Niangua Watershed
Snapshot Sampling

May 7, 2011

Water is a great solvent. The water in rivers and lakes dissolves various minerals as it flows over rocks and through soil. Many dissolved minerals are found in our waters, but eight tend to be more abundant: calcium, magnesium, sodium, potassium, bicarbonate, carbonate, sulfate, and chloride. When dissolved in water, these minerals contribute to its salinity.

The concentrations of the various dissolved minerals are dependent on a number of factors, but primarily the type of rock and soil found in the watershed. For example, limestone contains around 51 parts per million (ppm) calcium, while granite contains less than 1 ppm. A stream flowing across limestone will have significantly higher calcium concentrations than a stream flowing across granite. Another important factor is the amount of time spent in contact with rock and soil. During a rain event some water infiltrates the soil while the rest moves across the surface as runoff. The water that infiltrates will move slowly through the soil and may, over time, enter the stream as groundwater flow. This water contains substantially more dissolved minerals than the surface runoff due to the extended time in contact with rock and soil.

Washed out road

Because this snapshot sampling took place within a single watershed with similar geology throughout, we would expect the dissolved mineral content to be similar in samples collected throughout the watershed. Any sites with out-of-the-ordinary dissolved mineral concentrations could be influenced by a pollution source. One specific indicator of human influences is elevated levels of sodium and chloride. These minerals are found in high concentrations in waste water effluent due to the high salt content of human diets and the high sodium levels found in laundry detergent.

The mineral content of samples from the Niangua watershed were dominated by carbonate/bicarbonate, calcium, and magnesium. The highest values were found at spring sites, which is expected given the nature of springs. Along with higher concentrations, these minerals also showed the most variability among samples. In contrast, potassium and sulfate showed low values and little variability across the watershed. Chloride and sodium values also tended to be fairly low and stable across the sample sites, with the exception of one tributary site that receives effluent from a sewage treatment plant. This site had chloride and sodium concentrations that were three times higher (or more) than those found in the other tributaries.
The patterns of dissolved minerals were comparable in both the Little Niangua and Niangua rivers. Calcium, magnesium, and carbonate/bicarbonate levels were low at the upper-most sites due to runoff associated with the rain that fell the morning of the sampling event. Concentrations through the majority of the rivers were higher and stable, indicating the water was probably dominated by groundwater flow. Sample sites in the lake showed slight decreases in the calcium, magnesium and carbonate/bicarbonate levels, probably due to the large amount of surface runoff that had occurred in the watershed during the two weeks prior to sampling. Chloride concentrations differed from calcium and magnesium in that there was a steady decrease in concentrations across the rivers instead of stable levels. This may indicate that this mineral was being taken up and used by aquatic plants and animals. Sodium and potassium values were low and showed no true pattern across the rivers. Calcium by River

Magnesium, calcium, and alkalinity (carbonates and bicarbonates) data provided a way to estimate the relative influence of surface runoff and ground water flow at individual sites. This information, when combined with nutrient data, help us to distinguish between nonpoint and point sources of nutrients.
Elevated nutrient levels in the upper reaches of both the Niangua and Little Niangua rivers (as well as in a few of the tributaries) suggest that nutrient inputs occur throughout the watershed, and any future efforts to reduce nutrient levels at the Lake of the Ozarks will need to involve the entire watershed.

Note that the results of this sampling effort do not reflect average conditions at these sites, but rather show how water quality varied across this watershed on a single day.

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map of sample sites - raw data

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