Erosion and nutrient loading characteristics of two small agricultural watersheds in Piedmont Virginia

The erosion process was characterized on two small agricultural watersheds in Piedmont Virginia. Rainfall and runoff were measured for all storms at both watersheds over a two year monitoring period. Although the data base was relatively short, the data covered a wide range of rainfall and runoff conditions. Runoff samples were collected, analyzed, and used to compute loading rates of sediment, nitrate N, ammonium N, TKN, orthophosphate P, and total P on an event basis. Yields from missed storms were estimated from log-log linear least squares regression rating curves. Seasonal and annual totals of loading rates were computed by summing the yields for all storms.

Existing estimation techniques were used to calculate rainfall energy, rainfall energy contributing to rainfall, the runoff/rainfall ratio, gross erosion and delivery ratios. USLE C-factors for each field were evaluated for changes in crop and cover conditions. Enrichment ratios for available P, nitrate N, and TKN were estimated on an annual basis. Clay enrichment and particle size distributions of the surface soil and the sediment in runoff from each watershed were also determined.

These erosion characteristics were contrasted between the two watersheds whose land management practices differed. A comparison between years was also made on the conservation watershed, where part of the conservation plan was abandoned the second year. The use of conservation practices resulted in smaller estimates of gross erosion, smaller sediment and sediment-bound nutrient yields, and less runoff.