Much of what is known about changes in stream water quality comes from studies where basins have been impacted by human activity. Much less is known about trends over time in relatively undisturbed systems. This research intentionally focused on relatively undisturbed streams in seven experimental forests: H.J. Andrews, Hubbard Brook, Coweeta, Luquillo, Fraser, Marcel, and Fernow. These sites span a wide range of climatic, hydrologic and vegetation conditions across the country and are largely undisturbed by land use or land cover changes. Scientists found that even these near-pristine forested streams are showing changes in nitrogen concentrations; stream nitrate has declined in the Pacific Northwest, in the Northeast, and in Puerto Rico, but it has increased in the Mountain West and the South. Other key findings are that direction of trends in reference watersheds vary with length of record used and that adjacent watersheds within a site do not necessarily show similar responses. The study is part of a larger effort to understand the effects of forest management and disturbances on water quality and to inform nutrient criteria standards, using natural variability of high frequency stream chemistry concentrations.