Lichens, indicators of air quality Bellingham Port Angeles Seattle Tacoma Olympia
Data bite U.S. Forest Service lichen surveys enable scientists to map out relative air quality in various regions, as seen here in the Pacific Northwest; green is the best, darker red the worst (Environ. Pollut. 2007, DOI: 10.1016/j.envpol. 2006.03.024).
Portland Salem Eugene Roseburg Medford
Lichens are composite organisms assembled from fungi fused with algae or cyanobacteria and come in many colors and sizes. They look like plants, with some having leaflike structures or leafless branches and others forming flakes that look like peeling paint. Yet they don’t have roots, instead growing on trees, rocks, and concrete and absorbing nutrients from fog, wind, and rain. Because lichens have no specialized protective barriers, they also readily absorb contaminants and are among the first organisms to die when pollution increases, making them good sentinels for air quality. Lichens have been used to identify pollution hot spots since the 1860s, when botanists in Paris discovered that lichens thrive in areas where the air is clean and suffer in areas where it’s dirty. Early investigations focused on the direct effects of sulfur dioxide stemming from burning coal. Over time, scientists discovered that lichens are also good indicators of the regional effects of acid rain caused
by longer range transport of sulfur dioxide and other industrial emissions. Lichens are also sensitive to ammonia and nitrates that drift from agricultural areas where fertilizer is used, and they accumulate metals such as mercury from power plant emissions and lead and zinc from mining ore smelters. In the 1980s, the U.S. Forest Service started a lichen biomonitoring program in which scientists record census data on the diversity and abundance of lichens in thousands of designated survey plots across the country. They collect some samples and send them off to a lab for elemental analysis to identify the type and amount of pollutants. The data help federal agencies set pollution targets and map out areas where the targets are not being met, and they also help state and federal agencies that review emissions permit applications and existing regulations. Sources: Linda H. Geiser and Sarah Jovan, U.S. Forest Service; Peter R. Nelson, U.S. Forest Service/University of Maine, Fort Kent
C R E D I T: COU RTESY O F L I N DA G EI S ER ( MA P ) ; S H U TT E RSTO C K ( L I C HE N , CA RI B O U )
Caribou, Arctic environmental rangers Caribou (Rangifer tarandus), and its subspecies reindeer, are favored as sentinels for their large size and for the migrations of their herds that cover well-trodden annual routes near the top of the world. The animals feed on grasses in summer but eat mostly lichens during the long winters. Because lichens, another key sentinel, absorb a variety of contaminants from the atmosphere, caribou accumulate the pollutants too. And people who live in the far north eat caribou—researchers often rely on Arctic indigenous peoples to provide test samples from annual hunts. As sentinels, caribou have a niche role in providing some of the longest data sets for radioactive contaminants, such as 137Cs, from the fallout of nuclear weapons testing. Monitoring radioisotopes in caribou took on additional significance after the Chernobyl nuclear reactor accident in Ukraine in 1986 and the Fukushima reactor accident in Japan in 2011. Besides caribou, polar bears, seals, dolphins, and whales are important mammal sentinels. Polar bears are better Arctic sentinels than caribou because they are at the top
of the marine food chain and accumulate persistent pollutants that don’t show up in terrestrial ecosystems. But researchers have few opportunities to conduct longterm studies with bears because they are widely dispersed in winter. Seals, on the other hand, are useful for tracking such pollutants as flame retardants and mercury in large estuaries like San Francisco Bay, where they are year-round residents. Sources: Mary Gamberg, Canada’s Northern Contaminants Program; Margaret D. Sedlak, San Francisco Estuary Institute; Derek C. G. Muir, Environment & Climate Change Canada
Liver mercury level, µg/g 1.0 0.8
Data bite By examining caribou, researchers can study how pollutant concentrations vary over time and how they might affect animal health and herd survival, in particular as climate change alters the caribou habitat. In one case, scientists studying caribou livers in Greenland noticed that caribou with higher mercury levels appear less likely to become pregnant (Sci. Total Environ. 2016, DOI: 10.1016/j.scitotenv.2016.02.154).
0.6 0.4 0.2 0.0 Fall 96 Spring 97 Spring 08 ◾ Not pregnant ◾ Pregnant
NOVEMBER 20, 2017 | CEN.ACS.ORG | C&EN
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