Data were collected to investigate if formation of gully thermokarst (TK) results in lowering of the water table and more rapid evacuation of water from above the frost table. Data were collected from 24 shallow screened wells. 2 replicate rows of 4 wells were located at: (a) a hillslope (HS) ~120m away from the gully TK, (b) perpendicular to the gully TK (TK) and (c) perpendicular to an unimpacted water track (WT) upstream of the gully TK. Note that water levels are the distance below the ground surface and may have organic/peat layers of different thicknesses. Also note that sensors were progressively lowered deeper into the well during the season, resulting in steps in the temperature and raw depth data. Data were collected with support from the NSF ARCSS-TK project, (OPP – 0806399) .
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Methods and Notes:
Wells were first installed by manual coring using a PVC pipe with sharpened end and a mallet. Screened PVC pipe was inserted into the evacuated hole. Water level and temperature sensor (Onset HOBO U-20) was hung from either a fixed length of steel bailing wire (2010) or coated braided steel cable (2011-2013 seasons). In 2010, as the frost table lowered, wells were lowered once on 8/12/2010. Wells were not adjusted in depth from this point on but were downloaded one last time on 9/6/2010, 10:00. Water level loggers were left in the wells over the winter of 2010-2011. These winter data were not used.
Loggers were found frozen in silty ice in the wells when visited in the summer of 2011.
Loggers were extracted from the ice 6/10/2011 and reinstalled on 6/14/2011. Loggers reinstalled in the wells using a hanging cable. Some are found frozen back in following a rainstorm. Data during frozen periods is unusable. 6/30/2011, some loggers are lowered deeper into thawing wells. Wells are revisited and downloaded multiple times but apparently not lowered again. Loggers pulled on 9/19/2011 and stored at Toolik Field Station over winter.
Loggers deployed 6/21/2012. 7/24/2012 visit to DL and reset clocks. Loggers pulled on 8/17/2012.
Deployed on 7/28/2013. No barometric logger deployed. Using baro data from TRTK weather station at a sampling frequency of 1 hour but water level logger frequency of 5 minutes. Linear interpolation is used to create baro data during the missing times. This does not appear to affect the data in any way. Loggers pulled on 8/12/2013 and shipped to Crosby. Organization and analysis of all years of data by Crosby (while in Chile on sabbatical) before posting to LTER site.
All time data is in Alaska Standard Time (UTC -9)
Blog on data processing:
Water level logging in soils
Standard usage of a HOBO U20 Water Level Data Logger - U20-001-04