The use of fertilizers to grow crops is a key component in increasing food security globally. However, excessive use of these agricultural inputs poses a serious threat to aquatic ecosystems by largely contributing to eutrophication. This environmental concern therefore challenges modern agriculture, which intends to increase yields while minimizing environmental impacts. Best management practices (BMPs), which are implemented as structural or non-structural measures to reduce or avoid potential agricultural impacts, might be the hope for farming to become eco-friendly.
What is an OFWS system?
An OFWS system is a structural BMP that captures surface runoff and irrigation tail-water from small agricultural lands. To capture the water, this BMP combines open channels (i.e., tailwater recovery (TWR) ditches) and small-scale reservoirs (i.e., agricultural ponds).
Using water samples collected over a three-year period from an OFWS system implemented on a farm located in the upper Porter Bayou watershed, Mississippi, researchers investigated the spatial and temporal variations of water quality occurring at sampling points (M1: the inlet; M2: the TWR ditch; M3: the outlet; MP: the pond) throughout the system.
OFWS system nutrient reduction benefits
The benefits provided by the OFWS system reflected in 54% and 50% reduction of nitrate concentration in the TWR ditch during winter and spring, respectively. In addition, the system reduced 60% of the ammonia concentration also during spring. Dissolved phosphorus reduction varied from 26% to 65%, with higher values occurring during the transition from warmer to colder seasons.
Nutrient reduction varying with season is of interest as the hypoxia zone observed in the Gulf of Mexico which is greatly driven by agricultural runoff originating from the Mississippi River Basin, mainly occurs during the warmer seasons. Hypoxia zones can cause deleterious effects in aquatic ecosystems. Therefore, the implementation of BMPs such OFWS systems might be an effective measure in intensively managed agricultural lands to improve water quality.
More benefits provided by the OFWS systems
Most of the agriculture in the Mississippi Delta Region depends on irrigation practices to overcome crop water needs. Historically, the Mississippi River Valley Alluvial (MRVA) aquifer has provided the necessary water for farmers to irrigate crops. However, groundwater levels have been declining due to persisting over-pumping of the aquifer.
At this intersection, OFWS systems offer an additional benefit as the stored water can be used for irrigation during the growing season. Paz et al. (2016) reported groundwater savings up to 153.7 million gallons during three years of the system’s operation. This result is important as the irrigation water supply potential of OFWS systems could substantially benefit agricultural profitability while slowing the groundwater level decline of the aquifer.
USDA NIFA funded this project under the National Integrated Water Quality Program (Grant # 2011-51130-31168).
Paz, J.O., Tagert, M.L., Pérez-Gutiérrez, J.D., Karki, R. (2016). Monitoring of On-farm Water Storage Systems for Water Storage Reuse and Nutrient Reduction. University Council on Water Resources Conference. June 21-23, 2016, Pensacola, Florida (Oral Presentation).
Pérez-Gutiérrez, J.D., Paz, J.O., Tagert, M.L.M. (2017). Seasonal water quality changes in on-farm water storage systems in a south central U.S. agricultural watershed. Agricultural Water Management 187, 131-139. https://doi.org/10.1016/j.agwat.2017.03.014
Pérez-Gutiérrez, J.D., Paz, J.O., Tagert, M.L.M., Ouyang, Y. (2018). Understanding the hydrology and water quality of outflow events in on-farm water storage systems in a Mississippi Delta agricultural watershed: A seasonal scale approach. Water (In review).