Establishment and Monitoring of Saturated Buffers within High–Priority HUC–12 Watersheds
Issue
Riparian buffers are a proven conservation technology for reducing the movement of nutrients from surface and shallow subsurface flows into receiving waters. However, in artificially drained land in the Midwest, much of the nitrate-laden water leaching from row crop fields is routed through the buffers in drainage pipe and discharged directly into surface waters. A future research need identified in the Iowa Nutrient Reduction Strategy science assessment was finding ways to direct tile drainage water through riparian buffers.
Objective
One promising approach is to intercept the field tile outlet where it crosses a riparian buffer and divert a fraction of the flow as shallow groundwater within the buffer — termed a saturated buffer. The infiltrated water potentially would raise the water table within the buffer into organic-rich soil layers and provide an opportunity for the nitrate contained in the field tile drainage water to be removed by denitrification before entering the adjacent stream.
Approach
This project will establish saturated buffers within a subset of the high-priority HUC‐12 watersheds targeted for practice implementation by the Iowa Water Resources Coordinating Council. Newly developed software will be used to screen for suitable sites within the watersheds. This information will be shared with local natural resource professionals, who will help identify suitable sites based on contacts with potential cooperating farmers. Project personnel will install the saturated buffers by intercepting a field tile outlet before it enters the buffer. A control box will be connected to the field outlet and to a 4- inch perforated pipe installed 2-feet below the ground surface along the top of the buffer. The control box will divert water from the tile outlet into the buffer. Pressure transducers in the box will allow for continuous monitoring of the flow diverted into the buffer and any flow that still may enter the stream. A series of shallow, fully penetrating wells installed in the buffer will be used to monitor nitrate concentrations as the drainage water leaves the field in the tile outlet, enters the buffer and percolates through the buffer to the stream.
Project Updates
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
March 2016
Installation of a saturated buffer was completed in April 2016 on the Henry Sheppard farm as part of the Miller Creek Water Quality Improvement Project. Sample collection was ongoing at all seven sites (Bear Creek, Maass, Weber, Meirs, Roadman, Swenson, Sheppard) when tiles were flowing. Nitrate concentration analysis has been completed for all sites for samples collected during this project period. Concentrations at the Maass site were significantly lower than all other sites. While variable in performance, nitrate concentrations decrease from the distribution tile through the buffer at all sites.
December 2015
Installation of a saturated buffer was completed in October 2015 on the Swenson farm near Roland. This installation is in conjunction with a larger project that included additional establishment of filter strips and pollinator habitat enrolled in the Conservation Reserve Program. Project partners worked with members of the Iowa Monarch Consortium in formulating a seed mixture established within the saturated buffer. Sample collection was ongoing at all six sites when tiles were flowing. Data analysis was completed for the Bear Creek and Maass sites for 2015. At the Bear Creek site, 46% of the tile flow was diverted into the saturated buffer. This accounted for an efficiency of 50% removal, which equaled approximately 214 lb of nitrogen removed in the buffer. At the Maass site, 91% of the tile flow was diverted into the saturated buffer. This accounted for an efficiency of 94% removal, which equaled approximately 154 lb of nitrogen removed in the buffer.
September 2015
Installation of a saturated buffer was completed in August 2015 on the Roadman farm near Dike. Instrumentation installed includes monitoring wells to assess nitrate in shallow groundwater down-gradient from the distribution tile; pressure transducers to measure water level within the tile distribution box, and all datalogging and telemetry equipment. This installation is in conjunction with a larger project that includes the establishment of STRIPS buffers within the fields above the saturated buffer. Project partners have been active in outreach. An Iowa State University Extension publication entitled “Cleaning Iowa’s Waters with Saturated Buffers” was released. Sample collection was ongoing at all five sites when tiles were flowing.
June 2015
This project is establishing saturated buffers in some of the 16 Iowa Water Quality Initiative Demonstration watersheds. The first saturated buffer was installed in September 2014 in Tama County as part of the Benton/Tama Nutrient Reduction Demonstration Project, along with instrumentation within the monitoring wells. A second saturated buffer was scheduled for installation this spring in Black Hawk County as part of the Miller Creek Water Quality Improvement Project. Project partners have been active in outreach, with this effort featured in media stories and at the Iowa Nutrient Research Center legislative breakfast March 31.
March 2015
Saturated buffers are being installed within a subset of the high-priority HUC-12 watersheds targeted for practice implementation by the Iowa Water Quality Initiative. The first saturated buffer was installed in September 2014 in Tama County as part of the Benton/Tama Nutrient Reduction Demonstration Project, and was highlighted as part of the project’s fall field day. Instrumentation was installed within the monitoring wells to assess nitrate in shallow groundwater down-gradient from the distribution tile. A second saturated buffer was scheduled to be installed in fall 2014 in Blackhawk County as part of the Miller Creek Water Quality Improvement Project. Unseasonably cold weather and frozen soils prevented installation, so that will happen as soon as possible in spring 2015.
December 2014
The objective of another project is to establish saturated buffers within a subset of the high-priority HUC-12 watersheds targeted for practice implementation as part of the Iowa Water Quality Initiative. The first saturated buffer was installed in September 2014 in Tama County as part of the Benton-Tama Nutrient Reduction Demonstration Project. Monitoring wells were installed to assess nitrate in shallow groundwater down-gradient from the distribution tile. A second saturated buffer is being installed in Blackhawk County as part of the Miller Creek Water Quality Improvement Project. Additional sites are being assessed.
September 2014
The objective of another project is to establish saturated buffers within a subset of the high-priority HUC-12 watersheds targeted for practice implementation as part of the Iowa Water Quality Initiative. Project partners used precision technologies developed by USDA-ARS National Laboratory for Agriculture and the Environment to identify potential saturated buffer locations within the watersheds. A meeting of project coordinators was held in April 2014. Initial efforts for potential site identification focus on Eagle Creek and Prairie Creek sub-watersheds of the Boone River watershed, plus watersheds within the Benton/Tama Nutrient Reduction Demonstration Project and the Miller Creek Water Quality Improvement Project. Several locations have been visited and are being assessed for suitability. Site establishment is planned for fall 2014.
June 2014
The objective of another project is to establish saturated buffers within a subset of the high-priority HUC-12 watersheds targeted for practice implementation as part of the Iowa Water Quality Initiative (IWQI). Eight demonstration watersheds were announced in December 2013. Project partners used precision technologies developed by USDA-ARS National Laboratory for Agriculture and the Environment to identify potential saturated buffer locations within IWQI watersheds. A meeting of project coordinators was held in April 2014 to introduce the conservation-planning tool. Initial efforts for potential site identification focus on Eagle Creek and Prairie Creek sub-watersheds of the Boone River watershed. A peer-reviewed paper titled “Reconnecting Tile Drainage to Riparian Buffer Hydrology for Enhanced Nitrate Removal” was published in the Journal of Environmental Quality. This paper presents the findings at the initial saturated buffer site that redirecting tile drainage as subsurface flow through a riparian buffer increased its nitrate removal benefit, and is a promising management practice to improve surface water quality within tile-drained landscapes.
March 2014
A project to establish saturated buffers within a subset of the high-priority HUC-12 watersheds is in the beginning stages. Eight demonstration watersheds were announced December 8, 2013. Project partners met with IDALS representatives in early January to discuss the land use/terrain databases and conservation-planning tool that will be used in this project. Meetings with coordinators whose projects would contain artificial subsurface drainage are underway.