Edited 2020-10-16 to clarify a few sections, add references as links, and correct statements about trends. It has gotten worse
People swim, paddle, and wade in Iowa lakes and rivers. I’ve seen a lot of that this summer. We’d like those waters to be clean enough that it doesn’t pose a health risk. But see enough E. coli data, and it’s tempting to give up. There’s raccoons in the storm sewers, and geese on the lakeshore, and livestock on the farms, so therefore there will be poop in the rivers and lakes. How on earth would you ever figure out where it’s coming from, let alone improve the situation? I’ve said this once or twice, and I’ve heard it from experts I’ve consulted.
So hat tip to Chris Jones for putting our numbers into context. I love context! Let me add some more! (Check out his blog post to for some excellent background on what this bacteria is, and why we measure it).
It’s bad, and don’t blame the geese
I was inspired by Chris’s graph, which compares E. coli in the Raccoon and Des Moines Rivers in Des Moines to the Mississippi River in Minneapolis. That river has plenty of geese and raccoons, as I can attest to from having lived in the Twin Cities. So clearly there’s some additional sources of fecal contamination in these Iowa waters that we could do something about, if we had the will.
It’s very bad some places, fine in others
I love this metric: percent of days in the recreation season that E. coli exceeded the standard. Nobody knows what a geometric mean is, or how many samples you need before you can apply it. This is a simpler way of acknowledging that sometimes there will be poop in waters where people wade or swim (say because there are racoons in the storm sewers and it just rained) but we’d like that to be less often. Using my new powers of R scripting, I computed this metric for every water body in an Iowa DNR database that had at least 50 E. coli samples during April-Oct of 2010-2020, and when I couldn’t fit 160 bars on a graph, I pulled out an arbitrary selection to give you a sense of the range.
As I feared, the South Skunk River below Ames is even worse than the Racoon River, exceeding the standard 75% of the time, as are several rivers in central, western, and northeastern Iowa. As Chris mentioned, E. coli is lower downstream of reservoirs, which allow sediment to settle and light to disinfect. Some of the cleanest waters aren’t on here because DNR rarely finds anything, and thus has scaled back testing. This includes destination spots like Okoboji Lake, and my favorite local beach, the former gravel pit at Peterson Park, which is mostly groundwater fed.
It hasn’t gotten worse, has it?
I have fond childhood memories of wading and canoeing and fishing in Iowa rivers and lakes, including the South Skunk River. How bad was it then? I don’t know. I do have data from 2000-2004, when I was an ISU student hauling trash out of the river and planting willow stakes with Jim Colbert’s “Skunk River Navy.” At that time, the South Skunk upstream of Ames met (today’s) primary contact recreation standard, but started to exceed it in 2006. The South Skunk River downstream of Ames and below the confluence with Squaw Creek has exceeded the standard in every year it’s been measured, but was twice as high the last two years as it was in 2000-2004.
Here I’m using the geometric mean for April-October and the 126 CFU/100 mL standard that applies to it, since I already had that calculated. Apologies if you have trouble keeping track of the various standards.
The DNR was monitoring the South Skunk upstream of Ames at Riverside Drive for a special project, which ended in 2014. However, we’ve been monitoring that site and several others in Story County this year. So far, it’s higher there than it was in 2000-2004, barely meeting the standard, but I have one more month left in the “recreational season.” Every other site we monitored (that didn’t dry up this summer) was 2 to 9 times higher than the standard.
Confession: I am unwilling to give up playing in rivers or deny that experience to my kids because of a fecal bacteria problem that seems unlikely to be addressed. As a whitewater paddler, I’ve always been willing to take some risks to enjoy nature, and am not sure how the risk of waterborne illnesses compares to the more obvious risks of drowning and injury. I now make sure to pack hand sanitizer on river outings, and try to keep my head out of the water, but hey, sometimes your boat tips over and that’s part of the fun!
Can you keep your head above water?
Primary contact recreation uses “involve full body immersion… such as swimming and water skiing.” The same standard applies to smaller creeks “where children’s activities are common, like wading or playing in the water.” Small kids tend to splash and put their hands in their mouths. Water designated for secondary contact recreational uses, “such as fishing and shoreline activities” have a less stringent single sample E. coli criteria of 2,880 CFU/100mL. The South Skunk River exceeds the secondary contact standard less than 10% of the time, so if fishing is all you’re doing, you can worry less.
Wait, can I do that? Apply secondary contact criteria to a water body designated for primary use? The DNR doesn’t, even when it would make sense. Long Dick Creek is on the Impaired Waters List for E. coli levels above 235 but below 2,880. In reality, it’s too small to float a canoe and has no public access. If this decision affected anyone’s permit, someone would have asked for an assessment to rebut the presumptive designated use, but it doesn’t, so it will remain on the Impaired Waters List for the foreseeable future, last in line for a cleanup plan (TMDL). This underscores a frustrating truth about the Impaired Waters List and the broader Clean Water Act. It was set up to regulate point source polluters like wastewater treatment plants and industry. It’s not a very good framework for educating the public about risks, or for cleaning up waters affected by other (non-point) sources of pollution.
How risky is manure?
Which brings us to risk. Not only is it hard for most people to evaluate risks when they have the numbers, we don’t have numbers that are relevant for Iowa.
What does EPA mean by “protective of human health” when considering E. coli and contact recreation in a lake or stream, where immersion and ingestion of the water is likely? In this case, a threshold of 235 CFU/100ml (or a geometric mean of 126) would be expected to produce illness in no more than 36 people in 1000 (i.e. 3.6%). So meeting the standard does not equate to zero risk.
I’ll have to dig up the references, but as I recall, these risk calculations were based on epidemiological studies of GI infections at swimming beaches that were sometimes affected by human waste. Part of the debate in the scientific literature is whether those same rates risks apply when the source of E. coli is animal waste.
It’s a question of relatedness. Assuming there’s poop in the water and assuming you swallowed some water, and assuming the animal in question was sick, you’re less likely to contract an illness from poultry and geese manure than swine manure, which is less risky than cow manure, which is less risky than untreated human waste. On the other hand, here’s some research linking pathogens in central Iowa streams to swine manure.
Also, a single threshold is not that helpful for evaluating risks in the many waters that don’t meet the standard. If E. coli a stream is 10 times the standard, is my risk ten times as high? Probably not. Twice as high? The original EPA studies are no help here because not only is the risk model hard to interpret (I’ve tried), the numbers we have here in Iowa are well outside the range used to calibrate the model!
What are we gonna do about it?
As part of Story County’s 10-year Monitoring Plan, we’ve been monitoring E. coli in several local streams. Our partners at ISU, Story County, and City of Ames will be exploring the use of optical brighteners to track down wastewater discharge. We know there are some bad septic systems and aging sewer pipes contributing to high E. coli levels in the South Skunk River and Squaw Creek, and since those pose a higher health risk and are perhaps easier to address than livestock manure, that’s where we’ll start. But I’ve love it if we could talk about manure too, without it being seen as controversial.
I appreciate that Chris Jones brought up E. coli. Amid all the talk about nutrients, we often lose sight of another pollutant whose impact is easier to see locally.
On any field in Iowa, cover crops will improve soil health, sequester carbon, and prevent nutrients from washing down to the Gulf of Mexico. There are at least six situations where cover crops can add to the farmer’s bottom line, but in other situations, or to help encourage farmers to make that initial investment and get through the troubleshooting stage that comes with any new practice, public cost sharing can make a difference. Most taxpayers I talk to are quite willing to pay farmers who are employing conservation practices for the ecosystem services they provide. But we either can’t afford to or aren’t willing to invest at the scale needed to achieve universal adoption of cover crops and other conservation practices, and that means we have to make some decision about where to invest first, so as to get the most nutrient reduction (and hopefully carbon sequestration, soil protection, flood reduction, and other benefits) for our buck.
Most of those discussions are way above my pay grade. I suppose the legislators who draft the federal farm bill and the NRCS bureaucracy set payment rates and application scoring criteria for EQIP and other cost share programs. Iowa’s Water Resource Coordinating Council picked priority watersheds that can get special funding.
Planning at the local level can also influence where conservation investments are made. However, it’s not always clear what influence a Watershed Management Authority actually has over where 1000 acres of cover crops gets planted, or why it’s better to plant them in one part of a county rather than another. Same goes for other conservation practices. Here are 5 possibilities.
1. Plant cover crops where they can protect a local lake or water supply
In addition to Gulf Hypoxia, phosphorus that washes off the land is causing algae blooms in many of Iowa’s lakes. Overnight, these algae blooms can use up the oxygen that fish and other aquatic critters need to breathe. Some kinds of cyanobacteria can produce toxins that can harm people and pets. Algae blooms are nuisance for those who would like to swim, fish, boat, or water-ski in those waters. We can address two problems at once if those 1000 acres of cover crops are planted in the watershed of Hickory Grove Lake, Saylorville Lake or other water bodies suffering from an excess of green.
In addition to Gulf Hypoxia, nitrogen that washes off Iowa farmland can cause a problem for cities that pull their water from a river, or from wells close to and influenced by a river. The Des Moines Waterworks and the Raccoon River watershed have rightly gotten a lot of attention, but other cities in other watersheds (like Boone, on the Des Moines River) also are dealing with high nitrate in their source water. Cover crops in the right watersheds can help protect those water supplies.
Nitrogen and phosphorus can also cause algae blooms in creeks and rivers, but the science is more complicated than in lakes, and not often done. For example, while the Squaw Creek Watershed Management Plan demonstrates that nitrogen and phosphorus levels in the creek are high, it does not make the case that meeting our nutrient reduction goals will protect drinking water, improve fisheries, make for safer recreation in Squaw Creek. Maybe that’s a safe assumption, but I honestly don’t know.
2. Plant cover crops where they can reduce the most nitrogen
Here’s a map of nitrogen load by HUC-12 watershed in Story County, based on landcover. This kind of model would be handy if you wanted to guess which stream has higher nitrate levels at its outlet. If I plant 1000 acres of cover crops south of McCallsburg (in the “Drainage Ditch 81” hydrologic unit) will I get more nitrogen reduction than if I plant them west of Ames (in the Squaw Creek-Worrell Creek hydrologic unit)? Nope. The pounds/acre estimate here is for the whole watershed, and it’s based purely on landcover in that watershed. Unlike the larger watershed, a field west of Ames wouldn’t be 20% developed, it’d be 100% agriculture, so with this model we can’t assume it’d be different than a field anywhere else in the county. More sophisticated computer models like SWAT or SPARROW incorporate things like soils, slope, and county-level fertilizer sales as well as landcover, but it’s hard to tell which of those things is driving the results.
Other models like the Nutrient Tracking Tool are field scale, and can be used for this kind of prioritization. Running through some quick scenarios, I estimated that cover crops on a tile-drained field in the Squaw Creek watershed could prevent 9 lbs/acre of nitrogen loss each year, versus 3 lbs/acre in an undrained field in the watershed. Computer models can be helpful, if we’re clear about their purpose and limitations.
3. Plant cover crops where they can reduce the most phosphorus and sediment
Cover crops have gotten more traction in hilly southern Iowa, where soil erosion is a more visible problem and no-till is common. From a standpoint of tons of soil erosion prevented, or pounds of phosphorus loss avoided, it makes sense to plant on fields with steep slopes and erodible soils. Models like RUSLE can be helpful for this.
4. Plant cover crops where their water quality benefits can best be measured
1000 acres of cover crops will make a bigger splash in a small watershed than in a big one. A small change in water quality is difficult to detect. Just like a poll that talks to a small number of people has a margin of error, a water testing program that samples only 12 or 24 days out of the year will have some uncertainty attached to the results. I’ll be talking more about “minimum detectable change” in future posts, but suffice to say that margin of error is usually closer to 10 or 20 percent than 1 or 2 percent. That means we need to give some thought to where conservation practices will be located relative to long-term water monitoring sites if we hope to document their effects with water monitoring.
Location of monitoring sites in Story County, and agency monitoring
Row-cropped acres in watershed
Expected N and P reduction at monitoring station from 1000 acres of cover crops in watershed
5. Plant cover crops where it is most cost-effective for the producer
We do some of this unintentionally. A farmer who can figure out how cover crops will make financial sense for their operation–cutting a pass for weed control or loosening compaction, providing forage for cattle, or protecting yields in wet or dry years–is more likely to sign up when the cost share being offered is $25-$35/acre. Those that think they will lose money will pass until we offer better incentives–for example, Maryland was paying up to $90/acre and has gotten more takers.
This is also the idea behind “precision conservation” promoted by Land O’Lakes and other retailers. With precision yield monitoring, conservation practices like wetlands, prairie strips, or buffers can be placed so as to minimize lost revenue. Poorly draining or steep parts of a field might actually cost more to plant, till, and fertilize than it generates in revenue, so farmers could install conservation practices and even come out ahead.
That’s 5 ways to get more conservation bang for our buck. Let’s be more clear about which of these we’re hoping to achieve when we do watershed planning, and more creative about how we support good stewardship.
Does this make sense? Are there other ways to be more cost-effective with conservation? Leave a comment!
It turns out that stream monitoring is quite compatible with social distancing. 28 volunteers participated in the Squaw Creek Watershed Coalition’s 13th spring water quality snapshot on May 30 and 31. Together we tested water quality at 43 sites on Squaw Creek, its tributaries, and the South Skunk River! This time, Prairie Rivers of Iowa assembled the equipment, organized the event, and entered the data. We’re happy to support this dedicated group of citizen scientists in better understanding and drawing attention to our local rivers and creeks. Here’s a few selfies taken by participants, a mix of long-term volunteers and new faces.
The Kopecky family by the South Skunk River
Jeff White at Gilbert Creek
Kelly Nascimento Thompson at Glacial Creek
Kurt Plagge and Mary Burnet at Onion Creek
As the name implies, this is a snapshot in time. The water quality on one sunny weekend in May is not necessarily representative of the month, let alone the year. As described here and here, water quality can change dramatically in response to a big rainstorm. But for this moment in time, testing many sites gives us a very detailed picture of the Squaw Creek watershed.
For example, during May 30 and 31, nitrate in Squaw Creek at Moore Park and other locations in Ames was quite high (11-12 mg/L) exceeding the drinking water standard (10 mg/L). Where is that nitrate coming from? All over its 147,000 acre watershed, but in some tributaries more than others, as you can see in the color-coded chart below. Nitrate was especially high in the upper reaches of Squaw Creek, Gilbert Creek and Clear Creek and especially low in Glacial Creek (which has a series of constructed wetlands and a lot of pasture) and College Creek (which has an urban watershed). The upstream, rural parts of College Creek and Clear Creek have higher nitrate, which appears to be diluted they move through town.
For phosphorus some of the patterns are flipped. Glacial Creek has especially high orthophosphate (the dissolved form of phosphorus) while Clear Creek is especially low.
There’s lots of interesting patterns to explore, and more data from this and previous snapshot events here. If you’re curious about water quality, subscribe to our blog, I’ll be continuing to interpret data from this and other sources.
Thanks to all our volunteers for collecting it!
Questions about stream monitoring, or observations from our volunteers? Post a comment.
Last weekend’s rains (5-17-2020) provide a clear illustration of how water and nitrate make their way to Squaw Creek.
Squaw Creek at Brookside Park
How water reaches Squaw Creek after a rain
It started raining late Saturday night and stopped around 3AM Sunday. The rain gage outside my house in Ames showed 0.9 inches. The water hitting my driveway and other paved surfaces in my neighborhood enters a storm sewer that goes directly to a tributary of Squaw Creek. (In newer neighborhoods, the water would be slowed down by a pond or detention basin). This runoff takes about an hour to make its way down Squaw Creek to the USGS stream gage at Lincoln Way. In response to urban runoff and the rain that fell directly on the channel, we can see a quick rise in the water level, and quick fall. Over the next 15 hours, Squaw Creek rose another foot as it was joined by water that fell as far away as Stratford and Stanhope. Other than urban areas, we probably didn’t see much runoff from the storm, which was relatively gentle and fell on soils that weren’t particularly steep or waterlogged. The fall in water level Sunday afternoon and Monday was more gradual, reflecting the release of water from drain tiles and groundwater.
Figure adapted from University of Michigan Extension
How nitrate reaches Squaw Creek after a rain
It’s well-known that tiles and ditches provide a direct pathway for nitrogen to leak out of the soil in corn and soybean fields. Think of cover crops as a way to plug the leak, and bioreactors, saturated buffers, and wetlands as a bucket placed underneath. You can watch the leak from last weeks’ storm with IIHR’s nitrate sensors. This graph is from a sensor installed in Squaw Creek in Moore Park, where it enters Ames. (The colors are the reverse of what you’d expect–brown is streamflow, blue is nitrate). The nitrate concentration in Squaw Creek fell from 5 to 4 mg/L overnight, diluted by direct precipitation and urban runoff, and then rose to 14 mg/L as water from drainage tiles made its way downstream. As tile flow tapers off, nitrate concentrations gradually fall toward the lower levels seen in groundwater.
Nitrate drops as you move downstream
In Hardin County, there’s a nice set of three sensors that clearly showed what happens as water moves downstream during this storm. Not every stream demonstrates this behavior, but many do. At the tile outlet, nitrate levels are highest to begin with (10.9 mg/L) and show the sharpest increase, spiking to 18.3 mg/L by 5AM after some initial dilution. Since the water takes some time to reach the next downstream sensor, Tipton Creek near Hubbard, the peak doesn’t happen until 8 PM, rising from 8.6 mg/L to 17.1 mg/L. Further downstream in the South Fork of the Iowa River, near New Providence, water is reaching the sensor from several tributaries, smoothing out some of the changes. Nitrate rises from 4.5 mg/L Saturday night to a peak of 16.2 on Monday morning at 11:00. There are several reasons why nitrate tends to decline as you move downstream. First, tile systems drain mostly agricultural land, while a larger stream will also drain some field margins, pasture, and woodland. Second, nitrate is removed from the water by algae, plants, and microbes. Waterlogged organic matter, whether in a low spot in a field, a wetland, a stream bottom, or a woodchip bioreactor, is good habitat for denitrifying bacteria. Third, many Iowa streams flow from northern Iowa southeast to the Mississippi River, or southwest to the Missouri River, and as you get into southern Iowa, the land becomes hillier, tile drainage becomes less frequent, and pasture more common. Tile drained fields lose a lot of nitrogen in spring. That’s not news to anyone, but hopefully this helps you visualize and understand the process. Update, 5/29/2020: We had even bigger rains the following week, but spread over several days, so the pattern was less clear. We’re still seeing nitrate concentrations >10 mg/L in the rivers, and >15 mg/L at tile outlets.
We’re all a bit stir-crazy and can benefit from spring weather and spring flowers. If you’re in Ames, I recommend walking east of the ISU campus, where (as of April 5) the ground is carpeted with blue flowered squills, Scilla siberica. It’s not often that you see that color blue in nature, or in that quantity!
While you’re there, take a peek in College Creek. When I visited, the water was clear, the bottom was rocky, and it was full of 4-6 inch fish.
I should caution you that that E. coli levels in College Creek and other streams in Ames often exceed the primary contact recreation standard, but you’re washing your hands constantly anyway, right? (Bold values in the table below exceed the single-sample maximum of 235 colonies/100mL. Data are collected and posted by the City of Ames.)