Porewater Sampling and Processing
GSI Protocol #03
Published: February 2023
Prepared by: Stephen G. Hesterberg, Ph.D., Executive Director; Betsy Potter, M.S., Staff Scientist
Porewater Collection
MATERIALS
30 mL syringe
RhizonTM (with a porous white tip at 5 cm length)
Permanent waterproof marker and chemical labels
Galvanized landscape staples
Syringe plunger spacer (e.g., plastic landscape stake)
8” zip ties
Tubing (maximum 4’’)
1 male luer to hose barb adapter (if using tubing)
1 female luer to hose barb adapter (if using tubing)
INSTRUCTIONS
Assemble the RhizonTM and syringe apparatus by first connecting the 30 mL syringe with male leur to the female-end of the stopcock, then connect the RhizonTM with female leur to the male-end of the stopcock. Leave the middle valve open. If tubing is required, cut the desired tube length and attach one male luer-to-barb adapter at one tube end and a female luer-to-barb adapter at the other tube end. The male adapter will connect to the RhizonTM, and the female adapter will connect to the male-end of the stopcock.
To begin porewater collection, start with the stopcock turned to the “off” position, or pointing towards the syringe (Fig. 1a). Insert the porous, white portion of the RhizonTM completely into the sediment (approximately 5 cm).
Once the RhizonTM is inserted into the sediment, rotate the stopcock’s spin-lock 90° counter-clockwise so that the middle valve is now “off” (Fig. 1b).
Extend the plunger as far as possible and prop the plunger open by placing a spacer in-between the end of the plunger and syringe barrel. Secure the spacer to the plunger using a zip tie.
Place two garden staples along the syringe and plunger to hold the collection apparatus at the sediment surface (syringe and plunger are positively buoyant) (Fig. 2). Verify that the Rhizon’sTM porous area is still embedded in the sediment.
When at least 27 mL of porewater has filled the syringe (this can take about 15-25 min), close off the syringe by turning the “off” label on the stopcock towards the syringe (Fig. 1a). Carefully remove the RhizonTM from the sediment and bring the entire apparatus to the desired processing location.
Hydrogen Sulfide Processing
MATERIALS
30 mL syringe and stopcock with collected porewater sample
20-gauge beveled needle
20mL glass scintillation vial pre-filled with 3.5 mL of zinc acetate
Permanent waterproof marker and chemical labels
Cooler with ice
INSTRUCTIONS
1. Label the pre-filled glass scintillation vial (e.g., MM/DD/YYYY, Analysis, Site, Replicate).
2. Disconnect the RhizonTM from the stopcock but keep the stopcock and syringe connected.
3. Connect the 20-gauge needle with female leur to the male-end of the stopcock.
4. Rotate the stopcock’s spin-lock 90° counter-clockwise so that the middle valve is now “off” (Fig. 1b).
5. Discharge extra air and 0.5 mL of sample as waste and close the stopcock by rotating the spin-lock 90° clockwise (Fig. 1a).
6. Insert the needle below the surface of the zinc acetate solution in the 20 mL glass scintillation vial and dispense 3.5 mL of sample. If an amount other than 3.5 mL is added, record EXACTLY the volume of injected sample on the label.
7. Close the scintillation vial and place on ice until the sample can be frozen. Samples must be processed within 7 days of collection.
Other Dissolved Analyte Processing
MATERIALS
20 mL plastic scintillation vial
30 mL syringe with collected porewater sample
Permanent waterproof marker and label tape
Cooler with ice
INSTRUCTIONS
1. Label the plastic scintillation vial (e.g., YYYY/DD/MM, Analysis, Site, Replicate).
2. Remove the stopcock and any attachments from the syringe.
3. Depress the plunger to remove extra air, being careful not to lose a significant amount of sample.
4. Fill the plastic 20 mL scintillation vial until volume of water reaches the shoulder of the bottle. Do not fill to the top as water will expand during freezing.
5. Close the scintillation vial and place on ice until the sample can be frozen. Samples should be processed within one year of collection.
Rhizon Cleaning
INSTRUCTIONS
1. Assemble the RhizonTM and syringe apparatus by first connecting the 30 mL syringe with male leur to the female-end of the stopcock, then connect the RhizonTM with female leur to the male-end of the stopcock. Leave the middle valve open.
2. Begin cleaning with the stopcock turned to the “off” position, or pointing towards the syringe (Fig. 1a). Insert the porous, white portion of the RhizonTM completely into deionized (DI) water.
3. Once the RhizonTM is inserted into the DI water, rotate the stopcock’s spin-lock 90° counter-clockwise so that the middle valve is now “off” (Fig. 1b).
4. Extend the plunger as far as possible and hold for 30-60 seconds to flush the RhizonTM with DI water. Extrude the DI water within the syringe back through the RhizonTM.
5. Disassemble the RhizonTM apparatus, and fully submerge the syringe, plunger, and stopcock into DI water before the next use.
Fig. 1. (A) Position of stopcock spin-lock turned to the ‘OFF’ position and (B) stopcock position when the middle valve is off, allowing water to enter the syringe.
Fig. 2. Porewater collection apparatus with a 60 mL syringe attached to a RhizonTM SMS sampler. A spacer (black) and zip ties (yellow) are used to keep the plunger extended. Garden staples are used to prevent syringe from floating since the apparatus is positive buoyant.
REFERENCES
Protocol adapted from Dr. Ashley Smyth, Department of Soil and Water Sciences, Tropical Research and Education Center, University of Florida
