ecological engineering 27 ( 2 0 0 6 ) 71–78 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ecoleng Changes in sediment–water column phosphorus interactions following sediment disturbance D.R. Smith a,∗ , E.A. Warnemuende a , B.E. Haggard b , C. Huang a a USDA-ARS, National Soil Erosion Research Laboratory, 275 S. Russell St., West Lafayette, IN 47907, USA b USDA-ARS, Poultry Production and Product Safety Research Unit, 203 Engineering Hall, Fayetteville, AR 72701, USA article info Article history: Received 2 January 2005 Received in revised form 12 October 2005 Accepted 24 October 2005 Keywords: Nutrient transport Equilibrium phosphorus concentration Anthropogenic eutrophication abstract Stream and ditch sediments are an important part of the ecosystem that can play a piv- otal role in buffering nutrient and contaminant concentrations in surface water. Removal of existing sediments and deposition of new sediments will change the physiochemical parameters controlling P transport in drainage ditches; however, these phenomena are not well documented. This study was conducted to determine the impact of severe storms on sediment P interactions with water column P in tile-fed drainage ditches within agricul- tural watersheds in northeast Indiana. Easily exchangeable P (MgCl 2 extractable) in ditch sediments ranged from 0.5 to 1.32 mg kg -1 . The equilibrium P concentration (EPC o ) between the aqueous phase and sediments ranged from 0.02 to 0.11 mg L -1 . When comparing sed- iment EPC o with dissolved P concentrations in ditch water, sediments acted as a P sink in five of the seven data collection sites. The ability of the sediment to buffer water column P, as measured by the slope of the linear relation used to calculate sediment EPC o , ranged from 2.7 to 13.8 mg P sorbed kg -1 sediment per unit in mg P L -1 in the aqueous solution. In contrast to previous studies, chemical amendments did not alter easily exchangeable P in sediments nor sediment EPC o and the slopes observed in the linear P sorption isotherms. While chemical amendment can be used to increase P sorption by sediments and reduce exchangeable P in sediments, this showed that this practice should be targeted to times of the year when they would be the most effective. Published by Elsevier B.V. 1. Introduction Agriculture has been identified as one of the primary contrib- utors to non-point source nutrient losses in the USA (USEPA, 1990). Excessive phosphorus (P) has evolved to become the main concern in many freshwater systems where anthro- pogenic eutrophication is a water quality problem (Schindler, 1977). Despite efforts to minimize nutrient loss from agri- cultural sources, nutrients (particularly P) often reach sur- ∗ Corresponding author. Tel.: +1 765 494 0330; fax: +1 765 494 5948. E-mail address: drsmith@purdue.edu (D.R. Smith). face waters in sufficient amounts to accelerate or main- tain eutrophication in agriculturally dominated watersheds (Carpenter et al., 1998; Daniel et al., 1998). Nutrients are trans- ported from the landscape or discrete sources downstream to primary surface waters of concern and are subject to interac- tions with many abiotic and biotic processes in the stream and drainage ditch network. Some information is available on how fluvial processes affect nutrient transport in streams (Klotz, 1988; Haggard et al., 1999; McDowell and Sharpley, 2003), but 0925-8574/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.ecoleng.2005.10.013