Preliminary Estimation of Sediment Phosphorus Flux in Beaver Lake, Northwest Arkansas

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Phosphorus (P) release from bottom sediments is an important source, potentially enhancing andmaintaining algae growth in lakes and reservoirs. To date, the amount of internal P release from bottom sediments atBeaver Lake, Northwest Arkansas, has not been evaluated. The purpose of this study was to evaluate the ability ofbottom sediments in Beaver Lake to release P. Specifically, sediment P flux was quantified in Beaver Lake underaerobic and anaerobic conditions at three sites in the reservoir: the lacustrine, transitional and riverine zones. Sixintact sediment cores were collected from each zone during summer and fall 2003, and spring 2004. The sedimentcores were incubated at room temperature (22 oC) in dark for 21 d. Soluble reactive P (SRP) release rates weremeasured under aerobic and anaerobic conditions for each zone. The results suggested that P release from sedimentsincreased under anaerobic conditions. The average P flux from these three sites in Beaver Lake was 0.14 mg m-2 d-1under aerobic conditions and was 0.57 mg m-2 d-1 under anaerobic conditions. The maximum P flux (1.79 mg m-2 d-1for fall 2003) under anaerobic conditions was observed in the transitional zone during this investigation. Internal Pload under aerobic conditions was equivalent to 3 Mg P yr-1 and was estimated equivalent to 12 Mg P yr-1 underanaerobic conditions. Hence, the average load was equivalent to 15 Mg P yr-1. Beaver Lake has a surface area of 114km2; these estimates use average sediment P release rates and water column at the sediment-water interface wasaerobic for six months and anaerobic for six months. Internal P load from Beaver Lake bottom sediments was almost20% of the external P load (75 Mg P yr-1). The estimated internal load from this study may be overestimated,because the lacustrine zone of the Beaver Lake accounts for a majority of the surface area and has shown much lesssediment P release.