Introduction

Prairie Rivers of Iowa and its partners are in the sixth year of a water monitoring project in Story County. This report includes data from 15 sites that we monitor monthly, which a certified lab operated by the City of Ames tests for nitrate, total phosphorus, total suspended solids, and E. coli bacteria. It also includes data from 3 sites on the South Skunk River monitored weekly for nitrate, total phosphorus, and total suspended solids.

Our most recent results are from April 15. On the graphs below, that’s indicated as a red dot. A black square and line shows the median and range observed for each site since 2020. The pale gray shape is a violin plot–it provides some extra information about the distribution of the data.

Map

This interactive map shows the location of our sites. Click on a point to see the latest data. Worrell Creek could not be tested.

Conditions in April

Scattered showers deposited between 0.5 and 2.5 inches of rain in Story, Boone, and Hamilton counties on April 15. We sampled most of the South Skunk River tributaries before the second round of showers and most Indian Creek tributaries after.

The South Skunk River upstream of Ames was around 570 cfs on April 15 but started rising overnight and crested at 1800 cfs on Thursday afternoon. Ioway Creek showed a similar pattern.

Ballard Creek was high and muddy when we tested in April.
Ballard Creek was high and muddy when we tested in April.

Nitrogen

Nitrogen is an essential plant nutrient, but contributes to the “dead zone” when it reaches the Gulf of Mexico. Nitrogen losses are usually highest in watersheds with a lot of tile-drained agriculture, and during times when drain tiles are flowing.

If the soil isn’t too dry and the frost isn’t too deep, nitrate-rich water can flow from fields to tiles to rivers all winter long. We’ve certainly seen that this year. When we tested in April, nitrate ranged from 5 mg/L at College Creek to 24 mg/L in Long Dick Creek. Nitrate exceeded the drinking water standard (10 mg/L) at 13 sites.

Early spring is an unpredictable time for water quality in Story County streams, and we often see abrupt changes in nitrate concentrations in response to snowmelt, rain, and changing temperatures. This can be most clearly seen with real-time sensor data, but the nitrate sensor on Ioway Creek was removed last year due to state budget cuts.

Nitrate in Ioway Creek at Ames, in spring of 2022.
Nitrate in Ioway Creek at Ames, in spring of 2022.

Sediment

Total suspended solids (TSS) are a measure of water clarity that involves weighing the material that settles out the water. The material is usually sediment (mud) but can also include algae and other organic solids. More sediment can be carried when flows are high.

Ballard Creek had the highest concentration of suspended sediments on April 15, but this is partly an accident of rainfall and timing. The South Skunk River sites downstream of Ames were tested around 8AM and Ballard Creek was tested around 1pm. In between then, a band of storms passed through, with the heaviest rain falling in the southwest part of the county.

Phosphorus

Phosphorus is an essential plant nutrient that contributes to algae blooms when it gets to the water. Phosphorus is usually the limiting factor for algae in lakes and reservoirs. The laboratory test for total phosphorus has a lower detection limit of 0.1 mg/L.

Phosphorus can be bound to soil, so we often see higher phosphorus concentrations when water levels are high are streams are muddy.

Wastewater is another major source of phosphorus, although many facilities will be installing new systems to address this. We see the highest median phosphorus levels at West Indian Creek at 280th St (downstream of Nevada), the South Skunk River at 280th and 580th St (downstream of Ames) and Ballard Creek in Cambridge (downstream of Huxley). This is most apparent when water levels are low and effluent is a large fraction of the water in the stream.

When we tested on April 15, phosphorus levels were low at most sites. Scattered showers make this pattern difficult to interpret.

Bacteria

E. coli bacteria is an indicator of fecal contamination from human waste, livestock, pets, or wildlife, which could make people sick if they accidentally swallow water while recreating. Single samples are evaluated using a threshold of 235 colonies per 100 mL in waters designated for primary contact recreation and children’s play, and a threshold of 2,880 colonies per 100mL is used for waters designated for secondary contact recreation. (These are indicated with a yellow line and a red line on the graph). The standards apply from March 15-November 15 when recreation may be possible, and this is when most wastewater treatment plants run disinfecting equipment.

When we tested on April 15, E. coli met the primary contact standard at four sites and exceeded the secondary contact standard at two sites. Scattered showers make this pattern difficult to interpret.

Normally, E. coli is lowest in the South Skunk River just upstream of Ames and highest in College Creek.