Moss has a lot of challenges to face to grow in the dry valleys. It's very dry here, so they cannot get much water to grow. The only time water is plentiful is during the 14 weeks of the year when the meltwater streams are flowing, and that water is only available if you're right next to the stream. Sunlight is also a problem. During the winter there's no sunlight for photosynthesis, but during the summer the sun can be so intense that it can actually damage plants. So, it takes a very hardy plant to be able to grow here! Most of the time you do not find moss that is lush and green, because it's usually too cold, too dry, or there's too much sun damage. Sometimes, though, you find moss that was recently uncovered by the water or a rock, and it is green and happy.
But, moss is the only above-ground life in the dry valleys. All of the other organisms live in the soil, not on it. So, moss are in a way like the redwood forests of the Antarctic Dry Valleys! They are one of the few sources of food for soil organisms. When mosses die, they decompose in the soil, just like plants in warmer climates. The carbon and nutrients released from mosses when they decompose are probably a very important part of the soil food web.
We want to learn more about moss's role in the carbon and nutrient cycles in the dry valleys, so one of our projects is to find out where they are getting their nutrients. Mosses grow in the soil like other plants, but are always very close to water. Are their nutrients coming from the soil or the water? Do mosses take up all of the available nutrients, or just some? We're trying to find out by taking from each location a moss sample, soil sample, stream water sample, and groundwater sample. (Groundwater on the edge of a stream can be very different from the stream water, and is more likely the water being used by moss when stream flow is low, which is most of the time!) We will measure the ratio of carbon, nitrogen and phosphorus in the moss tissue and see if it reflects the ratio in the soil or the water. If the ratio (called "stoichiometry") of the moss is more like that of the water than the soil, that would suggest that the nutrient source is the water.
We've visited many of the streams and wet areas around Lake Fryxell and taken moss, soil, and water samples. You can see the patch of moss at the base of the rock that my backpack is on. Jenn is in Lost Seal Stream taking a sample of stream water. She pulls the water up into a giant syringe, then snaps a filter onto the end of the syringe and sloooooowly squirts the water through the filter to remove all of the sediment. If you click on the photo to make it bigger, you can see that between my backpack and Jenn is my setup for collecting groundwater. We use a miniature well system called a piezometer. I insert a long tube into the ground using stiff wire, then attach a hand-powered vacuum pump onto the end of it to suck water out from below the stream bed into a flask. The water comes out very, very silty so I will have to filter it using a more powerful setup back at the lab. You can see a groundwater sample on the rock next to my backpack (it's the bottle with the orange label).We've visited several streams to do sampling like this so far. Each stream that flows into Lake Fryxell has a different ratio of nutrients. If the nutrient content of moss changes the same way that the streams change, this would be a clue that nutrients are coming from the stream and that mosses use all the nutrients that are available. If the nutrient content of the moss doesn't change with the stream and soil, this would be a clue that the mosses only take up a certain amount of nutrients no matter what is available. That would suggest that their role in nutrient cycling is more stable and less likely to change if nutrient availability changes.
This is one of the projects that Jenn and I have been working on this field this past week. We are trying to return to McMurdo Station tonight to process our samples and get ready for the next field project, but the weather is bad and the helicopters can't come get us! Hopefully we will get home tonight or tomorrow morning.
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