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.
Watershed Management Authorities are authorities in name only, with no taxing or regulatory authority, and given no direct funding from the state. As a result, a WMA can go years without managing a budget or holding a vote—the members do their own thing and meet quarterly to give each other updates on anything water-related. More communication across counties and city lines is great, but we’d like to see more than that. Skimming the plan gives me hope that this group could be more productive.
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 projects on the ground, and getting some clean in 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.
Second, it reinforces a very human tendency to see what we expect to see. Over the last two years, nitrate in the South Skunk River was much lower than usual because of the drought—a median of 3.1 mg/L. And yet a graph showing the most recent two years of data was shown alongside the heading “high nitrate” and used to set a target that would very difficult to hit in a year with normal rainfall. Relative to the long-term average (8.8 mg/L), a goal of 1.8 mg/L would be an 80% reduction. It’s an easy mistake to make. I glanced at this poster twice, said “yep, that’s my data” and didn’t look at the y-axis on the graph or process what that numbers meant until the third viewing. This mistake should be easy to fix, but it does illustrate the challenge in connecting the dots between data, their implications, and action.
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.
Thanks to the 15 volunteers who helped to catch benthic macroinvertebrates (bugs) and test water quality over the weekend!
Ioway Creek “Snapshots” in May and October are a tradition going back to 2006. Volunteers test water quality at many locations on the same day to get a better picture of what’s going on in the watershed. Since the IOWATER program ended, Prairie Rivers of Iowa has gathered supplies and planned events to keep the tradition going, but this year there was just one little snag: there was barely any water in Ioway Creek or its tributaries!
Not a problem. The South Skunk River still had flowing water, and this was as good an opportunity as any to survey benthic macroinvertebrates (aquatic bugs), an indicator of water quality and habitat quality in rivers. We were helped in this task by Susan Heathcote, a trainer with the Izaak Walton League’s Save Our Streams program. If you’d like to become certified and missed out on this opportunity to complete the field portion of your training, keep an eye out for more training events with Susan in early spring.
In addition to crawfish and dragonflies (always a hit with kids), we found a variety of smaller critters, including sensitive mayflies and stoneflies. Overall, the invertebrate community in the South Skunk River was “good.” In contrast, another stream we surveyed this week (West Indian Creek south of Nevada) had a “poor” score with mostly net-spinning caddisflies. We’ll discuss some possible reasons for this difference at a webinar on November 2nd.
Another option for when streams are dry is to spend some time interpreting the data we have. Following some water quality testing in the Skunk River, I gave a presentation to put those measurements into context. I think the data feels more relevant when you’re at the water’s edge and have just gone through the process of collecting it! If you prefer to do your learning somewhere warm and comfortable, we’ll be covering similar information at a webinar on November 2nd.
Another hitch. Thunderstorms were forecast for Sunday! We changed the date to Saturday and are glad we did; the weather was beautiful. This also gave us the opportunity to set up equipment so we could capture water samples from the big rain on Sunday. Three volunteers helped me retrieve a dozen samples on Monday. The samples will be tested for E. coli bacteria and optical brighteners, which may help us find and fix septic and sewer leaks.
Many thanks to all who participated. We hope to see you at the next watershed snapshot in May, and hope the water levels will be back to normal!
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!
A big thank you to farmers who planted cover crops after this challenging year. Cover crops will hold soil and nutrients in place through the winter and early spring. That could be especially important this year.
After a drought, nitrogen that might normally have been taken up by a high-yielding crop or flushed away by rainfall remains in the soil. That leftover nitrogen could be available for next year’s crop, but only if:
A) we have a dry spring, or
B) farmers have made use of practices like cover crops or nitrification inhibitors that prevent nitrogen losses during the fallow season.
A drought in 2012 following by a wet spring in 2013 led to nitrate concentrations in excess of 20 mg/L in many rivers in Central Iowa. If we have a wet spring in 2021, we could see this happen again. As one scientific paper put it, “weather whiplash drives deterioration of water quality.”
“Weather whiplash” can also help explain the long-term trends I’ve been seeing in the South Skunk River and its tributaries: a decline in nitrate concentrations from 2005-2012, a big jump in 2013, and another decline over the past 7 years. I’ll walk you through my analysis.
Explaining nitrate concentrations in the South Skunk River
Technical details, feel free to skip: This data was collected by the City of Ames just upstream of wastewater treatment plant. The City has monitored the South Skunk River above and below its wastewater treatment plant almost every week since 2003! Flow is measured continuously at a few miles upstream USGS gage near S. 16th St. I’ve summarized nitrate concentrations and streamflow by season (Jan-Mar, Apr-Jun, Jul-Sep, Oct-Dec). At each step of the way, I apply a linear regression equation and graph the model residuals. Taken together, these three factors explain 59% of the variation. The effects of “weather whiplash” may extend beyond one year, since nitrate from some parts of the field may travel more slowly to streams via groundwater.
In a given quarter, nitrate concentrations in the South Skunk can be up to 10 mg/L higher than the long-term average, or as much as 10 mg/L lower. The following graphs show how much variation is left to explain after correcting for current weather, last year’s weather, and season.
The lowest nitrate concentrations can be explained by streamflow: when the weather is dry and tiles aren’t flowing, nitrate levels in rivers taper off to the background levels seen in groundwater.
The highest nitrate concentrations can be explained by weather over the previous 12 months: a wet period following a dry period will flush out nitrate that’s accumulated in the soil.
After that, there’s still a seasonal pattern independent of rainfall: nitrogen is most susceptible to loss in spring when soils are bare and microbial activity picks up (April-June) and least susceptible when the maturing crop is using up the available nitrogen (July-Sept).
Can some of the remaining pattern be explained by greater adoption of conservation practices in the watershed in the past 5 years? We hope so, but let’s see what happens next spring!
This is a good time of year to enjoy the South Skunk River Water Trail and other local waterways!
I joined the Skunk River Paddlers this weekend, paddling my kayak from Anderson Access to West Petersen Park. While the main purpose of the outing was fun, we also hauled out some tires, cleared some smaller obstructions, and made note larger logjams for followup. The water was chilly but the air was pleasant. Bluebells were blooming on the bank and we found live mussels in the water (this one is a plain pocketbook).
While central Iowa has been spared the extreme flooding that has devastated communities on the Missouri and Mississippi, it’s been a wet fall and a wet spring, and we saw the evidence of that on the river. Bark had been scraped off trees by ice flows, lots of bank slumping, and lots of exposed roots.
The roots here illustrate the value of riparian buffers. A good stand of perennial vegetation can hold a bank together and keep phosphorus out of the Gulf.
If you’re interested in establishing a riparian buffer on your farm, especially if you live near West Indian Creek, Long Dick Creek, Clear Creek, or Worrell Creek give Prairie Rivers of Iowa a call!