In low‐nutrient streams in cold and arid ecosystems, the spiraling of autochthonous particulate organic matter (POM) may provide important nutrient subsidies downstream. Because of its lability and the spatial heterogeneity of processing in hyporheic sediments, the downstream transport and fate of autochthonous POM can be difficult to trace. In Antarctic McMurdo Dry Valley (MDV) streams, any POM retained in the hyporheic zone is expected to be derived from surface microbial mats that contain diatoms with long‐lasting silica frustules. We tested whether diatom frustules can be used to trace the retention of autochthonous POM in the hyporheic zone and whether certain geomorphic locations promote this process. The accumulation of diatom frustules in hyporheic sediments, measured as biogenic silica, was correlated with loss‐on‐ignition organic matter and sorbed ammonium, suggesting that diatoms can be used to identify locations where POM has been retained and processed over long timescales, regardless of whether the POM remains intact. In addition, by modeling the upstream sources of hyporheic diatom assemblages, we found that POM was predominantly derived from N‐fixing microbial mats of the genus Nostoc. In terms of spatial variability, we conclude that the hyporheic sediments adjacent to the stream channel that are regularly inundated by daily flood pulses are where the most POM has been retained over long timescales. Autochthonous POM is retained in hyporheic zones of low‐nutrient streams beyond the MDVs, and we suggest that biogenic silica and diatom composition can be used to identify locations where this transfer is most prevalent.

The biogeochemical processing of nitrogen (N) in streams has drawn wide interest related to various water quality problems (Davidson et al., 2011) and the mobilization of N from local human activities adjacent to freshwater systems to downstream locations (Fowler et al., 2013). To date, most research has focused on how human manipulation of N sources-through fertilizer applications or emissions-increase the amount of reactive N that is transported from terrestrial to aquatic systems (

Concentration‐discharge (C‐Q) relationships are often used to quantify source water contributions and biogeochemical processes occurring within catchments, especially during discrete hydrological events. Yet, the interpretation of C‐Q hysteresis is often confounded by complexity of the critical zone, such as numerous source waters and hydrochemical nonstationarity. Consequently, researchers must often ignore important runoff pathways and geochemical sources/sinks, especially the hyporheic zone because it lacks a distinct hydrochemical signature. Such simplifications limit efforts to identify processes responsible for the transience of C‐Q hysteresis over time. To address these limitations, we leverage the hydrologic simplicity and long‐term, high‐frequency Q and electrical conductivity (EC) data from streams in the McMurdo Dry Valleys, Antarctica. In this two end‐member system, EC can serve as a proxy for the concentration of solutes derived from the hyporheic zone. We utilize a novel approach to decompose loops into subhysteretic EC‐Q dynamics to identify individual mechanisms governing hysteresis across a wide range of timescales. We find that hydrologic and hydraulic processes govern EC response to diel and seasonal Q variability and that the effects of hyporheic mixing processes on C‐Q transience differ in short and long streams. We also observe that variable hyporheic turnover rates govern EC‐Q patterns at daily to interannual timescales. Last, subhysteretic analysis reveals a period of interannual freshening of glacial meltwater streams related to the effects of unsteady flow on hyporheic exchange. The subhysteretic analysis framework we introduce may be applied more broadly to constrain the processes controlling C‐Q transience and advance understanding of catchment evolution.

In polar regions, where many glaciers are cold based (frozen to their beds), biological communities on the glacier surface can modulate and transform nutrients, controlling downstream delivery. However, it remains unclear whether supraglacial streams are nutrient sinks or sources and the rates of nutrient processing. In order to test this, we conducted tracer injections in three supraglacial streams (62 to 123 m long) on Canada Glacier in the Taylor Valley, of the McMurdo Dry Valleys, Antarctica. We conducted a series of additions including nitrate (N), N + phosphate (P), N + P + glucose (C), and N + C. In two reaches, N-only additions resulted in N uptake. The third reach showed net N release during the N-only addition, but high N uptake in the N + P addition, indicating P-limitation or N + P colimitation. Coinjecting C did not increase N-uptake. Additionally, in these systems at low N concentrations the streams can be a net source of nitrogen. We confirmed these findings using laboratory-based nutrient incubation experiments on sediment collected from stream channels on Canada Glacier and two other glaciers in the Taylor Valley. Together, these results suggest there is active biological processing of nutrients occurring in these supraglacial streams despite low sediment cover, high flow velocities, and cold temperatures, modifying the input signals to proglacial streams. As glaciers worldwide undergo rapid change, these findings further our understanding of how melt generated on glacier surfaces set the initial nutrient signature for subglacial and downstream environments. Plain Language Summary In polar regions most glaciers are frozen to their beds, meaning that meltwater from these glaciers comes from the surface, or "supraglacial" environment. Active biological communities exist in this supraglacial environment where they generate and recycle nutrients. However, it remains unclear whether nutrients are removed by the supraglacial streams, and what limits this removal process. We did experimental nutrient additions in three streams on Canada Glacier in the Taylor Valley of the McMurdo Dry Valleys, Antarctica. We found that nitrogen in the form of nitrate was quickly removed. In one of three locations, the addition of phosphorus stimulated more nitrogen removal than just adding nitrogen alone. We also found that at low nitrogen concentrations, the streams can be a net source of nitrogen. We confirmed these field experiment findings using laboratory nutrient incubation experiments on sediment collected from stream channels on Canada Glacier and two other glaciers in the Taylor Valley. Supraglacial streams act as a filter and can remove nitrogen from meltwater before it leaves the glacier and affect the quantity and type of nutrients transported to downstream ecosystems. This is important worldwide because glaciers are often the headwaters of the stream network.

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Practitioners and researchers in geoscience education embrace collaboration applying ICON (Integrated, Coordinated, Open science, and Networked) principles and approaches which have been used to create and share large collections of educational resources, to move forward collective priorities, and to foster peer-learning among educators. These strategies can also support the advancement of coproduction between geoscientists and diverse communities. For this reason, many authors from the geoscience education community have co-created three commentaries on the use and future of ICON in geoscience education. We envision that sharing our expertise with ICON practice will be useful to other geoscience communities seeking to strengthen collaboration. Geoscience education brings substantial expertise in social science research and its application to building individual and collective capacity to address earth sustainability and equity issues at local to global scales The geoscience education community has expanded its own ICON capacity through access to and use of shared resources and research findings, enhancing data sharing and publication, and leadership development. We prioritize continued use of ICON principles to develop effective and inclusive communities that increase equity in geoscience education and beyond, support leadership and full participation of systemically non-dominant groups and enable global discussions and collaborations. Plain Language SummaryThe Geoscience Education community describes the value, use, and future of ICON collaboration through three independent, community-produced commentaries focused on the practice of geoscience education; geoscience education research; and diversity, equity, inclusion, and justice.

Concentration-discharge (C-Q) relationships can provide insight into how catchments store and transport solutes, but analysis is often limited to long-term behaviour assessed from infrequent grab samples. Increasing availability of high-frequency sensor data has shown that C-Q relationships can vary substantially across temporal scales, and in response to different hydrologic drivers. Here, we present 4 years of dissolved organic carbon (DOC) and nitrate-nitrogen (NO 3 -N) sensor data from a snowmelt-dominated catchment in the Rocky Mountains of Colorado. We assessed both the direction (enrichment vs. dilution) and hysteresis in C-Q relationships across a range of time scales, from interannual to sub-daily. Both solutes exhibited a seasonal flushing response, with concentrations initially increasing as solute stores are mobilized by the melt pulse, but then declining as these stores are depleted. The high-frequency data revealed that the seasonal melt pulse was composed of numerous individual daily melt pulses. The solute response to daily melt pulses was relatively chemostatic, suggesting mobilization and depletion to be progressive rather than episodic processes. In contrast, rainfall-induced pulses produced short-lived but substantial enrichment responses, suggesting they may activate alternative solute sources or transport pathways. Finally, we observed low-level diel variation during summer baseflow following the melt pulse, likely driven by effects of daily evapotranspiration cycles. Additional contributions from in-stream metabolic cycles, independent from but covarying with diel streamflow cycles, could not be ruled out. The results clearly demonstrate that solute responses to daily cycles and individual events may differ significantly from the longer-term seasonal behaviour they combine to generate.

Practitioners and researchers in geoscience education embrace collaboration applying ICON (Integrated, Coordinated, Open science, and Networked) principles and approaches ICON principles and approaches have been used to create and share large collections of educational resources, to move forward collective priorities, and to foster peer-learning among educators. These strategies can also support the advancement of coproduction between geoscientists and diverse communities. For this reason, many authors from the geoscience education community have co-created three commentaries on the use and future of ICON in geoscience education. We envision that sharing our expertise with ICON practice will be useful to other geoscience communities seeking to strengthen collaboration. Geoscience education brings substantial expertise in social science research and its application to building individual and collective capacity to address earth sustainability and equity issues at local to global scales The geoscience education community has expanded its own ICON capacity through access to and use of shared resources and research findings, enhancing data sharing and publication, and leadership development. We prioritize continued use of ICON principles to develop effective and inclusive communities that increase equity in geoscience education and beyond, support leadership and full participation of systemically non-dominant groups and enable global discussions and collaborations.