Recovering Nitrogen from Farm-Scale Drainage: Mechanism and Economics

Abstract

A two-year study evaluated the nitrogen (N) fluxes, processing, and treatment efficiency (TE) of a 14.85 ha stormwater detention area (SDA) receiving drainage from a vegetable farm in subtropical Florida. The TE was 62% and 89% in years 1 and 2, respectively. Seepage N losses are often ignored in estimating stormwater treatment. Approximately 11% and 20% of the incoming N left the SDA through seepage, reducing the TE to 51% and 67% in years 1 and 2, respectively, indicating the importance of subsurface N losses for downstream water quality. Rainfall variability controlled the timing and volume of the inflow drainage and surface water levels inside the SDA. Variable water levels controlled the aerobic and anoxic conditions inside the SDA, thus controlling the N processing and treatment. Coupled nitrification-denitrification, as a result of frequent wetting-drying cycles, was the main N treatment pathway during year 1. Drought conditions in year 2 led to 89% less surface outflow compared to year 1, resulting in water volume retention being the main process for N retention. The N TE could be increased from 68% to 86% if about two-thirds (63%) of aboveground biomass in the SDA area is harvested annually during the dry season. A payment for environmental services (PES) framework, with the state as buyer and the SDA owner as seller of N treatment services, was evaluated with a 20-year net present worth (NPW) of biomass harvesting for enhanced N treatment. The economic analysis included the benefit from composting the harvested biomass for on-farm use. A positive NPW ($835,000) indicated the economic feasibility of the project, predicting an annual benefit of $42,000 year -1 for the 112 ha farm. Scale-up of the PES approach can offer additional N treatment and C sequestration services as well as increased farm productivity.

Developing Irrigation Management at District Scale Based on Water Monitoring: Study on Lis Valley, Portugal

“…Sectors C4 and C5 were analyzed together because they share the same surface drainage system, where the drainage water is reused for irrigation by pumping. A particular aspect of the runoff from rice paddies is that they drain to a ditch network that is an important water source for irrigation, implying a notable efficiency at the sector level, allowing the recovery of nutrients from drainage water [40]. The negative values of NID occur on decades, with a surplus of precipitation over the evapotranspiration, indicating that irrigation is unnecessary.…”

“…The saturation dissolved oxygen (SDO,%) values of water samples (Table 4) were often higher than 50% for drainage, and oftentimes higher than 90% for irrigation. Note that, according to Skula et al [40], though there are no references to irrigation water, it is recommended a value higher than 50% for drinking water, allowing the conclusion that dissolved oxygen in these water bodies is good or acceptable. The very low value for the groundwater sample (SDO = 28.9%) is explained by the local standing water condition on the piezometer.…”

Advances in Drainage: Selected Works from the Tenth International Drainage Symposium

“…The processes and mechanisms that control the volume and quality of drainage water leaving agricultural land are very complex. Stormwater retention areas receiving subsurface drainage from vegetative production in Florida were proven successful in reducing downstream N loads through both denitrification and water retention, and that retention could be enhanced through harvesting of biomass (Shukla et al, 2018). This work also evaluated the economic feasibility of harvesting biomass from the stormwater retention area to enhance N retention and then composting the biomass to be returned to the agricultural land.…”