Atmospheric nitrogen and phosphorus loading to Harp Lake, Ontario, Canada

Nitrogen and phosphorus in precipitation and dry fallout (aeolian sources), as well as the p H of rainfall, were measured over Harp Lake in Ontario during 1974. Weighted mean concentrations of total N and total P during the ice‐free period of collection were 1.91 mg N /l and 0.105 mg P /l. Winter concentrations of total N were similar, but total P concentrations were much lower, averaging 0.013 mg/l in fresh snow. Total atmospheric loading of P to the lake was 74.4 mg P/m 2 yr, and the total N loading was 1600 mg N /m 2 yr. About 52%, or 39.0 mg P /m 2 yr, of the total P loading from the atmosphere was total dissolved P (0.22‐µm filtrate), and 28%, or 20.6 mg P/m 2 yr, of the total P loading was dissolved reactive P (‘Orthophosphate’ P). Dissolved inorganic N loading at 1010 mg N /m 2 yr comprised about 63% of the total N loading from the atmosphere. Pollen, from a variety of trees surrounding the lake, contributed about 20% of the total P input. The p H of rainfall samples ranged from 3.2 to 5.1 with a median value of 3.9 ( n = 14).