As you may know, Prairie Rivers of Iowa has been working for several years on the outreach and data analysis for a local water monitoring program that includes volunteers led by Story County Conservation and lab-testing by the City of Ames. However, we’re not the only organization partnering with volunteers and local governments in Iowa to monitor streams and educate the public! In the coming year we have an opportunity to get to know one another, learn from each other, and do more in partnership. Actually, it’s already started.
In late May, Prairie Rivers organized a volunteer “snapshot” event to do same-day testing of sites throughout the Ioway Creek watershed. On that same day, Polk County Conservation tested over 100 sites as part of their spring snapshot. By coordinating our schedules, we can see how water quality compares across a broader swath of Iowa. Check out the Izaak Walton League’s nationwide Nitrate Watch map, which includes some of our results!
In mid-May, I added some extra stops to my route and was able to track down the main source of fecal bacteria affecting the lower part of West Indian Creek—it looks like the new wastewater treatment plant being built in Nevada will make a big difference for water quality. In our other creeks, the sources and solutions for E. coli are uncertain, so we’re anxious to hear what Partners of Scott County Watersheds is learning from its microbial source tracking projects in the Davenport area.
In early May, Prairie Rivers released a report analyzing the data that volunteers with Story County Conservation and the lab at the City of Ames have been collecting, including some good news! We’re learning a lot about waters in Story County, but we’re also learning how to work with data from national and statewide databases, account for the influence of streamflow, and make pretty graphs. The computer code, the skills, and the lessons learned are transferable, we just haven’t had an opportunity to apply them outside Story County… until now.
Prairie Rivers applied for a grant from the Mosaic Foundation, which reached out to the Water Foundation to fund our project! Both these foundations have an interest in “movement infrastructure”–building the capacity of the environmental movement to do more by working together. Between now and next April, we’ll be building a network of organizations in Iowa with an interest in water monitoring, developing some tools and guidance to help us make sense of our data, and translating data into action. The planning team includes Prairie Rivers and three other Resource Conservation and Development councils (RC&Ds), Partners of Scott County Watersheds, Polk County Conservation, Iowa Environmental Council, and the Izaak Walton League of America.
While we’re excited to see the growth of volunteer initiatives like Nitrate Watch, bimonthly monitoring with semi-quantitative test strips is not a substitute for equipment that can precisely measure nitrate in a stream every 15 minutes and immediately publish the data to the internet. In April and May we learned that the latest state budget included targeted cuts to University of Iowa’s nitrate sensor network. The decision has raised more than a few eyebrows, giving the impression that some legislators would rather the public not know how polluted our lakes and streams really are, or whether conservation efforts are working as expected. Let’s keep our leaders honest and Iowans well-informed!
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.
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!
Water quality in the South Skunk River is still poor but has gotten better in the last five years. One reason for improvement is a new disinfection system at the Ames wastewater treatment plant.
Dr. Chris Jones recently shared a water quality index he developed for Iowa rivers, combining five important water quality metrics. Of the 45 sites in the Iowa DNR’s ambient monitoring network, the South Skunk River near Cambridge scored “poor” and ranked 34th overall. This site also has the 3rd highest phosphorus and the 5th highest E. coli levels.
A follow-up article looked whether the current (2016-2020) water quality index has changed from previous decades. Most rivers have stayed the same or gotten worse, but the South Skunk had a better score. Three of the metrics (total phosphorus, total nitrogen, and E. coli bacteria) improved, while one (turbidity, a measure of sediment in the water) got worse.
Phosphorus and muddy water usually go together, so this odd pattern demanded some explanation. I did my own analysis of the data, curious if the changes were happening under drier conditions (when wastewater has a bigger influence), wetter conditions (when agricultural runoff has a bigger influence) or both.
See last week’s post for an explanation of the flow categories I’m using. I use a lot of boxplots, which show both the central tendency and the spread of the data. The lower end, middle, and upper ends of the box are the 25th, 50th (median) and 75th percentiles. The “whiskers” show the maximum and minimum, unless they’re really far out there, in which case the “outliers” represented by dots. Water quality data never fits a bell curve, so lopsided boxes and outliers are to be expected.
It turns out that the river didn’t get any muddier (it got less muddy) when you compare wet conditions to wet conditions and mid-range conditions to mid-range conditions.
It’s just that the past five years were a little wetter and so a larger share (43% vs 29%) of the samples were collected during wet conditions when the river was moving swiftly and carrying more sediment. A smaller share (25% vs 42%) of the samples were collected during dry and low-flow conditions when the water is usually clear. That made the average sediment concentration increase.
Weather also can explain trends in phosphorus. In the past five years, a smaller share of the samples were collected during dry and low-flow conditions when phosphorus concentrations are especially high. That made the average phosphorus concentration decrease.
Why is phosphorus so high when it’s dry? The monitoring site in question is just below the outfall of Ames Water Pollution Control Facility on 280th St, about 4 miles north of Cambridge. This facility discharges over 6 million gallons a day of treated wastewater. When conditions are dry, the effluent is less diluted, and so phosphorus in the stream approaches phosphorus levels in the effluent (which averages 3.8 mg/L), as shown in the graph below. This year we’ve also monitored West Indian Creek below the Nevada wastewater treatment plant and have seen the same pattern.
Wastewater treatment plants are regulated to minimize the impact on receiving waters and the Ames WPC Facility has one of the best compliance records in the nation. However, while the treatment process is very good at removing ammonia, solids, and oxygen-depleting substances, the process is not that effective for removing nutrients.
The Iowa Nutrient Reduction Strategy is not voluntary for wastewater treatment plants. The Ames Water and Pollution Control Department commissioned a feasibility study as a condition of its permit, which determined that the facility could achieve a 67% reduction in total nitrogen and a 75% reduction in total phosphorus by replacing its trickling filters with an activated sludge treatment system. This new system will be phased in as the filters reach the end of their useful life (starting in 2027) and will cost $39.6 million.
In the last five years we have not seen any reduction in phosphorus during dry and low-flow conditions when wastewater treatment systems have the biggest influence. However, there was a reduction in phosphorus* under mid-range and high flow conditions! This is really interesting–I’ll have to look at some other data sets to see whether it holds up and whether we can link it to conservation practices in the watershed.
For E. coli, we see improvement across all conditions, with the largest improvement during low-flow conditions* when wastewater has the biggest influence.
The effluent discharged to the river has gotten a lot cleaner since the Ames Water Pollution Control Facility built $2 million disinfection system using ultra-violet (UV) light. The system was completed in March of 2015. During the recreational season (March 15-Nov 15), treated effluent passes through two banks of lights that kill microbes. Prior to this, some E. coli and pathogens could make it through the system and end up in the river. Chlorination, a good solution for disinfecting drinking water and swimming pools, is not ideal for wastewater because it can harm fish.
Kris Evans, an environmental engineer for the City of Ames and the project manager, said this about the system:
“By using UV we continue to be “chemical free” for treatment of the wastewater and it’s much safer for staff since they don’t have to chlorinate and dechlorinate. When flow is low at the plant, we are able to lower the intensity of the bulbs to save energy and still meet permit limits; as flow increases so does the UV light intensity. The City started design of the UV system before it was mandated in a permit; we knew it was coming, but wanted to be proactive in the treatment of water, making it safer for those who recreated in the river. It was also the first project the department funded through an State Revolving Fund (SRF) loan.”
We still see high E. coli levels in other streams that receive effluent, but smaller wastewater treatment systems are also making the switch to comply with new permit requirements. In Story County, Gilbert added a UV disinfection system in 2019, the Squaw Valley HOA completed theirs in 2020, and Nevada will build a new wastewater treatment plant in 2022 that includes UV disinfection.
* I’ve written before about the challenges of detecting water quality trends. I’m pleased to report that two of the trends discussed here (a reduction in phosphorus at mid-range flow conditions, and a reduction in E. coli in dry and low-flow conditions) were statistically significant at 90% confidence level, using a test of the difference between medians. The approach employed here (sorting by flow conditions) may be a good way to control for weather and reach more reliable conclusions. It’s exciting to have some good news that holds up to further analysis!
Disclaimer: This article is not about politics. PRI is a non-partisan organization and does not want to get drawn into a discussion about the election. My intent here is to use an example that’s fresh in our minds to illustrate a challenge for progress tracking in water quality.
Polls are not always accurate. If you didn’t know that before November of 2020, you do now.
There are plenty of parallels with water, so if you’re looking to water quality monitoring to tell you whether or not conservation efforts in your watershed or your state are succeeding, read on.
Quinnipiac University can’t talk to every eligible voter in Florida, so they surveyed 1,657 people the week before the election.
Similarly, it’s not practical to test water quality in a stream 365 days a year, so we often make do with just 12 days a year. There are sensors that can test nitrate or turbidity continuously during the ice-free months, but they’re not cheap.
The voting patterns of those 1,657 people won’t be perfectly representative of Florida. How close do they expect to be? Based on the sample size, Quinnipiac calculates a margin of error: in this case 2.4 percentage points. Talking to more people would reduce the margin of error, but not enough to be worth the cost. In this case, Biden’s lead appears to be outside the margin of error.
Support for candidate
95% confidence interval
44.6% to 49.4%
39.6% to 44.4%
Similarly, the 12 days we test water quality won’t be perfectly representative of the year. How close can we expect to be? We can calculate a margin of error (here, the 95% confidence interval) around our water quality average. Did phosphorus decline in 2019? Too close to call!
Phosphorus in South Skunk River
95% confidence interval
0.20 mg/L to 0.40 mg/L
0.26 mg/L to 0.46 mg/L
Oops! This poll missed the mark, and by more than the margin of error. Trump actually won Florida with 51.2 percent of the vote. Well, some errors are unavoidable. If sampling error were completely random, we’d expect about 5% of polls to miss by more than the margin of error. That’s what “95% confidence” means. However, according to a new study of 1,400 polls from presidential primaries and general elections, 40% of polls conducted a week before the election missed the mark by that much.
That’s because sampling error isn’t all random. People who ultimately voted one way may have been less likely to appear on the list of phone numbers, less willing to respond, less likely to say what they truly intended, or were more likely to have changed their mind in the final week. And then there’s undecided voters, who don’t always split evenly between candidates. Any of these things can skew the results. Pollsters try to correct for some of these things by weighting various demographic groups, but it doesn’t always work. For “margin of error” to mean what we think it means, according to Kotak and Moore, it would need to be at least two times wider.
Similarly, if monthly samples are not collected on a fixed day of the month, you might underestimate phosphorus or sediment load by planning your week to avoid getting wet, and over-estimate it by going out of your way to capture a sample during a storm. This challenge is well understood in environmental science and there are sampling strategies and equipment to get around it.
What’s not widely appreciated is just how big purely random sampling errors can be. I’ve read the literature and run my own numbers. Even with a 3 years of sampling, you’re lucky to get below a 20 percent margin of error. The problem is more severe for phosphorus and sediment (which move with runoff and vary a lot within a month) than nitrate (which moves with groundwater and drainage water, and is less variable).
Knowing this can help us set realistic expectations. As much as we’d like to know whether conservation efforts on the land are translating into improvements in water quality in the river, we’re not going to be able to tell the difference between a modest improvement and no improvement unless we sample often enough or long enough to bring down the margin of error. Figuring out whether this is worth doing, how to sustain it, and what other things we can learn from water monitoring has been the task of PRI and our partners around Story County working on a ten-year monitoring plan.
A final note. Have some sympathy for pollsters and scientists who are doing their best to base their findings on data, acknowledge the uncertainty in their conclusions, and strive to be less wrong. There are plenty of people on both sides of the aisle who confidently make predictions based on anecdotes, are wrong more often than not, and never admit it. 😉
This post is part of a series for 2019 Watershed Awareness Month, comparing water quality in a pair of local creeks to learn how land and people influence water.
With such a big watershed—147,000 acres—we’ll need the help of a lot of people to improve water quality in Squaw Creek. However, some of the people I talk to assume that water quality is mostly someone else’s problem—it’s the CAFOs fault, or the golf courses, or the residential lawns.
By comparing smaller streams, volunteer monitoring can help us untangle some of the influences and serve as a reality check on the finger pointing. Thanks to the Squaw Creek Watershed Coalition we have some data on a lot of Squaw Creek’s tributaries, some with urban watersheds (College Creek) and some with rural watersheds, some with hog barns (Prairie Creek) and some without (Bluestem Creek). Some streams were even sampled monthly for a few years—not always the same years, but I’ve included some monthly averages to show the seasonal pattern.
May 2019 Snapshot
Squaw Creek @Duff Ave
Cropland in watershed
College Creek is almost entirely within the city of Ames. Urban streams have their own set of water quality challenges. Road salt applied in winter can lead to elevated levels of chloride. E. coli levels used to be very high due to issues with septic systems. Paved surfaces mean more runoff after heavy rains, carrying contaminants and worsening bank erosion. (A 2019 Water Quality Improvement project to install permeable pavement and tree trenches on Welch Ave will help reduce runoff to College Creek).
But despite all the athletic fields and residential lawns in the watershed, College Creek typically has lower nitrate levels than rural tributaries. If you’ve seen your neighbor over-fertilize their lawn and are wondering why that doesn’t have more of an impact, it’s worth remembering that turfgrass is a perennial and, like a good cover crop, is actively growing and taking up nutrients in April and May when most fields are bare.
Bluestem Creek is located in rural Boone County. It is usual in that it has no nearby hog barns, and presumably no hog manure applied in the watershed. It contributes plenty of nitrogen to Squaw Creek but appears to have lower phosphorus levels than Prairie Creek, another rural tributary with at least two hog confinements in its watershed. Hog manure is a good fertilizer (adding nitrogen, phosphorus, and organic matter to the fields where it is applied) but farmers don’t always account for it when applying commercial fertilizer.
Bluestem Creek does have cows, which entered the water for 5 minutes while I was doing water testing this spring. I have a soft spot for cows because their presence on the landscape can make cover crops and more diverse crop rotations financially viable. I’d rather see pasture along the creeks than have it plowed right up to the edge. But it’s true that cows can stir up sediment and poop in the water if they have access to the creek. I’ve heard feedlot owners complain that they have to fill out a lot of paperwork regarding their manure management and receive a lot of scrutiny from their neighbors, while smaller livestock producers are not held to the same standard.
Ultimately, I think stream monitoring data shows that we all have a role to play in improving water quality, whether that’s reducing runoff and erosion in urban streams through rain gardens and permeable pavement, improving soil health with cover crops and no-till, better management of manure and fertilizer, or removing nitrogen from drainage water with bioreactors and saturated buffers.