Melting Permafrost May Help Explain Why Many Denali National Park Wetlands Are Drying Up
Scientists working in Denali National Park suspect that permafrost melting that’s caused by climate warming might be an important reason why many of Alaska’s shallow lakes and wetlands have shrunk or disappeared. If the trend continues, wetland-dependent wildlife might be severely impacted.
Recall that Alaska is more than twice the size of Texas. Absorb the fact that almost half of the state, roughly a Texas-sized share, is covered by wetlands. Think of the vital ecological role of these wetlands, which provide habitat for vast numbers of aquatic animals, fish, and waterfowl. Now contemplate what might happen if a substantial share of those wetlands were to be lost in just a few decades. This will give you some idea of the magnitude, complexity, and sense of urgency involved in research focused on Alaska’s mysteriously shrinking wetlands.
Bush pilots and others familiar with the black spruce muskeg and treeless tundra that blankets vast areas of interior and northern Alaska have long known that many shallow lakes, ponds, marshes, and other wetlands have shrunk in size or completely disappeared in the last half-century. This has puzzled them, as has the fact that many wetlands seem not to have changed at all. Whatever is going on, it doesn’t seem to be affecting all wetlands in the same way.
Scientists paid little heed to this phenomenon until quite recently, but things have changed now. Concerns about the present and future impacts of climate change have spurred scientists across the globe to ask vital questions about the causes and consequences of changes in ecological systems that might be attributable to climate change. The drying of Alaskan wetlands falls comfortably with this category of scientific inquiry.
Amy Larsen, a National Park Service aquatic ecologist, has teamed with University of Alaska remote sensing specialist Dave Verbyla to study the wetlands drying phenomenon in Alaska’s Denali National Park. The two scientists have mutually-reinforcing interests and skills that are ideal for a study of this type.
Logistical advantages notwithstanding, Denali is a nearly ideal place to do a drying wetlands case study because it contains a representative sample of Alaska's wetlands and has many shallow water bodies that have shrunk or entirely disappeared over the past 50 years. On the downside, the Alaskan interior’s short summer season – basically just June, July, and August – gives the fieldwork a rush-rush character and limits data gathering to just a few lakes a year. While remote sensing provides a quick and cost-efficient way to extend the study in space and time, and can add important elements to the study, it can't replace careful, time-consuming fieldwork.
Although several years into their study, Larsen and Verbyla still have a way to go before they’ll have enough data on which to base definitive answers to the questions of how much of what kinds of wetlands in Denali National Park are drying at what rate for what reasons -- and with what short- and long-term implications for wetlands-dependent wildlife. Meanwhile, they believe they’ve spotted some things that could be very significant.
It seems that the shallow lakes and wetlands most prone to shrink or disappear in Denali are those that are underlain by sand and/or are partially rimmed by permafrost, the permanently frozen soil, organic matter, and ice that underlies vast areas of Alaska’s muskeg and tundra. The lakes and wetlands in this part of the world were formed about 8,000 years ago when the most recent glaciation ended, and many (but not all) owe their continued existence to the fact that permafrost helps to confine their water -- sort of like the sides of a bathtub – and keeps it from draining way.
The problem is, Alaska’s climate has warmed perceptibly in recent decades and much of the permafrost near the surface has melted or is close to doing so. Based on their research to date, Larsen and Berbyla are hypothesizing that warming temperatures are indirectly contributing to wetlands drying by breaching the permafrost containment of many shallow water bodies.
Since lots of wetlands aren’t getting smaller and shallower, it doesn’t appear that increased evaporation is a major player. However, what’s under a lake or wetland does seem to matter. All other things being equal, water bodies underlain by dense silt or clay tend to hold water much better than those underlain by sand. A sandy bottom makes it easier for water to percolate downward at a rate exceeding replenishment.
Whatever the underlying reasons for it -- and they are probably a good deal more complex than we yet realize –- this wetlands drying phenomenon is very worrisome. Even if a wetland is only partially dried, the results can be near catastrophic for wildlife. A lake, pond, or bog that gets shallow enough to freeze all the way to the bottom in the long, cold winter can’t sustain muskrats, beaver, fish, and other aquatic life.
Since climate change is a notoriously fickle thing, there’s no way to tell for sure if the conditions causing wetlands drying in Alaska will lessen, worsen, or remain the same. However, there seems to be plenty of reason to monitor this situation very carefully and learn as much about it as we can.
To read more about wetlands drying in Denali, visit this site.
Postscript: Worrying about wildlife impacts understates the seriousness of permafrost melting in the high latitudes. Permafrost deposits, which are hundreds of feet thick in areas measured in tens of thousands of square miles, contain vast amounts of partially decomposed organic matter (peat). If permafrost thawing were to expose this peat to rapid decomposition, which is actually quite plausible, the resulting release of carbon dioxide and methane into the atmosphere would accelerate climate warming. Since there is much more carbon stored in permafrost than is presently circulating in the entire atmosphere, and since methane is a potent greenhouse gas (much worse than carbon dioxide), even minor amounts of permafrost thawing could be very troublesome. All of this is not to mention the massive release of nitrates and phosphates (which would promote greater plant diversity in the tundra), the negative impacts on human systems (such the sagging or collapse of roads, pipelines, and buildings constructed on permafrost), and other consequences (including runoff-related impacts on downstream habitats and communities).