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.

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.

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.

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

Three fun facts about freshwater mussels

1. 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.
2. 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!
3. 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…

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.

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.

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?

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.

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. It’s not just about federal overreach, it’s also about state under-reach.

This election season, remember the true meaning of WOTUS. 

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.

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!

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.