Field Notes

<--2024-06-03 10:35:00 | 2024-06-25 09:00:00-->
Other sites visited today: Gilbert Tract | East End | Bouldin Corn | Bouldin Alfalfa
Phenocam link: Searching...

Mayberry: 2024-06-18 09:00:00 (DOY 170)
Author: Daphne Szutu
Others: Kyle, Charlie

Summary: Regular data collection/cleaning, Kyle's porewater samples, tried injecting dissolved gas and bubbles into LI-7810

2024-06-18
Mayberry

Kyle, Charlie, and I arrived at 9:00 PST (10:00 PDT). Kyle came in her own car because she was recovering from a cold. The air didn’t smell smoky here (unlike at Gilbert Tract), but maybe we were just used to it. The sky was hazy and the light still had that vaguely yellow color. It was breezy, warm and, and mostly sunny with scattered cirrus clouds. There was broken-down crayfish shells all over the lower boardwalk and walkway.

Charlie is an undergraduate student in Rob Rhew’s lab who came along today for more field experience—he has been incubating GT soil cores in the lab and measuring their fluxes with changing water levels.

The staff gauge read 50cm.

Kyle and Charlie got started with taking porewater conductivity measurements from the sipper profiles in the channel (open water sippers). The open water sippers seemed cooperative, but many of the vegetated sippers by the tower were clogged. Black and Green (the two lowest depths) worked for all of the profiles.

Charlie was wearing the Men’s size 10 waders and said it felt like the inside of the right boot was coming loose. He reached into the boot…and pulled out a red plastic core cap. All was ok after the plastic cap was removed. This was his first time wearing waders.

I downloaded met, cam, USB GHG, and miniDOT data, swapped the miniDOT and water level desiccant, cleaned flux and rad sensors, and topped off the wash reservoir. There were lots of spiderwebs on the flux sensors.

The 7500 read: 416ppm CO2, 523mol/m3 H2O, 28.1C, 100.2kPa, 98.5SS – 100 after cleaning
The 7700 read: 2.1ppm CH4, 47RSSI – 70 after cleaning

Today we are also testing out injecting small volumes of gas into the LI-7810 analyzer. Patty mentioned that dissolved gases in porewater were simple to analyze using the closed-loop technique. I had prepped some 12ml exetainer vials that I had rinsed with DI, dried, and flushed with N2 gas for 2 min. The plan today was to inject some porewater samples into the vial, equilibrate the headspace, and then withdraw the headspace to inject into the analyzer.

Kyle and Charlie collected a total of 5 samples using a 5ml syringe and a 25G needle. Sample #1 was a water sample that clogged the 25G needle almost immediately. Besides Sample #1, the syringe and needles were re-used for all the samples today. For the other water samples (2, 4, 6), Kyle pushed the water through a brand-new 0.45um filter upstream of the vial. Once in the exetainer, the water samples were shaken for at least 2 minutes before the headspace was sampled.

At the tower, I was running the LI-7810 analyzer with a small closed loop. A short piece of bev-a-line tubing connected the analyzer inlet and outlet, with a 3-way (T) compression fitting in the middle. The top of the T had a piece of blue septa, where I made the injections. I withdrew 5ml of gas from the vials and injected them into the closed loop. We could see an immediate, sharp increase in CH4 and CO2 concentrations which stabilized in maybe 30 seconds. Between each sample, I disconnected the 3-way fitting for about a minute to bring the loop back to ambient pressure (“OpenLoop” comment in analyzer data file). I reconnected the 3-way fitting and waited about a minute to check that the analyzer readings were stable (“CloseLoop” comment in analyzer data file).

Potential errors we noticed. We’ll have to figure out how much these matter.
- The filter absorbs a little water, so a little less than 5ml of water makes it into the vial. We’re not using a precision syringe, so I’m not sure if this is really going to matter. We could try a needle with a slightly larger diameter in case that would preclude needing a filter.
- The vials were out in the sun so they were warmer in the field than in the lab when they were flushed. The vials might also change temperature between injecting the sample and withdrawing to run in the analyzer. The temperature differences would change the pressure inside the vial, which would affect the number of molecules (n) that I’m withdrawing? PV=nRT
- Calculating the effective volume (Veff) of the closed loop should be done at the same temperature and pressure as when the samples are injected, but we are doing the samples in the field and the effective volume test in the lab. Pressure might be similar but temperature is way different.

Sample number, Sipper, Description, Approximate CH4 concentration (needs to be updated after doing Veff correction)
2, Open-Blu-Red, 5ml water pushed through filter, 1143440 ppb
3, Open-Blu-Red, 5ml gas from sipper, 4739330 ppb
4, Open-Blk-Wht, 4.5ml water pushed through filter, 960833 ppb
5, Open-Blk-Wht, 5ml gas, 7509480 ppb
6, Veg-Blk-Grn, 5ml water pushed through filter, 443178 ppb

Porewater conductivity data:
Open-red-yellow, 8.34 mS, 27.0C
Open-red-red, 6.75 mS, 28.2C
Open-red-white, 7.33 mS, 25.6C
Open-red-black, 6.95 mS, 23.8C
Open-red-green, 6.23 mS, 24.0C
Open-blue-yellow, 6.13 mS, 24.5C
Open-blue-red, 6.73 mS, 26.1C
Open-blue-white, 6.92 mS, 26.1C
Open-blue-black, 5.98 mS, 25.0C
Open-blue-green, 4.85 mS, 22.9C
Open-black-yellow, 7.80 mS, 29.8C
Open-black-red, 7.66 mS, 25.8C
Open-black-white, 7.56 mS, 25.2C
Open-black-black, 7.08 mS, 26.9C
Open-black-green, 7.12 mS, 25.6C
Veg-blue-yellow, 9.25 mS, 26.6C
Veg-blue-red, ,
Veg-blue-white, 8.80 mS, 27.6C
Veg-blue-black, 9.06 mS, 31.3C
Veg-blue-green, 6.92 mS, 27.4C
Veg-black-yellow, ,
Veg-black-red, ,
Veg-black-white, ,
Veg-black-black, 9.52 mS, 26.9C
Veg-black-green, 6.00 mS, 25.9C
Veg-red-yellow, ,
Veg-red-red, ,
Veg-red-white, ,
Veg-red-black, 5.32 mS, 29.2C
Veg-red-green, 5.41 mS, 26.8C
Veg-red-red-red, ,

We left at 13:40 PST (14:40 PDT). Kyle headed home and Charlie and I headed to Twitchell.

1 photos found

20240618MB_KyleCharlie.jpg ( 2024-06-18 12:16:41 ) Full size: 1920x1440
Kyle and Charlie taking porewater samples from the channel (unvegetated) sippers