http://hdl.handle.net/1957/14204 2013-06-20T03:53:18Z 2013-06-20T03:53:18Z Sanders, Emily C. Abou Najm, Majdi R. Mohtar, Rabi H. Kladivko, Eileen Schulze, Darrell http://hdl.handle.net/1957/36867 2013-02-13T22:09:38Z 2012-04-28T00:00:00Z

Field method for separating the contribution of surface-connected preferential flow pathways from flow through the soil matrix Sanders, Emily C.; Abou Najm, Majdi R.; Mohtar, Rabi H.; Kladivko, Eileen; Schulze, Darrell Liquid latex was used as a method to seal visible surface-connected preferential flow pathways (PFPs) in the field in an effort to block large surface-connected preferential flow and force water to move through the soil matrix. The proposed approach allows for the quantification of the contribution of large surface-connected cracks and biological pores to infiltration at various soil moisture states. Experiments were conducted in a silty clay loam soil in a field under a no-till corn-soybean rotation planted to corn. Surface intake rates under ponding were measured using a simplified falling head technique under two scenarios: (1) natural soil conditions with unaltered PFPs and (2) similar soil conditions with latex-sealed large macropores at the surface. Results indicated that the contribution of flow from large surface-connected macropores to overall surface intake rates varied from approximately 34% to 99% depending on the initial moisture content and macroporosity present. However, evidence of preferential flow continued to appear in latex-sealed plots, suggesting significant contributions to preferential flow from smaller structural macropores, particularly in two out of four tests where no significant differences were observed between control and latex-sealed plots. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/wr/.

2012-04-28T00:00:00Z McGough, Bruce Plantinga, Andrew J. Costello, Christopher http://hdl.handle.net/1957/14967 2010-04-28T16:37:17Z 2009-12-28T00:00:00Z

Optimally managing a stochastic renewable resource under general economic conditions McGough, Bruce; Plantinga, Andrew J.; Costello, Christopher Empirical evidence indicates that environmental fluctuations have important effects on fisheries production. However, existing analytical solutions of stochastic fisheries models have been produced only under highly simplified economic and biological conditions. The main contribution of this paper is to derive under general conditions a policy function for the management of a stochastic fishery. Our model includes general specifications of demand and cost relationships and a stochastic biological growth function with serially-correlated shocks. Applying methods from the theory of dynamic stochastic general equilibrium modeling and multivariate linear expectational difference equations, we derive a linear approximation of the solution to the model. Our main result is a reduced-form expression for an approximation to optimal escapement, which is shown to be a function of the current stock, past environmental shocks, and model parameters. This theoretically-grounded policy function has intuitive appeal, yields insights into comparative statics, and provides a theoretically-grounded, practical starting point for fisheries management. Article appears in and is copyrighted by Berkeley Electronic Press (http://www.bepress.com/)

2009-12-28T00:00:00Z