State Water Resources Research Institute Program

Project ID: 2008AR184B
Title: Role of Fluvial Sediments in Modifying Phosphorus Export from Northwest Arkansas Watersheds
Project Type: Research
Start Date: 3/01/2008
End Date: 2/28/2009
Congressional District: 3rd Congressional District of Arkansas
Focus Categories: Nutrients, Sediments, Water Quality
Keywords: Fluvial P transport, Streams, Rivers, Northwest Arkansas, Phosphorus
Principal Investigators: Sharpley, Andrew; Haggard, Brian E. (University of Arkansas)
Federal Funds: $ 24,098
Non-Federal Matching Funds: $ 48,196
Abstract: The quality of streams and reservoirs in the Northwest Arkansas region are influenced by watershed land uses, particularly areas draining agricultural lands (e.g., pastures) and urban-suburban development. Stream concentrations of nutrients, including phosphorus (P), generally increases with an increase in pasture land use and urban development. In the Ozark Highlands of Northwest Arkansas with rolling pastures intermixed with woodland, there is a high density of poultry (broiler) operations, which utilize litter as a fertilizer P source for pastures. In the last five years, several law suits have been filed in Oklahoma charging that drinking water impairment (taste and odor) from prolific algal growth was a result of excess P runoff from pastures fertilized with poultry litter and from wastewater discharge from several cities in Northwest Arkansas. Litigation activities have fueled extensive research on the relative amounts of P being lost from nonpoint agricultural and point sources as well as pasture and litter management on edge-of-field P loss. Although stream and reservoir sediments can act as a temporary sink for some of this P and can mediate the eutrophic response of receiving waters, little information is available of the role of fluvial sediments in modifying P export form Northwest Arkansas watersheds. Such information is critical to the broader implications of relative extent and time until water quality improvements are manifest in response to land management changes. In addressing these issues, this project will determine the role of fluvial sediments in modifying P loss during transfer from edge-of-field to receiving water by; (a) establishing a standard protocol for determining P sorption and desorption properties of fluvial sediments, (b) evaluating when sediments act as sinks or sources of P to stream flow, and (c) assessing the importance of abiotic and biotic process in fluvial P dynamics.

Project research will be conducted on fluvial sediments and streams in the Illinois River Watershed. Six sediment sampling sites will be selected to represent streams draining dominantly forested and agricultural watersheds as well as effluent-driven urban streams and will be paired with locations stream P concentrations that are being monitored by Brian Haggard (Co-Investigator). An impediment to more widespread and comparative studies of stream sediment chemistry has been a lack of standardized methodology. Traditionally the P sorption and desorption properties (P sorption maxima [Pmax; mg kg-1] and equilibrium P concentration [EPC0; mg L-1] of soils and stream sediments has been determined by laboratory equilibrations and calculated from Langmuir isotherms analysis. Equilibrating solutions of 0.01 or 0.003 MCaCl2 are most often used. Intuitively, stream water would provide the closest estimate of fluvial conditions, thus, we will compare EPC0 and Pmax values using CaCl2 solutions and filtered stream water, in support of standardized methodology for fluvial sediment P chemistry. To evaluate when sediments are sinks or sources of P to stream flow, we will use a purpose built fluvarium (10 m long). Water with varying levels of initial P concentration equivalent to runoff from pastures receiving poultry litter and point source urban inputs, will be circulated over collected stream sediments for up to 48 hours at flows and slopes representing field sites and samples of channel flow collected periodically for P analysis. The role of abiotic and biotic processes will be evaluated by determining sediment P chemistry on wet, dried, and sterilized (irradiated) sediment samples.

In better understanding the spatial and temporal extent of fluvial sediment - P processes via this project, we will be able to more reliably determine the magnitude and extent of change in P transport in river systems and the time between conservation practice implementation and water quality improvement.

Progress/Completion Report, PDF

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