Applied Engineering in Agriculture Vol. 23(5): 585‐595 2007 American Society of Agricultural and Biological Engineers ISSN 0883-8542 585 W ATER QUALITY SIMULATION OF RICE/CRAWFISH FIELD PONDS WITHIN ANNUALIZED AGNPS Y. Yuan, R. L. Bingner, F. D. Theurer, S. Kolian ABSTRACT. Rice and crawfish are important agricultural commodities in Louisiana and they are often managed as integrated cropping systems. The effluent from rice/crawfish ponds is an environmental concern because of potentially high sediment and nutrient concentrations. However, current available models used for TMDL development such as BASIN, SWAT, and AnnAGNPS do not have the capability of simulating rice/crawfish farming and their impact on water quality. The objective of this study was to develop a rice/crawfish module which can be integrated into the Annualized Agricultural Non‐point Source Pollution (AnnAGNPS) model to simulate rice/crawfish farming and its impact on water quality. Both hydrologic and pollutant mass balances are maintained for the crawfish ponds in AnnAGNPS. Inflows, outflows, precipitation, infiltration (or seepage), and evaporation (or evapotranspiration) are considered for hydrologic mass balance. Water release from the pond is added to the receiving reach of the AnnAGNPS cell in which the rice/crawfish pond is located. Pollutant mass balances are maintained based on the inflows and outflows to the crawfish pond and water quality characteristics of the flows. The dynamics of complicated nutrient reactions in the pond are not considered at this development stage. Water quality constituents considered in the model are suspended sediment, total nitrogen, total phosphorus, dissolved nitrogen, and dissolved phosphorus. Based on a detailed review of rice/crawfish management practices and their impact on water quality, a water quality database of rice/crawfish ponds has been built into AnnAGNPS and a user interface was designed to quantify the rice/crawfish farming processes. This water quality database provides an estimate of water quality in the crawfish pond effluent during simulations, and a more accurate quantification of effluent water quality can be achieved through analysis of water samples of the water released from the pond. Model testing of “proof of concept” showed that the model performed appropriately and provided logical results. Keywords. AnnAGNPS, Total Maximum Daily Loads, Rice/crawfish farming, Water quality, Simulation. ice and crawfish are important agricultural commodities in Louisiana, and they are often managed as integrated cropping systems. The integration of rice and crawfish farming allows crawfish to grow in the rice field after grain harvest where the rice ratoon serves as the food basis for crawfish. This integrated practice allows rice and crawfish to be double cropped and makes crawfish production more economical. However, because of the potential environmental degradation, the effluent from crawfish ponds is a concern when best management practices are not utilized (Romaire and McClain, 2000). Many stream segments in southern Louisiana, where a high percentage of rice/crawfish farming is present, have been identified as impaired water bodies for not fully supporting fish and wildlife propagation due to organic enrichment/low dissolved oxygen (DO) and excess Submitted for review in June 2006 as manuscript number SW 6530; approved for publication by the Soil & Water Division of ASABE in May 2007. Presented at the 2003 ASABE Annual Meeting as Paper No. 032061. The authors are Yongping Yuan, ASABE Member Engineer, Research Scientist, USDA‐ARS National Sedimentation Laboratory, Oxford, Mississippi; Ronald L. Bingner, ASABE Member Engineer, Agricultural Engineer, USDA‐ARS National Sedimentation Laboratory, Oxford, Mississippi; Fred D. Theurer, ASABE Member Engineer, Agricultural Engineer, USDA‐NRCS‐National Water and Climate Center, Beltsville, Maryland; and Steve Kolian, Environmental Scientist, Louisiana Department of Environmental Quality, Baton Rouge, Louisiana. Corresponding author: Yongping Yuan, USDA‐ARS‐NSL, P.O. Box 1157, Oxford, MS 38655; phone: 662‐232‐2913; fax: 662‐281‐5706; e‐mail: yyuan@msa‐oxford.ars.usda.gov. suspended solids or nutrients (Louisiana Department of Environmental Quality, 1990, 2000). Total Maximum Daily Loads (TMDLs) are required to be developed for the impaired water bodies. In such cases, a watershed management plan has to be outlined to address NPS pollution reduction strategies to meet the water quality standard and designated uses. Implementation of best management practices (BMPs) on watershed critical areas to reduce non‐point source pollutant loadings is one of the important strategies adopted in watershed management. Current available models used for TMDL development and watershed implementation plans, such as BASIN, SWAT, and Annualized Agricultural Non‐point Source Pollution (AnnAGNPS), do not have the capability of simulating rice/crawfish practices and their impact on the receiving water bodies. The objective of this study was to develop a rice/crawfish field pond feature that can be integrated into the AnnAGNPS model to simulate rice/crawfish farming and its impact on water quality of rice/crawfish pond effluent that affects the water quality of receiving water bodies. This article documents the rice/crawfish pond technical specifications and model development. BACKGROUND REVIEW OF CURRENT RICE/CRAWFISH FARMING PRACTICES A review of the current state of rice and crawfish farming practices provides the understanding necessary to develop R