Contribution of direct atmospheric deposition to nitrogen and phosphorus loads to reservoirs

Contributions of direct atmospheric deposition (DAD) to the total nutrient input were evaluated at three reservoirs in the Czech Republic. Atmospheric deposition of NO3-N, NH4-N, and P showed pronounced annual cycles, with de position rates lowest in winter and highest from April to August, and annua l averages of 1.2, 1.7, and 0.066 mg m(-2) d(-1), respectively. Nutrient lo ads from the catchment areas were one to two orders of magnitude higher tha n DAD. However, the nutrient inputs from the catchment sources followed inv erse seasonal trends to DAD and, moreover, nutrient concentrations decrease d along the reservoirs due to internal retention processes. These two patte rns resulted in a large seasonal and spatial variability of the relative im portance of DAD to the total nutrient input. This importance increased from the inflow part to lacustrine part and peaked in summer. The main paramete rs influencing the relative proportion of DAD in the total nutrient load we re: i) seasonality, extent, and character (diffuse/point) of nutrient sourc es in the catchment area, and ii) morphology and hydrology of the reservoir .