A comparison of the effects of sediments and standard elutriates on phosphorus kinetics in lakewater

Average rates of atmospheric deposition of total phosphorus (TP) and total nitrogen (TN) to Narrow Lake, located on sedimentary bedrock in the boreal forest of central Alberta, were 20 and 424 mg m^?2 yr^?1, respectively, between 1983–1986. There were no significant differences (P > 0.05) in deposition rates between sites on Narrow Lake, on the lake shore, and on land 18 km away. Deposition of TP, but not TN, followed a distinct pattern during the open-water season; TP was highest just after ice-off (May) and decreased throughout the remainder of the open-water season. Deposition during the winter accounted for only 4 and 12% of the annual TP and TN loads, respectively. Dry fallout contributed 50 and 33% of atmospheric deposition of TP and TN, respectively. In both dry and wet fallout, dissolved P (< 0.45 μm) and organic N were the predominant fractions of TP and TN, respectively. During July 1986, unusually heavy rainfalls caused an increase in TP, but not TN, concentrations in the epilimnion of Narrow Lake. Wet fallout accounted for only 9% of the observed increase of epilimnetic TP; the rest was from surface runoff from the drainage basin. The design of sampling programs to measure atmospheric deposition of nutrients to lakes is discussed.