You can lead a horse to water…

by Dan Haug | Jan 2, 2023

Prairie Rivers of Iowa is not the sort of environmental group that follows the goings on at the state capitol (that would be our friends at the Iowa Environmental Council) but the success of our watershed projects is very much affected by state and federal policy. A big part of our work is environmental education, but often “is a river still polluted and what can we do about it” is a legal and political question as much as a scientific question. I hope this tricky case study from the Cedar River will illustrate why we need more people to learn about and talk about environmental policy to make it more transparent, fair, and effective.

My New Year’s resolution for 2023 is to write fewer long articles like this one and more bite-sized lessons. For the 50th anniversary of the Clean Water Act, we’ll be sharing 50 short facts (one a week) on social media about that important and complicated law. Here are the first five:

1) The Clean Water Act (CWA) is 50 years old but it still has a big influence on how we evaluate and protect water quality in rivers and lakes.

2) The Clean Water Act is a federal law but is implemented at the state level, with oversight from the Environmental Protection Agency (EPA). In Iowa, the Department of Natural Resources (DNR) is responsible for issuing permits, setting standards, and assessing the condition of rivers and lakes.

3) The Clean Water Act requires public notice and public comment for many decisions. Staff at environmental agencies read and take seriously public comments, so it’s worth speaking up and having your voice heard.

4) The Clean Water Act also gives concerned citizens the standing to file suit if there is an ongoing violation that hasn’t been enforced, or if the Environmental Protection Agency is not fulfilling its mandatory duties.

5) Decisions by courts and federal agencies can come into conflict with state legislatures, which control the budgets for state agencies. For example, in Iowa there are over 700 river segments and lakes on the waiting list for a cleanup plan, because Department for Natural Resources doesn’t have enough staff to keep up with it.

We can sum that up with the old saying: “You can lead a horse to water, but you can’t make it drink.”

In November, the Iowa Department of Natural Resources (DNR) made the unusual decision to withdraw a cleanup plan (or TMDL) for nitrate in a part of the Cedar River that supplies drinking water to Cedar Rapids. Click here for the original plan, here for the public notice of its withdrawal, and here for the Iowa Environmental Council’s response, which provides some valuable context. TMDL stands for “Total Maximum Daily Load.” TMDLs are pollution budgets that explain where pollution is coming from and how much needs to be reduced in order to protect fisheries, drinking water, or recreation in an impaired river or lake. They are often used to set permit conditions for upstream sewage treatment plants and industrial facilities.

leading a horse to polluted water in the the Cedar River

There is a joke that TMDL stands for “Too Many D*** Lawyers.” Most state agencies ignored the part of the Clean Water Act dealing with TMDLs until a series of lawsuits by environmental groups in the 1990s. The Cedar River TMDL was actually written under a court order in 2006. The TMDL estimated that only 9% of the nitrogen in the Cedar River watershed was coming from regulated point sources of pollution like sewage treatment plants and factories. Most of the reductions would need to come from agriculture, through voluntary conservation programs. Still, the plan called for capping the pollution from point sources at the 2006 amount and not adding any more. However, it seems that the DNR did not follow the TMDL when writing permits over the next decade, and did not enforce permit violations.

One of the most surprising violations is from a drinking water treatment plant in Waverly. I don’t think of drinking water treatment as generating pollution, and maybe that’s why it was initially overlooked. The facility uses reverse osmosis, which gives you cleaner water on one side of the membrane and dirtier water on the other side. The facility has been discharging wastewater with 37.7 mg/L of nitrate into the Shell Rock River (a tributary of the Cedar). When the DNR added a permit condition that nitrate be brought down to 9.5 mg/L, the Iowa Regional Utilities Association protested, claiming that compliance would cost them $1 million. If my math is correct, bringing the facility into compliance would avoid only 5 tons of nitrogen pollution per year. The TMDL calls for a reduction of 9,999 tons per year. Enforcing this permit as written does not seem like a fair or effective way to protect water quality in the river, but I suspect there would be an easy fix if the TMDL were revised.

The Clean Water Act provides two ways to set the limits in a permit. Water quality-based effluent limits reference the pollution budget in a TMDL. They’re only for facilities that discharge to an impaired water body. Technology-based effluent limits are set statewide, based on the level of treatment that’s possible with widely available, not-too-expensive technologies. The Iowa Nutrient Reduction Strategy included new technology-based effluent limits for nitrate and phosphorus, affecting 157 municipal and industrial wastewater treatment systems. They must find a way to reduce their total nitrogen by 66% and their total phosphorus by 75% or else complete a feasibility study to show it would be cost-prohibitive to do so. Some facilities are already making the upgrades, some won’t be done until 2027. For the largest point source in the TMDL (the Waterloo sewage treatment plant), that means a reduction of some 333 tons of nitrogen a year.

Effluent from a wastewater treatment plant entering a river.

Of course, most of the nitrate reduction goal for the watershed (9,999 tons) will need to come from agriculture. We don’t know how that’s going because Iowa doesn’t have a current or complete tracking system. The most recent data I could find for cover crops by watershed is 7 years old. At that time, there were not enough acres to make a noticeable difference in water quality in the river.

Cover crops in the Cedar River watershed

Cedar River watershed map, courtesy of IIHR

Side note: The Cedar River starts in Minnesota and has several major tributaries, including the Shell Rock River, West Fork, and Winnebago. It’s a big watershed that usually gets divided into smaller chunks (i.e. there are separate watershed management authorities for the Upper, Middle, and Lower Cedar). The TMDL actually recommended prioritizing conservation in the Upper Cedar, but at some point, the focus got shifted to the Middle Cedar.

Are water quality based-effluent limits still needed? Maybe not, but the frustrating thing about this case is that we get don’t get a revised pollution budget that shows how other strategies will protect drinking water in Cedar Rapids. We don’t get a public debate over what’s not working with this law and an opportunity to change it. Instead, we get excuses for why a revised TMDL can’t be done and isn’t needed. Some of those excuses are legitimate: the chronically underfunded DNR has a lot of TMDLs to write and not enough staff to do it. Some of the excuses are flimsy: apparently, the document mishandled nitrogen units in a way that was too subtle for me to notice on the first read-through but serious enough to make the whole thing unworkable.

Another excuse—that the Cedar River is no longer impaired—seemed like a mistake at first but turned out to be technically correct on closer inspection. “No longer impaired” means that fewer than 10% of the samples collected during the last two assessment periods (2016-2018 and 2018-2020) exceeded the drinking water standard. I’ve double-checked this with another source of data and think this assessment holds up, even if we account for weather. It’s just premature. Nitrate was back up in 2022.

Well, you know what they say. You can lead a state agency to water, but they can’t make it drinkable.

(Apologies to my respected colleagues at DNR. I can’t resist a good pun!)

TMI stands for “Watershed Plan”

by Dan Haug | Nov 20, 2022

I missed the deadline for public comment on the new watershed plan for the Headwaters of the South Skunk River. We were given only two weeks and it’s a 200-page document. I can either respond with a quick text message: “TMI” (Too Much Information) or with a careful read and 700-word article. Since the deadline is passed, these comments are really meant for our readers who might be wondering what’s in the plan and what it will mean for the river.

An imaginary text message conversation about the watershed plan

Watershed Management Authorities (WMAs) are authorities in name only, with no taxing or regulatory authority, and given no direct funding from the state. Quarterly WMA meetings are a good forum for sharing news about water-related projects and opportunities, but some WMAs go years without managing a budget or holding a vote. Skimming the plan gives me hope that the Headwaters of the South Skunk River WMA could be more productive.

Roles of stakeholders in watershed, as shown in a handout for the open house.

One of the most illuminating parts of the plan is this piece, which explains the role of a Watershed Management Authority, its member jurisdictions, and some of its partners. Chapter 7 fleshes out what needs to be done and who’s responsible. Chapter 8 fleshes out where they could get the money to do it. Put together, it’s a road map for getting some conservation practices on the ground, and cleaning up the water.

The report includes a lot of good technical information about pollution and solutions. I especially like Chapter 5, with its emphasis on practices that can address both nutrient reduction and other issues like habitat and flooding. There are some new ACPF maps for Hamilton County that will be very helpful for working with farmers to find suitable places for bioreactors, wetlands, and other structural practices. There’s an eye-opening section on absentee-owned farmland (section 2.03) and why it might not be as big a barrier to conservation as people think it is.

But like most watershed plans, the emphasis is on all the tasks that were completed and all the information that was compiled, rather than what was learned and why it’s important. This style of technical writing has two negative consequences:

First, it makes it hard for a casual reader to tell the difference between what we know and what we don’t know. Here’s a table that looks like a list of invasive species in the watershed, but is actually a list of invasive species in the state, that may or may not be found in this river system. Then there’s a table of streams with designated uses, but it doesn’t actually tell us which ones can support fishing or swimming. Most of the smaller streams are only presumed to be swimmable, and if the DNR gets around to checking (through a field study called a Use Attainability Assessment), the rebuttable presumption would likely be rebutted. I have spent many hours dealing with the confusion resulting from this little caveat: see Chapter 2 of the Story County Water Monitoring Plan.

Skimming through page after page of maps and tables gives the impression that the watershed has been exhaustively researched, but some of the main recommendations of the plan are for additional assessments that wouldn’t fit in the budget.

We know that normal farming practices can leak nitrogen and phosphorus, but we don’t know which areas are leakier than average, to be able to prioritize conservation practices where they can do the most good. The plan recommends additional monitoring in Hamilton County and the construction of a computer model.
We don’t know much about flood risks and mitigation opportunities in the watershed. The plan recommends commissioning a hydrologic assessment.

existing conditions poster from open house

Second, it reinforces a very human tendency to see what we expect to see. If you expect to see high nitrogen levels in the South Skunk River, you have to look very carefully at the graph to realize that no, nitrate was actually quite low the last two years (a median of 3.1 mg/L) because of the drought. I didn’t notice it until my third look at the poster above. If the report is full of maps and tables that don’t seem important, or that tell you things you already know* then you stop looking carefully. And that’s how you end up setting a target that would require an 80% reduction in nitrate, relative to the long-term average (8.8 mg/L). Fortunately, I caught this during the public comment period, and authors are fixing it for the final draft. I mention this not to criticize anyone, but to illustrate why it’s important (and not easy) to connect the dots between data, their implications, and action.

* A lot of the inventory chapter reads like “Figure 1 – Central Iowa is flat, Figure 2 – Central Iowa has a lot of corn and soybean fields, Figure 3 – The fields have drainage tiles, Figure 4 – Central Iowa raises a lot of hogs.”

I hope that Prairie Rivers of Iowa can work with the new Watershed Management Authority to help connect those dots, and help to implement the recommendations in what I think is a solid plan.

South Skunk River after the first snows of November.

The Great Mussel Rescue of 2022

by Dan Haug | Oct 28, 2022

Updated 2022-11-14 with final count: 53 mussels rescued, 13 of them threatened species!

Three fun facts about freshwater mussels

Mussels keep streams clean. A mature freshwater mussel can filter 10 gallons of water a day, gobbling up algae and other microscopic organisms in the water. As this video shows, mussels can clean up muddy water, but too much silt in the water can bury them alive or clog their gills.
Mussels can hitch-hike long distances. Some mussel mamas have a special lure to flag down passing fish so that the baby mussels (glochidia) can hitch a ride as a parasite on the fish’s gills!
Mussels are in trouble. The United States is a hotspot for freshwater mussel biodiversity but many species were nearly wiped out by over-harvest for the button industry, dams and habitat loss, and too much silt in the water. For more about freshwater mussels, watch this PBS video.

Two state-threatened species of mussels have been found in Ioway Creek–the cylindrical papershell (Anodontoides ferussacianus) and the creek heelsplitter (Lasmigona compressa). An erosion control and stream restoration project is planned at Brookside Park in Ames, so the Department of Natural Resources required that they be relocated before construction begins. Mussel expert Brett Ostby of Daguna Consulting was hired to lead the effort, but finding all the mussels hiding in a patch of streambed is slow work, and there was a kilometer of stream to cover. We needed volunteers…

Volunteers collecting mussels in Ioway Creek

I had been planning volunteer events to monitor water in Ioway Creek and its tributaries and to pick up trash in West Indian Creek, but low water levels forced us to cancel. Low water levels make it easier to find mussels, so Prairie Rivers of Iowa and our partners at the Outdoor Alliance of Story County switched gears and recruited 12 volunteers to help. Five of the volunteers were students at Ames High School, where I’d been talking with earth science classes about runoff and water quality. Teachers Collin Reichert and Kean Roberts were kind enough to lend us some chest waders — essential gear if you’re planning to spend an hour or more in 45-degree water!

Since mussels can be buried in sand, we had to feel around or dislodge them with rakes. The three guys from Daguna Consulting used wet suits and snorkels to tackle some of the deeper pools. Volunteers helped when they were able over a three-day period. It’s slow, tedious work, leaving no stone unturned, but I can hardly complain about spending time in nature on a beautiful day. Ioway Creek has plenty of wildlife to see if you look long enough. I saw birds including a kingfisher, reptiles including a softshell turtle and northern water snake, and invertebrates including a hellgrammite, crayfish, and fingernail clams. For some of the students, being in the creek and seeing these critters was a new experience.

Mussels were fewer and farther between than we expected. We relocated 53 mussels (representing 5 species) to a stretch upstream of the park, where they seem to be more abundant.

8 Cylindrical papershell (Anodontoides ferussacianus)
5 Creek Heelsplitter (Lasmigona compressa)
1 Fragile Papershell (Leptodea fragilis)
37 Lilliput (Toxolasma parvum)
2 Pocketbook (Lampsilis caridum)

Compare that to the results of a DNR mussel survey this year in the Iowa River near Coralville (which found 28 species, and was catching an average of 22 mussels every hour) and it’s clear that the ecosystem in Ioway Creek is out of balance. Hopefully, this project will improve in-stream habitat so the populations grows. Our thorough search ensures that few will be lost during construction.

The Real Meaning of WOTUS

by Dan Haug | Oct 5, 2022

Last week at the Iowa Water Conference, I attended several sessions that illustrated of the consequences of paving over wetlands and streams.

This week, the Supreme Court is revisiting the question of which wetlands and streams are subject to the jurisdiction of federal agencies–another chapter in the Waters of the United States (WOTUS) controversy. The importance of this legal back and forth for agriculture and water quality has been greatly exaggerated. In practice, the definitions haven’t changed much and it mostly concerns Section 404 of the Clean Water Act: if your construction project involves running a bulldozer or backhoe in a stream or wetland, do you need to get a permit from the US Army Corps of Engineers?

UPDATE: The court’s decision on Sackett v. EPA was released in May of 2023. We discussed the ruling and shared some illuminating passages from the legal opinions in this post.

Prairie Rivers of Iowa generally avoids getting mixed up in politics and policy, but maybe I can shed some light on what’s at stake and what isn’t. Last week I was at the Iowa Water Conference with colleagues from Story County and the City of Ames to give a presentation on our locally-led water monitoring program. While at the conference, I attended several sessions that illustrated of the consequences of paving over wetlands and streams. Shout out to Michael Jansen of Strand Associates, Steve Brown from the City of Dubuque, and Tim Olson and Ryan Benjederdes of Bolton & Menck for sharing their projects.

In Dubuque, a creek called Bee Branch had been put into a pipe to build a business district and a residential neighborhood, but had the habit of backing up into the streets and basements whenever the Mississippi River was high and there was a summer downpour. What used to be the 100 year storm is now the 50 year storm, so the complaints from residents were getting louder and more frequent. The solution was to daylight the creek and turn it into an amenity. The Bee Branch Greenway is beautiful and very thoughtfully designed, but it took a decade to build and cost $250 million.

In a Minneapolis suburb, a wetland complex had been paved over for commercial development prior to the passage of the Clean Water Act. The water the wetlands used to store was regularly backing up into the streets: a 4 inch rain caused 3 feet of flooding). A new transit line opened up some redevelopment opportunities, but the water the wetlands used to store had to go somewhere, so they put it in massive underground chambers. The project included a lot of clever engineering to detain and treat the water within a limited footprint, and a lot of innovative construction to get it installed while keeping the restaurants and stores open, but it came at a cost of $10 million.

A highlight of the conference was seeing Tracy Peterson (who’s helped us with many watershed projects and events) get an award. As an engineer for the City of Ames, Tracy regularly deals with the consequences of past development on rivers in the City of Ames, overseeing projects to reduce flooding on South Duff, clean up runoff on Welch Ave, and control erosion on the South Skunk River and Ioway Creek.

Bottom line, when developers are allowed to pave over wetlands and streams without limit and without mitigation, we pay for it later with flooded basements or big infrastructure projects. There’s a debate to be had over what level of government has the authority to regulate construction in wetlands and waterways and how we should balance the competing interests, but that’s not the debate we’ve had. For a decade, some politicians and interest groups have been claiming that an expanded definition of WOTUS is a threat to farmers. I don’t get it.

In a previous job, I had the pleasure of reading boxes of old permit files and learning about what kinds of activities require a federal dredge/fill permit or state water quality certification. As I recall, farming activities are exempt except for cranberry bogs (this was Wisconsin) and some new drainage ditches. Best I can tell, this issue isn’t really about farmers, it’s about developers. It’s not really about water quality, it’s about flash flooding. It’s not really about the EPA, it’s about the US Army Corps of Engineers (correction: the USACE issues the permits, but the EPA enforces violations). It’s not just about federal overreach, it’s also about state under-reach.

This election season, remember the true meaning of WOTUS.

Six Tips to Enjoy Iowa Lakes

by Dan Haug | Aug 23, 2022

There is no better way to relieve stress and get an attitude adjustment than spending time by a lake, whether you’re fishing, swimming, paddling, watching wildlife, or watching the sunset. But it’s hard to enjoy a lake if it’s choked with toxic blue-green algae. Cleaning up Iowa lakes so we can enjoy them will require some shifts to our attitudes.

1. Don’t Panic

I’m sure you’ve all heard about the “brain-eating amoeba” Naegleria fowleri. Iowa and Nebraska both had their first cases in 2022 (both fatal), contracted at the Lake of the Three Fires and the Elkhorn River, respectively. While scary, cases are also extremely rare. Nationwide there have only been 157 cases in the past 60 years, concentrated in the South. And even where the amoeba is known to be present, there are ways to enjoy the water while minimizing risk.

2. Check Where the Beaches are Cleanest

Iowa Environmental Council maintains a map and puts out a weekly report showing where there are beach advisories. The map also shows many lakes with no advisories (the blue umbrellas). For example, in Story County, the beach house at Hickory Grove Lake is sometimes closed due to high E. coli levels, but at Peterson Park, E. coli has been consistently below the detection limit. Not every lake in Iowa is hopelessly polluted, and even the most troubled lakes will have their good days. Take advantage of them!

The beach at Peterson Park in Story County

3. Help clean up dirty lakes at the local level

Having spent some time enjoying a clean lake, hopefully, you are in a better frame of mind to tackle the not-so-clean lakes. There are lake improvement efforts all over the state that need the support of taxpayers or the help of landowners in the watershed. For example, Story County is planning a complete renovation of McFarland Park Lake, which recently suffered an algae bloom and fish kill.

“The renovation will: remove sediment, stabilize shoreline, increase lake depth, and improve lake habitat for aquatic plants and animals. Work will increase overall health of the lake, reduce the number of fish die offs in the future, and improve recreational opportunities.”

4. Keep clean lakes clean at the state and national level

It does no good to dredge out a lake if farmers in the watershed are going to plow up the hillsides around it. This is what happened to Lake of the Three Fires, as related by Chris Jones. When a third of the county was converted from pasture to corn ground, the lake gradually returned to its former shade of brown. We can’t do much about naturally occurring amoebas, but we can take a hard look at the policies, business and purchasing decisions, and attitudes that shape farming practices across Iowa.

5. Think globally, act locally

The warmer the water, the more cases of Naegleria fowleri. The same goes for harmful algae blooms, a much more common problem in Iowa that is getting even more common. If we don’t reduce our greenhouse gas emissions fast, hotter temperatures and more intense spring rainstorms will continue to worsen our water quality woes. Fortunately, there are opportunities to reduce greenhouse gas emissions in Iowa while at the same time improving water quality in the short term by planting more deep-rooted perennials and cover crops, building up organic matter in the soil, and using less nitrogen fertilizer.

6. Share your favorite water memories

A friend was visiting from out-of-state when I wrote this article. A family vacation to Iowa of course included time with the grandparents and a visit to the Iowa State Fair, but he also set aside time to take his kids wading in Ioway Creek, where they caught minnows and marveled at the weirdness of dragonfly nymphs. For my friend, time spent outdoors in creeks and lakes was an essential part of growing up in Iowa, and he wanted his children to share that experience.

What a wonderful mindset to cultivate as we work to improve water quality!

The Community Academy explores Ioway Creek

Peeling the Onion

by Dan Haug | Aug 3, 2022

We know that weather influences water quality in Iowa’s rivers. Last year, there was a drought and nitrate was lower than usual. This spring, it’s been wetter and nitrate is higher than usual. If you monitor for 10 years and the first 5 are a little wetter or drier than the last five, you’ll a water quality trend to go with it. Boring!

What we really want to know is how people are influencing water quality. We can get a lot closer to that answer by peeling away the obvious weather-related patterns to reveal underlying trends.

In statistics, it’s called a covariate or an explanatory variable. If there’s a relationship between your water quality metric and some other thing you’re not really interested in (i.e. streamflow), you can model that relationship to account for part of a water quality trend over time. What’s left over might be the things you’re really interested in (i.e. how water quality has been affected by changes in crop rotations, conservation practices, sewage treatment, manure management, and drainage). It’s common enough in the scientific literature (Robert Hirsch’s Weighted Regression on Time, Discharge, and Season is a good example), but should be used more often for progress tracking at the watershed scale.

To illustrate this general approach, I downloaded daily nitrate data from three stations maintained by the US Geologic Survey. The sensors at the Turkey River at Garber and the Cedar River near Palo (north of Cedar Rapids) were installed in late 2012; the sensor Raccoon River near Jefferson was installed in 2008. I wanted a high frequency dataset (to minimize sampling error) that included the episodes of “weather whiplash” in 2013 and 2022.

“Residuals” are the difference between what we predict and what we measured. In the first panel, that’s the difference between a measurement and the long-term average. In the second and third panels, we see how nitrate measurements differ from what we’d expect given flow in the stream today, and flow in the stream last year. Gray dots – daily measurements. Red dots- yearly averages. Blue dotted line – trend. If I did this right, some of the dots should get closer to the middle.

Nitrate concentrations in rivers increase as the weather gets wetter and streamflow increases… up to a point. When rivers are running very high, there’s a dilution effect and nitrate concentrations fall. Based on that relationship, we can explain high nitrate levels in the Cedar River in 2016 (a wet year) and low nitrate levels in 2021 (a dry year).

Nitrate concentrations tends to be highest on wet spring days following a dry summer and fall, as nitrate that accumulated in the soil during the drought is flushed into drainage systems or washed off the land surface and into rivers. Here I’ve calculated a moving average of flow over the previous 365 days, and compared that to nitrate concentrations during high flow or low flow conditions. Based on that relationship, we can explain high nitrate in the Cedar River on wet days in the spring of 2013 and 2022 (following a dry year) and low nitrate on wet days in the spring of 2019 (following a wet year).

relationship between nitrate and last year's flow

After making these adjustments, the downward trend in the Cedar River looks much smaller (0.53 mg/L per year, adjusted to 0.25) and is overtaken by the Turkey River (0.37 mg/L, adjusted to 0.28). The adjusted trends are statistically significant and could be attributed to conservation efforts in those watersheds.

How did I do this? For technical details, read here.

However, there’s still some weather-related patterns we haven’t accounted for. The Raccoon River near Jefferson also had a steep decline in nitrate since 2013 (1.42 mg/L per year, adjusted to 0.77 mg/L per year) but if you look at the entire record (going back to 2008), it’s part of an up-and-down cycle. I’ve seen that same pattern in the South Skunk River. The model explains some of those swings but doesn’t fully explain high nitrate in fall of 2014, spring of 2015 and spring of 2016. Perhaps the nitrogen that accumulated in the soil during the drought of 2012 took several years to flush out.

In addition to streamflow and last year’s weather (antecedent moisture is the technical term), nitrate can be explained by season, soybean acreage, and baseflow. If it’s not enough to know that water quality is improving or getting worse, and you’d also like to know why, then let’s peel that onion!

The Making of “Peeling the Onion”

by Dan Haug | Aug 3, 2022

How did I do this analysis for “Peeling the Onion“?

Easy peasy!

1. I plotted nitrate against log-transformed streamflow and realized that the linear regression I tried a couple years ago doesn’t actually work because the relationship is non-linear, even after log-transforming the data. The high R-squared and significant p-values were leading me astray because the data is skewed, auto-correlated, and heteroskedastic, violating all the assumptions of the statistical model!

2. I consulted Chapter 12 of Statistical Methods in Water Resources, which recommended fitting a loess smooth to the explanatory variable (discharge) and running a Mann-Kendall test on the residuals. In the presence of skewed data, Theil-Sen robust line works better than an OLS best fit line. Step 1, figure out what that means. Step 2, figure out how to do it.

3. But first, I plotted the residuals against a moving average of flow in the last 365 days to account for antecedent moisture conditions. Here I went with a linear regression, but got a poor fit until I realized I needed to include an interaction term in the model. There’s no relationship between antecedent moisture and flow-adjusted nitrate concentrations when there’s not enough water to flush nitrate out of the soil. Silly me!

4. I tried to correct for seasonal differences in nitrate concentrations, but realized it didn’t explain much unless you make it really complicated. The difference between spring (Apr-Jun) and summer (Jul-Sep) is already explained by lower flow in summer. The difference between summer and fall (Oct-Dec) is a difference in the shape of the nitrate-flow relationship. During low flows, nitrate will be higher in fall than summer because of denitrification in the stream.

5. I spent a long time debugging code to make that three pane graph with model coefficients.

Okay, that was really hard. I would never have done that if I’d known what I was getting myself into! However, now that the code is written, it’ll be relatively easy to redo this analysis for other streams in Iowa.

The Best Nitrogen Analogy Ever

by Dan Haug | Jun 26, 2022

Imagine the nitrogen cycle is a trust fund kid with a gambling problem.

The young man (a corn field) is very rich (has rich black soil) but the money (nitrogen) he inherited from his father (the prairie) is locked in a trust fund (soil organic matter). Only a small portion of the funds are released to him each year (mineralized) following a complicated schedule determined by the trustees (microbes in the soil). In order to maintain the lifestyle to which he has become accustomed (provide enough nitrogen to the crop for good yields), he needs supplemental income (nitrogen from commercial fertilizer or manure). His sister (a soybean field) does not need to work (apply fertilizer) because she can borrow money from her well-connected husband (symbiotic nitrogen-fixing bacteria) but she also receives payments from the trust (mineralization). She helps her brother out (corn needs less nitrogen fertilizer following soybeans) but not directly (soybeans actually use more nitrogen than they fix, so the benefits of the rotation has more to do with the behavior of the residue and disrupting corn pests).

A Richie Rich cartoon, but with nitrogen

Both siblings have a gambling (water quality) problem and are terrible poker players. Whenever they’re feeling flush with cash (when other forms of nitrogen have been converted to nitrate) they blow some of it playing cards (nitrate easily leaches out of the root zone when it rains), but the extent of the losses vary and debts aren’t always collected right away (nitrate leached out of the root zone may not immediately reach streams). They struggle with temptation more than their cousins (alfalfa and small grains) because they come from a broken home (the soil is fallow for large parts of the year) and because bills and income don’t arrive at the same time (there is a mismatch between the timing of maximum nitrogen and water availability and crop nitrogen and water use).

“”Okay, Dan, that’s very clever, but what’s your point?

Well, having compared the soil to a trust fund, I can now say “don’t confuse net worth with income.” You’ve probably heard that there 10,000 pounds per acre of nitrogen stored in a rich Iowa soil. That’s true but misleading. The amount actually released each year by decomposing organic matter (net mineralization) is only a few percent of that, comparable in size and importance to fertilizer or manure. Here’s an example nitrogen budget.

Example nitrogen budget, for Tipton Creek in Hamilton & Hardin Counties

On average and over the long-term, we know that fields and watersheds with higher nitrogen applications (taking into account both manure and commercial fertilizer) leach more nitrate into the water. On average and over the long-term, we know that that farmers can profit by reducing their application rate to the Maximum Return To Nitrogen (the point at which another pound of nitrogen does not produce a big enough yield bump to offset the fertilizer costs). Right now, with corn prices high but fertilizer prices going nuts, the MRTN is 136 pounds per acre for corn following soybeans, while in the most recent survey I could find, farmers reported applying an average of 172 pounds per acre. So there’s room to save money while improving water quality!

But having compared nitrate leaching to gambling, I can also say “don’t confuse a balance sheet problem with a cash flow problem.” In any given year, it’s always a gamble how much of the nitrogen that’s applied will be washed away and how much will be available to the crop. Maybe some farmers are passing up on an opportunity to increase their profits because they’re not comfortable with the short-term risks.

Farmers say that extra nitrogen is cheap insurance. If that’s true, maybe we need crop insurance that makes it easier to do the right thing, not a more precise calculator.

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.

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