Peruque Creek Sampling Results

Peruque Creek starts about halfway between Warrenton and Wright City and winds along the south side of I-70. Along the way it passes to the south of Wright City, Foristell, and Wentzville before entering Lake St. Louis. After leaving the lake, the creek crosses under I-70 and runs northeast to the Mississippi River.

A portion of the creek, from the headwaters to approximately Highway Z, is listed as impaired by the Missouri Department of Natural Resources due to low dissolved oxygen and low macroinvertebrate density. The draft TMDL document for this stretch of Peruque Creek shows that the watershed is covered by 46% agriculture (cultivated crops and hay/pasture) and 35% is forested. Approximately 16% of this portion of the watershed is covered by impervious surfaces (roads, parking lots, buildings, etc.).

According to a Stream Care Guide by the St Charles County Stormwater Collaborative, “Peruque Creek is home to 39 species of fish, including green and longear sunfish, orange-throated darters, bluegill, bass and stonerollers. It also provides habitat for egrets, foxes, minks, bluebirds, rabbits, owls, beavers and great blue herons.”

The impaired portion of Peruque Creek. Source Missouri DNR

On August 14 of 2024, the LMVP and St. Louis area volunteers conducted a snapshot sampling of Peruque Creek. For this one-day event, volunteers collected 28 samples along the creek, some of its tributaries, as well as in Lake St. Louis and Lake Ste. Louise. All samples were collected within 2-hours of one another.

The Aquatic Ecology Lab at the University of Missouri (home to the Lakes of Missouri Volunteer Program) analyzed the samples for a variety of chemical and biological characteristics. Here is a quick summary of what was measured:

• Phytoplankton

  • Chlorophyll

  • Cyanotoxins

• Nutrients

  • Nitrogen (total, dissolved, nitrate, ammonium)

  • Phosphorus (total, dissolved, soluble reactive)

• Particulates

  • Total suspended solids, particulate inorganic matter, particulate organic matter

• Salts

  • Conductivity

  • Chloride

• Dissolved Organic Carbon

• Temperature

In summary, there was a significant spike in nutrients and chloride downstream of Wright City that quickly dissipated downstream. Chlorophyll increased considerably as the water slowed in Lake St. Louis, with concentrations dropping as soon as the water left the lake. Particulate Inorganic Matter, typically sediment, was highest in the Wright City area.

By selecting a parameter from the pull down menu of the graph below, you can view the changes along Peruque Creek. The sites are shown in the graph with upstream on the left and downstream on the right. Tributary site data are not shown in the graphs, but the results can be viewed by clicking on the map below the graph and selecting a site. The pop up window will show all results for that site.

All results and sampling locations can be viewed by clicking the map above.

Keep scrolling to read more about what was measured.

Phytoplankton

Chlorophyll is a photosynthetic pigment used to process sunlight into energy. Aquatic ecologists use chlorophyll to estimate the amount of phytoplankton (algae and bluegreen algae) in the water. Sometimes we scrape rocks to measure attached algae, but not in this case. Phytoplankton in streams is usually attached to rocks, sediment, or debris in the water. In lakes, phytoplankton is more likely to be suspended in the water. For this event we only looked at the chlorophyll suspended in the water. High concentrations of chlorophyll often indicate nutrient pollution.

Cyanotoxins are compounds produced by cyanobacteria (bluegreen algae) that can be toxic to humans and other animals. We measured two cyanotoxins, cylindrospermopsin and microcystin, both hepatotoxins that affect the liver. We found no measurable cylindrospermopsin and only a small amount of microcystin, well below safe drinking water recommendations.

Nutrients

Nutrient concentrations varied more than twenty-fold across the watershed. The highest concentration of every nutrient was found near the Stringtown Road bridge, downstream of Wright City. At the next site (Schaper Road, roughly 2 miles downstream) concentrations decreased twenty-fold or more. For example, total nitrogen at Stringtown Road was 5,427 µg/L, but dropped to 220 µg/L at Schaper Road. Total phosphorus similarly decreased from 2,021 to 91 µg/L. Ammonium decreased more than a hundred-fold from 1,508 µg/L to 10 µg/L. It is important to note that while we measured the concentrations of nutrients, we did not measure the water volume or flow. It’s likely that the total amount of nutrients did not decrease significantly within 2 stream miles. It’s more likely that either the volume of water increased downstream, thereby diluting the nutrients, or that the high nutrients at Stringtown Road were trapped in a pool.

Particulates

Suspended particulate matter is measured as total suspended solids. Water is filtered and the particulates trapped on the filter are dried, weighed, burned, and weighed again to estimate the inorganic, organic, and total suspended particulate matter. The inorganic portion (Particulate Inorganic Matter, typically sediment) was highest at two upstream sites south of Wright City. The concentration was more than a hundred times lower at the next site downstream. It’s possible that the sampling device disturbed the abundant sediment while sampling these shallow sites.

Salts

Chloride is a component of salt. Table salt, for example, is sodium chloride. A few other examples are calcium chloride, potassium chloride, and magnesium chloride. Salts are commonly applied to roads during winter to prevent ice from bonding to road surfaces, making the ice easier for plows to clear. In a lake or stream, excess salt is bad for aquatic life. Each species of plant and animal has different tolerances for chloride, but chloride is ultimately toxic at high concentrations. The highest concentration we found (169 mg/L) was in an unnamed tributary draining to Lake Ste. Louise and was three times higher than any other value recorded that day. Despite the single comparatively high value, chloride concentrations on the sample date are not alarming. Sampling in winter after road salt application or sampling the sediment could yield different results. Specific conductivity is a measure of the water’s ability to conduct electricity and will increase as salt concentration increases. As expected, specific conductivity generally followed the same pattern as chloride in Peruque Creek.

Dissolved Organic Carbon

By harnessing the power of the sun, plants and phytoplankton can harvest inorganic carbon (e.g., CO2) from the atmosphere and water via photosynthesis. Most other organisms are dependent upon photosynthesis for organic carbon. Dissolved organic carbon (DOC) refers to carbon that has been processed in this way and is dissolved in the water. It can enter water via runoff, from groundwater, and from rainfall. Phytoplankton in the water can also “leak” DOC during photosynthesis. Microbial activity in lakes and streams is heavily dependent on DOC. In addition to natural sources, DOC can be introduced by humans via urban and agricultural activities in the watershed. DOC ranged from 1.8 to 9.0 mg/L, with the highest value found nearest the creek’s mouth at the Mississippi River. These values are all within the range observed in a statewide examination of DOC.