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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.

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.

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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