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 February 18. 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. Clear Creek, College Creek, and Worrell Creek were not sampled in February due to ice or lack of flowing water.

Conditions in February

February 18 was the last day of a 2-week warm period, so there was open water at most of our sites. Ballard Creek, College Creek, Worrell and Clear Creek still had ice cover and limited flow. Water levels in the Skunk River appear to be normal or above average for this time of year, but ice is interfering with stream gage readings. There was only trace precipitation in the previous week.

GBear Creek in Feburary.
GBear Creek in Feburary.

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. When we tested in February, nitrate ranged from 7 mg/L at East Indian Creek to 14 mg/L in Long Dick Creek, down significantly from January.

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.

The water was relatively clear and sediment concentrations were low at most sites on February 18. The South Skunk River below Ames had the highest levels, 16 mg/L.

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 February 18, phosphorus was at or below the detection limit (0.1 mg/L) at most sites but measured 0.65 mg/L in West Indian Creek at 280th St.

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.

February is outside the recreation season so E. coli is less of a concern and wastewater treatment plants are not required to run disinfection equipment. On February 18, E. coli levels were low at most sites. Only West Indian Creek at Nevada and Ballard Creek at Cambridge exceeded the primary contact recreation standard.

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