Agricultural practices influence flow regimes of headwater streams in western Iowa

• Published in: Journal of environmental quality Vol. 34; no. 5; pp. 1547 - 1558
• Main Authors: Tomer, M.D, Meek, D.W, Kramer, L.A
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01.09.2005; Crop Science Society of America; American Society of Agronomy
• Subjects: Agricultural management; Agricultural practices; Agricultural runoff; Agriculture - methods; Agronomy. Soil science and plant productions; Applied sciences; Base flow; Biological and medical sciences; Biotechnology; Chemical Precipitation; Conservation; Conservation of Natural Resources - methods; Conservation practices; conservation tillage; Contaminants; Cropping systems. Cultivation. Soil tillage; Drought; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environment and pollution; Environmental impact; evapotranspiration; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Hydrology; Industrial applications and implications. Economical aspects; Iowa; Longitudinal Studies; Models, Theoretical; Pollution; Pollution, environment geology; precipitation; regression analysis; Rivers; Runoff; Seasonal variations; Seasons; Soil tillage; statistical models; Stream discharge; stream flow; Streams; temporal variation; Terraces; Tillage; Tillage. Tending. Growth control; Water conservation; Water Movements; Watersheds; Iowa; United States; North America; America; United States > US; Monocotyledones; First record; Modeling; Slope; Pollution; Flow regime; Gramineae; Seasonal variation; Ridge tillage; Conventional tillage; Angiospermae; Watershed; Motion study; Agriculture; Drought; Subsurface; Loess; Cultural practice; Soil tillage; Zea mays; Annual variation; Pollutant behavior; Stream discharge; Runoff water; Topographic form; Persistence; Weather; Hydrology; Terrace; First order; Conservation tillage; Spermatophyta; Infiltration; Contaminant
• DOI: 10.2134/jeq2004.0199
• ISSN: 0047-2425

Agricultural tillage influences runoff and infiltration, but consequent effects on watershed hydrology are poorly documented. This study evaluated 25 yr (1971-1995) hydrologic records from four first-order watersheds in Iowa's loess hills. Two watersheds were under conventional tillage and two were under conservation (ridge) tillage, one of which was terraced. All four watersheds grew corn (Zea mays L.) every year. Flow-frequency statistics and autoregressive modeling were used to determine how conservation treatments influenced stream hydrology. The autoregressive modeling characterized variations in discharge, baseflow, and runoff at multi-year, annual, and shorter time scales. The ridge-tilled watershed (nonterraced) had 47% less runoff and 36% more baseflow than the conventional watershed of similar landform and slope. Recovery of baseflow after drought was quicker in the conservation watersheds, as evidenced by 365-d moving average plots, and 67% greater baseflow during the driest 2 yr. The two conventional watersheds were similar, except the steeper watershed discharged more runoff and baseflow during short (<30 d), wet periods. Significant multi-year and annual cycles occurred in all variables. Under ridge-till, seasonal (annual-cycle) variations in baseflow had greater amplitude, showing the seasonality of subsurface contaminant movement could increase under conservation practices. However, deviations from the modeled cycles of baseflow were also more persistent under conservation practices, indicating baseflow was more stable. Indeed, flow-frequency curves showed wet-weather discharge decreased and dry-weather discharge increased under conservation practices. Although mean discharge increased in the conservation watersheds, variance and skewness of daily values were smaller. Ridge tillage with or without terraces increased stream discharge but reduced its variability.