Dan Haug - Prairie Rivers of Iowa

High nitrate this spring: where and why

by Dan Haug | Jun 22, 2022

The Des Moines Waterworks was forced to use their nitrate removal system for the first time in five years. Our spring snapshot found high nitrate concentrations in streams across Story County. On my way to speak at the CCE Environmental Expo in Mitchell County, I dipped a test strip in the Cedar River near Osage and measured 16 mg/L. Looking at the Iowa Water Quality Information System there’s orange (nitrate greater than 10 mg/L) across much of the state and spots of dark red (nitrate greater than 20 mg/L) in Story, Hamilton, and Hardin counties. What’s going on?

Well, differences in land use, soils, topography, and farming practices make for strong regional differences in water quality. For some streams like the North Raccoon River, this is a return to normal. For some streams, like the Cedar River, current conditions are unusual. To illustrate this, I’ve invented my own graph, which compares highest nitrate concentrations observed this spring (the blue dot) to the entire 10-20 year record (a black band showing the range, and a black square showing the median). The data comes from Iowa DNR’s Ambient Stream Monitoring Network; I will update these graphs once June data is available. A sampling of sites is shown at right, but the entire graph can be downloaded as a PDF here.

Northwest Iowa is still suffering from drought, and that means the Floyd River near Sioux City (which usually has some of the highest nitrate concentrations in the state) is barely flowing and has very low nitrate concentrations. As we saw last year, nutrient concentrations tend to be low during dry conditions except where there is a strong influence from point sources of pollution. Most of the rest of the state is back to normal, and nitrate that accumulated in the soil during two dry years is now getting flushed out. These maps are taken from the National Drought Mitigation Center at the University of Nebraska-Lincoln. I’ve drawn in the approximate location of the watersheds for the monitoring sites in my example.

“Weather whiplash in agricultural regions drives deterioration of water quality.” That’s the title and conclusion of a paper that studied previous episodes when a wet spring followed a dry summer and fall. The 2012 drought was much more severe than 2021, impacting yields so that less nitrogen was taken up by the crop and removed in the grain, and maybe that’s why nitrate in 2013 and 2014 was so much higher than it is now. I’ve compared spring highs for several sites and years, normalizing by the long-term average. It’s not clear to me whether weather whiplash increases the overall mass (load) of nitrogen that gets washed away, or just alters the timing (moving in one year what would have been parceled out over two), but high concentrations are a concern for communities like Des Moines and Cedar Rapids that get their drinking water from a river or river-influenced wells.

map showing shift out of drought in 2013

graph showing when nitrate was higher than usual for select sites

I’m procrastinating on the work I’m supposed to be doing because “Hey look! Data!” and I have to satisfy my curiosity. If you’d like to see us do more water quality analysis beyond Story County, let us know, and support us with a charitable donation so it can become work I’m supposed to be doing!

It’s Rude to Point, but…

by Dan Haug | May 27, 2022

By my calculations, over 65% percent of the nitrogen load in Ioway Creek on May 20 came from less than 1 percent of the land area in the watershed. We still don’t know why.

Revised May 31

Many people assume that fertilizer applied to turf grass is a major source of nitrogen and phosphorus pollution in Iowa. At a presentation to the Ames City Council, I was asked if a public awareness campaign aimed at lawn care professionals and homeowners would be an effective way to improve water quality in Ioway Creek. If we’re talking nitrogen, I don’t think so:

Because turfgrass covers a tiny proportion of the land in most Iowa watersheds, compared to cropland.
Because turfgrass is a perennial. Having something growing and taking up available nutrients year-round is the principle on which cover crops reduce nitrogen loss.
Because there was a study by Dr. Keith Schilling that found very low nutrient levels in shallow groundwater below six Iowa golf courses.

To that list, I can add local water quality monitoring including lab testing and sensor results from May. Nitrate in Ioway Creek and the South Skunk River were the highest we’ve seen for a few years, but while rural tributaries ranged from 12-20 mg/L of nitrate, College Creek (an urban watershed with plenty of turf grass) measured only 2.3 mg/L.

But even if turf grass in general isn’t a serious water quality problem, maybe some specific areas of turf grass are a problem. That’s what I thought after reviewing the data from our spring water quality snapshot on May 17. Volunteers found a big difference in nitrate levels between South Duff Ave and other sites in Ames. I wondered if it could be a mistake, so I went back out on May 20 with a bottle of test strips and a smartphone app that enables more precise measurements. It wasn’t a mistake (nitrate in Ioway Creek increased from 8.6 mg/L to 24 mg/L in two miles), but the results still weren’t making sense, so I kept testing and testing until I assembled the map below. By my calculations, 65% of the nitrate load in Ioway Creek that day was coming from just 1,500 acres!

The 1,500 acres includes Coldwater Golf Links, and the pattern looks like what I’d expect to see if the golf course was overapplying fertilizer. However, the golf course superintendent has informed me that fertilizer has not been applied since fall, and then only at a low rate. A volunteer tested two ponds on the course and found low levels of nitrate (1-2 mg/L).

The 1,500 acres include some developed areas north of creek drained by storm sewers, but I tested water trickling from two outfalls on May 20 and found very low nitrate levels: 0.5 mg/L and 3.1 mg/L.

The 1,500 acres acres also includes two construction sites: a flood mitigation project near South Duff Ave and an ISU recreation complex east of Jack Trice Stadium. The photo shows severe bank erosion where drainage from the ISU construction site enters the creek. An inspector with the Iowa DNR noted problems with erosion control earlier this spring on the South Duff project. However, if the nitrate spike were linked to erosion, I’d expect to see high phosphorus and low transparency.

Honestly, I’m not sure what’s going on here. It’s not a pattern we’ve seen in previous years.

erosion on Ioway Creek between Grand and Duff avenues

When interpreting this kind of data, there is a risk of jumping to conclusions and unfairly pointing fingers. In my first draft of this article, I suggested that Coldwater Golf Course was the source of the nitrate and the bank erosion. That was premature.

However, there is also a risk that we will waste time and money on the wrong solutions or the wrong areas if we don’t test water or don’t follow where the data is pointing. It’s clear from this month’s data and many other rounds of testing that water quality impacts are not uniformly distributed across the landscape.

Volunteers in the Creek All Week

by Dan Haug | May 23, 2022

Trash Cleanup

Ioway Creek recently got some love from the community. On Saturday, May 21, a group of seventeen volunteers (plus another four helping on land) loaded nine canoes with trash as we floated from Brookside Park down to S. 16th Street in Ames. We hauled out 14 tires and 1,560 pounds of other trash including 3 shopping carts, a tent, and two bicycles. Assembling the tools, canoes, food, and people was a collaborative effort involving Prairie Rivers of Iowa, the City of Ames, Story County Conservation, the Skunk River Paddlers, and the Outdoor Alliance of Story County. A few people got wet, everyone got dirty, my muscles are still sore, but we all had a good time on the river!

Citizen Science

On Tuesday May 17, fourteen volunteers tested water quality in Ioway Creek and its tributaries. This is the fifteenth Spring Watershed Snapshot, and the fourth that Prairie Rivers organized. Thanks to the Outdoor Alliance of Story County for help with supplies. This year, some volunteers were already doing regular monitoring of a site for Story County Conservation and adjusted this month’s schedule to coordinate, or picked up a few extra sites. If we include other watersheds and other days tested during the same week, the count is 22 volunteers (and also some Story County Conservation staff) and 47 sites in Story, Boone, and Hamilton counties.

We scheduled the event for a weekday this year to coincide with Polk County’s snapshot, so while the event was less social than it sometimes is (volunteers could pick up a kit any time on Tuesday and test their assigned sites alone or with a friend), they were monitoring as part of a big coordinated effort of the kind that we haven’t seen since before the IOWATER program was cancelled! In Polk County, 75 people covered 115 sites!

A table with our findings are shown below, and a map of the sites can be found here. On Tuesday, the water was clear and phosphorus was low at all our sites. Chloride was highest and nitrate lowest in creeks with more urban watersheds. Dissolved oxygen fell into the “fair” range at several sites in Hamilton County, as well as the south fork of Worrell Creek in Ames. Nitrate was 10 mg/L or higher at most sites, but reached 20 mg/L in the middle sections of Ioway Creek and several rural tributaries. I did some followup testing to make sense of the high nitrate levels at Duff Ave, more on that later.

Thanks to all the volunteers who spent some time in a creek last week!

Rivers Routinely Ruin Riprap Revetments

by Dan Haug | Apr 5, 2022

This island in the middle of the South Skunk River used to be riprap armoring the outside bend. (I turned my kayak upstream to take this photo). Rick Dietz pointed this out to me during the Skunk River Paddlers’ annual “Pancake Paddle” on April 2. Five of us bundled up and enjoyed canoeing and kayaking from South 16th St in Ames to Askew Access near Cambridge. Back at the office, I looked at some aerial photos. The riprap near Ken Merrill Road must have been installed some time in the ’90s, but by 2009, the concrete had slumped to the bottom of the channel and the river had started carving away the bank behind it.

The Skunk River south of Ames reflects an old attitude toward rivers. We straightened the bends in the river, which made the water go faster. The faster current caused banks to cave in, so we dumped concrete (and sometimes old cars) on the banks to armor it. This didn’t always work. Hopefully we’ve learned something from these failures and are exploring how to manage rivers by working with nature: this can include setting aside floodplain areas to allow rivers to meander, using stumps and rock structures to redirect the current away from unstable banks, reshaping the channel so that the river can overtop its banks and dissipate its energy without causing property damage, and protecting the banks with a mix of rocks and native vegetation. Riprap and levees should be used sparingly.

As for the paddling, the water was cold, so water proof gear and dry bags are a must, but early spring on the Skunk is a great time to see birds. We saw several flocks of mergansers, wood ducks, a yellowlegs, bald eagles, and herons. We’ve got some nice water trails in Iowa, so take advantage!

The Mystery of the Orange Creek

by Dan Haug | Mar 30, 2022

“Is this pollution?” I received this photo, taken at 1PM on March 24, from Ames High School student Oskar Niesen. I met Oskar and other students in Mr. Todd’s environmental science classes for the first time in February, when we talked in the classroom about issues and solutions in Iowa waterways. The class was interested in testing water quality, so I met them again at the creek on March 22 and showed them how.

Later that evening, I visited the site and chatted with Jake Moore and Liz Calhoun with the City’s stormwater program. If someone had let muddy water wash off a construction site, or someone was pouring chemicals down the storm sewer, this would violate city ordinances and they would be the people to check up on it. But the timing wasn’t consistent with construction site runoff. There hadn’t been more than trace rain since Tuesday March 22nd.

Oskar had talked with a geology professor at Iowa State (Dr. Elizabeth Swanner) and suggested another possibility: iron oxide (rust), perhaps formed by naturally occurring bacteria. As Oskar explained “there are generally 3 types of iron oxide formations. One is a stain that we see now, the second is called flocculent iron which is a cloud that I saw then, the third is an iridescent film on the top. Bacteria tend to form all three.” At 5:00 on March 24, when I followed up on Oskar’s tip, the water had cleared up and there was no iridescent film, but there was stain on the rocks and at the water’s edge all the way up to the storm sewer outlet.

Hydrant flushing is done every year with the express purpose of flushing out iron oxide and other mineral deposits that can clog water mains. Liz Calhoun confirmed that crews flushed hydrants in neighborhoods connected to this storm sewer on March 24. A little rust in water can stain laundry but is harmless to people and fish. A release of drinking water can kill fish if it causes a sudden temperature change (this happened last summer when a water main broke) but in this case, we think there’s nothing to worry about. Mystery solved! The only thing more gratifying than working with curious young people and helpful colleagues is a happy ending for water quality!

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