Phosphorus Concentrations Have Been Declining In The Illinois River: Was It Point Sources, Farm-Level Nutrient Management, Or What?

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Elevated phosphorus concentrations in the Illinois River Watershed (IRW) have long been an environmental issue between the states of Arkansas and Oklahoma, which has led to the development of a watershed-reservoir model and future TMDL by the U.S. Environmental Protection Agency.  Here, we examine phosphorus concentrations from multiple sources, including the Arkansas Water Resources Center and the U.S. Geological Survey, to evaluate trends in flow-adjusted concentrations.   Flow-adjusted phosphorus concentrations have been decreasing in the Illinois River at Arkansas Highway 59, and this translates into decreases further downstream to Tahlequah, Oklahoma.  However, flow-adjusted concentrations in Flint Creek have been increasing over time until the last few years.  These decreases are tied to the reductions in effluent phosphorus, which have occurred over the last couple decades.  But, the application of poultry litter has also likely decreased within the IRW.  A nutrient mass balance of the Watershed Research and Education Center in Fayetteville, Arkansas showed that reduced litter applications and increased forage export (i.e., hay being removed from fields) can result in phosphorus export at the farm-scale.  The missing piece of this study would be understanding legacy phosphorus, and how this influences source apportionment and changes over time.


Brian Haggard, Arkansas Water Resources Center,

Thad Scott, Crop, Soil and Environmental Sciences Department, Division of Agriculture, University of Arkansas System


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