Results

Twin Watersheds Spring Runoff

Spring sampling was conducted on the Twin Watersheds for nitrogen, phosphorus and sediments from 1992 to 1997. In 1994 organic carbon and major ions were added to the list.

The spring of 1997 produced very unusual hydrologic conditions, influenced by heavy winter snow, a late spring breakup and a major April snowstorm. In addition the east watershed had standing stubble (no tillage the previous fall) and was converted to no tillage beginning with the 1997 crop year.

1992-1996

From 1992-1996 with similar land management practices, the concentrations of all nutrients in spring runoff varied only slightly between the two watersheds for each of the sampled years.

Total Nitrogen concentrations in spring runoff varied considerably from year to year. The lowest year was in 1994 with 1.8 – 3.4 mg/L to a high in 1996 of 7.4 – 10.4. Nitrogen concentrations were also high in 1993 with some samples exceeding 15 mg/L, which may have been related to the application of anhydrous ammonia the previous fall.

Total Phosphorus concentrations varied less from year to year in spring runoff than nitrogen. The lowest year was 1993 at 0.20 – 0.68 mg/L, at times when nitrogen concentrations were high. The highest concentration of phosphorus occurred in 1994 at 0.91 – 2.0 mg/L. Majority of the year to year spring runoff total phosphorus concentration was in the dissolved form, however particulate phosphorus was observed to make a slightly greater contribution in spring runoff in the 1995 and 1996 runoff years.

Total Organic Carbon (TOC) concentrations varied little from year to year in spring runoff from 1994 – 1996, falling within the range of 10 to 17 mg/L. Majority of the year to year spring runoff TOC concentration was in the dissolved form. The April 9, 1996 event was the exception to this with maximum TOC of 49.6 mg/L and with the majority TOC concentration in the particulate form.

Sediment concentrations during spring runoff events were relatively low, ranging from 3 – 120 mg/L. 1993 was the only year in which spring runoff contributed majority of the annual sediment loading.

Although limited data is available for the Pristine (Natural Wooded) site, higher peak sediment concentrations were observed in 1994 and 1995 than either Twin Watershed sites. In 1997 the East Watershed contributed the higher sediment concentration.