Long-term fluctuation and regional variation of nutrient loads from the atmosphere to lakes

The atmospheric depositions were collected by ordinary bulk-samplers mounted with a glass or polyethylene funnel of 30 cm orifice. A long-term observation was carried out at a site (35°01′30″N, 135°58′07″E) in the urbanized area for 21 years since 1974. The annual volume-weighted average concentrations of total nitrogen (TN) and phosphorus (TP) were 1.02±0.30 and 0.031±0.015 mg l⁻¹, respectively, and the loading rates were 14.5±2.8 and 0.43±0.16 kg ha⁻¹ yr⁻¹. The rates neither had a relationship with the precipitation (1,492±343 mm yr⁻¹) nor showed any diachronic tendencies. In order to obtain the loading rate of TN and TP within 10% uncertainty under the significant level of 0.01, there is no way but to continue the observation for seven and eleven years or more, respectively. In order to clarify the regional variation of the loading amounts of the depositions, the samplers were set at 12 sites distributing throughout the Kinki District for two years. The distance from northernmost (2322 mm yr⁻¹) to southernmost (1242 mm yr⁻¹) is about 150 km. The average loading rates of the 12 sites were 16.2±2.5 kg ha⁻¹ yr⁻¹ of TN and 0.730±0.247 kg ha⁻¹ yr⁻¹ of TP. The depositions of NO₃-N, NH₄-N, and TN as well as TP showed tendencies with distances neither from a big city nor from Japan Sea.