In this thesis the relationship between background ammonium concentration, season and ammonium uptake/ retention ability of streams was determined within the frame of the project “PowerStreams”. Consecutive short-term nutrient addition experiments (with NH4Cl as nutrient and NaCl as conservative tracer) were conducted in spring and summer 2015 at 9 low- order streams located in Lower Austria, a region showing big differences in land use intensity. Nutrient spiraling metrics were calculated from the longitudinal decline in NH4-N concentration during the experiments. Hydrologic retention and whole-stream metabolism were calculated, hydromorphology was recorded, water and sediment samples were taken and analysed for NH4-N, NO3-N and NO2-N concentration. Biofilm samples were analysed for chlorophyll-a concentration, sediments for microbial abundance. A close connection between surrounding land use and ammonium concentration in the water was found, as well as a connection between nutrient load and ammonium uptake performance: mass transfer coefficients significantly decreased with increasing nitrogen and DOC loading level, uptake lengths generally increased. At the same time highly loaded streams saturated earlier (regarding relative increase in NH4-N concentration), showed higher uptake lengths and declining uptake rates. There was no significant difference between uptake parameters in spring and summer. Wetted perimeter and streambed width were positively correlated with mass transfer coefficient and negatively with uptake length, underlining the importance of streambed heterogeneity. No significant correlations could be found for other hydromorphological parameters or retention. Uptake length decreased and mass transfer coefficient increased with increasing community respiration, indicating higher uptake with increasing microbial abundance. Neither microbial abundances nor chlorophyll-a concentration alone did prove to be a good predictor for ammonium uptake.