State Water Resources Research Institute Program

Project ID: 2007OK79B
Title: Subsurface Transport of Phosphorus to Streams: A Potential Source of Phosphorus not Alleviated by Best Management Practices
Project Type: Research
Start Date: 3/01/2007
End Date: 2/28/2008
Congressional District: 3
Focus Categories: Water Quality, Nutrients, Groundwater
Keywords: Phosphorus, Subsurface Flow, Cherty/Clarksville Soils, Best Management, Non-point Source Pollution
Principal Investigators: Fox, Garey; Storm, Daniel E. (Oklahoma State University)
Federal Funds: $ 25,000
Non-Federal Matching Funds: $ 50,000
Abstract: The environmental risk associated with excess phosphorus (P) is the eutrophication of freshwater bodies in Oklahoma, many of which are used as drinking water supplies. Continued taste and odor problems caused by excessive P will sustain the high cost of drinking water treatment. Long-term planning and the development of a comprehensive water plan require a complete understanding of the potential threats to drinking water reservoirs. Efforts to address P issues require an understanding of the transport mechanisms from the landscape into adjacent receiving waters. Subsurface transport is a potential transport mechanism that has received relatively less attention compared to dissolved and attached P transport in runoff, even though orthophosphate concentrations are commonly measured in well water. The objective of this research is to determine the importance of subsurface transport of P to streams or rivers. Recent research has suggested that P leaching and subsurface transport should be considered when assessing long-term risk of P loss from waste-amended soils.

In eastern Oklahoma, cherty soils adjacent to rivers in the Eucha/Spavinaw basin consist of gravelly silt loam to gravelly loam substrate below a thin layer of organic matter. These soils possess infiltration rates as high as 6.0 cm/hr; therefore the potential for subsurface transport is significant. Current best management practices aimed at reducing P load through surface runoff are ineffective if subsurface flow is a significant transport mechanism and therefore could impact long-term planning of available water supplies in Oklahoma. At a selected river site, we will install a 1-m wide, 1-m deep, and 15 m long trench approximately 7 to 15 m away and parallel to the river. The site will be selected at a location where the cherty soils are bounded by a relatively impermeable bedrock layer. Tensiometers and suction lysimeters will be installed at the centerline of the trench every 1 to 2 m between the trench and river for monitoring flow and water quality. Prior to the experiments, soil samples will be acquired at a the site to quantify soil and hydraulic properties, soil properties relevant to P sorption and retention, and P sorption characteristics. Two different experiments will then be performed by pumping water from the river into the trench such that a constant head is maintained: (1) using a conservative tracer with little to no adsorption in the river water which contains in-stream P concentrations and (2) using water from the river spiked at a higher P concentration.

We will monitor water pressures in the cherty soils, P concentrations extracted from installed piezometers, and P concentrations in the adjacent stream flow. Information from this research will be critical for watershed scale analyses of P loading to streams as current watershed models do not account for this transport mechanism. Data obtained from this experiment will be directly incorporated into these models. Results will provide information on the ability of subsurface soils to remove P from P rich subsurface flow. Also, the validity of installing riparian buffers or other best management practices on these cherty soils will be assessed.

Progress/Completion Report, PDF

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