Carol A. Kelly

R&K Research Inc., Canada

Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wildlife worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in...

We studied the effect of increasing hydrogen ion (H+) concentration on the uptake of mercury (Hg(II)) by an aquatic bacterium. Even small changes in pH (7.3-6.3) resulted in large increases in Hg(II) uptake, in defined media. The increased rate of bioaccumulation was directly proportional to the concentration of H+ and could not be explained by ass...

Experimental flooding of a boreal forest wetland caused the wetland to change from being a small, natural carbon sink, with respect to the atmosphere, of −6.6 g of C m-2 yr-1 to a large source of +130 g of C m-2 yr-1. This change was caused by the death of the vegetation, which eliminated the photosynthetic CO2 sink and stimulated the microbial pro...

Ponds on peatlands of the Hudson Bay Lowlands (HBLs) are complex ecosystems in which the fluxes to the atmosphere of CHâ and COâ were controlled by interacting physical and biological factors. This resulted in strong diel variations of both dissolved gas concentrations and gas fluxes to the atmosphere, necessitating frequent sampling on a 24-hour s...

Between 1962 and 1969, 10 tonnes of mercury were discharged from a chlor-alkali plant in Dryden, Ontario, to the English–Wabigoon River. Present-day fish mercury concentrations are amongst the highest recorded in Canada. In 2017, the Grassy Narrows Science Team found no evidence of ongoing discharges from the plant site to the river water, even tho...

Anthropogenic releases of mercury (Hg)1–3 are a human health issue⁴ because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorganic Hg in aquatic ecosystems, bioaccumulates to high concentrations in fish consumed by humans5,6. Predicting the efficacy of Hg pollution controls on fish MeHg concentrations is co...

Trailblazing aquatic researcher, advocate, and whole-ecosystem experimentalist

Greenhouse Gases in Reservoirs

Fifty years ago, the Penobscot Estuary was contaminated by mercury discharged from the chlor-alkali plant located in Orrington, Maine, USA. Almost all of the mercury was discharged from the plant during the late 1960s and early 1970s. Despite the much lower mercury discharges in recent decades, present-day concentrations in surface sediment remain...

As part of the Mercury Experiment to Assess Atmospheric Loading in Canada and the U.S. (METAALICUS), different stable Hg(II) isotope spikes were applied to the upland and wetland areas of a boreal catchment between 2001 and 2006 to examine retention of newly deposited Hg(II). In the present study, a Geographical Information Systems (GIS)-based appr...

Effects of changes in DOC concentrations, pH, and microbial respiration rates on specific rates of mercury methylation and demethylation in lake water were studied using radioisotopic techniques. Increased concentrations of DOC resulted in decreased specific rates of net methylation, possibly as a result of complexation of inorganic mercury with DO...

Methylation and demethylation of mercury were studied in sediments and surface waters of several remote lakes on the Canadian Shield. Radiochemical assays of mercury methylating activity, which peaked during summer, were 20–40 times faster in epilimnetic than in hypolimnetic sediments. Demethylation rates were usually highest during winter and in h...

Although there is now a general consensus among mercury (Hg) biogeochemists that increased atmospheric inputs of inorganic Hg(II) to lakes and watersheds can result in increased methylmercury (MeHg) concentrations in fish, researchers still lack kinetic data describing the movement of Hg from the atmosphere, through watershed and lake ecosystems, a...

The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we are conduct...

Although a positive relationship between atmospheric loadings of inorganic mercury (Hg(II)) to watersheds and concentrations of methyl mercury (MeHg) in fish has now been established, net wet and dry deposition of Hg(II) and MeHg to watersheds remains challenging to quantify. In this study, concentrations and loadings of total mercury (THg; all for...

The effects of pH on the uptake and accumulation of Hg(II) by Escherichia coli were determined at trace, environmentally relevant, concentrations of Hg and under anaerobic conditions. Hg(II) accumulation was measured using inducible light production from E. coli HMS174 harboring a mer-lux bioreporter plasmid (pRB28). The effect of pH on the toxicit...

Many studies on bioavailability of toxic metals have made the assumption that observation of toxicity is evidence thatthe metal was taken into the cells (i.e., was "bioavailable"). A second assumption is that results at the high concentrations necessary for toxic effect are applicable to the lower concentrations more commonly found in the environme...

For the past 9 years, we experimentally flooded a wetland complex (peatland surrounding an open water pond) at the Experimental Lakes Area (ELA), northwestern Ontario, Canada, to examine the biogeochemical cycling of methyl mercury (MeHg) in reservoirs. Using input-output budgets, we found that prior to flooding, the wetland complex was a net sourc...

Reservoirs are sources of greenhouses gases to the atmosphere, primarily due to organic carbon mineralization in flooded plants and soils to carbon dioxide (CO2) and methane (CH4). Floating peat islands are common in reservoirs that inundated peatlands. These islands can decompose on mass, or small pieces of peat can erode from islands to decompose...

A method for measuring net community photosynthesis and respiration based on changes in PCO 2 is described. Samples were incubated in serum stoppered bottles and successive pCO 2 measurements taken from the bottle headspace. At the end of the incubation, samples were acidified with concentrated phosphoric acid and total dissolved inorganic carbon (...

The METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the US) project is a whole ecosystem experiment designed to study the activity, mobility, and availability of atmospherically deposited mercury. To investigate the dynamics of mercury newly deposited onto a terrestrial ecosystem, an enriched stable isotope of mercury (20...

A mer-lux bioreporter was used to study uptake of inorganic mercury, Hg(II), at trace concentrations by two facultatively anaerobic bacterial species, Vibrio anguillarumand Escherichia coli. Uptake of Hg(II) by these bacteria appeared to be facilitated, rather than by passive diffusion. Three lines of evidence support this conclusion. First, under...

The forest canopy was an important contributor to fluxes of methyl mercury (MeHg) and total mercury (THg) to the forest floor of boreal uplands and wetlands and potentially to downstream lakes, at the Experimental Lakes Area (ELA), northwestern Ontario. The estimated fluxes of MeHg and THg in throughfall plus litterfall below the forest canopy were...

Methane emissions were measured from a bog andlake in the Experimental Lakes Area in Northern Ontario in 1992and 1993, prior to and following flooding. Bog fluxes were smallin 1992 (0.27 mg m-2 d-1) but increased 5-fold in 1993 afterflooding. Over the bog, there was a diel cycle of nighttimeemission and daytime uptake in 1992 in contrast to constan...

The variability of surface water carbon dioxide concentration, or partial pressure ( pCO2), was studied in 11 lakes of greatly varying size (2.4 ha up to 8 million ha) in Northwest Ontario, Canada. Six of these lakes were chosen to be as similar as possible in all respects except surface area (the Northwest Ontario Lake Size Series (NOLSS), which r...

We studied fluxes of methylmercury (MeHg) through a Precambrian Shield lake using a mass balance approach. The primary goal of the study was to determine the importance of various sources of MeHg to the water column of the lake. The relative importance of all sources was: in-lake production ... inflow from a brown-water lake with riparian wetlands...

Methane emissions were measured from a bog and lake in the Experimental Lakes Area in Northern Ontario in 1992 and 1993, prior to and following flooding. Bog fluxes were small in 1992 (0.27 mg m −2 d −1) but increased 5-fold in 1993 after flooding. Over the bog, there was a diel cycle of nighttime emission and daytime uptake in 1992 in contrast to...

The effect of flooding on methane (CH4) fluxes was studied through the construction of an experimental reservoir in a boreal forest wetland at the Experimental Lakes Area in northwestern Ontario. Prior to flooding, the peatland surface was a small source of CH4 to the atmosphere (1.0 ± SD of 2.3 mg CH4 m−2 d−1). After flooding, CH4 fluxes from the...

Recent studies have found that "pristine" peatlands have high peat and pore water methylmercury (MeHg) concentrations and that peatlands may act as large sources of MeHg to the downstream aquatic system, depending upon the degree of hydrologie connectivity and catchment physiography. Sulphate-reducing bacteria have been implicated as principal meth...

Dimethyl sulfide (DMS) concentrations were measured over 2 years in 10 lakes situated in northwestern Ontario. Concentrations varied from 0.1 nmol L-1 to 100 nmol L-1 (geometric mean of 1.2 nmol L-1) during the ice-free season (April to November) of 1995 and 1996. Shallow (1-5 m depth and 1-5 ha area) and medium depth (5-10 m depth and 5-15 ha area...

Flooding of a small boreal forest wetland (979) in northwestern Ontario, caused the formation of peat islands, which resulted in an approximate 10 C increase in peat temperatures at a depth of 50 cm. Peat collected from the flooded wetland and a natural unflooded wetland was incubated anaerobically at temperatures of 4 C, 15 C, and 20 to 25 C. Floo...

One of the major routes of human exposure to mercury is by the consumptron of contammated fish and shellfish. Mercury, in the form of methyl mercury (MM), accumulates in these biota by biomagnification through the aquatic food chain, to concentrations orders of magnitude higher than its levels in the water (1, 2). Dissolved MM is absorbed by unicel...

One of the major routes of human exposure to mercury is by the consumptron of contammated fish and shellfish. Mercury, in the form of methyl mercury (MM), accumulates in these biota by biomagnification through the aquatic food chain, to concentrations orders of magnitude higher than its levels in the water (1, 2). Dissolved MM is absorbed by unicel...

The substantial size of some hydroelectric projects and the extensive total surface area covered by reservoirs globally require that research determining the impacts of these developments be done at ever-increasing spatial and temporal scales. As a consequence of this research, new views are emerging about the spatial extent and longevity of the en...

Four terrestrial boreal forest catchments containing different types of wetlands were studied to determine their strength as sources or sinks of methylmercury (MeHg) and total mercury (THg) to downstream ecosystems and to determine if patterns seen in one year were consistent over several years. All catchments were sinks for THg. The wetland type,...

METHYLMERCURY can accumulate in fish to concentrations that threaten human health1. Fish methylmercury concentrations are high in many reservoirs2 and acidic lakes3, and also in many remote lakes4,5—a fact that may be related to increased atmospheric deposition of anthropogenically mobilized mercury during the past few decades6. Although sources of...

Experimental acidification of a softwater lake to below pH 5 fundamentally changed the sulfur cycle and lowered internal alkalinity generation (IAG). Prior to reaching pH 4.5, the balance of sulfur reduction and oxidation reactions within the lake was in favour of reduction, and the lake was a net sink for sulfate. In the four years at pH 4.5 the b...

Three parameters must be known to use the thin boundary‐layer model (or other bulk transfer models) for CO 2 flux between water and air: the concentration of dissolved CO 2 , CO 2(aq) , the concentration of CO 2 in the air immediately above the water, CO 2(atm) , and the wind velocity, which is used to determine the appropriate transfer coefficient...

Methyl mercury (MeHg) concentrations were compared to total mercury (THg) concentrations in a variety of types of aqueous samples collected at the Experimental Lakes Area during 1991 through 1993. In several streams, an experimentally flooded wetland, and peat pore water, there was no relationship between MeHg and THg concentrations. %MeHg (compare...

Concentrations of methyl mercury (MeHg) and total mercury (THg) in precipitation were measured at the Experimental Lakes Area (ELA), a remote field station in northwestern Ontario. We found that precipitation was a source of both MeHg and THg to boreal ecosystems, but at lower rates than in industrialized regions of North America and Scandinavia. M...

Organic volatile sulfur compounds (VSCs) were studied in six hypersaline lakes (southern Saskatchewan) and in dilute wetland ponds (Hudson Bay Lowlands, HBL). (SOa2-) (0.0002-64 g liter-') and salt con- centration (0.003-370 g liter-') ranged over 5 orders of magnitude. Organic VSC concentrations in ponds and lakes with (SOd2-) < 7 g liter-' were s...

Wetlands were found to be important sources of methyl mercury to the boreal forest ecosystem. Yields of methyl mercury were about 26-79 times higher from wetland portions of catchments (1.84-5.55 mg.ha-1.yr-1) than from purely upland areas (0.07 mg.ha-1.yr-1). Mass-balance estimates using methyl mercury inputs in wet deposition and outputs in runof...

Based on point measurements of methane flux from wetlands in the boreal and subarctic regions, northern wetlands are a major source of atmospheric methane. However, measurements have not been carried out in large continuous peatlands such as the Hudson Bay Lowland (HBL) (320,000 sq km) and the Western Siberian lowland (540,000 sq km), which togethe...

Carol A. Kelly, Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2; John W. M. Rudd, Freshwater Institute, Department of Fisheries and Oceans, Winnipeg, MB R3T 2N6; Vincent L. St. Louis, Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2; Tim Moore, Department of Geography, McGill University, Montreal, Qu...

Three protocols for the determination of inorganic and organic sulfur fractions were tested for their suitability to estimate total indigenous organic sulfur (Sorg) and35Sorg formed from added35SO42− in sediments of chemically dilute lakes in the ELA. The protocols tested have all been reported in the literature. It was found that two protocols inv...

Mercury concentrations in planktivorous, omnivorous, and piscivorous fishes were inversely related to lake size in six lakes in northwestern Ontario. The lakes were remote from direct anthropogenic influences and ranged in surface area from 89 to 35 000 ha. Fish mercury concentrations were not related to ratios of drainage basin area to lake size,...

Estimates suggest that, per unit of energy produced, greenhouse-gas flux to the atmosphere from some hydroelectric reservoirs may be significant compared to greenhouse-gas emission by fossil-fuelled electricity generation. Greenhouse gases (CO2 and CH4) are produced during bacterial decomposition of flooded peat and forest biomass. The amount emitt...

Effects of natural factors (drought and forest fire), and experimental perturbations (fertilization and acidification) on dissolved organic carbon (DOC) concentrations and ratios to other nutrients in lakes of the Experimental Lakes Area are examined using data obtained over a period of 20 years. DOC concentration, and the ratio of dissolved iron t...

Identities, concentrations, and fluxes of volatile sulfur compounds (VSCs) were determined in 11 lakes in northwestern Ontario. Carbonyl sulfide (COS: up to 1.1 nM) and dimethyl sulfide (DMS: up to 11 nM) were present in surface waters during most of the ice‐free season. Depth profiles showed accumulations below the mixed layer of methane thiol (MS...

Whole‐sediment molecular difusion coefficients ( D s ) for tritiated water in pore waters of various lakes were determined experimentally by adding ³ H 2 O to the overlying water of asphyxiated (without bioirrigation) and unasphyxiated cores and measuring the resulting pore‐water profiles after a period of time. Our objectives were to determine the...

The acidification efficiencies of nitric and sulfuric acids were compared for 5 yr by separate experimental additions of the acids to the partitioned north and south basins of Lake 302. In the epilimnion, nitric acid was 70% as efficient as sulfuric acid in reducing alkalinity. On a whole‐lake basis, acidification by nitric acid was about half as e...

HNO3 is more efficient in acidifying lakes than has been generally believed. This is because as nitrate loading to lakes increases, the efficiency of in-lake nitrate removal decreases markedly. Efficiencies decrease because algal N requirements are exceeded and because denitrification, which becomes an important removal process, is not as efficient...

The factors controlling the biogeochemistry of sulfur (S) in dimictic northern temperate lakes are reviewed. The primary means of sediment S accumulation in lakes is through bacteria sulfate (SO{sub 4}{sup 2{minus}}) reduction coupled with reaction of product sulfide with either iron or organic matter. Accumulation of S by sedimentation of organic...

Experimental acidification of two small soft-water lakes caused nitrification to cease at pH values of 5.4 to 5.7. The resulting blockage of the nitrogen cycle caused a progressive accumulation of amnonium. When the epermental acidification of one of the lakes was ended and the pH was raised to 5.4, nitrification resumed after a time lag of 1 year.

Three additions of inorganic 14C were made during midsummer to the mixed layers of two small lake basins in northwestern Ontario. The incorporation of this 14C into organic matter was mon- itored, and the resulting rates of daily primary production measured in the open water were compared with those derived from bottles incubated both in the labora...

Sulfate and nitrate removal, and the resulting sulfuric and nitric acid neutralization within acid-sensitive lakes, were predicted from a simple model requiring knowledge only of water residence time, mean depth, and average mass transfer coefficients for nitrate and sulfate removal. The model applies to lakes with oxic hypolimnia which are typical...

Sulfate reduction and the accumulation of reduced sulfur in epilimnetic sediments were studied in lakes in southern Norway, the Adirondack Mountains, and at the Experimental Lakes Area (ELA) of northwestern Ontario. In all of the lakes, in addition to the previously known formation of acid volatile sulfur, sulfate reduction also produced substantia...

Rates of sulfate reduction and denitrification were measured in the sediments of unacidified, experimentally acidified, and atmospherically acidified lakes in North America and Norway. These data, plus profiles of porewater and sediment chemistry, demonstrated that in all of the lakes H/sup +/ was being actively consumed by both sulfate reducers an...

A freshwater wetland at the Experimental Lakes Area in northwestern Ontario stored most of the SO4 2– received annually from precipitation, runoff and experimental additions. The S budget was determined for a small fen spray irrigated with H2SO4 and HNO3. Annual S retention was greatest during the first year of experimental addition of H2SO4 (73% o...

Parts of the sandy littoral sediment of a Precambrian shield lake (Lake 302s) were intermittently covered with a layer of flocculent organic-rich material l-20 mm thick. Sandy sediments with flocculent surface sediment had higher rates of respiration (31-105%) and photosynthesis (37- 224%) than those without. Densities of invertebrate macrofauna we...

The experimental acidification of Lake 223 (Experimental Lakes Area, northwestern Ontario) with sulfuric acid in 1976–1983 allowed a detailed examination of the capacity of the lake to neutralize hydrogen ion. A whole‐lake alkalinity and ion budget for Lake 223 showed that 66– 81% of the added sulfuric acid was neutralized by alkalinity production...

A method has been developed for studying direct and indirect responses of microbial processes in lake sediments to environmental perturbations. Responses of the entire microbial community as well as specific members of the community were studied using in vitro sediment systems for periods of weeks or months under control and experimentally perturbe...

Summer hypolimnetic and whole-lake under-ice measurements in an experimentally acidified lake suggested that rates of in situ decomposition in sediments (measured as methane and inorganic carbon release) were unaffected over an epilimnetic pH range of 6.7-5.1. This was apparently because microbial processes kept the pH at 6.0 or above just a few mi...

Sulfate reduction occurred from 0–3 cm below the surface of the epilimnetic sediments of three northwestern Ontario lakes, including L.223, which has been experimentally acidified by additions of sulfuric acid. Shallow water sites were conducive to SO4 2– reduction because decomposition in these predominantly sandy sediments caused oxygen concentra...

Rates of microbial reduction of O 2 , Fe ³⁺ , Mn ⁴⁺ , NO 3 ⁻ , and SO 4 ²⁻ , and total generation of CO 2 and CH 4 were measured in the hypolimnia of three Canadian Shield lakes. Methanogenesis accounted for 72–80% of anoxic carbon generation, while sulfate reduction contributed 16–20%. The remainder of anoxic carbon generation (2–8%) originated fr...

Ahstruct The roles of temperature and organic input in determining the rate of methane flux from anoxic sediments were examined under various laboratory and field conditions in two small Michigan lakes. As in other studies, rapid temperature increases in incubating sediment caused immediate increases in methane production rates (avg Q10 = 2.4). Und...

Anaerobic lake sediment incubated in vitro was investigated for its ability to mimic natural in situ sediment activities, using rate of methane production for the comparison. Two lakes with different rates and seasonal patterns of methanogenic activity were compared. There was good agreement (at the 97.5% confidence level) between rates of in situ...

Description A broad yet specific discussion of the theoretical basis and practical problems of current methods in aquatic microbiology. The first two sections address the problem of how to arrive at an accurate enumeration of the bacteria present in aquatic environments. The third section describes and evaluates methods for measuring specific metab...