We conducted biophysical simulations using MAPSHED to determine the effects of adopting best management practices to reduce nutrients and sediment in a watershed dominated by row crop agriculture and poultry production. Reduction of three water pollutants nitrogen, phosphorus and sediment from adopting different BMPs are used in the cost reducing optimization model. We considered three weather scenarios (dry, normal and wet) and various levels of BMP parameter efficiencies. The nutrient management plan and vegetative buffer are the dominant cost-effective BMPs in the normal and wet weather conditions. In the dry weather scenario, vegetative buffer and stream-bank stabilization are the most cost effective BMPs. The cost of per kilogram of phosphorus reduction ranges from $10 to $40 depending on levels of desired phosphorus level reduction and efficiency parameters used in the model. It is costly to reduce phosphorus in a dry weather scenario perhaps because runoff is minimal and total costs associated with BMPs do not get distributed much on a per unit effluent basis.