Increased nitrogen pollution threatens drinking water quality and aquatic habitats. Riparian buffers can reduce the amount of nutrients that reach streams from upland sources and are common restoration approaches to combat nutrient pollution. Some models treat buffer retention as a fixed percentage of nutrient inputs, depending only on vegetation type and buffer width. However, the amounts of nitrogen stored in plant and soil organic matter can vary greatly with buffer age. Similarly, ecosystem theory predicts that buffer retention will saturate if inputs are high, with any additional nutrients potentially lost to the environment. This project seeks to quantify how long-term storage of nitrogen changes as riparian buffers age, and under different levels of nitrogen inputs. This information will help define potential limits of riparian buffers to attenuate nitrogen from anthropogenic sources, which is essential for targeting best management practices to reduce nutrient loss. This study will take place in the Nooksack River Watershed in Whatcom County, Washington. We will sample from two subwatersheds, one with high and one with low inputs from agricultural sources. Within each subwatershed, we will measure plant and soil N pools from five sites along an age gradient, from 1-50 years after initial restoration. Differences in pool sizes among sites of different ages will provide a metric of rates of absolute N retention. We expect that nitrogen retention will be higher in buffers receiving higher inputs, and that mature buffers will have the highest nitrogen pools sizes, but the lowest rates of accumulation.