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Stream bryophytes (mosses and liverworts) are widely recognized as important macroinvertebrate habitats, but their overall role in the stream ecosystem, particularly in nutrient cycling, remains understudied. Hubbard Brook Experimental Forest in New Hampshire, USA, contains some of the most extensively researched streams in the world, yet few studies mention their bryophytes. Perhaps this is because early estimates place bryophyte coverage in these streams at an insignificant 2%. However, data from 2019 show that contemporary coverage ranges from 4 to 40% among streams. To investigate how stream bryophyte cover may be changing over time and influencing stream nutrient stocks, we conducted field surveys, measured the mass of organic and inorganic bryophyte contents, and quantified nutrient uptake with bottle incubations of bryophyte mats. This study marks a novel attempt to map stream bryophyte coverage with estimates of C, P, and N stocks and fluxes. From our 2022 field surveys, we found that median bryophyte coverage varied across streams in the same catchment (0–41.4%) and shifted from just 3 y prior. We estimate that these bryophyte mats stored between 14 and 414 g of organic matter per m2 of stream in the form of live biomass and captured particulates. Within 12 h of light incubation, 35 out of 36 bryophyte clump samples sorbed peak historical water-column concentrations of PO43– as measured in the Hubbard Brook stream chemistry record. In Bear Brook, our scaled estimate of bryophyte mat NO3– uptake (2.3 g N/y) constitutes a substantial portion of previously estimated whole-stream NO3– uptake (12 g N/y). Cumulatively, our data demonstrate that bryophytes and their associated mineral substrates and biota—known as the bryosphere—are crucial in facilitating headwater stream nutrient cycling. These bryospheres may contribute significantly to interannual variability in stream nutrient concentrations within nutrient-poor streams, especially in climate-sensitive regions. 

Stream bryophytes (mosses and liverworts) are widely recognized as important macroinvertebrate habitats, but their overall role in the stream ecosystem, particularly in nutrient cycling, remains understudied. Hubbard Brook Experimental Forest contains some of the most extensively researched streams in the world, yet few studies mention their bryophytes. Perhaps this is because early estimates place stream bryophyte coverage at an insignificant 2%. However, data from 2019 show that contemporary coverage ranges from 4%–40% among streams. To investigate how stream bryophyte cover may be changing over time and influencing stream nutrient stocks, we conducted field surveys, measured organic and inorganic mass contents of bryophytes, and quantified nutrient uptake with bottle incubations of bryophyte mats. This study marks a novel attempt to map stream bryophyte coverage with estimates of carbon, phosphorus, and nitrogen stocks and fluxes. From our 2022 field surveys, we found that median bryophyte coverage can vary greatly across streams in the same catchment (0%–41.4%) and can also shift from just three years prior. We estimate that these bryophyte mats store between 14–414 g of organic matter per m2 of stream in the form of live biomass and captured particulates. Out of 36 bryophyte clump samples, 35 sorbed peak historical water column concentrations of PO43- measured within the Hubbard Brook stream chemistry record within 12 hours of light incubation. In Bear Brook, our scaled estimate of bryophyte mat nitrate uptake (2.3 g N y-1) constitutes a substantial portion of previously estimated whole-stream nitrate uptake (12 g N y-1). Cumulatively, our data demonstrates that bryophytes and their associated mineral substrates and biota—known as the bryosphere—are crucial in facilitating headwater stream nutrient cycling. These bryospheres may contribute significantly to interannual variability in stream nutrient concentrations within nutrient-poor streams, especially in climate-sensitive regions. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

This is the data and code associated with "Stream bryophytes promote 'cryptic' productivity in highly oligotrophic headwaters. Recent observations document increased abundance of algae in the headwater streams of Hubbard Brook Experimental Forest (HBEF). It is possible that this 'greening up' of HBEF streams may be due to climate change with rising temperatures, altered terrestrial phenology, and shifting hydrologic regimes. Alternatively, stream 'greening' could be due to the slow recovery of stream chemistry from decades of acid rain, which have led to rising stream water pH, declining concentrations of toxic Al3+, and extremely low solute concentrations. Three years of weekly algal measurements on contrasting substrates, 6 nutrient enrichment experiments reveal important new insights about the interactions between these two groups of autotrophs. We predicted that light availability, hydrologic disturbance and nutrient limitation were all important determinants of algal biomass in streams. To evaluate the relative strength and hierarchy of these limiting factors, we used nutrient diffusing substrates to investigate the role of nutrients for algae and compared algal accrual rate on artificial rock vs. moss substrates in stream channels vs. weir ponds to assess the role of hydrologic disturbance and scour. Our surveys and experiments spanned across seasons and local light regimes. Algal biomass was substantially higher in protected weir ponds than in stream channels, and in both habitats, algal biomass was substantially higher on artificial moss substrates than on tiles. Taken together, these results suggest that moss can provide physical protection from flood scour. Algal biomass instream on both substrate types was higher in high light seasons (pre-leaf out) and well-lit habitats indicating strong light limitation. Results from a series of 6 nutrient diffusing substrate experiments over the course of 2 years provided little evidence of nutrient limitation instream. The most striking finding of our investigation is the previously unsuspected role of stream bryophytes in providing critical refugia for algae in these steep, heavily shaded and oligotrophic headwaters. Shifts in stream productivity over time are likely to be closely tied to changes in bryophyte cover. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

Abstract The future of our planet relies on scientists' ability to effectively translate knowledge into action, and researchers have an imperative commitment to leverage their understanding. As aquatic early career researchers (ECRs), we draw upon personal experiences to share our learnings about how individuals can drive change. We showcase diverse approaches for ECRs to create meaningful impacts by connecting with other researchers, broader society, and decision‐makers. At the same time, institutional challenges inhibit scientific engagement beyond academia, particularly for ECRs. Such barriers include (1) lack of value and support for engagement activities, (2) limited training opportunities, (3) research siloes, and (4) rigid funding structures. We offer potential systemic solutions, from developing and adopting new performance metrics for academic researchers to enhanced flexibility with grant timelines and spending. Academic systems need to change and so does the way scientists engage. Our future depends on it.