Our Better Nature: Think Snow — Forests and Fields Need It

In her poem “It Sifts from Leaden Sieves,” Emily Dickinson lauds the sublime splendor of new snow that fills nooks and crannies in the yard and leaves wind-sculpted ringlets around trees and fence posts. While I find the poet’s sense of wonder inspirational, a blanket of white stuff is less magical when you have to extricate your car from it before risking a slushy drive to work, and Dickinson’s “alabaster wool” loses its charm when the plow wings a mountain of it onto the driveway you just cleared.

In early December of this year, a lake-effect storm brought as much as six feet of snow within just 48 hours to parts of Ohio, Michigan, Pennsylvania, and New York. When frigid air passes over the relatively warm, open waters of the Great lakes, those living to the east and south of the lakes regularly get several feet of snow at a time until the lakes ice over. It’s why Syracuse, New York is the snowiest city in the country, with an average snowfall of 114.3 inches annually.

But that’s nothing compared to mountainous regions out West. In Washington State, Mount Rainier gets a yearly snow dose of around 640 inches, and in some parts of the Rockies, 400 to 500 inches of snow every winter is normal. I imagine no one who lives near those places bothers to dream about a white Christmas – they can count on it.

Over 70 percent of the continental U.S. gets significant snow each winter. But regardless of how much you get in your neck of the woods, snow does a lot more than make skiers happy and pedestrians and commuters miserable. Where ecosystems have evolved with annual snow cover, they need it to stay healthy. This is in large part because snow carries with it trace elements crucial to plant life.

Most important is the fact that snow contains plant-available forms of nitrogen, a nutrient often in short supply. When snow releases a whole winter’s worth of nutrients in the spring, it can make a difference to trees and crops. Some people even call snow “the poor person’s fertilizer.”

Since air is 78 percent nitrogen, you’d think plants would have all they need. But atmospheric nitrogen, N₂, is a stable, inert molecule that plants are unable to absorb. Lightning can zap nitrogen gas and change it to a plant-friendly form, but this accounts for very little of a plant’s nutrient budget.

The majority of nitrogen used by plants is made by soil bacteria that break apart gaseous nitrogen, converting it to water-soluble forms that plants can slurp up. Ironically, the process of breaking N₂ into compounds plants can use is called nitrogen fixation.

Snow is a better fertilizer today than it was years ago. There’s an outfit called the National Atmospheric Deposition Program (NADP) that measures stuff that falls out of the sky that isn’t some form of water. According to the NADP, the vast majority of today’s snow-borne nitrogen is from pollution.

Coal-burning power plants and motor vehicles spew out various nitrogen oxides, which are not great for us to breathe, but when they get washed into the soil, they act as fertilizers. Ammonia, another type of plant-available nitrogen, escapes from manure piles and lagoons. How much fertilizer a winter’s worth of snow contains varies by region. Due to wind patterns, the Northeast and upper Midwest get more nitrogen in their snow than the national average, around 10-12 pounds of nitrogen per acre. Compared to the high nitrogen requirements of corn, which needs about 200 pounds of nitrogen per acre, this is small potatoes (which also need 200 pounds per acre). But it’s not chopped liver, either, which is high in nitrogen but not an ideal soil amendment.

Snow-based nitrogen won’t replace the nitrogen needed by most agricultural crops, but it can be a significant boon to ecosystems on marginal soils. In a year with abundant snowfall, maple-sugar bushes, timber lands, and pastures benefit from “poor person’s fertilizer.” Snow also brings a fair bit of sulfur, an essential plant nutrient. In northern states where glacial action resulted in soils unable to offset the acidifying effects of sulfur, it can be a mixed blessing if it makes the pH drop below what is ideal for crops.

We depend on the moisture from snow as well. In most years, snow melts gradually, with nearly all the moisture going into the soil. This gentle percolation is in contrast to summer rains, a percentage of which – sometimes a large portion – runs off and doesn’t benefit the soil.

When topsoil is saturated, or at field capacity, excess water seeps down through the soil profile. Eventually it becomes groundwater, raising water tables and recharging our aquifers. In general, most water wells tap into unconfined aquifers, meaning water that goes into the ground in a given location is the water that comes out of the well there. Such aquifers depend on snowmelt for recharge. Unfortunately, winters are on average getting warmer and shorter, thanks to climate change. As snow packs dwindle, groundwater recharge in spring will diminish.

Gardeners, farmers, and nature-lovers should take heart at the mounting snowbanks, not despair of them. Unless they’re up to your second-story windows, in which case you have a right to complain.