South Tobacco Creek Main Channel – Miami and HWY 240

Generally speaking, greater concentrations of suspended sediments (non-filterable residue) are expected at higher stream flows and lower concentrations of dissolved solutes would be expected. This held true for the two South Tobacco Creek (STC) main channel stations (Miami and HWY 240), although the response to flow was evident it was not considered particularly strong.

Most of the spring runoff nitrogen, phosphorus and carbon were in the dissolved form in the STC main channel, while particulate nitrogen, phosphorus and carbon dominated the rainfall runoff events. The late March 1995 samples had somewhat higher sediment concentrations than in other snowmelt years, which increased the relative amounts of particulate carbon and phosphorus in these event samples.

Concentrations of nutrients and sediment from the STC main channel were compared with those from the Pristine Site (natural wooded area). As expected concentrations in the creek main channel near Miami were considerably higher than the natural wooded area.

The export coefficients (kg/ha/yr.) for nitrogen, phosphorus and carbon at the two STC main channel sites were of the same order of magnitude, only slightly higher than the Twin watersheds. However, export coefficients for sediment were significantly higher on the STC main channel.

Average (1993 – 1997) Annual Export Coefficient - South Tobacco Creek

(spring and summer combined)

(Export coefficient = kg/ha/yr.)

The South Tobacco Creek  Watershed, at the Miami site generated a range of 1.3 - 6.7 kg/ha/yr of nitrogen. This is slightly higher than the initial review of 1992-1993 results (0.39 - 1.1 kg/ha/yr, Neil Zakrevsky 1995), but is within the range generally related to rural cropland. Similarly, the phosphorus loading ranged higher than the initial review of 1992-1993 results (0.06 - 0.34 kg/ha/yr, Neil Zakrevsky 1995), but were still on the low end of the range generally seen for rural cropland and other non-point sources of phosphorus.