Wetland sampling 101
Do you lie awake at night wondering what it would be like to be a freshwater ecologist? Are you itching to get out in the field but have to live vicariously through others? Yes & yes?
Then this is the blog post for you!
I suppose it might also be useful for my fellow graduate students/researchers who may be doing similar work😊
To back up a little bit, I did this sampling as part of my dissertation research focused on understanding feedbacks between water management decision-making in the Tampa Bay area (particularly related to groundwater pumping) and wetland condition. Specifically, I wanted to know how wetland hydrology, plant communities and soil properties have responded to changes in groundwater pumping, which is the primary mechanism used in the area to get people drinking water and irrigation for agriculture. To read more background information, check out my dissertation research page here.
To look at these connections between pumping and wetland condition, I sampled freshwater, depressional (meaning not permanently connected via surface water to other freshwater resources like streams/lakes/etc.) wetlands within a wellfield, or designated area for groundwater pumping as well as in a control site, where no pumping has occurred.
Wellfields where my sampling took place as well as my control site (the Green Swamp Wilderness Preserve). Within each wellfield/control site, I sampled 2–9 wetlands, ultimately sampling 30 total wetlands.
I also selected wetlands across a range of plant communities including: marshes, which are dominated by only herbaceous plants like grasses & sedges and swamps, which are contain trees like cypress and tupelo to see if different plant communities responded differently to pumping.
I planned to sample these wetlands in May, which is the very end of the dry season in Tampa and thus would correspond with when these wetlands would be at their driest so I could more easily access soils. Throughout April, I began gathering my supplies!
Not pictured: sunscreen, bug spray, snacks, quadrats for plant sampling, soil core driver, soil sleeves and caps, waders incase of severe flooding, and your best resource of all, UNDERGRADUTE RESEARCH ASSISTANTS!
While this first pass of supplies seems like a lot, after a few pilot sampling trips, the soil sampling proved difficult to say the least...
Some common problems: wet soils got caught in the PVC corer and we had no tools besides shaking to get them out (yikes!); the metal corer tips weren't sharp enough to break through the top soil layer when it was comprised of finely matted roots, so they ultimately compressed the soil too much (double yikes!); the metal soil corer caps sometimes got stuck meaning we couldn't get the soil samples out and the corer was essentially useless for the rest of the trip (SUPER yikes!).
OH! And, we also had a peat corer that we promptly snapped in half on day 2 when using it on particularly compressed (e.g., not peat) soil.
All in all, not our best work.
Peat corer in action before it's untimely demise. RIP.
After troubleshooting with my advisor, I gathered the tools shown above.
A long flathead screwdriver helped remove flooded soils from the PVC corer. The meter stick also proved useful in this capacity.
The wrench helped to unscrew the metal soil corer cap when we had to bang pretty hard on the soil driver (pictured to the far right). This was usually when we hit a root.
Finally, the most useful addition was a sharp trowel, which allowed us to cut a circle (of roughly the same diameter as the metal corer) through the top layer of finely matted roots. When that layer ran deep, we used the trowel to extract the first 10cm of soil and then either the metal or PVC corer to do the bottom 20 cm (I wanted 30cm total of soil).
Check out how we did it in the video below!
Here's a good look at some soil cores with relatively clean delineations between soil layers (dark brown organic-matter-rich top layer followed by a beige sandy layer). In this photo, soils were able to be collected solely with the metal corer (no trowel needed!)
If you can believe it, soil core samples were not the only things I was planning to collect during my field sample trips. I also wanted to collect information on the plant communities.
To do that, I collected herbaceous plant samples within quadrats at the same elevation as my soil samples (we used a field manometer for elevation measurements).
In these side-by-side pictures, you can see that we used the shears/scissors and Ziploc bags shown above to clip and collect the fern stems to get estimates on herbaceous biomass.
In addition to herbaceous biomass, swamps have tree communities that greatly contribute to the wetland ecology. To study those, I used the transect tape to create a much larger plot than the quadrats. I then recorded the species present as well as their diameter at breast height (DBH) shown below.
Just me measuring a cypress tree with some DBH tape.
After five grueling weeks, we had all 30 wetlands sampled! We tackled 2-3 a day depending on a number of factors: how spread out the wetlands were within the wellfield/control site, how easily accessible they were (paved roads to wetland edge or park and hike), how many undergrad assistants I had each day, what wetland type (marsh or cypress), and how easily maneuverable the wetland was (lot of overgrowth or not much).
And, while it took 8 hours to do one marsh the first day of sampling (Yes, I did almost quit, right then and there!), by the end of the sampling schedule, we were crushing some wetlands in 2 or so hours!
Ready to try it yourself?
(If you have more specific questions about sampling methods, don't hesitate to shoot me a line!)
Special thanks to so many people:
My amazingly talented and dedicated undergraduate research assistants who donated upwards of 150 hours in the field and lab (in alphabetical order): Amadeo Brandon, Kelli Elliott, Christina Iovino, Maximilian Lombillo, Alexis Marino, Shania Rodriquez, and Evan Worden
My lab mates: Cassie Campbell, Carley DeFillips, and Cody Stewart for help in the field, lab, and endless encouragement
This project is partially funded by the Garden Club of America's Coastal Wetlands Award, the Florida Native Plant Society's Dan Austin Award for Ethnobotany, the Society for Freshwater Science's General Endowment Award, and the Society of Wetland Scientists' Research Grant.
