determine the dominant sources and sinks of mercury in this environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river to develop the model. The inflow of mercury was the major source to this system, accounting for 0.42 mol month-1, or 95.5% of all mercury inputs, whereas outflow was 0.28 mol month-1, or 63.6% of all losses, and sediment deposition was 0.12 mol month-1, or 27.3% of all losses. Uncertainty estimates were greatest for advective fluxes in surface water, porewater, periphyton, and benthic invertebrates. © 2012 Elsevier Ltd. All rights reserved.


Fathi M.,University of Ottawa | Ridal J.J.,St Lawrence River Institute Of Environmental Science | Lean D.R.S.,Lean Environmental | Blais J.M.,University of Ottawa
Journal of Great Lakes Research | Year: 2013

The St. Lawrence River near Cornwall Ontario is affected by industrial mercury contamination of sediments and biota. It has been suggested that pulp and paper mill effluents may stimulate bacterial mercury methylation in these sediments, leading to contamination of aquatic biota. To test this hypothesis, we examined sediment-porewater dynamics of total mercury (THg) and methyl mercury (MeHg) at a site with high concentrations of wood fibers from a pulp and paper mill effluent and a nearby reference site with low wood fiber content. Dissolved phase THg (THgdiss) and MeHg (MeHgdiss) in porewater profiles showed that 38±30.9% (SD) of THg in porewaters was in the methylated form regardless of wood fiber content. MeHgdiss and THgdiss concentrations were homogeneous between porewater and overlying water, indicating (a) that there is minimal net diffusion of MeHgdiss and THgdiss and (b) that redox-dependent processes such as sulfate reduction and Fe reduction were not associated with MeHgdiss distribution in these sediment profiles. MeHg and THg in solid phase showed coincident subsurface peaks at depths>40cm suggesting either that historical deposits of MeHg on particles (MeHg(p)) are preserved in deep sediments, or that Hg methylation is active in deep sediments. © 2013 International Association for Great Lakes Research.


Lessard C.R.,University of Ottawa | Poulain A.J.,University of Ottawa | Ridal J.J.,St Lawrence River Institute Of Environmental Science | Blais J.M.,University of Ottawa
Science of the Total Environment | Year: 2014

A dynamic mass balance model was developed for the St. Lawrence River near Cornwall, Ontario that predicts and hindcasts mercury concentrations and fluxes in three forms, elemental Hg (Hg0), divalent mercury (Hg2+), and methyl mercury (MeHg), in a six compartment environment (air, water, porewater, sediment, periphyton, and benthic invertebrates). Our objective was to construct a dynamic mass balance model for mercury in the St. Lawrence River near Cornwall, Ontario based on the framework and results of a steady-state mass balance model developed previously for this site. The second objective was to estimate industrial mercury emissions based on mercury residues deposited in sediments prior to 1970, the year when regulations were implemented to reduce mercury pollution in the environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river (area of approximately 100km2) to develop the model. Estimated mercury concentrations in all media were similar to measured data (R2=0.99), with only minor exceptions, providing a satisfactory overall description of the mercury loadings and transformation rates of the different mercury species. The estimated historical emissions prior to 1970 from local industries along the Cornwall waterfront were approximately 400kgyear-1. A storm sewer discharge of 5000m3/day resulted in a significant increase in mercury concentrations, particularly in sediment (617ngg-1 to 624ngg-1; p=0.004). Model results suggest that discharges of mercury from sources such as local industries and storm sewers have an impact on mercury in media such as sediment and water. This model should provide a basis for predicting and hindcasting mercury concentrations in other river environments as well, because it considers three distinct forms of mercury, and contains environmental media common to all rivers, including some (e.g. periphyton) not typically included in previous mercury models. © 2014 Elsevier B.V.

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