The Everglades Agricultural Area (EAA) is an important agricultural region that covers about 500,000 acres to the southeast of Lake Okeechobee and to the north of the Everglades system. The area has primarily flat organic soils with naturally high water tables (Histosols). When these Histosols are drained for agriculture, aerobic mineralization releases both phosphorus (P) and nitrogen (N) from the organic matter. The nutrient loss from these soils is of concern to the downstream Everglades ecosystem, since it can cause vegetation changes through eutrophication, especially in an oligotrophic system like the Everglades.
EAAMOD was developed to test the effectiveness of BMPs for reducing the P losses from EAA farms, and to evaluate the long-term effects of various BMPs at the field and farm scale.
In the EAA, an organic topsoil covers the marl bedrock, and is often separated by an impeding layer. Water content and redox potential change with depth, affecting phosphorus mineralization and partitioning. The marl layer has a high affinity for P as indicated by the low P concentration of drainage water from ditches penetrating this layer. Lateral drainage is sometimes to two different ditches (field and regional). This level of physical complexity steered the model design to a two-dimensional multi-layered approach.
The EAAMOD-FIELD model is a two-dimensional model that predicts flow and P losses from a field. The hydraulic flow model divides the field into four vertical layers within the soil profile and numerous horizontal cells across the field. These zones can vary in both hydraulic conductivity and aerobic state. Any one of the cells can be a ditch and an impeding layer can be implemented.
The P model tracks the size of the mineral P pools (adsorbed and soluble/labile P). Because the soil organic matter pool is dominant in size, it is the only organic matter pool considered, and it is assumed to be infinite. Modeled P processes include mineralization and sorption-desorption while inputs of P can be from fertilizer, rainfall, and irrigation water.
AAMOD-FIELD is a complex model that uses input files to change the parameters for the model. These files allow the model to be used over a wide range of farming practices encountered in the EAA, but they are difficult for the casual user to change. When the files are manipulated manually, an engineer or scientist experienced in modeling is required to use the model effectively and appropriately.
Recently, a user-friendly Windows-based interface was developed for the EAAMOD-FIELD model. The interface is designed to make the model useable by farmers, agricultural technical advisers, and governmental personnel. It provides access to pre-defined EAA farming scenarios and the ability to manipulate the soils, phosphorus, and management parameters. Farming scenarios include a number of soils, crops, water management options, and a large record of weather data. Output is presented graphically or in tables and extensive on-line help is available.