Curtis Prairie and Teal Pond WetlandsSUNDAY, JULY 6, 2014
As a direct result of scouting for and leading this tour, and with the help of two different experts, I solved two mysteries – one botanical and one entomological. But more about that later; our stated purpose on Sunday afternoon was to trace the path of water through the Curtis Prairie and the wetlands associated with Teal Pond.
Stormwater runoff enters the Arboretum at numerous different points. According to the most recent stormwater flow map I have seen, the single largest entry point is near the intersection of Nakoma Road and Manitou Way, which explains why a large new settling pond was constructed there recently. About 36 percent of the total stormwater entering the Arboretum flows in at that location.
The second-highest amount of runoff water comes in at the southwest corner of the Grady Tract, which receives about 28 percent of the total. All of the input points affecting Curtis Prairie and Teal Pond combined fall far short of either of those two, totaling less than 10 percent. That said, more than 350 acre-feet of water enters the prairie or the pond system annually, which is quite a bit of H2O. No wonder it has profound effects on the ecosystem, and requires some handling.
To back up just a bit – the aggregate amount of stormwater runoff which hits the Arboretum averages over 1,400 acre-feet per year; an “acre-foot,” as you might expect, is the amount of water which would cover one acre of land to a depth of one foot. Now, some further perspective: the Arboretum is approximately 1,200 acres in size. That means that in a year’s time, if the water did not drain away, the entire Arboretum – every prairie, woodland, and marsh area – would be covered more than one foot deep in water. Please take a moment to visualize that amount of liquid.
But of course the water DOES drain away, and some of it soaks in, so the Arboretum has not become an adjunct to Lake Wingra. And it’s not just the amount of water, it’s the speed with which it travels that matters.
The faster rainwater flows – because it strikes impermeable surfaces such as rooftops, roads, driveways, and parking lots – the more it carries in the form of silt, litter, plant seeds, chemicals, etc. Rain that lands on entirely natural, non-compacted soil is much more easily absorbed, and most of it does not run off.
I saw that fact demonstrated very dramatically once on a tour in the Grady Tract. A storm came up when our group was a considerable distance from the parking lot. As we hurried back toward cover, we could not help but notice how the hard rain was forming rivulets and gushing down the packed soil of the trail, but was completely soaking in only a few feet away in the prairie or woodland.
Back to Sunday . . . we set off in a westerly direction around the perimeter of the Curtis Prairie. Our first “water feature stop” was at Curtis Pond, a constructed settlement pond in the middle of the prairie. First built in the 1970s and repaired/reconstructed a couple of times, this pond attempts to deal with runoff from the Beltline Highway. The rainwater pools for a while, allowing chemical and physical contaminants to settle to the bottom so they will not be carried further along in the system. (Think about it . . . highway sand is not exactly a natural component of prairie loam.) Over time these sediments must be removed and disposed of.
Although we did see a doe in the Curtis Pond area, generally artificial ponds such as this are not used by wildlife as much as natural ponds are. However, a day earlier on a scouting expedition, I had seen two painted turtles and heard at least one green frog there.
Next we traversed the diagonal trail across the prairie, noting the area where a raised boardwalk is necessary because of water flowage. Basically, in spite of the settling pond’s best efforts, a stream of water makes its way across the prairie toward lower ground. One thing it has carried with it are the seeds of reed canary grass, which has formed a sizable colony. Efforts to discourage this alien intruder are ongoing.
As we passed through the prairie we observed that it’s mostly green at this point – the colorful mid- to late-summer bloom period has not yet begun. Bright yellow color showed on a few sawtooth sunflower buds, however, and the small white flowers and minty-fresh leaves of mountain mint were a pleasure to discover. We also found the first new ball galls of the season on Canada goldenrod stems, and a bumper crop of water hemlock in full bloom!
A smaller pond, Coyote Pond – located due east of Curtis Pond – helps handle the runoff from yet another stormwater entry point. Nearby there is a clone of willow trees, always an indicator of wettish conditions. Redwinged blackbirds are among the birds which nest nearby; some years sandhill cranes are, too.
At this point time was becoming short, so we did not loop all the way around to the far southeast corner of the Arboretum to view the SMRF, or Stormwater Management Research Facility. Designed to filter the water coming in from a commercial parking lot adjacent to Arboretum land, this system features a forebay and several swales, each of which is planted with a different combination of wetland plants. The idea is to see which plants do the best job of filtering contaminants (including toxins and excess nutrients) out of the water, and to speculate why.
We did get to Teal Pond, which is one beneficiary of all this mediation. Teal Pond is in many ways a natural pond, but it has been enhanced and deepened. It’s widely used by wildlife: painted and snapping turtles, waterfowl, muskrats, mink, toads, and several species of frogs have been observed there. Insects, especially dragonflies, are abundant. On Sunday we watched a blue dasher; the previous day, when it was sunnier, widow and 12-spotted skimmers also danced above the water surface, and delicate bluets browsed the bulrushes.
Had we another half hour to spend, we could have continued north to the Icke Boardwalk and its cattail/horsetail marsh. Eventually the Teal Pond wetland system drains to Lake Wingra.
Oh, but the mysteries! On Saturday while scouting, I’d seen many black aphids clustered on the tips of common milkweed plants in the McCaffrey Savanna area. They were being tended by ants, suggesting that they were a type of aphid which produces the sweet secretion called “honeydew”.
I’d seen orange-yellow or reddish oleander aphids on milkweeds before, but never these dark ones. I checked with Andrew Williams, who knows more about milkweeds and their associated fauna than anyone else I know. He says they are most likely the black bean aphid (Aphis fabae), a generalist insect which hangs out on many different plants. It’s a major pest of some crops, including sugar beets, beans, and celery.
And right at the end of the tour, as we paused to admire the mesic-prairie section of the Native Plants Garden, a visitor pointed to a showy pinkish-purple flower spike and asked what its name was.
I was stumped! It was not one of the tick trefoils or vervains – it’s too late in the season for lupine – and too early for blazing star. It certainly appeared to be in the pea/bean family. Turns out that it’s everlasting pea or pea vine – Lathyrus latifolius – an unwanted and potentially aggressive intruder in the prairie garden. My thanks to Native Plant Gardener Susan Carpenter for that identification. By now the offending plant has doubtless been removed.
Next Curtis Prairie tour is in two weeks – will you be there?
Kathy Miner, Arboretum Naturalist