• The Mississippi: A Visual Biography by Quinta Scott

    "Great book and great blog - thanks for the first book I have seen that addresses the contemporary river, headwaters to gulf." Dan McGuiness, Audubon, St. Paul, Minnesota

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Dead Zones, Lake Pepin

“This is a beautiful place; the contrast of the Mississippi full of islands and the lake with not one in its whole extent, gives more force to the grandeur of the scene.” –Lt. Zebulon Pike, 1805

“Speaking of Lake Pepin, in the early days it was evidently a game fish glory hole. There was nothing else like it, really–a huge natural impoundment of the main river by barrier sandbars at the mouth of the Chippewa. Unlike most conventional lakes, this flowing lake-river was an ecological mix of the best of the riverine and lacutrine, with a variety and abundance of fish rarely found in typical lakes. There were walleyed pike, northern pike, pickerel, muckellunge, smallmouth and largemouth black bass, sauger, yellow perch, crappies. bludgills, and rock bass, to say nothing of catfish and sturgeons. Before the channel dams blocked them forever, there were skipjacks that rose to the fly and tasted like shad.” —John Madsen, 1985

I have written many times about the Dead Zone in the Gulf of Mexico, about how Chicago is the largest contributor to the Dead Zone, about conservation buffers on the Mississippi to retain nutrients we spray on our crops–soybeans, corn, golf courses, lawns, and backyard tomatoes–in the uplands and out of the Gulf of Mexico, where the BP Oil Gusher is contributing mightily to the Dead Zone.

We forget that all those nutrients flow to each of the navigation pools that are locked behind dams on the Upper Mississippi River and to each of the magnificent oxbow lakes that bracket the Lower Mississippi River, creating dead zones. And with the nutrients come sediments, washed down from the uplands on the Upper River and washed in from the farm fields that surround the oxbow lakes.

Chippewa Delta, Swinger Slough

When a fast moving river meets a slow moving or still body of water, it almost comes to a halt and deposits its load of sediment, eroded from the uplands in the still body of water. This is how the Chippewa River created Lake Pepin when it deposited more sediment than the slow moving Upper Mississippi could move downstream and dammed the river. Lake Pepin pooled behind it, reaching clear north from Wabasha, Minnesota to St. Paul.

Mississippi Delta, Head of Lake Pepin, Trenton Slough, Pierce County, Wisconsin

Then the Mississippi itself began to deposit its sediment into the head of the still body of water that was Lake Pepin and built a delta that reached south to Red Wing.

Lake Pepin, Central Point, Lake City, Minnesota

Gilbert Creek, flowing out of the uplands, deposited its sediment in Lake Pepin and formed Central Point, just north of Lake City, where Central Point supports a floodplain forest.

Quite apart from the delta of the Mississippi and the small spits of land like Central Point, Lake Pepin is filling with sediment, which has covered most of the presettlement lake bed. Only the very foot of the lake retains the original gravel bed. If the rate of sedimentation continues at its present pace, Lake Pepin will become terrestrial. For the moment, the lake provides an excellent habitat for walleye and other species of fish who swam there before the Corps of Engineers completed Lock and Dam 4 and raised the level of the lake.

Last week the Minnesota Pollution Control Agency Citizen’s Advisory Board approved a measure that would reduce by half the amount of sediment that could be washed into Lake Pepin and sent the measure to the EPA for approval. In doing so it would reduce the turbidity of the lake, the muddiness  of the lake. With less mud in the lake, more sunlight can penetrate it shallows and allow submerged aquatic plants to grow, food for fish and waterfowl. [i]

Read more about Dead Zones in The Mississippi: A Visual Biography.

[i] Pike, Appendix to Part I, 49; Madsen, 137; U.S. Army Corps of Engineers, St. Paul District, “Desired Future Conditions in Pool 4, Mississippi River,” 3, http://www.mvp.usace.army.mil/enviro_proection/poolplans/Pool_04

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3 Responses

  1. As simple as it is, your description of the formation of oxbows is more undertstandable than many I found when I was trying to get a grasp of Moon Lake’s formation in Mississippi.

    As for “dead zone” – it’s a phrase that just makes my blood run cold. Every year we’ve watched it expand a bit in the Gulf, and now, I’m just afraid of what’s coming.

    Between the natural inclination of BP and the government to minimize the situation and the desire of the media to hype everything beyond all reason, it’s hard to know what to believe. It’s going to take time to sort it all out. Unfortunately, it seems that if the well were capped tomorrow the damage has been done.

    I have spent a good bit of time on The Oil Drum. I saw your blog referenced there today, and a number of approving comments. 😉

  2. Hi, Shoreacres:

    I will be doing more on the oxbows, which are in very bad shape. Too many nutrients and too much sediment washing into them.

    Quinta

  3. […] willing to control the amount of fertilizers we contribute to the Dead Zone. And, by the way, there are Dead Zones in the navigation pools of the Upper Mississippi and in the great oxbows of the Lower Mississippi […]

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