Runoff generation mechanisms in pastures of the Sand Mountain region of Alabama—a field investigation

Abstract

Abstract:Excessive application of poultry litter to pastures in the Sand Mountain region of north Alabama has resulted in phosphorus (P) contamination of surface water bodies and buildup of P in soils of this region. Since surface runoff is recognized as the primary mechanism of P transport, understanding surface runoff generation mechanisms are crucial for alleviating water quality problems in this region. Identification of surface runoff generation mechanisms is also important for delineation of hydrologically active areas (HAAs). Therefore, the specific objective of this study was to identify surface runoff generation mechanisms (infiltration excess versus saturation excess) using distributed surface and subsurface sensors and rain gauge. Results from three rainfall events (2Ð13-3Ð43 cm) of differing characteristics, and sensor data at four locations with differing soil hydraulic properties along the hillslope showed that the main surface runoff generation mechanism in this region is infiltration excess. Because of this, rainfall intensity and soil hydraulic conductivity were found to play dominant roles in surface runoff generation in this region. Further, only short periods of a few rainfall events during which the rainfall intensity is high produce surface runoff. This study indicates that perhaps subsurface flows and transport of P in subsurface flows need to be quantified to reduce P contamination of surface water bodies in this region. Current studies at this location are identifying spatial and temporal distribution of HAAs, quantifying rainfall characteristics that generate runoff, and estimating runoff volume that results from connected HAAs.

Spatial–temporal variability and hydrologic connectivity of runoff generation areas in a North Alabama pasture—implications for phosphorus transport

“…Events were spread out throughout the year (Figure 2). As presented in Sen et al (2008), very few rainfall events generated surface runoff at this study site.…”

Managing agricultural phosphorus for water quality protection: principles for progress

“…It is clear that site and watershed hydrology exert an overwhelming effect on whether agricultural P will become a downstream water quality concern (Gburek et al 2002;Pionke et al 2000). Within watersheds, variable source area hydrology (Hewlett and Hibbert 1967) can produce severe spatial heterogeneity in the potential for P to be transferred from field to water body (Sen et al 2008;Srinivasan and McDowell 2009;Walter et al 2000). Watersheds prone to variable source area hydrology possess zones that contribute disproportionately to runoff (e.g., Pionke et al 1997), with the size and location of runoffgenerating areas determined by the interaction of soil moisture, topography and geomorphology (Buda 2011;Needleman et al 2004).…”

Estimating greenhouse gas emissions from soil following liquid manure applications using a unit response curve method

“…Some differences between UH and UR and their derivations are summarized as follows: (i) UH in hydrology, used in the runoff-routing process, transforms the areal excess rainfall to a direct runoff (the difference between total runoff and baseflow) process at a specific cross section, viz, the outlet of a watershed; however, for GHGs, it is expected to estimate the average areal excess GHG emission process from excess manure application. (ii) The excess rainfall can be estimated by certain runoff-generation mechanisms (Latron and Gallart, 2008;Sen et al, 2008) before UH is used for flow routing, but it is not easy to determine the excess (effective) nitrogen/carbon for N 2 O, CO 2 , and CH 4 emissions. (iii) Long-term continuous runoff data are available for many watersheds, but GHG flux data are available only if a specific experiment is implemented.…”