Naturalism in "Ethan Frome"

I don't think there's a question whether or not Frome is a naturalist novel. Natural symbolism is around every corner, whether it's the snow that traps the townspeople in for months every year, the barren fields on the Frome farm, the constant references to spring and summer when Ethan thinks of Mattie, or even the references to illness when Zeena, physical presence or not, appears.

Even with Mattie's spring metaphors, nature tends to be a negative force in this novel (novella?). However, I don't think that I would go so far as to say that it's malicious. Instead, nature seems to both reflect what goes on in peoples' hearts and minds, even if they don't realize it themselves. For example, when Mattie and Ethan pause by the lake on the way to Mattie's train out of Starkfield, Wharton writes, "Across its frozen surface, from the further bank, a single hill rising against the western sun threw a long conical shadow which gave the lake its name. It was a shy, secret spot, full of the same dumb melancholy that Ethan felt in his heart." 

Ethan's mind is capable of being as melancholy and deep as a lake, and there is a shadow over his life—Zeena's—but he also gives into what 19th century readers might call "base" desires. His lust for Mattie is forbidden but untamed; he allows it to lead him. In some ways this is understandable, as nothing changes much in a small town except the inside of the body (the heart/soul) or sometimes the outside, as Zeena exemplifies.

Is Zeena truly ill? When I first read Frome I thought, No, hypochondriac, pure and simple. But this second reading has complicated that idea. "Then [Zeena] too fell silent." What is silencing about the country around the Frome farm? Is the winter so very taxing on the mind that Zeena finds solace in trying to "heal" her body? "I'm a lot sicker than you think I am," she says. What defines sickness in this novel? Is it a broken body, or is it a broken spirit?