Sunday, August 31, 2014

Water, Water Everywhere…But Where Does It Go?

One of the organizing themes of the NGEE Arctic project is hydrology. It is important both for our field and laboratory measurements and especially for our modeling. We are exploring the question of how water distribution across polygonal landscapes will be impacted as permafrost thaws and topography changes due to melting ground ice and ice wedges underlying polygons. Our hydrologists and their modeling colleagues are finding that a key uncertainty in determining water distribution, in addition to topography in these low gradient environments, is the saturated hydraulic conductivity (Ksat) of soils. Knowing Ksat allows us to better understand the movement of water through saturated media and facilitates accurate modeling of water flow in soils. Modelers on our team need this information for the parameterization of our fine-scale models of low- and high-center polygons and for use in our global land surface models.

Today Cathy, Go, Larry, and I left our apartment and stepped out into the windy, cold, and unusually rainy weather. It was slightly annoying at the time, but surely the weather would get better right? As we pulled sleds full of our equipment to the field we soon realized that the sun was not going to appear, that the winds were not going to subside, and that the rain was not going to stop. On the contrary, this was going to be (not withstanding mosquitos) one of the more miserable days on the tundra that I have experienced in the last three years.
Once at the field site Cathy unpacked our Guelph Permeameter that she had purchased some time ago from Soil Moisture Equipment (Santa Barbara, CA). The equipment can be transported, assembled, and operated presumably by one person. However, we found that in rainy weather with winds upwards to 20 mph that two people were needed to stabilize the unit, position the tripod, and get it ready for operation. Once assembled, the permeameter enabled measurements of Ksat to be determined in 35 minutes to an hour. Although all the calculations still need to be completed, it is clear that Ksat values for the silty soils commonly found across our field sites on the Barrow Environmental Observatory (BEO) are low. This means that water movement, especially lateral movement, is very slow. Our team has noticed this in trying to collect samples for water chemistry, etc. It is simply difficult to get water from these soils. We think that once incorporated into models, the consequences of low Ksat – now that we have direct measurements – will become evident in the distribution of water across the landscape and the cascade of other processes of biogeochemistry and vegetation dynamics. We should know more about this before too much longer…