Global warming taking toll on ice- and snow-dependent ecosystems
By Summit Voice
SUMMIT COUNTY — Decreasing snowfall and declining snow and ice cover are starting to take a toll on small burrowing mammals and makes the roots of some plants more susceptible to frost damage, according to a new study published in the April issue of BioScience that tracks global warming research by the Long Term Ecological Research Network.
Ecosystem changes due to shrinking sea ice, snow, and glaciers have already been well-documented, especially in high-latitude regions where water is frozen for at least a month each year. In this so-called cryosphere, scientists have recorded how some larger animals, such as penguins and polar bears, are responding to loss of their habitat. The BioScience article surveys some of the best recent science to paint a global picture. Find a link to the study here.
For example, well-documented research has shown a large-scale decline in krill populations in the South Atlantic sector of the Antarctic seas. Meanwhile, the number of salps — pelagic, gelatinous, ice-avoiding tunicates (filter feeders) with few predators—has increased; “they have, in effect, replaced krill as an intermediate species in Antarctic marine food chains.”
Adelie penguins in Antarctica have been hit especially hard by sea ice decline in some parts of Antarctica. Since 1975, population of ice-dependent Adélies nesting near Palmer Station have declined by about 80 percent in response to a host of environmental changes, including habitat loss and altered food availability.
Studies suggest changes in the sea-ice season have shifted the period of maximum krill stocks away from the penguins’ peak foraging season.
Scientists are just now starting to uncover other less-obvious effects. The BioScience article outlines research showing that a decline in sea ice has decreased the abundance of diatoms at the base of aquatic ecosystems. Diatoms are a key source of food for krill, which, in turn, is important to many sea birds and and mammals.
Shrinking glaciers add pollutants and increased quantities of nutrients to freshwater bodies, and melting river ice pushes more detritus downstream. These effects seem subtle, yet can have a significant impact on nutrient cycles, especially nitrogen. From the paper:
“Glacier retreat and rock glacier shrinkage expose new landscapes that are typically carbon poor yet nutrient rich because of rock weathering. Microbial life—particularly nitrogen fixers—occupy these new landscapes (Nemergut et al. 2007), which increases the nitrate levels of streams and lakes down valley. These conditions are transient and slowly change as higher plants occupy the landscape over time scale of decades to centuries.”
The amount and timing of snow cover can also affect microbial activity in the soil. A thick blanket of snow insulates the ground and keeps winter temperatures at or near freezing, enabling many biologically mediated processes.
“Snow fence experiments, which enhance winter snow accumulation, have shown that higher rates of soil microbial respiration and nitrogen mineralization occur under deeper snowpacks in subalpine forest and Arctic tundra environments because of warmer soil temperatures that result from the thermally insulating effects of the snow.”
A loss of snow cover could freeze the bacteria, resulting in shortage of soil nutrients during early spring, when plants come out of their winter dormancy.
Other impacts can be expected in the tundra, both at high latitudes and high elevations. Some plants have evolved to take advantage of spring snowpack and snowfall, even becoming photosynthetically active in a shallow spring snowpack, which gives them a competitive advantage in regions with short growing seasons.
As the climate warms, the disappearance of snow cover and the increased length of the growing season may benefit some plants at the expense of others, potentially shifting the composition of vegetation, which, in turn, has impacts on the animals that rely on those plants for food.
Many alpine and tundra plants are attuned to habitat where the range of snow depths is optimal. Although the snow-free period will lengthen in a warmer climate, the lack of snow cover during colder months will increase soil temperature variation, making roots susceptible to winter injury.
The authors argue that place-based, long-term, interdisciplinary research efforts such as those supported by the Long Term Ecological Research Network will be essential if researchers are to gain an adequate understanding of the complex, cascading ecosystem responses to the changing cryosphere.