Friday, March 27, 2015

How water tracks influence soil biology: the results

You might remember the field work we were conducting a couple years ago on water tracks. (You can read more about them in my posts from October 2012.) Water tracks are a type of groundwater where water from melting ice trickles down through the soil and moves along the permafrost, kind of like slow-moving underground streams.
Water tracks are a common feature in the McMurdo Dry Valleys, but we actually don't know much about how they change the soil they're flowing through. The water they bring would of course be important for the soil organisms living in an otherwise very dry desert. But they also bring a lot of salt, which can mess with the osmotic balance of the organisms, making it hard for them to survive. (Just like how animals living in freshwater have a hard time surviving in the ocean.) We wanted to know what the net impact is of these water tracks on soil biology. Is life better for them in a water track, or does it harm them?

In December 2012, I collected soil samples from inside and outside of three different water tracks. Those soil samples were shipped back to Arizona State University, and we measured a lot of important chemical properties of the soil.We measured the pH, salinity, and nutrient levels. We also measured the "texture" of the soil, which refers to the size of the soil particles. In other words, is it very sandy soil or is it made of finer particles? We also measured the amount of bacteria and fungi in the soil, and how much CO2 is being respired from the soil.

Overall, we learned that water tracks can have a big influence on soil, changing the water availability (obviously), salinity, amount of carbon, and texture. Those changes in the soil relate to changes in the microbial biomass and the amount of CO2 respired from the soil. In the graphs to the left, you can see that position "A", which is outside of the water track, is drier and less salty. It also has a higher pH than the other positions inside the track.

Also, Position "A" outside the track respires more CO2 and has more bacteria living in the soil.

However, this is just for one of the water tracks. As it turns out, each water track was different, so we can't assume that they'll all change the soil in the same way. They might hinder the soil microbes, or they might promote them. That means that, if the climate gets warmer in the Dry Valleys and more water tracks appear, we can't predict exactly what will happen. Some water tracks will stimulate biology, and some will hinder it.

The citation for the paper publishing these results is:
Ball, B.A. and J. Levy. 2015. The role of water tracks in altering biotic and abiotic soil properties and processes in a polar desert in Antarctica. Journal of Geophysical Research: Biogeosciences.  120: 270-279.

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