Nitrate in streams is derived from anthropogenic and natural sources including land use, atmospheric deposition, organic matter and minerals. Baseflow nitrate concentrations not only depend upon the size of local sources, but also local and regional lithology, channel characteristics, hydrology, and the presence or absence of other nutrients. Through intensive sampling in one forested and four urban/urbanizing watersheds in Montgomery County, Maryland, we found surprisingly high within-site temporal variability in baseflow nitrate concentrations, with maximum values ranging from 9 to 334% above the average concentration at each site. We used these data in combination with county and state-wide data sets to investigate the effects of various controls on background nitrate concentrations. We also conducted microcosm experiments to investigate the influence of limiting nutrients and water residence time on nitrate concentrations at small scales. Recognizing how multiple controls influence baseflow nitrogen concentrations allows us to have a more comprehensive understanding of functional dynamics (nutrient uptake) in streams. Furthermore, knowledge of why nitrogen concentrations in streams vary across the landscape is critical for making decisions regarding in-channel and land based management for nitrogen reduction.