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Glacial ice gave us this marsh

August 20, 2011
By GARRY BRANDENBURG , Times-Republican

HENDRICKSON MARSH may not be a big wetland complex, but it is one of many "stepping stone" wildlife areas in Iowa that are utilized by migrating critters big and small each spring and fall. It is an important resting and feeding area for birds especially when the cold icy winds of winter start to lock up the last open waters of northern Iowa.

This wetland area we know today has an interesting natural history that is thousands of years old. Glacial history buffs and scientists of earth history know that rocks and sediments in Iowa tell of at least eight past glacial advances during the last 2.5 million years. The most recent glaciation, the Wisconsinan, was at its maximum about 15,000 years ago. Since glaciers, in human terms, don't do anything fast, the gradual natural earth warming cycle that would bring on the present interglacial, began to melt the ice. The retreating leading edge of the ice left markers on the landscape all the way from Des Moines northward into the Dakotas, Minnesota and Canada. There were even short 'bursts' of readvancing ice but in the long run, ice was turning into water.

Hendrickson Marsh is a marker of its glacial past. Along the lateral edge of the Wisconsinan ice, a block of ice filled with rock, gravel and other debris broke off from the main ice mass. While the main ice mass continued to melt, the ice block at Hendrickson sat in place. It melted slowly with the inevitable outcome being that the sands, gravels and mix of other organic debris accumulated along its margins. Over time, water did find an escape route. That route today is called Clear Creek. The main depression left by the ice block is now the main water impoundment area of Hendrickson Marsh.

Article Photos

Hendrickson Marsh, an 802 acre state wildlife area, is getting ready for more water. Today’s photo was made on Aug. 13 with the view looking southeast. Water levels are low now. Stop logs at the dam control structure are in place to allow any late summer or early fall rains to fill this old geologic basin. The marsh has benefited greatly from a complete drawdown of the water in 2007, killing and removal of rough fish, which in turn allowed emergent vegetation to grow on the mud flats. When water fills the basin this fall, migrating waterfowl and many other small birds will have a great place to rest and feed before continuing on their migration.

During late Pleistocene time in Iowa, the land was recently ice free but still under the intense impact of severe cold. Tundra-like conditions existed in Iowa from 21,000 to 16,500 years ago. Plant life slowly gained a foothold, filling the void first with coniferous forests of spruce, larch, hemlock, fir and yew. As the ice edge made its way toward Canada, vegetation zones migrated northward too. The coniferous forest gave way to deciduous trees which in turn gave way to more grasses typical of prairie grasslands as the climate became warmer and drier.

Iowa's glacial and interglacial sediments also tell the story of animal life roaming the tundra and forests. The list includes mastodon, mammoth, musk ox, bison, caribou, camel, deer, moose, giant sloth, giant beaver, and wolf. Human occupation goes back to about the Paleo-Indian interval of 9,500 to 7,500 years B.C. All of these are documented and on display at the State Historical Museum in Des Moines.

Fast forward to the present. In the mid 1960s, Kimberly Marsh as it was then called, was purchased by the Iowa Conservation Commission. It was given the name Hendrickson Marsh in honor of Iowa State University George Hendrickson, a professor of wildlife management. A dedication ceremony was held on June 13, 1970 to recognize the teacher. The land purchase started out with 601 acres. In 1988, an additional 178 acres became available. A few years ago the final 35 acres were acquired.

Waterfowl management is the main focus of the area by DNR wildlife professionals. There always are spinoff benefits for other wildlife such as deer, beaver, muskrat, rabbit, pheasant and a host of songbirds, shorebirds and predators such as eagles and hawks. For the duck or goose hunter, it is a great place to spend time. For any casual observer of wildlife, it is a must stop during forays in the outdoors. Even the bald eagle nested here in 2011. Next time you visit Hendrickson, remember this wetland is an important 'stepping stone' for wildlife survival.


A recent sighting in Asher Creek was recorded by video cameras. A pair of large snapping turtles was in the shallow water in what appeared to be a lock down battle of snapping jaws and churning water. As it turned out, this was part of the mating ritual for snappers. Mating can happen any time between April and November throughout the nationwide range of this reptile. The female has the ability to store sperm for up to two years or until conditions are just right for her to allow fertilization. Later she will crawl onto dry land looking for soils that will be warmed by summer sunshine. She digs a hole with her very muscular back legs, deposits up to 80 eggs, refills the hole with soil and returns to the safety of water. Incubation is left to the sun, soil temperature and time. Young snappers have a shell about the size of wristwatch face. They instinctively crawl toward water after hatching. The system works well since snapping turtles are a common critter.


Recent summer heat caused several 'blowups" of the concrete surface of the bike path paralleling highway 330. Marshall County Conservation Board staffers Marty Malloy and Jeremiah Mankin have been working to remove the damaged sections and prepare them for new concrete. If all goes as planned, the patches will be done next week. Be alert for workers on the trail.

Recent wind storms took out lots of trees and damaged many others in county park areas. Most of the damages have been cleaned up but there will always be new discoveries along foot trails. For Iowa River fishermen or canoeists, all the boat ramp access sites are usable. Boat ramps are located at Three Bridges, Furrow Access, Timmons Grove and at the Forest Reserve.

The water in the Iowa River continues at very low rates. For those segments of the river downstream from Marshalltown, numerous tree snags litter the river bed. In some places, getting a canoe through them will remain a challenge. Use caution if boating. Even seemingly mild flow rates can lock a canoe against debris and not let you escape. Always respect the power of water.


Garry Brandenburg is a graduate of Iowa State University with BS degree in Fish & Wildlife Biology. He is the retired director of the Marshall County Conservation Board. Contact him at PO Box 96, Albion, IA 50005.



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