Canaries (and caribou) in the coal mine

S

cience is a broad and encompassing term which extends from the imaginative fiction of historians to the precise analytical answers of mathematicians. Each discipline deals with data in its own – and sometimes unique – ways.

Different areas of science also have to deal with their own limits in terms of variables. In mathematics, the number of variables might be one – as in “find x.”

In physics and chemistry, the number of variables in any given experiment tend to be small and this allows us a reasonably good chance of covering all of the vari- able-space for a given problem. It is why chemical results tend to be achievable with a great deal of certainty.

But other disciplines can have much larger variable sets. Indeed, the more complete and complex a system, the more variables involved. For example, a discipline such as ecology can examine whole ecosystems with thousands of individual species and millions of individual organisms. The possible interactions and as a consequence variables can easily number in the millions. How do you sort out all of the relationships in such a crowd?

Perhaps more to the point, how does a scientist go about assessing the impact of a significant change in the environment? For example, it is hard to understand the impact of climate change at an ecosystem level as some species will benefit, some will fail, and some won’t be severely affected all. Then there are the invasive new species.

One method ecologists employ is through the use of sentinel species. These are the proverbial “canaries in the coal mine” referring back to the miner’s practice of taking the small birds with them into deep shafts. If the bird stopped singing and/or died, it was an indication of dangerous gases and time to get out!

Ecologists have followed a number of species for a very long time. A classic example are lichens, which have been used to identify pollution hot spots since the 1860s.

Lichens are composite organisms. They are assembled from the fusion of an algae or a cyanobacteria with a fungi. Essentially two organisms living in such a close symbiotic relationship as to be one. They come in a variety of colors, shapes, and sizes.

Lichen look like plants, gener- ally having leaf-like shape, but are missing many of the fundamental features such as roots. Instead, they grow on trees, rocks, and even on concrete. They obtain their nutrients from fog, wind, and rain but they have no special protective barriers so they readily absorb other compounds in the air.

Lichen are often the first organisms in an ecosystem where to show the effects of changes in contaminants or changes in climate. They are a good sentinel species for any environment. In the mid1800s, botanists in Paris were able to correlate the quality of the air with the health of lichen throughout the city.

These early investigations focused on the direct effects of sulfur dioxide, an industrial by-product generated during the combustion of coal and by other processes. This research evolved into an understanding of the distribution and impact of acid rain as seen throughout the eastern seaboard of North America.

Lichen are also sensitive to other compounds such as the ammonia and nitrates utilized in agriculture and mercury, lead, and zinc emissions from smelters and power plants. In the 1980s, the U.S. Forest Service started a lichen bio-monitoring program carrying out an annual census of thousands of plots across the United States.

Samples from these sites were analyzed by chemical techniques and the results have led to extensive mapping of pollutants. This has allowed the U.S. Government agencies to map out trouble spots.

Caribou, and its sub-species reindeer, are another sentinel for environmental health.

In this case, they are an organism which moves over large areas of land but the annual migration routes are well established. As caribou live in Arctic and other marginal habitat zones where they eat grasses during the summer and mostly lichen in the winter, they are particularly sensitive to disturbances in their ecosystem.

And like the lichen they eat, they accumulate a variety of contaminants. For example, one of the longest running data sets on radioisotopes from nuclear fallout, such as cesium-137, comes from examining caribou livers. This study took on additional significance after the nuclear accidents at Chernobyl in 1986 and Fukushima in 2011.

Researchers have also been able to show how pollutant concentrations vary over time and their impact on caribou herds. Increased levels of mercury, for example, correlate with decreased reproductive success.

Whether this is through an effect on the reproductive system or overall animal health is still not known.

Sentinel species are one way of sorting through the thousands of variables involved in studying any ecosystem. These species tell us a great deal about the world around us provided we are willing to listen.