Journal of Water Resource and Protection, 2013, 5, 591-603 http://dx.doi.org/10.4236/jwarp.2013.56060 Published Online June 2013 (http://www.scirp.org/journal/jwarp) Phosphorus Mass Balance of the Illinois River Watershed in Arkansas and Oklahoma Bernard Engel 1 , Meagan Smith 2 , John Berton Fisher 3 , Roger Olsen 4 , Laurent Ahiablame 1* 1 Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, USA 2 Alexander Consulting 5802 South 129th East Avenue, Tulsa, USA 3 Lithochimeia, Inc., 110 West 7th St., Tulsa, USA 4 CDM, Inc. 1331 17th Street, Denver, USA Email: * lamah@purdue.edu, engelb@purdue.edu, mbsmith@flash.net, bfisher@lithochim.com, olsenrl@cdm.com Received April 13, 2013; revised May 15, 2013; accepted June 9, 2013 Copyright © 2013 Bernard Engel et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Water quality degradation in the Illinois River Watershed (IRW) has been linked to excess nutrients, primarily phos- phorus (P). A mass balance study was performed on the IRW in Oklahoma and Arkansas to quantify the magnitude of P entering the watershed between the closure of Lake Tenkiller’s dam in 1954 to 2006. Results showed that a substantial mass of P was, and is, being imported into the watershed relative to the mass of P leaving the watershed. The study demonstrated that poultry production has been the major contributor of P imported to the watershed since 1964, and is currently responsible for more than 76% of the net annual P additions to the IRW. Between 1949 and 2002, more than 200,000 tonnes of P was added to the IRW. A P delivery ratio for the IRW was computed from the mass balance results and observed loads indicating that 4% of annual P applied to the IRW landscape reached Lake Tenkiller between 1999 and 2006. Allocation of P loads from 1949 to 2002 to Lake Tenkiller computed with the delivery ratio showed that wastewater treatment plant (WWTP) discharges were responsible for more than 50% of P reaching Lake Tenkiller in 1949, followed by dairy cattle (32% of loads). Poultry contribution to P reaching Lake Tenkiller was 5% in 1949 but increased rapidly to become the largest source in 1969 at approximately 49%, and in 2002 at 54%. Both dairy and WWTP portions of the loads declined from 1949 levels with less than 4% attributable to dairy and less than 34% as- signed to WWTP in 2002. Keywords: Phosphorus; Nonpoint Source Pollution; Lake; Watershed 1. Introduction The Illinois River Watershed (IRW) encompasses nearly 4257 square kilometers in northeast Oklahoma and north- west Arkansas (Figure 1). Land uses in the IRW are do- minated by agricultural activities (poultry and beef cattle production, with minor dairy and swine production) and forests. Urban areas in the IRW are located largely along the watershed’s northeastern boundary. The watershed spans seven counties and feeds the largest reservoir in Eastern Oklahoma, Tenkiller Ferry Reservoir (locally known as Lake Tenkiller). The Illinois River was desig- nated a “Wild and Scenic River” by the State of Oklahoma in 1970 and benefits from protections this designation provides. This promotes tourism in the IRW, which sees its peak between April and September when stream flow and temperatures are best for river activities [1]. The main recreational activities in the watershed are canoeing/ka- yaking, camping, fishing, hiking, hunting, horseback rid- ing, wildlife viewing, and sightseeing. Reports of diminishing water quality caused by eutro- phication of Lake Tenkiller and the water quality degra- dation of the Illinois River and its tributaries have prom- pted concerns from both local citizens and state officials [2-5]. Eutrophication has been attributed to excess nutri- ents, specifically phosphorus (P) in fresh water systems [6]. These concerns resulted in a series of Total Maximum Daily Loads (TMDLs) to reduce P loads in the Illinois Ri- ver segments that are currently on the States of Okla- homa’s and Arkansas’ 303(d) list for TP; http://www.aquaterra.com/projects/descriptions/illinois.p hp. Several prior studies of the IRW attempted to identify the potential sources of P reaching the IRW streams and rivers and Lake Tenkiller [3,7-9]. Point source discharges * Corresponding author. Copyright © 2013 SciRes. JWARP