Measurements of Specific Rates of Net Methyl Mercury Production in the Water Column and Surface Sediments of Acidified and Circumneutral Lakes

1987 ◽  
Vol 44 (4) ◽  
pp. 750-757 ◽  
Author(s):  
Luying Xun ◽  
N. E. R. Campbell ◽  
John W. M. Rudd
Keyword(s):  
Water Column ◽  
Water Samples ◽  
Methyl Mercury ◽  
Lake Acidification ◽  
Sediment Surface ◽  
Mercury Methylation ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Decreasing Ph ◽  
Mercury Production

Specific rates of mercury methylation and demethylation were determined for water and surficial sediment samples taken from several lakes located in the Experimental Lakes Area, northwestern Ontario. Specific rates of mercury methylation were found to increase with decreasing pH in epilimnetic water samples in which pH was adjusted prior to incubation and in epilimnetic water samples taken from lakes of different pH. Reduction of pH also increased methyl mercury production at the sediment surface. Both increases and decreases in pH reduced specific rates of mercury demethylation. However, these changes were smaller than for methylation. Proportionally, specific rates of methylation increased faster than increasing concentrations of Hg2+, while specific rates of mercury demethylation increased linearly with increasing concentrations of methyl mercury. Overall, this study predicts that the net rate of methyl mercury production in the water column and at the sediment–water surface will increase as a result of lake acidification, and this may at least partially explain why the mercury concentration of fish appears to increase during lake acidification.

The Effect of pH on Methyl Mercury Production and Decomposition in Lake Sediments

1985 ◽  
Vol 42 (4) ◽  
pp. 685-692 ◽  
Author(s):  
P. S. Ramial ◽  
John W. M Rudd ◽  
Akira Furutam ◽  
Luying Xun
Keyword(s):  
Lake Sediments ◽  
Methyl Mercury ◽  
Inorganic Mercury ◽  
Mercury Methylation ◽  
Surficial Sediments ◽  
Experimental Lakes Area ◽  
Effect Of Ph ◽  
Northwestern Ontario ◽  
Acidified Lakes ◽  
Mercury Production

Mercury methylation was measured in surficial sediments taken from unacidified and experimentally acidified lakes in the Experimental Lakes Area, northwestern Ontario. A reduction in the pH of sediments lowered the rate of 203Hg methylation. Methylation was undetectable at pH <5.0. This decrease in mercury methylation was probably related to a shortage of available inorganic mercury when the pH of the sediment porewater was reduced. Below pH 6.0, inorganic mercury concentrations in porewater, measured with 203Hg, were reduced to less than 20% of that found at unaltered pH. A comparison of methylation and demethylation rates was made at various pH's. The rate of demethylation decreased to a lesser extent than methylation as the pH was lowered. This research indicates that enhanced mercury methylation in the sediment is not responsible for the observed increase in mercury levels in fish from acidified lakes.

Phosphorus Budgets and Stoichiometry during the Open-Water Season in Two Unmanipulated Lakes in the Experimental Lakes Area, Northwestern Ontario

1994 ◽  
Vol 51 (12) ◽  
pp. 2739-2755 ◽  
Author(s):  
P. Campbell
Keyword(s):  
Water Column ◽  
Bottom Sediments ◽  
Open Water ◽  
Short Term ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Phosphorus Budgets ◽  
Mass Balance Approach ◽  
Primary And Secondary Producers ◽  
Column Total

A comparative mass-balance approach is used to describe and quantify phosphorus (P) cycles during the open-water season in two unmanipulated Experimental Lakes Area (ELA) lakes. A bimodal cycle generally prevailed, in which water-column total phosphorus (TP = total dissolved P plus sestonic particulate P) peaked just after ice-out and again late in the summer. Changes in mass of water-column TP were often much larger than corresponding net external inputs. Shifts of P to and from either zooplankton or fish in the water column do not explain the P residuals. Rather, the bottom sediments must have been adding P to the water column. Short-term regeneration of P from the bottom sediments also probably occurs in artificially eutrophied ELA lakes. The mechanism of regeneration is probably biological. Other aspects of P cycling and P stoichiometry are discussed, particularly in relation to nutrient control of population structure and the function of primary and secondary producers.

Methyl mercury in aquatic insects from an experimental reservoir

1998 ◽  
Vol 55 (9) ◽  
pp. 2036-2047 ◽  
Author(s):  
B D Hall ◽  
D M Rosenberg ◽  
A P Wiens
Keyword(s):  
Aquatic Insects ◽  
Methyl Mercury ◽  
Fold Increase ◽  
Fish Tissue ◽  
Functional Feeding Groups ◽  
Experimental Lakes Area ◽  
Major Pathway ◽  
Natural Lakes ◽  
Northwestern Ontario ◽  
Before And After

Our objective was to study the effects of experimental flooding of a small wetland lake on the methyl mercury (MeHg) concentrations in aquatic insects and to compare MeHg concentrations in insects with those in water and fish from the same system. Insects were collected from the shorelines of the experimental reservoir before and after flooding, an undisturbed wetland lake, and an oligotrophic lake, all in the Experimental Lakes Area in northwestern Ontario. Samples were identified to the lowest possible taxon and categorized into functional feeding groups (FFGs; predators or collector/shredders). The insects were analyzed for MeHg and total Hg using clean techniques. Contamination was not a problem because levels of MeHg in insects were much higher than background concentrations. Odonata, Corixidae, Gerridae, Gyrinidae, and Phryganeidae/Polycentropodidae exhibited increases in MeHg concentrations in response to flooding. When data were grouped into FFGs, increases were observed in predators. There were insufficient numbers of collector/shredders collected to make a definitive conclusion on MeHg increases. Predators exhibited an approximately threefold increase in MeHg concentrations after flooding compared with a 20-fold increase in water concentrations and a four- to five-fold increase in fish concentrations. Trends in MeHg concentrations in aquatic insects from reservoirs and natural lakes in Finland and northern Québec were similar to ours. Evidence of an increase in MeHg concentrations in the lower food web helps explain increases in MeHg concentrations in fish from reservoirs because food is the major pathway of MeHg uptake in fish tissue.

Bioavailability of Polychlorinated Dibenzo-p-dioxins in Lake Enclosures

1992 ◽  
Vol 49 (4) ◽  
pp. 735-742 ◽  
Author(s):  
Mark R. Servos ◽  
Derek C. G. Muir ◽  
G. R. Barrie Webster
Keyword(s):  
Water Column ◽  
Food Chain ◽  
Chain Model ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Sediment Slurry ◽  
Food Chain Model ◽  
Food Chain Transfer ◽  
Kinetics Of ◽  
Detrital Food Chain

The bioavailability of 1,3,6,8-tetra- (T4CDD) and octachlorodibenzo-p-dioxin (O8CDD) was examined in large (40 m3) lake enclosures at the Experimental Lakes Area in northwestern Ontario. The polychlorinated dioxins (PCDDs) were added to replicate enclosures as a sediment slurry at a nominal concentration of 58–59 ng∙L−1. T4CDD was more bioavailable to caged benthic invertebrates and fish (white sucker, Catostomus commersoni) than O8CDD immediately after the addition to the enclosures. However, as the concentration of T4CDD in the water column rapidly declined, the bioavailability of T4CDD also declined. Sorption of PCDD to organic matter and rapid partitioning to sediments might have reduced the uptake of PCDDs directly from the water column. Accumulation of PCDDs in biota appeared to shift from direct equilibrium partitioning during the first few days, when the concentrations in the water column were relatively high, to a detrital food chain transfer as the freely available PCDDs in the water declined. This conclusion is supported by the results of the simple, four-compartment food chain model of Thomann and Connolly based on the uptake kinetics of PCDDs from water and food.

Environmental Fate of Polychlorinated Dibenzo-p-dioxins in Lake Enclosures

1992 ◽  
Vol 49 (4) ◽  
pp. 722-734 ◽  
Author(s):  
Mark R. Servos ◽  
Derek C. G. Muir ◽  
G. R. Barrie Webster
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Particulate Organic Matter ◽  
Environmental Fate ◽  
Aquatic Environments ◽  
Surficial Sediments ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Chlorine Substitution ◽  
Sediment Slurry

The environmental fate of 1,3,6,8-tetra- (T4CDD) and octachlorodibenzo-p-dioxin (O8CDD), two major dioxin congeners emitted into the environment, was studied in large (40 m3) lake enclosures at the Experimental Lakes Area in northwestern Ontario. The polychlorinated dioxins (PCDDs) were added to replicate enclosures as a sediment slurry at a nominal concentration of 58–59 ng∙L−1. Both congeners partitioned/settled rapidly to the surficial sediments where they persisted over the 2 yr of the study. Initially the concentrations of the T4CDD in water were higher than those of O8CDD, but the concentrations of the T4CDD in the water column declined more rapidly than those of O8CDD, with t1/2 of 2.6 ± 0.2 and 4.0 ± 0.3 d, respectively. Approximately 10–15% of the T4CDD and < 1% of the O8CDD detected in the water column during the first 48 h were determined to be truly dissolved. The rapid partitioning of O8CDD and to a lesser extent T4CDD to dissolved and particulate organic matter in the water column and sediments limited their bioavailability. Increased retentive capacity of the higher chlorinated PCDDs may explain the pattern of increasing concentration of PCDDs in sediments with increasing chlorine substitution observed in the Great Lakes and other aquatic environments.

Population Collapse of the Crayfish Orconectes virilis in Response to Experimental Whole-Lake Acidification

1989 ◽  
Vol 46 (6) ◽  
pp. 910-922 ◽  
Author(s):  
I. J. Davies
Keyword(s):  
Population Size ◽  
Population Decline ◽  
Fish Predation ◽  
Reference Population ◽  
Lake Acidification ◽  
Orconectes Virilis ◽  
Microsporidian Parasite ◽  
Experimental Lakes Area ◽  
Recruitment Failure ◽  
Northwestern Ontario

A population of Orconectes virilis in Lake 223 at the Experimental Lakes Area, northwestern Ontario, was monitored from 1976 to 1982 during an acidification experiment. O. virilis from nearby Lake 240 served as a reference population. Crayfish abundance remained stable as average epilimnion pH was gradually lowered from 6.49 (1976) to 5.93 (1978). In 1979 (pH 5.64) recruitment of young was poor and the overall population size [Formula: see text] fell from 105 800 to 60 300 animals. The decline continued in the complete absence of recruitment during 1980 (pH 5.59, [Formula: see text] and 1981 (pH 5.02, [Formula: see text]. Few crayfish survived until the spring of 1982. None were present from mid-summer 1982 to fall 1983 (average pH 5.09 to 5.13). Hatchling mortality and some egg loss appeared to have been the causes of recruitment failure. Acidification also produced a noticeable softening in the carapace of all intermoult crayfish. Growth, mortality, behaviour, and the basic reproductive functions of juvenile and adult crayfish did not change in response to acidification. Fish predation and the incidence of a microsporidian parasite apparently contributed little to the population decline.

Reproductive Impairment of the Crayfish Orconectes virilis in Response to Acidification of Lake 223

1987 ◽  
Vol 44 (S1) ◽  
pp. s97-s106 ◽  
Author(s):  
Robert L. France
Keyword(s):  
Egg Production ◽  
Lake Acidification ◽  
Orconectes Virilis ◽  
Experimental Lakes Area ◽  
Rate Of Development ◽  
Northwestern Ontario ◽  
Reproductive Impairment ◽  
Cement Compound ◽  
Acidification Of Lake ◽  
Egg Capsule

Reproductive characteristics of crayfish (Orconectes virilis) were examined during 1979–81 in four small Canadian Shield basins in the Experimental Lakes Area, northwestern Ontario. One of these lakes, Lake 223 (L223), has been experimentally acidified since 1976. Egg resorption, fertilization, and rate of development were not seriously affected by lake acidification to pH 5.1. Incomplete hardening of the glair–cement compound forming the egg capsule membrane and stalk resulted in a loss of eggs from the pleopods, causing the L223 population to suffer decreased reproduction. On an egg production basis, the reproductive impairment (defined as the % decrease in number of viable eggs prior to hatching) in reference populations averaged 3.2 ± 1.8 (95% C.I.) compared to levels of 18.7, 36.2, and 29.4% during 1979–81 in L223 at pH 5.2–5.6. Direct mortality of eggs accounted for little of the reduced natality in the L223 population and did not occur in reference lakes. Loss of crayfish populations exposed to lake acidification will probably result from reproductive failure before lake water becomes acid enough to be directly toxic to mature crayfish.

Fates of Metal Radiotracers Added to a Whole Lake: Sediment–Water Interactions

1980 ◽  
Vol 37 (3) ◽  
pp. 378-386 ◽  
Author(s):  
R. H. Hesslein ◽  
W. S. Broecker ◽  
D. W. Schindler
Keyword(s):  
Water Column ◽  
Environmental Fate ◽  
Particulate Material ◽  
Experimental Lakes Area ◽  
Suspended Particulates ◽  
Northwestern Ontario ◽  
Suspended Particulate ◽  
Suspended Particulate Material ◽  
Deep Sediments ◽  
Dissolved Form

A whole-lake radiotracer experiment with the isotopes Se-75, Hg-203, Cs-134, Fe-59, Co-60 was carried out in Lake 224 of the Experimental Lakes Area, northwestern Ontario. The results of the analyses of isotopes in the water column show an exponential decrease in concentration with time. The rate of loss from the water column does not show dependence on the affinity of the isotope for suspended particulate material. This affinity ranged from 98% for Fe-59 to < 1% for Cs-134 over the first 65 d. The major sink for isotopes lost from the water column is the sediments. Ratios of isotopes in the sediments show that those isotopes associated with suspended particulates more easily reach deep sediments than those in dissolved form which are restricted by the thermocline to adsorption to epilimnion sediments.Key words: Experimental Lakes Area, metal and radioisotope budgets, environmental fate of radionuclides

Changes in methyl mercury concentrations in zooplankton from four experimental reservoirs with differing amounts of carbon in the flooded catchmentsThis paper is part of the series “Forty Years of Aquatic Research at the Experimental Lakes Area”.

2009 ◽  
Vol 66 (11) ◽  
pp. 1910-1919 ◽  
Author(s):  
Britt D. Hall ◽  
Katharine A. Cherewyk ◽  
Michael J. Paterson ◽  
R. (Drew) A. Bodaly
Keyword(s):  
Food Web ◽  
Methyl Mercury ◽  
Dry Weight ◽  
Experimental Lakes Area ◽  
Organic C ◽  
Dissolved Organic C ◽  
Northwestern Ontario ◽  
Highly Correlated ◽  
Source Waters

Methyl mercury (MeHg) concentrations in zooplankton were compared from four experimental reservoirs at the Experimental Lakes Area in northwestern Ontario, Canada, to test the hypothesis that increases in concentrations of MeHg in zooplankton would be proportional to C availability. The experimental reservoirs included three upland reservoirs flooded between 1999 and 2003 that differed in amounts of flooded organic terrestrial C (high, medium, and low C) and an experimental reservoir created over a wetland–peatland complex in 1993. After flooding, MeHg in zooplankton increased from <100 ng·g dry weight–1 in inflow source waters to >500 ng·g dry weight–1 in all reservoirs. In the first two years of flooding, MeHg in zooplankton was not correlated with amounts of flooded C, but the rates of decline in mean annual concentrations were negatively correlated with the amount of C stored in flooded catchments. Concentrations of MeHg in zooplankton were highly correlated with MeHg concentrations in unfiltered water, with reductions in bioaccumulation associated with increases in dissolved organic C and decreases in pH. Overall, our results suggest that reservoir designs that minimize the amount of flooded terrestrial C should result in shorter periods of elevated MeHg in the food web.

Methyl mercury in pristine and impounded boreal peatlands, Experimental Lakes Area, Ontario

2000 ◽  
Vol 57 (11) ◽  
pp. 2211-2222 ◽  
Author(s):  
A Heyes ◽  
T R Moore ◽  
J WM Rudd ◽  
J J Dugoua
Keyword(s):  
Surface Water ◽  
Methyl Mercury ◽  
Important Variable ◽  
Mehg Concentration ◽  
Experimental Lakes Area ◽  
Riparian Wetland ◽  
Near Surface ◽  
Boreal Peatlands ◽  
Northwestern Ontario ◽  
Peat Surface

Methyl mercury (MeHg) concentrations were measured in peat and peat porewater of pristine wetlands and an impounded riparian wetland at the Experimental Lakes Area in northwestern Ontario, Canada. In pristine wetlands, MeHg concentrations in peat ranged from 0.1 to 60 ng·g-1 and in peat porewater from 0.02 (the detection limit) to 7.3 ng·L-1, with higher concentrations in wetlands that received upland runoff. Impoundment increased the average MeHg concentration in the near-surface peat porewater from 0.2 to 1.0 ng·L-1. As the increase was most dramatic near the peat - surface water interface, we suggest that the elevated MeHg concentrations resulted from an increase in net MeHg production associated with the decomposition of inundated vegetation. Impoundment increases the area of potential Hg methylation by imposing anoxia over the entire wetland surface and by facilitating the exchange of nutrients and MeHg between the peat surface and the surface water. No clear chemical control on MeHg concentration was observed among the pristine wetlands or in the impounded wetland. However, in laboratory incubations of peat, porewater MeHg concentration increased upon the addition of sulfate. We propose that sulfate availability is an important variable in Hg methylation in pristine northern wetlands.

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