My graduate advisor always said that the three most important determinants of wetland character are “hydrology, hydrology, and hydrology.” No one would deny that the presence and quality of water really will make or break the ecosystem. But, how does hydrology work? And how can you tell?
It’s a lengthy discussion—you could take whole classes in wetland hydrology! It’s tricky because of course you can’t always see the water entering or leaving the wetland, let alone monitor it day by day. Still, sometimes field observations give us clues.
See the Prickly Pear cactus (Opuntia) in the foreground of this photo? It is perched, high and dry (literally!) on a very large sand dune near Eddyville, just southeast of town near US highway 63. The site has a number of large dunes covered with arid “sand prairie,” including many clumps of cactus!
“But Paul,” you say. “Iowa gets plenty of rain—how can that spot be so dry, as to result in cactus growing?” Well, most of Iowa has high-quality soil that holds moisture (from rain) quite well. But a sand dune? Holds water poorly indeed…in fact, that water seeps right through the sand. And where does the water go? Perhaps that wetland in the background of the photo answers that question: water travels down through the sand until it hits an impervious layer (blocking further infiltration) and then runs laterally (to the side)…and into that wetland.
It’s a reminder that localized “microsite” differences matter. And hydrology is both crucial to consider, and difficult to understand. So thank a hydrologist!
UPDATE, MAY 10, 2018: Visited the site today with my Intro to Environmental Science class. We found no standing water at that pond, and dry crispy plants in the middle. Around the edge, the Sweet Flag (Acorus calamus) was coming up tall & green. My students snapped pictures (this one is by Katie Z—thanks to her for sharing). We enjoyed the citrus/spice/vanilla aroma and its snorkel-like spongy texture.