Raymond H. Hesslein

Prediction of biological acid neutralization in acid-sensitive lakes

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 of acid-sensitive lakes. Average mass transfer coefficients for sulfate and nitrate were obtained by two independent methods which agreed well with each other. A model such as this is necessary for predicting the rates at which different lakes acidify and recover from acidification, and explains why lakes with short water residence times are especially susceptible to acidification.

The influence of trophic level as measured by δ15N on mercury concentrations in freshwater organisms

The relationship between mercury (Hg) concentrations in freshwater biota and trophic position, as defined by stable nitrogen isotope ratios (δ15N), was examined in 6 lakes in northwestern Ontario. The heavier isotope of nitrogen (15N) increases an average of 3 parts per thousand (‰) from prey to predator and is used as a measure of an organisms trophic position. Dorsal muscle from lake trout, burbot, walleye, northern pike, white sucker, lake cisco, lake whitefish, and yellow perch was analyzed for Hg and δ15N using flameless atomic absorption and mass spectrometry respectively. Within each lake, log Hg was significantly related to δ15N (r2 ranged from 0.47 to 0.91,P<0.01). For four species, yellow perch, northern pike, lake cisco, and lake trout, log Hg was positively related to δ15N (r2 ranged from 0.37 to 0.47,P≤0.09) across all lakes. We also used δ15N measurements (assuming a 3‰ shift between an organism and its diet) and the developed within-lake regression equations to calculate a prey Hg for each individual fish. These food Hg values were then used to predict predator Hg using Norstromet als bioenergetics model. Predicted results were strongly correlated to measured Hg concentrations (r=0.91,P<0.001), indicating that δ15N has potential to be used in modeling.

Flux to the atmosphere of CH4 and CO2 from wetland ponds on the Hudson Bay lowlands (HBLs)

Ponds on peatlands of the Hudson Bay lowlands (HBLs) are complex ecosystems in which the fluxes to the atmosphere of CH4 and CC2 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 schedule to enable accurate estimates of daily fluxes. Ponds at three sites on the HBL were constant net sources of CH4 and CO2 to the atmosphere at mean rates of 110–180 mg CH4 m−2 d−1 and 3700–11,000 mg CO2 m−2 d−1. Rates peaked in August and September. For CH4 the pond fluxes were 3–30 times higher than adjacent vegetated surfaces. For CO2 the net pond fluxes were similar in magnitude to the vegetated fluxes but the direction of the flux was opposite, toward atmosphere. Even though ponds cover only 8–12% of the HBL area, they accounted for 30% of its total CH4 flux to the atmosphere. There is some circumstantial evidence that the ponds are being formed by decomposition of the underlying peat and that this decomposition is being stimulated by the activity of N2 fixing cyanobacteria that grow in mats at the peat-water interface. The fact that the gas fluxes from the ponds were so different from the surrounding vegetated surfaces means that any change in the ratio of pond to vegetated area, as may occur in response to climate change, would affect the total HBL fluxes.

High Concentrations of Toxaphene in Fishes from a Subarctic Lake

Concentrations of toxaphene and other organochlorine compounds are high in fishes from subarctic Lake Laberge, Yukon Territory, Canada. Nitrogen isotope analyses of food chains and contaminant analyses of biota, water, and dated lake sediments show that the high concentrations of toxaphene in fishes from Laberge resulted entirely from the biomagnification of atmospheric inputs. A combination of low inputs of toxaphene from the atmosphere and transfer through an exceptionally long food chain has resulted in concentrations of toxaphene in fishes that are considered hazardous to human health.

Bioaccumulation of organochlorines through a remote freshwater food web in the Canadian Arctic

Abstract Persistent organochlorines (OCs) were measured in water, sediment and biota from a remote lake in the Canadian Arctic to examine the bioaccumulation of atmospherically deposited OCs through a high-latitude freshwater food web. All major OC groups (polychlorinated biphenyls [PCBs], dichlorodiphenyl trichloroethane and metabolites [DDT], chlordane [CHL]-related compounds, and hexachlorocyclohexane [HCH] isomers) were detectable at sub-ng liter −1 concentrations in lake water and at low ng g −1 levels (dry wt) in surface sediments. Estimates of air–water exchange using a two-film model suggested that lake waters were close to equilibrium with the atmosphere for αHCH, trans -nonachlor and p,p ′-DDE but that PCB congeners 52 and 153 were undergoing volatilization. Despite the relatively short open water season, gas absorption was found to be a major input pathway into the lake, when compared to estimated inputs from precipitation. Mean concentrations of ΣHCH, ΣDDT, ΣCHL and ΣPCB ranged from 1 to 10 ng g −1 wet wt in arctic char and from 2 to 82 ng g −1 in lake trout and were comparable to results from other lakes in the Canadian Arctic. Exceptionally high concentrations (six- to 10-fold higher than mean values) of these OCs were observed in a few lake trout and were explained by the larger size, longer lifespans and higher lipid contents of these individuals. Trophic interrelationships of food-web organisms were characterized using their tissue stable carbon and nitrogen isotope ratios. Through the food web, lipid-adjusted concentrations of αHCH, trans -nonachlor, p,p ′-DDE, and PCB congeners 52 and 153 in biota were significantly related to their trophic position as determined by measurements of tissue stable nitrogen isotope ratios. In addition, the slopes and coefficients of determination for these relations increased with the lipophilicity and recalcitrance of the OCs, demonstrating that the more lipophilic OCs bioaccumulated to a greater degree through this food web even after accounting for the effects of lipid.

Correlation between stable nitrogen isotope ratios and concentrations of organochlorines in biota from a freshwater food web

The relationship between total concentrations of hexachlorocyclohexane (sigma HCH), sigma DDT, and chlorinated bornanes (toxaphene, sigma CHB) and the trophic position of biota from a subarctic lake was investigated using stable isotope ratios of nitrogen (15N/14N). Zooplankton, benthic invertebrates, and forage and piscivorous fishes were analysed for 15N/14N and organochlorines using mass spectrometry and high resolution capillary gas chromatography (GC-ECD), respectively. The trophic relationships of the biota were clearly defined, with 15N/14N increasing an average of 3.3/1000 from prey species to predator. Mean concentrations of sigma HCH were lowest in chironomids (subfamily Chironominae, 0.2 ng/g wet wt.) and highest in burbot liver (Lota lota; 30.2 ng/g wet wt.). Mean concentrations of sigma DDT and sigma CHB ranges from 0.5 and 2.0 (ng/g wet wt.), respectively, in snails (Family Limnaeidae), to 3430 and 2820 (ng/g wet wt.) in burbot liver. Regression analyses indicated that both the wet and lipid weight concentrations of sigma HCH, sigma DDT, and sigma CHB in the biota from this food web were significantly related to trophic position, as defined by delta 15 N. Results from this study indicated that delta 15 N can be used to predict concentrations of organochlorines in freshwater biota.

Mercury Concentrations in the Food Web of Lake Malawi, East Africa

Little is known about the concentrations of mercury (Hg) and factors affecting this contaminant in tropical freshwater biota. Lake Malawi, an East African Rift Valley lake, is internationally renowned for having the highest diversity of fish species in the world, and the lake supports subsistence fisheries for the three riparian countries. In this study the concentrations of Hg in fish and invertebrates collected from the lake in 1996 and 1997 were examined, and tissue stable carbon (δ13C) and nitrogen (δ15N) isotopes were used to distinguish and contrast those consumers relying upon carbon fixed by either benthic or pelagic primary producers, and their trophic positioning. Concentrations of Hg were generally low (2 to 200 ng/g wet weight) in fish from Lake Malawi. In addition, pelagic fish contained significantly higher concentrations of Hg than the benthic species. As in temperate systems, log-transformed Hg concentrations were significantly predicted by δ15N and the highest concentrations of Hg were found in the largest fish within each species. The rate of Hg accumulation was not significantly different between the pelagic and benthic fishes but pelagic species had significantly higher Hg concentrations at a common weight and trophic position. The slope of the Hg-δ15N relationship in Lake Malawi was comparable to what has been found in temperate and arctic lakes, suggesting that Hg accumulation in freshwater food webs is independent of climatic factors and species composition.

Acidification and alkalinization of lakes by experimental addition of nitrogen compounds

Fertilization of a small lake with ammonium chloride for four years as part of a eutrophication experiment caused it to acidify to pH values as low as 4.6. Implications for acidification of lakes via precipitation polluted with ammonium compounds are discussed.When phosphate was supplied with the ammonium, biological nitrogen uptake, apparently by phytoplankton, was the main mechanism causing acidification. When ammonium was applied without phosphate, it accumulated to high concentrations in solution, after which nitrification caused rapid acidification. In both cases, the whole-lake efficiency of acidification was low, averaging about 13% of the potential acidification of supplied ammonium chloride (Table 2).Subsequent application of phosphate plus sodium nitrate for two years caused the pH of the lake to increase. The efficiency of alkalinization was higher than for acidification, averaging 69% of the potential alkalinization of the supplied sodium nitrate.

Losses of biota from american aquatic communities due to acid rain

Models based on chemical survey data and geochemical assumptions were calibrated for areas where rates of acidification are known, then used to predict the declines in alkalinity and pH of lakes in the eastern and midwestern U.S.A. These results were combined with known acid tolerances of different taxonomic groups to estimate the extent of damage caused by acid rain to biological assemblages.An average of over 50% of the species in some taxonomic groups have probably been eliminated from lakes in the Adirondacks, Poconos-Catskills and southern New England. Moderate damage to biotic communities was predicted for lakes in central New England, and north-central Wisconsin. Damage predicted in Maine, upper Michigan, northeastern Minnesota and the remainder of the upper Great Lakes region was slight. Crustaceans, molluscs, leeches and insects were among the most severely affected groups. Among fishes, species of minnows (Cyprindae) were depleted in the most heavily acidified regions, with some declines in salmonid and centrarchid species.Predicted damage to individual lakes in all areas was highly variable. In areas receiving highly acidic deposition, 100% of the species in acid-sensitive taxonomic groups were eliminated in some lakes, while damage to other lakes was predicted to be slight.Estimated damage varied from lake to lake within each subregion, based on chemical characteristics. The most heavily damaged lakes in the Adirondacks and Pocono-Catskills have probably lost all species of molluscs, leeches and crustaceans. On the other hand, lakes of the Midwest showed either slight increases or decreases in the richness of predicted biotic communities.The possible ranges of original sulfate concentrations in lakes and the proportion of sulfuric acid in precipitation that liberated base cations from catchments were confined to relatively narrow limits by the model.