Linda M. Campbell

A REVIEW OF MERCURY IN LAKE VICTORIA, EAST AFRICA: IMPLICATIONS FOR HUMAN AND ECOSYSTEM HEALTH

Lake Victoria, East Africa, has been the site of many recent studies measuring mercury (Hg) concentrations in water, fish, sediment, soil, and humans. Most of these studies were motivated by concerns about Hg contamination from processing of gold ore on the southern shores. Total Hg (THg) concentrations in fish were usually below permissible World Health Organization (WHO) concentrations and international marketing limits and do not threaten the lucrative export industry. Nile perch 3-10 kg and most >10 kg had THg concentrations above the WHO threshold concentrations for at-risk groups (200 ng/g). Elevated THg concentrations in large Nile perch are not of major concern because Nile perch are rarely consumed by the people living on Lake Victoria and very large Nile perch are becoming increasingly rare in catches. Water THg concentrations were below Canadian drinking water guidelines but were elevated relative to those in the northern Great Lakes. Sediment and soil THg concentrations were within inter-national guidelines and are comparable to those in northern latitudes but are lower than those in the Amazon basin. Biomass burnings and soil erosion are estimated to be the major sources of THg for the lake and probably constitute a larger source of THg than gold mining in Tanzania.THg concentrations in urine and hair from human volunteers indicate that while gold miners and frequent skin-bleaching cream users are at risk of inorganic mercury poisoning, the rest of the population, including fishermen, is not. Human exposure assessments demonstrated that fish consumption and soil geophagy constitute major sources of THg for humans, but the total estimated daily intake of THg was below the Health Canada tolerable daily intake (TDI) limits. The use of beauty creams containing high inorganic Hg concentrations, however, caused the estimated THg exposure to exceed the TDI. The high THg content in the hair of regular cream users supports this assessment. The nutritional benefits of fish and soil geophagy outweigh the risk of THg poisoning. Still, due to the importance of those natural items as a THg source to humans, as well as the changing nature of Lake Victoria, regular monitoring and risk assessments need to be carried out in the Lake Victoria catchment.

Biomagnification of Mercury in Aquatic Food Webs: A Worldwide Meta-Analysis

The slope of the simple linear regression between log10 transformed mercury (Hg) concentration and stable nitrogen isotope values (δ(15)N), hereafter called trophic magnification slope (TMS), from several trophic levels in a food web can represent the overall degree of Hg biomagnification. We compiled data from 69 studies that determined total Hg (THg) or methyl Hg (MeHg) TMS values in 205 aquatic food webs worldwide. Hg TMS values were compared against physicochemical and biological factors hypothesized to affect Hg biomagnification in aquatic systems. Food webs ranged across 1.7 ± 0.7 (mean ± SD) and 1.8 ± 0.8 trophic levels (calculated using δ(15)N from baseline to top predator) for THg and MeHg, respectively. The average trophic level (based on δ(15)N) of the upper-trophic-level organisms in the food web was 3.7 ± 0.8 and 3.8 ± 0.8 for THg and MeHg food webs, respectively. For MeHg, the mean TMS value was 0.24 ± 0.08 but varied from 0.08 to 0.53 and was, on average, 1.5 times higher than that for THg with a mean of 0.16 ± 0.11 (range: -0.19 to 0.48). Both THg and MeHg TMS values were significantly and positively correlated with latitude. TMS values in freshwater sites increased with dissolved organic carbon and decreased with total phosphorus and atmospheric Hg deposition. Results suggest that Hg biomagnification through food webs is highest in cold and low productivity systems; however, much of the among-system variability in TMS values remains unexplained. We identify critical data gaps and provide recommendations for future studies that would improve our understanding of global Hg biomagnification.

Joint analysis of stressors and ecosystem services to enhance restoration effectiveness

With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through large-scale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in near-shore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments.

AN ECOLOGICAL REVIEW OF CLADOPHORA GLOMERATA (CHLOROPHYTA) IN THE LAURENTIAN GREAT LAKES1

Cladophora glomerata (L.) Kütz. is, potentially, the most widely distributed macroalga throughout the world’s freshwater ecosystems. C. glomerata has been described throughout North America, Europe, the Atlantic Islands, the Caribbean Islands, Asia, Africa, Australia and New Zealand, and the Pacific Islands. Cladophora blooms were a common feature of the lower North American Great Lakes (Erie, Michigan, Ontario) from the 1950s through the early 1980s and were largely eradicated through the implementation of a multibillion‐dollar phosphorus (P) abatement program. The return of widespread blooms in these lakes since the mid‐1990s, however, was not associated with increases in P loading. Instead, current evidence indicates that the resurgence in blooms was directly related to ecosystem level changes in substratum availability, water clarity, and P recycling associated with the establishment of dense colonies of invasive dreissenid mussels. These results support the hypothesis that dreissenid mussel invasions may induce dramatic shifts in energy and nutrient flow from pelagic zones to the benthic zone.

Effects of Round Gobies (Neogobius melanostomus) on Dreissenid Mussels and Other Invertebrates in Eastern Lake Erie, 2002–2004

From 2001 through 2004, the densities of Dreissena bugensis and Amphipoda (Gammarus fasciatus and Echinogammarus ischnus) decreased by 94% and 85%, respectively, in the rocky northern nearshore (2–10 m depth) zone of eastern Lake Erie. Densities of Chironomidae and Oligochaeta did not change. The decline in D. bugensis was most evident for individuals with shell lengths in the 3 to 14 mm range. The mean (±SD, n) abundance of round gobies (Neogobius melanostomus) at 10-m depth increased from 6.5 (± 1.9, 12)/m2 in 2001 to 14(±1.0, 15/m2 in 2002. Analyses of stomach contents in 2001 and 2003, and stable isotopes of carbon in prey and muscle tissue in 2002, indicated that the diet of round gobies in 2001 was predominately dreissenids, but that chironomids and amphipods became more important as the abundance of appropriately sized mussels declined. Round gobies collected in 2003 contained more individual prey, but less total mass of prey than did gobies collected in 2001. Our observations suggest that round gobies probably became food-limited in eastern Lake Erie by 2002.

Toxicity of dietary methylmercury to fish: Derivation of ecologically meaningful threshold concentrations

Threshold concentrations associated with adverse effects of dietary exposure to methylmercury (MeHg) were derived from published results of laboratory studies on a variety of fish species. Adverse effects related to mortality were uncommon, whereas adverse effects related to growth occurred only at dietary MeHg concentrations exceeding 2.5 µg g(-1) wet weight. Adverse effects on behavior of fish had a wide range of effective dietary concentrations, but generally occurred above 0.5 µg g(-1) wet weight. In contrast, effects on reproduction and other subclinical endpoints occurred at dietary concentrations that were much lower (<0.2 µg g(-1) wet wt). Field studies generally lack information on dietary MeHg exposure, yet available data indicate that comparable adverse effects have been observed in wild fish in environments corresponding to high and low MeHg contamination of food webs and are in agreement with the threshold concentrations derived here from laboratory studies. These thresholds indicate that while differences in species sensitivity to MeHg exposure appear considerable, chronic dietary exposure to low concentrations of MeHg may have significant adverse effects on wild fish populations but remain little studied compared to concentrations in mammals or birds.

Distribution and Food-web Transfer of Mercury in Napoleon and Winam Gulfs, Lake Victoria, East Africa

Abstract Mercury (Hg) concentrations were measured for the food webs and water of Napoleon Gulf (Uganda) and Winam Gulf (Kenya) in northern Lake Victoria. Water total mercury (THg) concentrations in Lake Victoria range from 1.7 to 5.8 ng/L, while methylmercury (MeHg) concentrations range from 0.2 to 1 ng/L. Water Hg concentrations in Lake Victoria are higher than in temperate great lakes, including Lakes Baikal, Michigan, and Ontario, but the top predator Nile perch have relatively low THg concentrations compared to temperate piscivorous fish. While the water Hg concentrations are similar between Napoleon and Winam gulfs, the THg concentrations in biota are significantly higher in Napoleon Gulf than in the same species from Winam Gulf, which may be due to biogeochemical differences in each gulf. THg concentrations in Nile perch and Nile tilapia consistently increase with total length in both gulfs and the rates of increase are similar. The rates of THg bioaccumulation, as indicated by the regression slopes of log-THg vs. stable nitrogen isotope values for each food web (slopes of 0.163 and 0.165 for Napoleon and Winam gulfs, respectively), are within the ranges of bioaccumulation rates observed in temperate and tropical lakes elsewhere which suggests that Hg bioaccumulates at a similar rate in diverse aquatic food webs, regardless of latitude or species composition.

Stable Isotope Analyses of Food Web Structure and Fish Diet in Napoleon and Winam Gulfs, Lake Victoria, East Africa

The food web structures in Napoleon and Winam gulfs, Lake Victoria, were characterized using stable nitrogen and carbon isotope analyses. Similar biota in Napoleon Gulf had significantly lighter δ15N values and heavier δ13C values than similar biota in Winam Gulf, indicating different basal isotopic values. In both gulfs, Nile perch (Lates niloticus) was the top trophic predator while Nile tilapia (Oreochromis niloticus) was littoral and feeding at lower trophic levels. Rastrineobola argentea and Yssichromis laparograma had surprisingly high δ15N values, close to those of Nile perch, which were not consistent with the high isotopic values of their assumed zooplankton prey. Caridina nilotica, a freshwater shrimp, had a wide range of δ13C values but low δ15N values, consistent with their appearance in nearly all habitants in the lake, and their presence in the stomaches of most fish species. Nile perch showed an increase in δ15N and δ13C values with size, signifying that piscivory increases and their dietary reliance on invertebrates decreases as they mature. Stable isotope values for Napoleon Gulf biota which were adjusted for different basal values were not statistically different from those of Winam Gulf biota, suggesting that stable carbon and nitrogen isotopes fractionate consistently through trophic transfers in Lake Victoria. The stable isotope data illustrate a short food web, with the top predator Nile perch feeding on a restricted set of fish and macroinvertebrate species, including its own young.

Mercury biomagnification in the food web of Lake Tanganyika (Tanzania, East Africa)

Lake Tanganyika is a globally important lake with high endemic biodiversity. Millions of people in the lake basin depend on several fish species for consumption. Due to the importance of fish consumption as an exposure route of mercury to humans, we sampled Lake Tanganyika in 2000 to assess total mercury concentrations and biomagnification of total mercury through the food web. Stable nitrogen and carbon isotope analyses of food web structure indicate a complex food web with overlapping omnivory with some specialist fish species. Stable nitrogen isotope analyses further confirm that mercury is biomagnifying through the Tanganyika food web at rates similar to those seen in Lakes Malawi and Victoria, the other two African Great Lakes. Most collected fish species and all invertebrate species had mercury concentrations below 0.2 microg Hg/g wet weight. However, several fish species, Ctenochromis horei (average 0.15 microg/g ww), Neolamprologus boulengeri (0.2 microg/g ww) , Bathybates spp.spp. (0.21 microg/g ww), Mastacembelus cunningtoni (0.22 microg/g ww) and Clarias theodorae (0.22 microg/g ww) approached or slightly exceeded the World Health Organization (WHO)s recommended guideline of 0.2 microg Hg/g for vulnerable populations with high rates of fish consumption. Two individuals of the piscivorous fish species Lates microlepis (0.54, 0.78 microg/g ww) and a Polypterus congicus (1.3 microg/g ww) exceeded the international marketing limit value of 0.5 microg/g ww. Because C. theodorae and L. microlepis are also important market fish species, there is a need to monitor mercury concentrations in internationally marketed fish from Lake Tanganikya to ensure that those fish do not present a risk to human consumers.

Regional and species specific bioaccumulation of major and trace elements in Arctic seabirds

Twenty-five essential and nonessential elements were analyzed in Arctic seabirds to study the influence of phylogeny, tissue, Arctic region, and diet on avian element accumulation and to identify co-occurrence among metals. Muscle and liver concentrations were positively correlated, generally being higher in liver than in muscle, and generally did not differ by sex. Zinc showed the highest absolute concentrations in all samples (mean, 11.2-26.7 microg/g in muscle, depending on species and area), followed by copper (5.2-7.5 microg/g), arsenic (0.5-5.4 microg/g), selenium (1.0-5.8 microg/g), rubidium (1.4-2.2 microg/g), and cadmium (0.04-1.2 microg/g). Mercury levels ranged from 0.05 to 0.8 microg/g in muscle. The concentrations varied among species (dovekie [Alle alle], black guillemot [Cepphus grylle], thick-billed murre [Uria lomvia], black-legged kittiwake [Rissa tridactyla], northern fulmar [Fulmaris glacialis], ivory gull [Pagophila eburnean], Thayers gull [Larus thayeri], and glaucous gull [Larus hyperboreus]), and between the northern Baffin Bay (Canada) and the Barents Sea, depending on the element. Whereas some elements (e.g., mercury and zinc) increased in absolute and standardized concentrations with trophic level in the northern Baffin Bay, most elements showed no relationship with trophic level or other dietary descriptors. In absolute concentrations, nonessential elements differed between regions, whereas essential elements differed among species but not within a species across the two regions. Standardized concentrations (element pattern) of both essential elements and nonessential elements generally did not differ between regions but was highly species specific and, thus, determined by the phylogenetic element regulation capacity. The usefulness of multivariate ordination in element wildlife studies is illustrated, which provides additional insight regarding element co-occurrence in wildlife, allows inclusion of species with low sample number, and reduces the possibility of type II errors created by low sample size.