Farming Water Management on the Edge of a Fragile Ecosystem

Farming Water Management on the Edge of a Fragile Ecosystem Ricardo A. Lesmes-Vesga (bio) and Hardev Sandhu (bio) The Everglades, a unique subtropical region that embraces a variety of landscapes with diverse ecosystems, is the largest wetland in North America. It starts in Orlando and ends in Florida Bay, by the Keys, covering 15,000 km2 (5,600 mi2) (Finkl 1995). Known as the "river of grass", the Everglades provides the drinking water for South Florida, which includes one out of every three people living in the state of Florida. This area is also key to water resources that sustain agricultural businesses, among other enterprises in Southern Florida (Gaiser, Trexler and Wetzel 2012). The Everglades Agricultural Area (EAA), at southern Lake Okeechobee, is one of the most important regions for crop production in the state of Florida, where Best Management Practices (BMP) are needed to maintain sustainability of agricultural production (Whalen et al. 1992). Improper management of agricultural activities may generate nonpoint source pollution (NPS) (Yoder, Chowdhury and Hauck 2020). Such BMPs mainly consist of minimizing water table fluctuations in cultivated fields and controlling nutrient losses. Proper water management decisions help to reduce the load of nutrients such as nitrogen (N) and phosphorous (P), by controlling the volume of drained water from the field (Daroub et al. 2018). Building and managing ditches and canals in the farm hydraulic system allows for control of the discharge rates of drainage water. This infrastructure reduces the impact of drained water on downstream receiving systems by holding water until conditions for release are met. In the meantime, they reduce the amount of discharge because some of the stored water is lost to percolation, transpiration, or evaporation (Howell 2013). BMPs also include monitoring of farm discharge waters for flow volume and maintaining the proper level of soil moisture to reduce the output of nutrients such as P (Izuno and Rice 1999, Daroub et al. 2003) and N (Wright, Hanlon and Rice 2013, Frydenborg and Frydenborg 2015). Furthermore, the South Florida Water Management District has included water management BMP practices that include tools to improve water quality in the watersheds draining agricultural areas in the EAA basin. Other water management BMPs consist of recirculating the drainage water before it is pumped off the farm and optimizing draining and irrigation schedules to minimize water discharge. Efforts End Page 157 also target the reduction of particulate P and sediment in farm drainage waters (Daroub et al. 2018). Despite the flat landscape of most of the EAA, leveling the fields using laser-guided leveling machinery is an important pre-planting practice that forms part of these BMP activities. This is done to reduce potential sheet and rill erosion processes into drainage canals and field ditches, especially due to intense rainfall events. Proper field leveling improves the irrigation efficiency, allowing a more uniform covering of the irrigated and drained water that was applied on the soil, avoiding over-draining of higher areas of the field as well as over-irrigation of low-lying areas. On the other hand, the construction of raised berms parallel to the ditch and canal banks that surround EAA fields minimizes the soil runoff into field ditches and drainage canals. This forces the water that may pond on the soil surface to percolate, preventing the soil from being eroded via sheet and rill erosion after heavy rainfall events. Additionally, the construction of sediment sumps in field ditches helps to trap heavy sediments that have been deposited in the ditches, especially by wind erosion or surface water runoff during field preparation. However, it is worth mentioning that a canal cleaning program is essential to eliminate the accumulated sediment. Slowing the drained water near exit pump stations by installing culverts with risers in field ditches allows a more uniform draining rate between fields that are closer and more distant from the pump station. Also, this practice avoids the risk of transporting sediment and potentially P pollution from the fields, due to the velocities that can be reached by the drainage flow. Finally, covering ditches and canal banks with vegetative species, especially grasses with extensive root systems capable of holding the soil in place, reduces the...