ResearchMWatch Researchers have found that zooplankton bioaccumulate less mercury under laboratory conditions that mimic eutrophic, algae-filled lakes than under clear-lake conditions. The findings could explain why higher levels of mercury are found in fish from clear lakes with fewer nutrient inputs than in fish from eutrophic lakes. Additionally, the results could have important implications for the timing of sampling for fish advisory determinations. In laboratory tanks with eutrophic conditions and large concentrations of algae, the researchers found that increasing the levels of algae reduced methyl mercury (CH3Hg+) concentrations in zooplankton, which feed on the algae, by two- to threefold. Zooplankton are, in turn, eaten by a large number of fish species. The result of this so-called bloom dilution is reduced bioaccumulation of mercury throughout the aquatic food chain. To show these results, Paul Pickhardt at Dartmouth College and colleagues spiked tanks with inorganic 201Hg2+ and CH3200Hg+, both stable mercury isotopes, and used isotope ratio measurements to determine accumulation. The isotope method offers a 50- to 100-fold improvement in detection limits over more traditional analytical techniques. Moreover, by using different isotopes for inorganic Hg and CH3Hg+, the researchers were able to distinguish between intakes for each mercury source. In the experiments, algae growing rapidly under eutrophic conditions accumulated a lower amount of mercury per gram of algal material than those growing at lower nutrient levels. Consequently, CH3Hg+ concentrations were lower in zooplankton feeding in high-nutrient tanks. In contrast, there was no measurable effect on the accumulation of inorganic mercury in the zooplankton, suggesting that CH3Hg+ is preferentially accumulated by invertebrates grazing
on phytoplankton. (Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4419–4423)
Climate change predicted to rearrange species The geographic distribution of species will look dramatically different in 50 years because of climate change, predict computer models developed by ecologist A. Townsend Peterson of the University of Kansas and colleagues at Universidad Nacional Autónoma de México and the University of California’s San Diego Supercomputer Center. The modeling projections provide the first look at the biodiversity consequences of climate change across an entire region, rather than
on a species-by-species basis. The scientists plotted the geographical distribution of 1870 species of mammals, butterflies, and birds in Mexico using museum specimen data. They then predicted the distribution under liberal and conservative climate-change scenarios, using three dispersal assumptions about the types of barriers organisms face when they redistribute. Although only a limited number of species were predicted to face conditions that are entirely unsuitable for their survival, the distribution areas of some species were predicted to be drastically reduced and fragmented, while others expanded. In some communities, more than 40% of the
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Algal blooms lower mercury uptake
Conservative scenario
Liberalscenario Computermodelspredictthatglobalclimate change w illaffectthe geographic distribution of multiple speciesin M exico.Grayareasare suitable undercurrentconditionsand underclimate change scenarios;w hite areasare unsuitable undercurrentconditionsand climate change scenarios;red areasare suitable undercurrentconditionsbutare predicted to become unsuitable; and blue areasare unsuitable undercurrentconditionsbutare predicted to become suitable. JUNE 1, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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Gram-negative bacterium degrades estradiol Researchers in Japan have isolated a previously unidentified bacterium from samples of activated sewage sludge that degrades 17-estradiol, the most potent of the natural estrogens, into nontoxic metabolites. Data suggest that the bacterium can be classified as a new Novosphingobium species. Other bacteria in this genus have been previously shown to degrade compounds that are resistant to biodegradation. Katsuhiko Fujii and colleagues at the Muroran Institute of Technology, the Fisheries Research Agency, Keio University, and the National Institute of Advanced Industrial Science and Technology (all in Japan) started a search for microorganisms that break down estrogens because of concern about current widespread endocrine disruption effects, such as feminization of male aquatic species. 17-estradiol is ubiquitous in the environment and is believed to enter water systems via human and animal waste products. Sewage treatment is estimated to remove only 50–90% of these natural estrogen hormones. In laboratory experiments, the newly isolated bacterium steadily degraded 30-, 10-, and 5-milligram quantities of 17-estradiol in 30 milliliters of solution. It degraded other forms of estrogen, including estron and estriol, to a lesser degree, but was completely unable to break down ethynylestradiol. The researchers could not measure 17-estradiol below microgram-per-liter levels and therefore did not show whether the new bacterium can degrade nanogram-per-liter concentrations, the level at which estrogens are typically found in the environment. More sensitive analytical methods are 238 A
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needed to address this issue. (Appl. Environ. Microbiol. 2002, 68, 2057–2060)
Frog deformities caused by parasites The dramatic rise in frog deformities in the western United States is driven in part by parasitic worm infections, according to the first wide-ranging survey of frog populations, conducted by Pieter Johnson at the University of Wisconsin−Madison and colleagues. The findings hint that increasing numbers of nutrient-rich artificial wetlands are boosting parasite populations by providing breeding grounds for the parasite’s intermediate snail hosts, species of the genus Planorbella.
and the resulting malformations may contribute to declines in amphibian populations. (Ecol. Monogr. 2002, 72, 151–168)
Protecting endangered populations, not just species A broader scope is needed if conservationists’ efforts are to succeed in protecting species from extinction, report Gerardo Ceballos of the Instituto de Ecologia at the Universidad Nacional Autonoma de Mexico and Paul R. Ehrlich of Stanford University. Preserving ecological hot spots is not sufficient to maintain species diversity, they assert. Many species have already lost a substantial portion of their populations, particularly in areas where human activity is intensive, but they are not counted in current biodiversity assessments because they are unlikely to become extinct globally. Expanding efforts to map population extinctions in addition to species extinctions could correct underestimates of biodiversity loss. Ceballos and Ehrlich compared geographic ranges of medium to large terrestrial mammals in Australia, Africa, Southeast Asia, Europe, and North and South America, and they found that collectively, these species have lost more than 50% of their range area since the 19th century. Factors in the dramatic narrowing of range area for mammals in these regions are high human population densities, unsustainable forestry practices, and intensive agriculture, grazing, and hunting. Although most mammal species lost more than 50% of their range, some species, such as the Pere David’s deer (Elaphurus davidiamus) have become extinct in the wild, whereas others, such as the spotted hyena (Crocuta crocuta), with its higher tolerance for human disturbance, lost 14% of its range. The decline in species populations has been most acute in the large and species-rich regions of Africa and Southeast Asia. The number of species under study was limited by the availability of data sets. Although the authors admit the crudeness of their estimates of population losses, they emphasize that the estimates are conservative and might lead to a substantial underestimation of population extinctions. (Science 2002, 296, 904–907) PHOTODISC
species were predicted to have high turnover rates. This reorganization will create new communities, with new combinations of organisms, which may or may not be compatible. Ultimately, the researchers hope to combine the new models with other scenarios, such as species invasions, to better address questions related to emerging diseases and productivity in economically important ecosystems. (Nature 2002, 416, 626–629)
The researchers surveyed more than 12,000 amphibians, including frogs, toads, and newts, at 101 sites in California, Oregon, Washington, Idaho, and Montana. Although no correlation was found between pesticides and the frequency of malformations, amphibians at sites with the parasitic worm, Ribeiroia ondatrae, had 6 times more deformities than amphibians at sites without the parasite. Immature stages of R. ondatrae hatch from Planorbella snails and burrow into the base of young amphibians’ limbs, forming cysts that lead to extra or missing legs. When an infected frog is eaten by a bird or mammal, the worm matures, releasing eggs via the host’s feces. The eggs hatch in water and enter the snails, starting the cycle all over again. The only habitat factor related to the presence and abundance of worm infections was the presence and abundance of Planorbella snails, the researchers say. In the study, species of Planorbella were associated with nutrient pollution and constructed wetlands such as stormwater impoundments, farm ponds, and dams. Johnson suspects that widespread worm infections
ENVIRONMENTAL SCIENCE & TECHNOLOGY / JUNE 1, 2002
