title: Role of rainfall intensity and hydrology in nutrient transport via surface runoff.
abstract: Loss of soil nutrients in runoff accelerates eutrophication of surface waters. This study evaluated P and N in surface runoff in relation to rainfall intensity and hydrology for two soils along a single hillslope. Experiments were initiated on 1- by 2-m plots at foot-slope (6%) and mid-slope (30%) positions within an alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) field. Rain simulations (2.9 and 7.0 cm h(-1)) were conducted under wet (spring) and dry (late-summer) conditions. Elevated, antecedent soil moisture at the foot-slope during the spring resulted in less rain required to generate runoff and greater runoff volumes, compared with runoff from the well-drained mid-slope in spring and at both landscape positions in late summer. Phosphorus in runoff was primarily in dissolved reactive form (DRP averaged 71% of total P), with DRP concentrations from the two soils corresponding with soil test P levels. Nitrogen in runoff was mainly nitrate (NO3-N averaged 77% of total N). Site hydrology, not chemistry, was primarily responsible for variations in mass N and P losses with landscape position. Larger runoff volumes from the foot-slope produced higher losses of total P (0.08 kg ha(-1)) and N (1.35 kg ha(-1)) than did runoff from the mid-slope (0.05 total P kg ha(-1); 0.48 kg N ha(-1)), particularly under wet, spring-time conditions. Nutrient losses were significantly greater under the high intensity rainfall due to larger runoff volumes. Results affirm the critical source area concept for both N and P: both nutrient availability and hydrology in combination control nutrient loss.
authors.affiliation: USDA-ARS, Pasture Systems and Watershed Management Research Unit, 3702 Curtin Road, University Park, PA 16802, USA. Peter.Kleinman@ars.usda.gov
authors.forename: Peter J A
authors.initials: PJ
authors.lastname: Kleinman
authors.forename: M S
authors.initials: MS
authors.lastname: Srinivasan
authors.forename: Curtis J
authors.initials: CJ
authors.lastname: Dell
authors.forename: John P
authors.initials: JP
authors.lastname: Schmidt
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Sharpley
authors.forename: Ray B
authors.initials: RB
authors.lastname: Bryant
mesh_terms: D004784:Environmental Monitoring; D005068:Eutrophication; D000455:Medicago sativa / Q000254:growth & development; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D010758:Phosphorus / Q000032:analysis* / Q000378:metabolism; D006109:Poaceae / Q000254:growth & development; D011891:Rain / Q000737:chemistry*; D012621:Seasons; D012989:Soil Pollutants / Q000032:analysis* / Q000378:metabolism; D013997:Time Factors; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis* / Q000378:metabolism
chemical_list: D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus; D009584:Nitrogen