Niangua Watershed
Snapshot Sampling

May 7, 2011

The Nutrients
Total phosphorus (TP) and total nitrogen (TN) are the two nutrients primarily responsible for algae growth. Measuring these nutrients provides an estimate of the potential for algal growth. In lakes, the concentrations of these nutrients are typically highest at the end with the inflowing stream and decrease toward the lower end of the lake. On May 7, we found a different result.

In the Little Niangua River concentrations of both nutrients were highest at the uppermost site (near Tunas). By the next site, 18 miles downstream, concentrations dropped significantly and remained fairly constant until the lake arm, where both nutrients increased considerably (more than 4-fold for phosphorus and 6-fold for nitrogen). Niangua River nutrient concentrations were also highest in the upper reaches and had approximately double the nutrients found in the upper Little Niangua. Unlike the Little Niangua, nutrients did not increase dramatically in the lake arm. Tributaries tended to have somewhat less phosphorus but similar amounts of nitrogen compared to the Niangua and Little Niangua Rivers.

The high nutrient levels at the upper sites of both the Niangua and Little Niangua probably reflect surface runoff following the rain that fell on the morning of the sampling day. The increased phosphorus in the lake arm of the Little Niangua is likely either backflow from the Niangua River or runoff from heavy rainfall event in mid-April.

Locations for reference

TP by River

Suspended Sediment
As water scours the landscape following a storm, it picks up soil particles and carries them downhill to the stream or lake below. Once in the water body, the soil particles remain suspended in the water until the force of gravity's downward pull exceeds the force of the water's flow and the particles settle to the bottom. The movement of soil from higher elevation to lower elevation is natural, but it happens much faster when the land has been disturbed.
In general, we found more suspended sediment (inorganic suspended sediment, or ISS) in the river and tributary sites than in the spring and lake sites. The Little Niangua had considerably lower concentrations throughout than did the Niangua River. Both rivers had their highest concentrations at the uppermost reaches.
ISS by Site Type

Lake Niangua

Back to Page 1 ----------------------- Continue to Page 3

map of sample sites - raw data

Brought to you by the Lakes of Missouri Volunteer Program