Many headwater streams have mosses present, yet these plants are rarely included in current conceptual models of stream ecology. Bryophytes, including mosses, liverworts, and hornworts, are common in small streams where they can provide critical habitat for other aquatic organisms, and store large quantities of carbon, nitrogen, and phosphorus. This project will study the role of stream bryophytes as hotspots of freshwater biodiversity and nutrient cycling, with a particular focus on how bryophyte presence in small streams may have large impacts on water quality downstream. The project supports fifteen or more early career researchers across all career stages and multiple institutions. The research team will disseminate findings to broader audiences at conferences, local homeowners’ meetings, and field trips, and is partnering with the Hubbard Brook Research Foundation and a local school to develop environmental science curricula (5th-12th grades) that enable young students to examine and study mosses in nature. The research uses three complementary approaches to evaluate how and where aquatic bryophytes contribute to the structure and function of headwater stream ecosystems. First, researchers will experimentally remove bryophytes from two stream segments within the Hubbard Brook Experimental Forest (New Hampshire) to directly measure the impact of bryophytes on nutrient uptake, organic matter storage, and in-stream biodiversity. Second, the research team will conduct a r