Effects of Iron Bacteria on Subsurface Tile Drains: Influence on Hydraulic Efficiency and Nutrient Transport
Anaerobic ground water entering tile drains forms an ecological niche for iron-oxidizing bacteria. These bacteria obtain energy from converting ferrous iron and oxygen into ferric iron and water. This ferric iron forms highly insoluble ferric oxyhydroxides and along with the slimy mass of iron bacteria they both tend to plug the tile drain system. However, with respect to nutrient transport, ferric oxyhydroxides adsorb phosphorus (P) and iron bacteria denitrify nitrate concentrations in the tile effluent. By using Reclamation's Best Management Practices (BMP) research field in the Oakes Test Area (OTA), we propose to answer:
* Can a documented nitrate loss associated with iron oxidizing bacteria and P uptake be quantifiably linked to tile drain efficiency and transferred Reclamation-wide for better management of drain tile maintenance?
Need and Benefit
Irrigation projects are often tile drained. The installation and maintenance of these drains results in considerable cost for Reclamation and its partners . Existing practices are to clean drains either as they become nearly plugged or on an arbitrary rotation as part of a budgeted maintenance item.
The goal of the described work is to develop a tool and BMP that can reduce long-term maintenance and operation costs by helping to develop a more efficient balance of hydraulic efficiency and water quality. This would reduce the costs associated with regular cleaning and downstream water quality monitoring and mitigation measures. The use of this tool, once developed, would also contribute towards a BMP improvement throughout Reclamation and its partners where irrigation water, native ground water, or soils contain iron. This tool would also contribute to better tile drainage water quality, improved compliance with nonpoint source pollution under the Clean Water Act, and improved relations with regulatory agencies and downstream water users that have a vested interest in preventing the eutrophication of surface waters affected by tile drainage.
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