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Grading on a Curve

Posted on May 6th, 2021

More than three years ago now I published a paper with colleagues Jacob Nielsen, Keith Schilling and Larry Weber titled Iowa stream nitrate and the Gulf of Mexico. This paper appeared in the journal PLOS ONE which is an open access journal, meaning anyone can read it for free. Here is the link.

In that paper we quantified Iowa’s relative contributions of nitrate and water to the Missouri, the Upper Mississippi, and the entire Mississippi basins for the period 1999-2016. The beautiful map below, once again made by Dan Gilles, was used in the paper and illustrates the three basins. In terms of area, Iowa land comprises 3.3% of the Missouri Basin, 21% of the Upper Mississippi Basin, and 4.5% of the greater Mississippi Basin.

Iowa areas draining to the Missouri, Upper Mississippi, and Greater Mississippi Watersheds.

Since it has been three years, I thought I would update the data. Nitrate data for the larger basins is quantified by USGS and is available through 2019. Iowa data is an aggregate of that collected by UI-IIHR, Iowa DNR, and USGS.

The graph below illustrates the Iowa fractions for area (red line), and the updated Iowa fractions nitrate (green bars) and water (blue bars). A green bar with a magnitude of 0.4 would mean Iowa contributed 40% of the nitrate to that basin in that year, for example.

Iowa fractions of water and nitrate to the Greater Mississippi River Basin (top), Upper Mississippi River Basin (middle) and Missouri River Basin (bottom).


Overall average contributions from Iowa for the entire period of record are shown in the table below.


Basin Area Nitrate Water
Greater Mississippi 4.5% 29.5% 6.0%
Upper Mississippi 21% 44.5% 21.2%
Missouri 3.3% 57.2% 12.2%


In 2001 the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, a consortium of tribes and federal and state agencies (including those from Iowa), issued an Action Plan to serve as a strategy for hypoxic area (otherwise known as the Dead Zone) reduction. The group’s long-term goal was to reduce the Gulf area where dissolved oxygen is less than 2 ppm to 5000 square km by 2015. Low oxygen levels are driven by nutrients (nitrogen and phosphorus) discharged by the Mississippi River. A revised plan was created in 2008, and 12 US states draining to the Mississippi-Atchafalaya River Basin (MARB) continue to implement the 2008 plan. As of 2017, the 5-year running annual average size of the hypoxic area had remained mostly unchanged since 1994, and the Task Force extended the goal target date to 2035.

The task force uses the 5-year running annual average because this buffers the large year-to-year swings that can result from weather. Dry weather in the corn belt and hurricanes in the Gulf can both greatly reduce the size of the Dead Zone; likewise floods in the Mississippi Basin can increase it.

I decided to look at the Iowa fractional contribution of nitrate in 5-year running annual averages as well. This is illustrated in the graph below. Our relative nitrate contribution is increasing for all three basins over the period of record. I should also state that our relative contribution for water is also increasing. The nitrate contribution has increased slightly more than the water contribution for the Greater Mississippi and Upper Mississippi Basins; the water contribution is increasing more than the nitrate contribution for Missouri River Basin.

Five-Year Running Annual Average Nitrate Contributions to the Missouri, Upper Mississippi, and Greater Mississippi Basins.


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5 Responses

  1. dmf says:

    thanks for the OA link (should be required for state funded research results) , this seems to pretty much capture the political economy we are drowning in:

  2. Zach from WI says:

    Iowa plays an interesting role in nutrient pollution politics in the upper Midwest. When I was writing nutrient management plans for landowners with tractors in Wisconsin, Iowa was the failed foil to Wisconsin’s successful nutrient regulatory scheme. This is a line of reasoning I observed to be widespread throughout those of us in the state who made our money through the Big Pollution machine. If we were ever concerned that we weren’t doing enough, we could always say that at least we weren’t as bad as Iowa.

    There are some very real ways that this is true. For example, WI state law includes groundwater in the Public Trust Doctrine, which means that it can be regulated like surface water. From what I understand the feds and other states only include surface water.

    But mostly I just think it is a manifestation of Wisconsinite chauvinism that works in the interests of our state elites. We never talked much about these nutrient task forces when I was working in Big Pollution, so I took a look at the most recent progress report available from WI DNR. They have some hard data on reducing nutrient pollution from municipal sources, but the ag runoff stuff is just fluff. Lots to say about the increase in acres under an NMP, but not so much on hard data to prove the effectiveness of the NMPs. This is strong proof to me that NMP is a political tool rather than a serious tool to reduce nutrient pollution.

    As a Wisconsin chauvinist, I emphasized our progressive political history to explain our superiority over Iowa. It’s clear to me now that my life doesn’t depend on believing it that this is not a useful framework. In both states Big Pollution is working in lockstep to protect their property interests, and make sure no significant change occurs.

    • A.M. says:

      Zach, I always appreciate your interesting comments, and not just because I have rural relatives in Wisconsin. Thank you.

  3. Steve Roe says:

    Thanks for the update. The nitrate to area ratio is staggering. It makes Mike Naig’s “propaganda” statement quite inaccurate and foolish.

  4. A.M. says:

    Thanks for another illuminating post, Chris. At this point, I don’t know which is the bigger challenge, or even which is more important — getting more Iowans to know, or getting more Iowans to care.

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