Baseline Assessment of Geisler Farm Site: Collection of Pre-BMP Monitoring Data
Being able to document water quality improvements produced by best management practices (BMPs) is important. Yet improved water quality demonstrated at the plot scale on research farms under controlled environments is difficult to replicate at the larger scale of producer fields because of variations in topography, soil types, hydrology and other factors. Confounding the process of demonstrating success is the absence of baseline monitoring data prior to BMP installation.
Baseline monitoring data will be collected at the 160-acre Jake Geisler farm located in Calhoun County, Iowa. The project objective is to characterize the soil, geology, hydrology and water quality conditions of the farm prior to the establishment of conservation BMPs. The assessment will provide baseline data so future land and water quality change implemented at the site can be more easily detected.
The farm site is bisected by two drainage ditches and recently was extensively tiled with more than 65,000 feet of new tile. The assessment will include collection of water samples from the tiles and ditches using grab sampling and a continuous Nitratax sensor, installation and sampling of shallow groundwater wells, geophysical investigation, and soil health assessment. Monitoring will begin in the fall of 2017 and continue through 2018. BMPs will be installed in 2018-2019 using funds provided by traditional federal and state programs.
In intensively drained regions, the major transport pathways of nitrate (NO3-N) and orthophosphorus (OP) from cropped fields to streams are through tile drainage and groundwater seepage. This study estimated the nutrient load contribution of tiles and groundwater from a single cropped field to a segment of Hardin Creek in north-central Iowa. Based on monitoring of eight tile outlets, nine groundwater wells and the receiving stream over a two-year period, nutrient loads were found to be dominated by tile discharge. Nitrate loads from tiles averaged 28.8 kg/day (95.6% to 99.6% of the load), Compared to loads from groundwater discharge, which averaged 0.21 kg/day. The loading pattern was similar for orthophosphorus, which was also dominated by tile discharge (99.7%).
Results from the single farm field fit within the scaling pattern observed within the Des Moines Lobe region of Iowa showing that water yields and nitrate loads are dominated by tile drainage at the field and local watershed scale. Bioreactors installed to intercept drainage from one or multiple tile sites would reduce nitrate export by 0.4 to 28%, whereas installing a saturated buffer along the north side of the creek would reduce the total annual export by an estimated 42.8%. Study results are consistent with local and regional assessments showing the overwhelming impacts of tile drainage on water and nutrient export in the US Cornbelt.
Other activities and accomplishments:
- Findings from this project were presented at the 2019 AGU conference in San Francisco. The presentation was titled "Using a multi-method approach to quantify the spatial extent and hydrologic and water quality effects of subsurface tile drainage at local and regional scales."
Well, tile and stream sampling at the Geisler farm led by Iowa Geological Survey was completed in December 2018. Ongoing monitoring of flowing tiles and the stream is being conducted by the Iowa Soybean Association. IGS is also collecting high frequency stream stage and water table measurements in 2019. During the reporting period, water level and quality data were compiled and analyzed. A groundwater flow model was built for the farm field to estimate groundwater discharge into the ditch. Nutrient loads exported from tiles and groundwater have been calculated. A final project research paper is being drafted.
Results from the Geisler project will be shared as part of a presentation at the 2019 AGU meeting in San Francisco in December.
From July to September, bi-weekly water sampling has been completed for all wells, flowing drainage tiles and stream water at the study site. Analysis of the soil samples has been completed and results are being compiled.
From April to June, bi-weekly water sampling has been completed for all wells, flowing drainage tiles and stream water at the study site. Results are being compiled. Each well was installed with a pressure transducer last fall and continues to monitor groundwater fluctuations 4 times per hour. Interestingly, even with the extensive rains in the area and the high water table, three drainage tiles have been consistently dry. Analysis of the soil samples continues with an anticipated completion sometime in August.
Bi-weekly water sampling of monitoring wells and flowing tiles got underway this quarter. Lab analysis for soil samples taken in November continues.
A detailed analysis of the project area was conducted by the IGS team. Geophysical studies were completed for the study area, including six electrical resistivity transects and a deep electrical conductivity survey. Sixty soil cores were collected in six transects. Shallow electrical conductivity was measured at each soil sampling location. Nine groundwater monitoring wells were installed, with three in each of three transects. Pressure transducers were installed in each well to continuously monitor water levels.