This turkey is going to take a long time to bake and my guess is the title makes you hungry, so I’ll let you have a small piece of pie for now. The list below ranks 45 Iowa stream sites for water quality, top to bottom, over the last five years (2016–20). A good story (I think) follows the list.

Overall water quality in streams is a function of what the water dissolves or transports on its way to lakes, oceans and aquifers. As such, it can be difficult to make objective judgements about whether water is of a good, medium, or poor quality based on an almost-always-long list of its dissolved and suspended components and the amounts in which they are present. In some circumstances, these materials may be seen to enhance a water’s quality for people and animals, and a component may also enhance water quality at one level and degrade it at another. And what is “bad” water in one place may be “natural” in another. So determining whether water is good, bad or something in between is not at all straightforward.

THE STORY

Once various water quality parameters have been quantified in a sample or group of samples, a need arises to translate the data in ways that can be understood by lay people and policy makers. For this reason, using a single value index that is representative of not one data point, but rather the entire body of data, is a popular concept that dates back at least to 1848.

A good water quality index is a composite representation of the available data reflecting the condition or situation of a stream, lake or aquifer. Government agencies are among the strongest advocates for the development and use of water quality indices (WQIs) because these agencies often communicate information about water quality to the public, elected officials and media while providing oversight for municipal water supplies and control of water pollution.

Water monitoring is conducted for many reasons: research, environmental planning, assessment, utilization, municipal water supply treatment, resource allocation and public information, to name a few. A credible and accurate WQI can inform all these areas while making water monitoring more purposeful and cost effective. A well‐designed and objective WQI can make data collection and communication more efficient and save money within an agency.

Iowa had a WQI from 2000 until 2015. The index was calculated from data generated by Iowa DNR  monitoring using data from eight groups of contaminants, including pesticides. In 2014, budgetary considerations required that pesticide monitoring be eliminated and this caused the WQI to become meaningless. Iowa DNR suspended the use of the WQI in March of 2015.

The next year (2016), Iowa DNR contracted with me to evaluate potential alternatives for a new WQI. I reviewed the scientific literature on the subject, and working with Rick Langel of the Iowa Geological Survey, derived a new index formula based on the WQI used by the province of Alberta. The Alberta model was selected because it provided the user flexibility on what and how many parameters to use in the calculation and, importantly, the thresholds of what would be considered acceptable water quality.

We based our proposed Iowa WQI on a small number of easily monitored parameters hoping to avoid a 2015 repeat of budget-driven collapse. Our parameters were also selected with the idea that they are the key drivers of water quality in Iowa streams in the present day: dissolved oxygen (DO), E. coli bacteria, total nitrogen (nitrate+ammonia+organic N), total phosphorus (TP) and turbidity (cloudiness of the water). This is not to say that nothing else is important, mercury for example. But mercury (and a whole host of other things) is not driving overall water quality in Iowa right now.

We considered and evaluated four different threshold scenarios that weren’t radically different from one another, but did have minor differences in turbidity and phosphorus. The one I favor, and the rationale behind it, is outlined below.

Dissolved Oxygen: 5 mg/l (ppm). Both Illinois and Minnesota use a standard of 5 mg/L with some caveats. Illinois rules state DO must always exceed 5 mg/L with a daily mean over a week‐long period exceeding 6.25 mg/L. Minnesota does have a more stringent standard for trout streams of 7 mg/L, but since so few of Iowa DNR’s long term monitoring sites are trout streams, we chose to not go that direction. DO in Iowa waters rarely falls below 5 mg/L, but when it does, the effect can be catastrophic and the deaths of fish and other aquatic life can result. Streams can recover, but repeated occurrences change the species assemblages of the streams and recruitment of young individuals into adult stages becomes difficult.

E. coli: We used the current sample maximum listed in IAC 61.3(3) for Class A1 waters of 235 Most Probable Number (MPN) per 100 ml. This is perhaps the most controversial of our suggested thresholds because there are some that believe E. coli is a not suitable indicator of good water quality at all. I disagree. We hear a lot about how DNR staff “just follow the law” when it comes to CAFO permitting and regulation. Well, E. coli is the law that we have right now for recreational suitability, and I must say that the range of moods that we have on “the law” when it comes to pigs and their shit is interesting, to say the least. DNR went so far as to propose a rule change (link, link) related to E. coli in 2017. Sometimes I wonder if the real DNR decision makers haven’t been working remotely from a western suburb, long before COVID was a thing.

Total Nitrogen. The work of Li et al. (2013) found that ending mean N concentrations in Iowa streams (trends analyzed from 1998‐2012) was 6.37 mg/l. Nitrate is by far the largest component of TN. Since Iowa’s agricultural community is committed to a 45% reduction outlined in the Iowa Nutrient Strategy, we proposed 3.5 mg/L as our threshold, as this represented a 45% reduction. There is also some evidence in the literature that levels near this proposed threshold are protective of sensitive fish species (Camargo et al., 2005). I want to emphasize the consistency of our proposed threshold with Nutrient Strategy objectives, and what scientists and policy makers have already deemed “success” for this pollutant. It is reasonable in my view for Iowans to consider this level of stream nitrogen (3.5 mg/L) to be acceptable.

Total Phosphorus. We considered two possibilities here. The first was a total phosphorous threshold of 0.18 mg/L. This is slightly higher than the Minnesota standard for southern region streams (0.15 mg/L) but much higher than the Illinois standard for streams entering reservoirs (0.05 mg/L). We settled on 0.18 because this represents an agriculture-endorsed 45% reduction from the recent average measured in Iowa streams (2011-2015) of 0.32 mg/L. The fact that this 45% reduction results in stream phosphorous levels near the Minnesota standard lends credibility to this threshold.

Turbidity. We considered two thresholds. The first was 25 NTU (turbidity units), which is the Minnesota stream standard for all waters except Class 2A waters, where the standard is 10 NTU. We also ran some scenarios at 50 NTU, but going forward here I am going to use 25 as the threshold. At turbidity of 25 NTU, water is starting to get noticeably turbid or unclear–my observation only there.

We then adopted the Alberta WQI calculation which uses actual water quality data from the selected parameters and the set thresholds to quantify an index number. There are three components to the equation: 1) the number of parameters that do not meet objectives in at least one sample during the time period under consideration; 2) the number of individual measurements that do not meet objectives relative to the total number of measurements made; and 3) the amounts by which measurements depart from objectives.

So that’s it, that’s the WQI we came up with. As far as I know, our proposed Water Quality Index remains unadopted by DNR and sits on a shelf somewhere in the Wallace Building. Or West Des Moines. Again, who knows.

Five years have passed and I feel like it’s time to do something with it.

THE TURKEY (not the river)

So I retrieved data for 45 long-term monthly monitoring sites from DNR’s ambient monitoring network and chucked it into my meat grinder to see what sort of sausage (i.e. WQI) might emerge. Along with that, I summarized the data for the individual parameters, and this is shown in the tables below. Remember that these averages for the individual components (median for E. coli) don’t go into the equation; what’s important are individual measurements relative to the previously discussed thresholds. The worst and best of the data is highlighted in red and green. For brevity, I am just going to show the last 5 years’ of data, although my analysis extended back to 2000. I will talk about some of the older data later.

Data Discussion

Streams flowing to the Missouri River are far worse than Upper Mississippi tributaries. There are some real lost-cause rivers in Western Iowa. I used to hate it when I heard people talk like that, but my thinking has changed. A lot of this has to do with the Missouri River itself. Channelization and flood control on the Missouri have destabilized the outlets of these Iowa streams, many of which have been channelized themselves, all so that we could get a few more acres to farm. The Little Sioux River above Larabee is still a beautiful meandering stream, and the water quality there is far better than the other Missouri tributaries. Lesson: hydrology matters.

Floyd River

And manure matters. If you don’t think it does, look at the livestock-dense Floyd River, which somehow managed to have the highest N and the highest P in the state over the past five years. It also has the 3rd-worst turbidity and the 6^th-worst E. coli. There is no question this is the worst stream of its size in Iowa. Which is why I do an eye roll every time I hear the ag propagandists say “but manure is not allowed to enter streams”. While that surely must be a joke, folks, water quality in the Floyd is no joke. That is one bad river. If you haven’t yet, see for yourself the Floyd watershed. This is the Iowa the livestock industry wants for you.

At the other end is the Upper Wapsi, Bloody Run Creek, and headwater tributaries of the Cedar River. While these streams all carry nitrate (N) on the high side, they have relatively low turbidity and low E. coli. If you’re looking to visit a decent Iowa stream that is reasonably clear and relatively feces-free, draw a line from Webster City (Boone River) to McGregor and go someplace north of it. But don’t wait too long, because the livestock industry has their eye on the area too.

Trends

The data from 2000–2020 represents a nice 21-year record that can be divided into three 7-year periods: 2000–2006, 2007–2013, and 2014–2020. The overall statewide WQI average for the three periods was 38.1, 40.8, and 37.5, respectively. Two streams are on a continuous decline (Old Man’s Creek and the West Nodaway) while one is seeing continuous improvement (North River). Almost every other stream, it’s business as usual, which is pretty much the case for what’s happening on the land that drains to them. That being said, the last five years (2016–2020) have a lower statewide average WQI than any of the three 7-year periods beginning in 2000. Long and short, things may or may not be getting worse, but for damn sure they aren’t getting better.

Narrative descriptor for WQI scores

Here’s where things get really controversial. The Alberta formula rated a score of 96 as excellent, 81 as good, 67 as fair, 46 as marginal, and 10 as poor (presumably below 10 is very poor). My work as presented here would leave almost all our streams between poor and marginal, and only a handful between marginal and fair. Of our two best streams, Bloody Run Creek has exceeded 81 (Alberta-good) twice in the last 21 years; the Upper Wapsi no times. Both have exceeded 67 (Alberta-fair) many times over the last 21 years.

The chances of Iowa DNR adopting the approach as outlined here, with these parameters and these thresholds and the Alberta narrative descriptors, are about as good as them rejecting a CAFO permit application. Not good ’uhtall, as my dad used to say. I have no hope that this work will make it off the bookshelf in the Wallace Building, let alone in West Des Moines. All that being said, in the report I submitted to DNR, I made it clear the agency had wide latitude to pet the dog however much they wanted in order to make it more friendly. In other words, if they wanted to call a score of 60 excellent, they could. If they wanted to set the threshold for phosphorus at 0.5 mg/L, they could. If they wanted to add or subtract parameters, they could. The structure would still be in place to generate a credible index number. But still no WQI. Some people don’t want us to make comparisons at all, I guess. As Orwell said, deprived of a reference, the public doesn’t know what is good or what is bad. That’s the level of respect the industry and the agencies have for you.

But is what I have outlined here unreasonable? My thresholds are based on the agriculture-endorsed Iowa Nutrient Reduction Strategy, acceptable levels for bordering areas (southern Minnesota and Illinois for TP, TN, turbidity and DO) and Iowa code (E. coli). Probably our very best stream over the long haul, Bloody Run Creek, exceeds the threshold for TN 100% of the time over the last 20 years; 15% of the time for E. coli, 8% of the time for TP and 6% of the time for turbidity. It’s had E. coli counts as high as 131 times the threshold value. So, are you prepared to call a stream like Bloody Run “excellent”, based on what I show here? And, should our expectations as Iowans be lower than our neighbors in Minnesota, Illinois, and Alberta?

I say no on both accounts.

Camargo JA, Alonso A, Salamanca A. 2005. Nitrate toxicity to aquatic animals: a review with new data forfreshwater invertebrates. Chemosphere. 2005 Mar 31;58(9):1255‐67.

Li D, Chan KS, Schilling KE. 2013. Nitrate Concentration Trends in Iowa’s Rivers, 1998 to 2012: What Challenges Await Nutrient Reduction Initiatives? Journal of environmental quality. 2013;42(6):1822‐8.