Twin Watersheds - 1997

The unusual hydrologic conditions in 1997, between the two watersheds and previous years should be interpreted with caution.

In 1997, the first year of no-till (zero tillage) in the east watershed, nitrogen concentrations were markedly higher in the west watershed during initial spring runoff. However this difference was not evident later in the season, and cannot be explained by fertilizer application differences. Over the several samples taken during the 1997 spring runoff, greater variability in concentrations and higher peaks of total nitrogen concentrations were experienced, higher than any previous year, 1.4 – 16.0 mg/L for the west watershed and 1.0 – 4.4 mg/L for the east watershed. This may have been related to the greater runoff volumes and multiple flow peaks experienced in that year.

Generally, concentrations of nutrients can be expected to be lower when flow volumes are higher because of the dilution effect. However that was not the case in 1997 (or in 1996). Fertilizer applications in these years preceding the spring runoff events were not greater than in previous years. This is leading researchers to consider the higher concentrations may have been the result of higher ionic concentration originating in vegetative leaching.

Total phosphorus concentrations in 1997 spring runoff varied from 0.2 - 1.1 mg/L for the east watershed to 0.3 – 1.0 mg/L for the west watershed. Similar to other spring runoff events, total phosphorus loss was dominated almost completely by dissolved form.

Total organic carbon (TOC) concentrations in 1997 varied widely within the samples, ranging from 3.7 – 23 mg/L, again likely due to the unusual hydrologic conditions. Similar to other spring runoff events, TOC loss was dominated almost completely by dissolved materials.