PHOSPHORUS CYCLING AND THE EFFECTIVENESS OF RECENT ALUM TREATMENTS IN HONEOYE LAKE, NY (USA)

Phosphorous (P) is usually the limiting nutrient and controls the level of primary productivity in most lakes. Previous study indicates that 40% of the P load in Honeoye Lake (NY, USA) is endogenic. To combat P-loading, liquid alum was applied to the lake bottom in September 2006. We collected three short (~20-30 cm long) box cores from the deepest region of the lake, 9 m water depth, in order to document any significant changes in nutrient availability (e.g., P) and primary productivity resulting from these alum applications. The longest core was analyzed for ¹³⁷Cs and ²¹⁰Pb and was used to calculate the average linear sedimentation rate of 0.45 cm/y, and determine an age-depth profile. All cores were analyzed for bulk magnetic susceptibility, loss-on-ignition (% organic matter, % carbonate, % terrigenous), mean grain size, % sand, and P. Over the ~60-year record recovered by the box cores, the % carbonate and % organic matter did not significantly change. There is no carbonate preserved in the mud. Organic matter preserved in the lake sediment increased slightly, from 3.4 to 5.3 wt. % since ~1970 A.D., suggesting higher productivity levels in the lake over the last few decades. The source and amount of material entering the lake has also changed since ~1970. Both MS and grain size parameters (mean grain size, % sand) indicate an increase in the volume of terrigenous sediment supplied to the lake. P also changes in concentration in the sediment over the same time interval. Between 1947 and 2000, the average P in the lake sediment was 2.1 mg/g whereas post-2000, the average concentration was 5.5 mg/g. We attribute this sudden increase in the lake sediment to the successful liquid alum treatments applied to the hypolimnion of the lake during September 2006. Despite the increase in P retention by the sediment, P levels in the lake water column continue to increase, likely as a result of external P-loading via runoff and stream influx.