Amazing, what a humble moss can tell us about life
Over Thanksgiving, I went to a family reunion in Hawaii, where I grew up. While body surfing at Makapu'u on Oahu, I marveled that the beach seemingly hadn't changed since I first started playing there 50 or so years ago. However, my nephew corrected me by pointing out the small fragments of colored plastic that I had overlooked in the sand. Much of this debris originates from the Great Pacific Garbage Patch (GPGP), a morass of floating and suspended plastic and chemical sludge that circulates in the North Pacific Gyre. The GPGP may be "twice the size of the continental U.S.," although it's difficult to measure from satellite imagery as much of it is submerged. I wish I were making this up, but the GPGP really has an entry in Wikipedia.
The GPGP is certainly alarming to hear about, but easy to dismiss as we live in the Last Frontier. After all, everywhere else is "outside" of Alaska. Besides, the Hawaiian Islands are so far out in the Pacific Ocean that Captain James Cook (namesake of the Cook Inlet) didn't "discover" them until almost 300 years after Columbus mistook islands in the Caribbean for the East Indies.
But over in the real Far East, where the equivalent of two 500-megawatt coal-fired power plants comes online every week in rapidly-developing China, contaminants are literally pumped into the atmosphere. While most of this industrial pollution falls back to earth on the other side of the Pacific Rim, some of the fine particulates that make it into the troposphere can be transported to North America's west coast, including Alaska. In one study published in 2006, Asian dust was documented at elevations above 3,000 meters in the St. Elias Mountains.
Partly in response to concern about this "Asian dust," as well as contaminant sources closer to home in the Cook Inlet basin, Kenai National Wildlife Refuge biologists, working collaboratively with their National Park Service counterparts, launched a study in 2008 to establish baseline estimates of heavy metals. We chose to use a species of feather moss, Hylocomium splendens, as a bio-indicator of airborne contaminants.
This species has great attributes as a medium for monitoring. Mosses lack vascular systems and so readily absorb contaminants from rain, melting snow, and dry deposition. Like other pleurocarpic mosses, Hylocomium forms a "carpet" and is not rooted in a substrate, ensuring that the uptake of elements from the soil is negligible. Another unusual characteristic of Hylocomium is that annual increments of plant growth can be readily distinguished so that samples of known age can be selected. Because of these attributes, in addition to its circumboreal distribution, Hylocomium has been used widely in northern Europe for monitoring the regional atmospheric deposition of trace elements and heavy metals.
Here on the Refuge, we knew from previous surveys that H. splendens was commonly found in our forests. And, quite coincidentally, J. G. Crock and colleagues from the U.S. Geological Survey estimated elemental metal concentrations in H. splendens in a study area near Nikiski in 1988.
We visited 71 sites on the Refuge, collecting Hylocomium with latex gloves. In addition, we obtained samples from Arctic and Kodiak National Wildlife Refuges. All samples were later cleaned of visible debris, cropped to include only the most recent (~3 years) growth, and air-dried in an enclosing canopy (to prevent incidental contamination). The Research Analytical Laboratory at the University of Minnesota used emission spectrometry to estimate concentrations of 26 trace and heavy metals including some of the worst offenders to wildlife and humans: mercury, cadmium, lead, and copper.
So what did we find? There was no consistent spatial pattern either on the Kenai National Wildlife Refuge or among the three refuges. These elements were widely distributed over the Refuge and in low concentrations roughly on par with measurements from another moss species in Sweden during 2010.
Comparing our sample values with data collected near Nikiski in 1988 is problematic. Much of the earlier data was collected immediately east of the Tesoro Refinery and the Agrium plant (now closed), at one time the two largest point sources of atmospheric contaminants in Alaska. For example, in 2002, the U.S. EPA reported that these two facilities released almost 1.9 million pounds of contaminants onsite into the air and water.
Concentrations detected in the 1988 study were at least an order of magnitude higher for some elements than what we found two decades later. While it's possible that airborne contamination has declined, it's much more likely that these local point sources were contributing relatively more than long-range air transport to the chemical composition of Hylocomium. The National Park Service found a similar pattern in contaminant loads in H. splendens around the Red Dog Mine north of Kotzebue.
Nonetheless, findings from another study suggest airborne contaminants on much of the Refuge may be from distant sources. A study by Mari Reeves and her colleagues in 2010 found that total polychlorinated biphenyls (PCBs) exceeded toxic thresholds for wood frogs in the 21 lakes sampled on the Refuge. Several pesticides, including organochlorines, aldrin, dieldren, lindane, and mirex, were detected in several of the lakes. Perhaps more disturbing (but insightful) was that some of the highest concentrations were found in the Fuller Lakes area, high in the Kenai Mountains, where local sources of these contaminants simply don't occur.
In the past, H. splendens was used commercially in floral exhibitions, and for lining fruit and vegetable storage boxes. It was also used as a covering for dirt floors, and it is still used for filling gaps between timber in log cabins in bush Alaska and northern Canada. Voles graze on feather moss and it is used as nest material by birds.
Here on the Kenai National Wildlife Refuge, H. splendens will almost certainly be used for the long-term monitoring of airborne contaminants. We have a few methodological issues to still work out, but the chemistry of this humble moss can help us assess toxic threats to wildlife and perhaps whether or not Asian dust is something we need to worry about.
John Morton is the supervisory biologist at Kenai National Wildlife Refuge. You can find more information about the Refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.